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2014/2015/2016 Ian’s Home Projects 11/20/2014 The Stuart Half Beam Engine
2014/2015/2016
Ian’s
Home Projects
11/20/2014
The Stuart Half Beam Engine
November 20, 2014
1 The Stuart Turner Half Beam Casting Kit
The Stuart Half Beam Engine
Table of Contents The Stuart Turner Half Beam Casting Kit ................................................................................................ 3
Machining the Baseplate ........................................................................................................................ 5
Bearings................................................................................................................................................... 6
Various spindles, shafts, spacers, bosses and pins ................................................................................. 7
The Piston and Piston Rod ...................................................................................................................... 9
The Cross Heads, Links and Levers ........................................................................................................ 10
Main Bearings ....................................................................................................................................... 13
The Pedestal .......................................................................................................................................... 15
The Crank .............................................................................................................................................. 16
The Glands ............................................................................................................................................ 18
The Steam Chest ................................................................................................................................... 19
The Steam Chest Cover ......................................................................................................................... 21
Bottom Cylinder Cover .......................................................................................................................... 22
Top Cylinder Cover ................................................................................................................................ 24
The A-Frames ........................................................................................................................................ 27
The Cylinder .......................................................................................................................................... 31
The Eccentric Sheave and the Eccentric Strap ...................................................................................... 34
The Eccentric Rod and Eccentric Clevis ................................................................................................. 36
The Flywheel ......................................................................................................................................... 37
The Beam .............................................................................................................................................. 40
The Connecting Rod and Big End Sleeve Bearing ................................................................................. 42
The Pulley .............................................................................................................................................. 45
The Assembly & Finishing ..................................................................................................................... 46
2 The Stuart Half Beam Engine
November 20, 2014
This page is left unintentionally blank.
November 20, 2014
3 The Stuart Turner Half Beam Casting Kit
The Stuart Turner Half Beam Casting Kit The Stuart Half Beam Engine is built from a kit given to me by Brenda for Christmas. The drawings
are detailed in imperial sizes so being a child of the SI system I created a 3D CAD model in imperial
units and then converted them to metric dimensions and recreated the drawings with metric
dimensions for manufacture. I added limits and fits and some geometric tolerances where I thought
it applicable. The final drawings are included in an appendix at the back of this document.
Figure 1 - Stuart Half Beam 3D CAD Model
The kit comes in a sturdy box with most of the parts vacuum packed; only the main castings are
loose within the box. It is worth checking that all the parts are there. I was missing the casting for the
pulley wheel, although Stuart Turner happily sent the missing item on to me when I requested it.
The material supplied within the kit for the spindles was mostly carbon steel to imperial sizes. To
maintain metric limits and fits (as the reamers and drills I own are nearly all metric) I purchased
some metric stainless steel round bar and used this for the spindles and shafts. The stainless steel
also polishes to a more pleasing lustre than the supplied carbon steel.
I decided that it would be a good idea to record the process of building the engine in some kind of
log. I had meant to do this when building the ‘Stuart 10V’ Vertical steam engine completed last year.
However, I kept forgetting to take the photos. I will try not to forget this time!
4 The Stuart Half Beam Engine
November 20, 2014
Hopefully this will be something that is fun to look back on…
Figure 2 - Stuart Half Beam; The box it all came in
Figure 3 - Stuart Half Beam; The contents of the box.
Note… I forgot … and had already started to machine the base plate when I took this photo…
November 20, 2014
5 Machining the Baseplate
Machining the Baseplate The ‘Baseplate’ is one of the largest castings to be processed within the kit but certainly not the
most complex. The edges of the casting were filed flat, true and square with respect to each other. I
did contemplate machining the rear of the casting to ensure it was level when machining the raised
pads. However, my machine does not have the lateral travel to machine the base completely.
Therefore I opted to level the part on the machine table and using shims. This ensured that the
minimal material had to be removed and that the machined pads would remain at a similar height
and not become unsightly.
Figure 4 - Preparing the ‘Baseplate’ by filing Figure 5 - Machining the cast raised pads
The raised pads were machined with a 14mm diameter cutter in two setups. The first, machining the
cylinder, valve gear and crank bearing interfaces; the second, machining the beam support interface.
Between each setup the part was re-levelled and
‘clocked’ to ensure the flatness across the pads
was less than 100m.
After machining the pads I marked out and centre
punched the holes to be drilled and used the borer
to drill the various holes. Those that required
tapping were tapped carefully by hand to ensure
the thread was square to the part.
Finally, the underside of the ‘Baseplate’ was filed
flat to ensure that it sits evenly onto the surface
plate without rocking. This will then sit down level
on the base when that is made.
Figure 6 – Marking out the holes prior to drilling
6 The Stuart Half Beam Engine
November 20, 2014
Bearings The bearings that constrain the ‘Beam Support’ and the ‘Valve Spindle’ assembly are manufactured
from bronze alloy material that is supplied as an extrusion. The extrusion was mounted in the 4-jaw
chuck and the ¼” diameter circular feature was clocked in to run true.
Figure 7 – Small ‘Bearings’ being centre drilled Figure 8 – Drilling and reaming each ‘Bearing’
The 3mm hole was centre drilled, drilled and reamed out to the 3.0mm H7 tolerance and to a depth
that exceeds the width of the final part. The ‘Bearing’ was then parted from the extrusion. The part
was de-burred and a reamer, run through the hole to clean up any deformation caused by the
parting process.
Figure 9 – Small ‘Bearings’ being ‘Parted off’ Figure 10 – Drilling holes in the base of each ‘Bearing’
The holes in the base of each bearing were marked out with the height gauge on the surface plate.
The markings were used as a visual guide to ensure that when the table was indexed, the centre drill
was in the correct location. The bearings were held in a small toolmaker’s vice and were then
clamped to the table of the borer. The holes were then centre drilled and then drilled through at
2.8mm diameter. The parts were then each de-burred for trial assembly. All the bras components
will be cleaned up using successively finer grades of ‘wet and dry’ before using ‘Brasso’ to provide a
polished finish on final assembly.
November 20, 2014
7 Various spindles, shafts, spacers, bosses and pins
Various spindles, shafts, spacers, bosses and pins There are numerous shafts, spacers and spindles required for the ‘Valve Gear’, ‘Beam’ and ‘Crank
Shaft’. The material supplied in the kit is mostly carbon steel so I decided to purchase some stainless
steel alternatives. Each of these parts was machined to drawing, taking special care to ensure
minimise ‘run out’ and to maintain the fit where required. A number of the ‘Valve Spindles’ need to
fit to levers. An easy running fit H8-f8 was used to for these parts. The ‘Valve Spindles’ were turned
to diameter ready for their and their corresponding holes to be reamed.
All parts were held in a three jaw chuck with thin shim stock used to prevent the chuck jaws from
‘marring’ the surface of the parts. The scroll of the 3 jaw chuck is kept clean and I have found that I
can get a nominal dimensional repeatability of around 10-15um from this chuck. This allows me to
turn the features on one end of the spindles, turn them around and machine them to length and put
the features on the other end. Where the parts required a thread, such as the ‘Valve Rod’; a die was
used mounted in the tail stock die holder.
The ‘Crank Shaft’ and ‘Crank Pin’ were machined with a close running fit H7-g6 to minimise the
potential play in these parts. A precision run fit is used as the ‘Crank’ is made from cast iron and the
amount of strain needs to be minimised when it is fitted to the shaft. The ‘Crank Shaft’ itself is a
relatively simple component that only requires the feature to fit the ‘Crank’ to be turned and the
part can be faced to length.
The ‘Crank Pin’ was machined in one
setting. The two precision diameters, 6mm
f8 and 5mm g6 were machined to size and
faced to length. The M5 threaded portion,
which is approximately 6mm long, was
formed using a die mounted in the
tailstock holder to ensure the thread was
square and true. The final operation was to
part off the pin from the bar stock.
The ‘Beam Linkage’ requires tapers to be
turned on them, to give that ‘bellied’ look.
This was done by tilting the compound
slide. The parts diameter reduces from
8mm to 5mm over a distance of 30mm.The
angle was set by tilting the compound slide
in increments and measuring the run out
using a dial test indicator. We could quickly
and accurately set the angle by ensuring a
gradient of 0.5mm for every 10mm of
compound slide motion.
Figure 11 – Turning the taper on the ‘Beam Linkages’
Once the taper was machined the parts were smoothed and polished with wet and dry before
removing from the machine and final polishing with ‘Brasso’.
8 The Stuart Half Beam Engine
November 20, 2014
The ‘Beam Pivot Supports’ are machined from brass stock round bar. The female has the boss faced
and turned to diameter and length. It is then centre-drilled to allow the part to be supported with a
‘live’ centre whilst the radius is machined with a form tool. The process applies a considerable
amount of force and the adequate support prevents the tool from chattering. Finally an M5 thread
was drilled and tapped into the boss. The part was then taken out of the chuck and the part sawn
off. The part was then held in the 3 jaw chuck by the boss. Thin sheet was used to protect the part
from being ‘marred’ in the jaws and the part was faced to length and a chamfer applied to the edge.
Figure 12 – Machining the ‘Beam Pivot Supports’ Figure 13 – Threading with the die in the tailstock
The male ‘Beam Pivot Support’ was machined using a similar process. However, the end was first
faced and then lightly centre-drilled; deep enough to allow adequate support but not too deep to
use up the remaining material. The radius was formed and the diameter for the M5 male thread was
turned and faced to length. I then reversed the part in the 3 jaw chuck gripping the 5mm diameter
portion and faced the part to length and chamfered the edge. The part was then reversed once again
in the 3 jaw chuck and the M5 thread formed with a die in the tailstock die holder.
Care was taken to ensure the orientation of the part in the chuck was maintained and thin sheet was
used to prevent the jaws of the chuck ‘marring’ the parts.
Figure 14 – Finished ‘Beam Pivot Supports’ assembled to the ‘Beam Linkages’
November 20, 2014
9 The Piston and Piston Rod
The Piston and Piston Rod The ‘Piston Rod’ was machined in the 3 jaw chuck. The surface finish of the ‘Piston Rod’ requires a
bit of extra care and attention as any damage to the surface will affect the seal at the stuffing box
gland. I used thin sheet, shim stock to protect the rod whilst forming the threads at both ends and
facing the rod to length.
The ‘O’ ring supplied as part of the kit for the ‘Piston’ is an inch series BS 1806 type 210. This has an
outside diameter that matches the 1” bore of the cylinder. Changing to a metric 25mm bore means
that a change is required to the ‘O’ ring and the groove machined on the piston. The closest metric
equivalent is the BS 4518 type 0195-30. The groove was resized to match the ‘O’ ring but I decided
that due to the width of the piston I would slightly reduce the groove width. The remainder of the
dimensions are as specified in the standard.
The ‘Piston’ was machined in the 3 jaw chuck. The clearance hole was centre drilled and drilled
through. The counter bore feature was machined using a slot drill mounted in the tail stock. The
outside diameter was left 0.25mm over size whilst the ‘O’ ring groove was machined to the correct
depth compensating for the larger outside diameter. The piston was then parted off. I did this
slightly longer so that I could reverse the ‘Piston’ in the 3 jaw chuck and face the part to length.
The reason for leaving the outside diameter over-sized was to machine this when it is assembled to
the ‘Piston Rod’. This will ensure the ‘concentricity’ tolerance between the rod and the piston is
maintained. The assembled piston and rod was mounted in the 3 jaw chuck by the ‘Piston Rod’.
Again thin sheet was used to protect the surface finish of the rod. The outside diameter was then
brought to size.
Figure 15 – Finished ‘Piston Rod’ Assembly with ‘O’ ring fitted
With the ‘Piston Rod’ assembly removed from the lathe and de-burred. The assembly was the
thoroughly cleaned and degreased using brake cleaner from ‘Carplan’ which was purchased for
around £2 from local motor factors. The ‘O’ ring was then fitted and the ‘Piston Rod’ polished using
‘Brasso’.
10 The Stuart Half Beam Engine
November 20, 2014
The Cross Heads, Links and Levers The ‘Valve Shaft Cross Head’ is made from 6.35mm square bar. The square bar was ‘clocked in’ to
the 4 jaw chuck to better than 10um. Then the cylindrical feature was turned to diameter and
length, the hole for the valve shaft drilled and tapped and the component ‘parted off’ to length.
Figure 16 – Machining the ‘Valve Cross Head’ Figure 17 – Drilling the ‘Valve Cross Head’
The hole for the ‘Valve Spindle’ was marked out and drilled to 3.8mm before reaming to 4mm H8.
The part was then de-burred and cleaned up.
The remainder of the 6.35mm square section bar is for the manufacture of the 2 off ‘Valve Levers’
and the 1 off ‘Eccentric Lever’. Both parts are very similar, though the ‘Valve Levers’ have a clevis
machined into one end to allow for the ‘Valve
Linkage’.
Each of the levers was faced on one side and
then reversed in the chuck and faced to length.
The 3mm holes were marked out, drilled to
2.8mm diameter and reamed to 3mm H8. The
two ‘Valve Levers’ were then mounted on the
milling machine and the slot drill used to
machine the clevis.
Figure 18 – ‘Valve Levers, Spindle and Rod Assembly’
The rectangular bar stock for the ‘Beam Cross Heads’ was ‘clocked’ into the 4 jaw chuck to better
than 10um. The diameter of the boss feature was machined and faced to length. The thread then
drilled and tapped using the tailstock to guide the tap to ensure the thread was square and true. The
‘Beam Cross heads’ were then parted off and faced to length. I re-clocked the bar stock into the 4
November 20, 2014
11 The Cross Heads, Links and Levers
jaw chuck for every one of the crossheads to ensure that the boss feature on each of them would be
central to the bar stock.
The parts were then mounted on the mill and a slot drill used to drill down and machine the material
away to make the square form of the clevis. The remaining material was removed by using the side
cutting action of the cutter. Incremental cuts were then taken to ensure the depth and gap between
the clevis was correct and even about the central axis defined by the boss. Once this was completed
the distance across the outside of the clevis was brought in by milling each of the half of the clevis to
size. The 3mm hole was marked out, drilled to 2.8mm diameter and reamed to 3mm H8. The radius
at the end of the clevis was then carefully filed on each of the cross heads.
Figure 19 – Machining the ‘Beam Cross Head’ boss Figure 20 – Milling the ‘Beam Cross Head’ clevis to size
The ‘Piston Cross head’ was manufactured in a similar way. The main difference is the orientation of
the part with respect to the milling cutter when the radius form of the clevis is machined. An 8mm
slot drill was used to bore a series of holes these were then milled out to form the clevis.
Figure 21 – Machining the ‘Piston Cross Head’ Figure 22 – Milling the ‘Piston Cross Head’ clevis to size
12 The Stuart Half Beam Engine
November 20, 2014
Again a series of incremental cuts were taken to ensure the depth and gap between the clevis was
correct and even about the central axis defined by the boss. The crosshead was milled to size on
each of the four sides in turn. The 3mm hole was marked out, drilled to 2.8mm diameter and
reamed to 3mm H8. The radii at the ends of the clevis were then carefully filed on each of the cross
heads.
Figure 23 – Machining the ‘Piston Cross Head’
The ‘Link Arms’ for the valve gear were manufactured from the supplied carbon steel flat bar. In an
attempt to make the profiles identical the two pieces were mounted back to back with double-sided
tape. The holes were then drilled using the borer and the outline marked on and the profile filed
using a combination of round and half round files. The surfaces were then cleaned up using a series
of needle files.
Figure 24 – Filing the ‘Link Arms’ Figure 25 – Finishing ‘Link Arms’ with wet and dry
The parts were then split with a razor blade and the two main faces filed to bring the thickness to
size. The edges were draw filed with the needle files and the faces of each link was ground using wet
and dry paper on the surface plate. This process was continued until all the file marks had been
removed. The parts were then ready for trial assembly and then polishing.
November 20, 2014
13 Main Bearings
Main Bearings The ‘Main Bearings’ are machined from a bronze alloy that is supplied as an extrusion which has the
correct approximate shape and size. I had wanted to split the bearings to allow for wear over time.
However, after checking the size of the supplied material it quickly became apparent that the there
was insufficient material to allow for this. Therefore, the ‘Main Bearings’ were manufactured
without the split as detailed in the Stuart drawings.
The material was mounted in the 4-jaw chuck and clocked in, to minimise the run-out on the curved
feature at the top of the bearing extrusion to better than 50um. This ensures that the position of the
centre of rotation is within an acceptable tolerance to the location of the bore required for the main
shaft. The next task was to face the material and form the cylindrical boss.
Figure 26 – Facing the ‘Main Bearing’ stock Figure 27 - Machining the cylindrical boss
The hole for the ‘Crank Shaft’ was then centre-drilled and bored out undersize to nominally 10mm.
To ensure the bore is perpendicular to the faces of the ‘Main Bearing’ the bore is not finished until
the other faces of the part are machined.
Figure 28 – ‘Main Bearing’ faced to length Figure 29 – Bore drilled and reamed 12mm H7
With the 10mm bore defining the bearing axis I removed the part from the chuck and sawed it into
two equal parts. I re-chucked the first bearing clocking in the bore and tapping the machined face
back onto parallels to ensure the part was reasonably square. The part was then faced to length and
14 The Stuart Half Beam Engine
November 20, 2014
the boss feature machined. The 10mm was drilled out to 11.5mm diameter and then reamed to a
diameter of 12mm H7.
The second ‘Main Bearing’ was machined in a similar way by clocking in the 10mm diameter bore
and machining the main faces and cylindrical boss before drilling and reaming the bearing diameter
to size.
The two bearings were then assembled to the ‘Crank Shaft’ this co-locates the two ‘Main Bearings’
relative to one another to ensure that they will be machined relative to one another. The assembly
was then clamped to the machine table of the borer and ‘clocked in’ to ensure that the minimum of
material was removed to clean up the interface surface. The surface was milled removing only
150um of material to bring the surface to form and size. The clearance holes for mounting the
bearings to the baseplate and support pedestal were then centre drilled and drilled 5.0mm through
to suit the 2BA fasteners.
Figure 30 – The ‘Main Bearings’ Assembled to the ‘Crank Shaft’.
The parts were then cleaned up with a file and emery paper. On assembly I intend to polish these
parts with ‘Brasso’
Note: Not only did I find that the material stock was not sized to allow the ‘Main Bearings’ to be split
but they were not quite tall enough to obtain the 22mm (Stuart Drawing specifies 7/8”) dimension
from the axis of the crank bore to the base of the part. Even with cleaning up a very small amount
around 150um I could only get this dimension to nominally 21mm. I did this for both bearings and
checked the effect on the CAD model. In fact the change meant that the piston stroke was much
more central to the cylinder than it had been with the bearings at 22mm. An Improvement all
around!
November 20, 2014
15 The Pedestal
The Pedestal The ‘Pedestal’ is like many of the components supplied as a casting. It tapers from the base to the
surface that interfaces to the ‘Main Bearing’. The part was set down on parallels with a packing piece
used to set the part level. The base surface was then orientated to keep the pedestal nominally
orthogonal and then machined to provide a datum surface. Once complete the table was indexed
and the top surface machined and the part brought to the correct height.
Figure 31 – The mandrel used to machine the ‘Flywheel’
With the mating surfaces machined and parallel the part was removed from the mill and the holes
for the base and the bearing were marked out and centre punched. The part was then clamped to
the vertical slide mounted on the cross slide of the lathe. The clearance hole in the base were then
machined, the part was then reversed and aligned to allow the holes for fixing the ‘Main Bearing’ to
be drilled. These holes were then tapped by hand on the bench.
The part was then finished by removing the flash and casting marks with a file.
16 The Stuart Half Beam Engine
November 20, 2014
The Crank The casting required filing all over to remove the flashing left from the casting process. The ‘Crank’
was mounted in the 4-jaw chuck and the larger of the two bosses ‘clocked in’ to run true. Machining
the castings does require some thought and planning to ensure that the components are finished to
the correct nominal sizes and that you do not run out of material. I took time to calculate how much
would have to be removed from the various surfaces in each of the machining operations to
maintain the components nominal dimensions. I marked the drawing up to indicate the depth of cut
of each of the surfaces being machined.
Figure 32 – The ‘Crank’ in the 4-jaw chuck Figure 33 – ‘Crank’ bore drilled and reamed
The main boss that interfaces to the ‘Crank Shaft’ was faced and enough material removed to ensure
the part would be at nominal size when the crank web (on the other side of the part) was machined
to size. The smaller boss that interfaces to the ‘Crank Pin’ was faced and machined to ensure the
offset dimension between the two surfaces was nominally correct.
The boss was then centre-drilled, pilot drilled to 5.5mm diameter, drilled out to 9.5mm diameter
and then finally reamed to a diameter of 10mm H7. The fit with the shaft was checked and the edges
of the bore broken to allow a snug fit of the ‘Crank Shaft’ to the ‘Crank’.
Figure 34 – Drilling and Pinning the ‘Crank’
November 20, 2014
17 The Crank
The ‘Crank’ and ‘Crank Shaft’ are assembled and mounted into the vertical slide where the assembly
is drilled for pinning. A 2mm diameter hole machined though the boss feature of the ‘Crank’ and the
‘Crank Shaft’. This hole is then reamed by hand to suit the tapered dowel.
With the dowel in place the ‘Crank’ and ‘Crank Shaft’ assembly can be mounted in the 3-jaw chuck.
Thin sheet was used to prevent the jaws of the chuck ‘marring’ the parts and the ‘Crank’ web
machined to bring it to the correct dimension.
Figure 35 – Facing the ‘Crank’ to size
The ‘Crank’ was then removed from the ‘Crank Shaft’ by removing the tapered pin and mounted to
the borer using the small tool makers vice. The dimension of the hole centres are given as 17.5mm
(11/16”). However, this means the hole would not be central to the boss feature. In this case, the
actual dimension takes only a secondary importance over the aesthetic; it was modified to 17.8mm
and the hole located at the nominal centre of the boss. The hole was then centre drilled, drilled to
4.8mm diameter and reamed to size of 5mm H7.
Figure 36 – Drilling the ‘Crank’
18 The Stuart Half Beam Engine
November 20, 2014
The Glands The material supplied in the kit for the glands is a brass elliptical shaped extrusion. This generally
simplifies the machining operations to reasonably simple turning operation. The material is held in
the 4-jaw chuck and centred to run true using a dial test indicator to equalise the minima and
maxima readings.
The machining operations for each of the glands are basically identical. The gland boss is faced and
turned to length. (See figure below) The bore is then centre drilled, drilled and then reamed for the
piston and valve glands. The steam port gland is then drilled and tapped. The gland can then be
parted off the bar at length. Two off of the steam port glands were made, one for the steam chest
and a second for the exhaust port.
Figure 37 - Machining the ‘Piston Gland’ Figure 38 – Drilling the flanges
Each gland requires two additional holes to be machined into their flanges. These holes are marked
out and drilled with their corresponding parts to ensure the parts to ensure alignment. A centre drill
is used to provide an accurate pilot to ensure both holes are in position. The holes are then drilled
through at 2.8mm for clearance for a 7BA thread.
The parts are then de-burred and polished using a fine abrasive. These parts will be polished with
‘Brasso’ prior to assembly.
November 20, 2014
19 The Steam Chest
The Steam Chest The ‘Steam Chest’ requires filing to clean up the flashing in particular in the central bore for the slide
valve. The drawings from Stuart do not indicate that machining of the external surfaces is required.
However, the split mould line was very clear and there was an offset between the two halves of the
casting. So I decided to machine each face that I could, the face with the valve stuffing box port not
being practical because of the shape of the gland interface. Each surface was machined removing
only the minimal amount of material to ensure the surfaces ‘cleaned up’. This did bring the surfaces
only fractionally under size but I am happier with the overall appearance.
Figure 39 – Machining the ‘Steam Chest’ boss feature Figure 40 – Machining the external faces
Once again I surveyed the part and marked up the drawing to show the depth of cuts required to
bring the part to size. The casting was then mounted in the 4-jaw chuck and the cylindrical boss was
‘clocked in’ to run true. The part was awkward to hold in the chuck so packing pieces were used to
ensure the grip was firm without over tightening. As this may result is a cracked casting, something
we want to try to avoid! The boss was turned to a diameter of 7.5mm, at which point the adjacent
surface was cleaned up. I faced the boss to a length of 9.5mm and machined a radius feature. See
Figure 39.
The part was then repositioned in the 4-jaw chuck to machine the two sides of the casting whilst
trying to maintain the 35mm width dimension. Care was taken to ensure that the machined surfaces
were square to each other. This is important not only for aesthetic reasons but also because these
surfaces will be used to hold the ‘steam chest’ whilst the port faces are machined. The faces cleaned
up with a width dimension of 34.7mm which is acceptable at 0.3mm below size and a length
dimension of the rectangular portion of 38.9mm which is only 0.1mm below size.
With the sides of the ‘Steam Chest‘, now machined, the part was re-orientated in the 4 jaw chuck
and the port face ‘clocked in’ to ensure it was square to the machine. The face was machined to size
with the gland port boss used as a reference. The part was then reversed in the chuck tapped down
onto parallels and the opposite face brought to size nominally 11.5mm. The two port faces were
parallel to around 50um. See Figure 41
The next operation was the machining of the interface for the ‘Valve Rod’ and the ‘Valve Gland’ the
part was again re-orientated into the 4-jaw chuck and the valve port boss was ‘clocked in’. The boss
20 The Stuart Half Beam Engine
November 20, 2014
was then faced, and centre drilled. The 3mm and 6.5mm hole features were then drilled into the
boss. See figure below.
Figure 41 – Machining the ‘Steam Chest’ port face Figure 42 – Machining the ‘Valve Gland’ Interface
It was at this stage where I hit a bit of a problem. The design requires a 2.5mm diameter hole to be
drilled to depth of 51mm from the face of the Valve Boss. Its purpose is to guide the ‘Valve Rod’ as it
moves back and forth. Unfortunately when I drilled this hole, the drill wandered on the cast surface
and the hole was out of position.
I machined a piece of mild steel to 2.5mm diameter and filled the hole. It was bonded in with Loctite
638 and left it overnight. Then, the following morning, filed the face flat. Using a pistol drill I carefully
re-drilled the hole. This was tricky as the drill bit desperately wanted to wander again. I would
suggest that this operation is done with great care and with plenty of visibility of where the drill
contacts the cast material. However, after a small amount of fitting work with the gland in place I
was able to ensure the valve rod ran nice and smoothly in the ‘Steam Chest’.
Figure 43 – Marking out the ‘Steam Chest’ port face Figure 44 – Machining the ‘Valve Gland’ Interface
The remaining holes were then machined into this component. The first a set of 6 through holes
3mm diameter was marked out on the surface plate and then drilled using the borer. The second a
set of 2 blind 7BA tapped holes to secure the ‘Valve Gland’ were drilled through at 2.0mm and then
tapped on the bench and the ‘Valve Gland’ drilled out for 7BA clearance.
November 20, 2014
21 The Steam Chest Cover
The Steam Chest Cover The material for the cover of the steam chest is supplied as a cast blank. The surface finish was quite
rough and the part looked like it was open cast. I held the part in the 4 jaw chuck. The part is thin at
around 5mm thick and so work holding has to be done with care. I tapped the part down onto a
parallel and sequentially tightened each of the jaws taking great care not to over tighten the chuck.
The intermittent cut required the spindle speed to be set to no more than 150 RPM. The part was
then faced until the entire surface cleaned up.
The part was then reversed in the 4 jaw chuck and again tapped down onto a parallel. The part was
then faced to a length of 3mm. The work holding was tricky and I struggled, but managed to achieve
a parallelism of better than 0.2mm for this part. The outer dimensions were then brought to size by
filing. I did consider machining these edges. However the part is so close to the final dimensions of
the ‘Steam Chest’ there is very little work to do.
Figure 45 – Drilling the 7BA clearance holes Figure 46 – Marking out steam port gland holes
There are 3 sets of holes that require machining into the ‘Steam Chest Cover’. The first are the
clearance holes for the 7BA studs that mount the ‘Steam Chest’ and the ‘Steam Chest Cover’ to the
‘Cylinder’. These were drilled through from the ‘Steam Chest’ to ensure they were well matched.
The remaining 3 holes; the two 7BA threaded
and the 5mm diameter steam port, were
marked out, centre punched and drilled using
the borer. The 5mm diameter hole was pilot
drilled at 3mm before finishing at 5mm. The
7BA holes were drilled through at 2mm
diameter and then tapped on the bench. The
holes in the steam port gland were marked out
and drilled to 2.5mm to provide clearance for
the 7BA fasteners.
Figure 47 – Drilling the 7BA clearance holes
22 The Stuart Half Beam Engine
November 20, 2014
Bottom Cylinder Cover The ‘Bottom Cylinder Cover’ is machined from a relatively thin square section casting with a similar
thickness to the ‘Steam Chest Cover’. This was again mounted in the 4-jaw chuck, the part tapped
down on to parallels. Care being taken not to over tighten the chuck. The cast boss feature was
‘clocked in’ so that the part was reasonably well centred. The boss feature and the ‘Main Cylinder’
mating surface were faced and brought to size. The diameter of the boss was then machined,
bringing it to ф25mm f8. The intermittent cut meant that the RPM and feed rates had to be kept
low.
Figure 48 – Machining the location boss
Figure 49 – Machining the part to size
The part was then reversed, and the part mounted in the chuck via the boss feature. Thin shim stock
was used to protect the machined surface of the boss from damage from the jaws of the chuck. The
surface was then faced and the plate machined to the final thickness. The spindle speed and the
feed rate were kept at low until the surface was cleaned up.
November 20, 2014
23 Bottom Cylinder Cover
The rotary table was set up on the cross slide. The centration of the rotary table was achieved by
clocking in the chuck by mounting a DTI to the lathe spindle and measuring the run-out. The lateral
adjustment was achieved using the cross slide. The vertical was more subtle as this required
shimming. Using shim stock I was able to get the rotational centre to within 50um.
The ‘Bottom Cylinder Cover’ was mounted in the rotary table chuck via the cylindrical boss feature.
The part was brought to vertical using an engineer’s square from the bed of the cross slide. The first
set of holes was equally spaced on a PCD. These were marked out with a scribe mounted in the lathe
chuck; the position of each one being indexed around with the rotary table. The positions were then
checked and the holes then centre drilled, drilled to size before they were countersunk.
The second set of holes were on a square pitch, but were also centred on the axis of the part. So, I
decided to calculate the relevant angle 45 degrees in this case and PCD for the holes. The holes were
then marked out, again using the scribe in the lathe chuck. These positions were then checked using
the linear pitch dimensions as the reference. Each of the holes was centre drilled, then drilled to
size.
Figure 50 – The Rotary Table used to index the holes during drilling operations
24 The Stuart Half Beam Engine
November 20, 2014
Top Cylinder Cover The ‘Top Cylinder Cover’ is machined from a shaped casting. As with the other cast components care
and planning is required to ensure that the finished sizes can be achieved. Initially the part was set
up in a 3-jaw chuck via the chucking piece that forms part of the casting. The gland port face and the
bolting face were machined, leaving a 25mm diameter by 2mm thick cylindrical feature of cast
material. The holes for the gland, the 5mm and 8mm diameter holes were then drilled into the face.
Figure 51 – Drilling the Gland Boss
The part was then reversed in the 3-jaw chuck and mounted on the 25mm diameter boss. Thin shim
stock was used to protect the machined surface of the boss from being bruised and the chuck only
lightly tightened. The intermittent cuts caused the part to flex at the corners making controlling the
thickness more difficult. Light cuts of around 30m to 50m were then taken to bring the square
section to the correct thickness. The cylinder location boss was then turned to the correct diameter,
ф25mm f8 and then faced to length. To ensure the part can be accurately located onto the rotary
table for drilling the cylinder interface the chucking piece was machined to ensure it was concentric
with the location boss.
Figure 52 – Machining the Location Boss
November 20, 2014
25 Top Cylinder Cover
The rotary table was set up on the cross slide and the axis of the table clocked into the axis of
rotation of the chuck. The required adjustments were made as discussed previously. The part was
mounted in the rotary table chuck via the chucking piece. The part was brought to vertical using an
engineer’s square from the bed of the cross slide.
Figure 53 – Rotary Table mounted to the Lathe
The first set of holes, that interface to the cylinder, were equally spaced on a PCD. These were
marked out with a scribe mounted in the lathe chuck; the position of each one being indexed around
with the rotary table. The positions were then checked and the holes then centre drilled and then
drilled to size.
The second set of holes were on a rectangular pitch, but were again centred on the axis of the part.
So, I decided to calculate the relevant angles and PCD for the holes. The holes were then marked
out, again using the scribe in the lathe chuck. These positions were then checked using the
rectangular pitch dimensions as the reference. Each of the holes was centre drilled, then drilled to
size.
Figure 54 – Drilling the 7BA clearance holes Figure 55 – Marking out steam port gland holes
26 The Stuart Half Beam Engine
November 20, 2014
The part was then mounted in the 3-jaw chuck and the chucking piece removed and the face of the
location boss cleaned up. The final operation was to drill and tap the two threaded holes for the
gland. This was done by spotting through the holes drilled into the gland and then drilling the two
holes in the boss using the borer. The two holes were then tapped to 7BA and the gland trial fitted.
An alternative method of machining the part, possibly more accurate came to mind during the
machining of this part. If I was to do this again I would probably follow this procedure:
Mount the part in a 4-jaw chuck via the square portion with the chucking piece facing
outwards.
‘Clock in’ the cast boss feature so that the part is reasonably well centred.
Machine the ‘Main Cylinder’ mating surface and turn and face to length the location boss. At
this time machine the chucking piece to ensure that when the part is reversed and mounted
in the 3-jaw chuck the features machined will be nominally concentric to the location boss.
Reverse part mount in the 3-jaw chuck.
Machine the gland port face and drill the holes as required.
Machine the boss feature and the bolting face.
Machine the holes on the PCD’s using the rotary table.
Re-mount the part in the 3-jaw chuck via the gland port boss and face off the chucking piece,
bringing the cylinder location to size.
November 20, 2014
27 The A-Frames
The A-Frames The ‘A-Frames’ are supplied in the kit as two identical castings that require filing to remove the
flashing and casting marks. Extra care was taken when filing the outer edges of the parts so that they
could be polished. A range of files were used from a fine second cut to a needle file that could access
the rather hard to reach areas.
Figure 56 – Filing the ‘A-Frame’ removing the casting marks
Periodic checks of the surface were made using a surface plate and engineers blue. The high points
Identified were then filed in an attempt to keep the surfaces reasonably flat. The next stage was to
polish the edges with progressively finer grades of wet and dry on the surface plate.
.
Figure 57 – Removing the filing marks
28 The Stuart Half Beam Engine
November 20, 2014
This removed any machining marks and brought the parts to a reasonable finish. Oil was used with
the wet and dry to assist with the polishing process.
The ‘A-Frames’ were then mounted in toolmakers vices and clamped to the milling table. The parts
were then machined along the face that mates with the ‘Top Cylinder Cover’. This brought the
overall height of the components to 77mm from base to apex.
Figure 58 – Machining the base of the ‘A-Frame’
The part were then removed from the vice and clamped directly to the milling table. The raised
edges were then machined to bring the part to the correct thickness. This required approximately
0.5mm to be removed from each side, bringing the width of the part to 6mm. It is important to note
that these parts will be clearly visible in the final assembly and so care was taken to ensure that as
far as possible a reasonably uniform distance remained between the machined lips and the lower
cast area to maintain the aesthetic.
Figure 59 – Machining the ‘A-Frames’ raised features
November 20, 2014
29 The A-Frames
The faces of the parts were then polished with progressively finer grades of wet and dry on the
surface plate.
Figure 60 – Comparison of the ‘A-Frame’ before and after
The holes were then marked out on a surface plate with the height gauge. With the parts aligned
and clamped to the table of the borer, the spindle was positioned to drill the hole in the apex of the
‘A-Frame’. The hole was centre drilled and then drilled to size. The table was then indexed to the
position of the second hole which was centre drilled and then drilled to size.
Figure 61 – Drilling the clearance holes in the ‘A-Frame’
The last pair of holes in the base of the ‘A-Frames’ were drilled using the vertical slide on the cross
slide of the lathe. The holes were marked out on the surface plate with the height gauge and the
parts then clamped to the vertical slide. To ensure that the holes were drilled reasonably square, the
other ‘A-Frame’ was used as a setting piece. The position of the holes was then checked using a
scribe mounted in the chuck as shown in the figure below. The holes were then centre drilled and
then drilled to a 2.5mm diameter; the cross slide being used to index between each position. The
holes were then tapped 5BA on the bench.
30 The Stuart Half Beam Engine
November 20, 2014
Figure 62 – Holes being marked out ready for drilling and tapping in the base of the ‘A-Frames’.
The parts were then ready for a final polish with wet and dry to remove any remaining marks and
then finished with ‘Brasso’. However, before that a trial assembly of the ‘A-Frames’ together with
the ‘Top Cylinder Cover’, ‘Beam Pivot’, and ‘Piston’ assembly was carried out to ensure the parts
fitted well.
Figure 63 – ‘A-Frames’, ’Top Cylinder Cover’, ‘Beam Pivot’ trial assembly
November 20, 2014
31 The Cylinder
The Cylinder The casting supplied for the cylinder was excellent and only required a small amount of preparation.
There was some flashing around the ports in the bore and mould marks along the centre line of the
part, both of these were removed using a file. Time was taken to dimensionally assess the casting
and plan the operations and each face to be machined was marked with the amount of stock
removal with an indelible marker.
Figure 64 – Cylinder mounted in the 4-Jaw Chuck Figure 65 – Marking out steam port gland holes
The first step was to machine the interface for the ‘Steam Chest’. The cylinder was mounted into the
4-jaw chuck using the recess for the jaws to work as a location for the round section of the cylinder.
The face to be machined was orientated using an engineer’s square off the saddle to minimise the
metal to be removed from this face. Shim stock was used to prevent the chuck jaws from marring
the cast surface. As the cuts initially were intermittent only small cuts were taken at a low speeds.
The spindle speed was increased for the last cuts and the feeds reduced.
The cylinder was then set up on a Keats angle plate that was mounted to the lathes faceplate. The
cast bore was centred using a combination of the centre on the tail stock and a DTI. The bore was
located to within 0.5mm of total run out.
Figure 66 – ‘Cylinder’ boring
32 The Stuart Half Beam Engine
November 20, 2014
The cylinder end was faced removing nominally 1mm of material. It was then bored through to
25mm diameter H7 tolerance as specified for the ‘O’ Ring (BS 4518 type 0195-30) in the same setting
to ensure the bore and the top end face are perpendicular. This is important as it will ensure the
piston can run true in the cylinder without binding.
The cylinder was then reversed in the Keat’s angle plate using the port face again as the reference
and the reverse, bottom end was faced. Nominally 1mm was removed to bring the length of the
cylinder to within tolerance. The parallelism of the two faces was checked using the surface plate
and the height gauge and found to be within 100m.
The cylinder was then mounted on to some 25mm diameter ground silver steel. The cylinder bore
was a snug fit and a small amount of tape held the part fast. The six holes in each of the end faces
were then indexed and drilled. The figure below shows the arrangement. Care was taken to ensure
the drill did not break through and the holes were each drilled to a depth of 3.5mm.
Figure 67 – Drilling the holes in the ‘Cylinder’ end faces
Figure 68 – Port face holes drilling
The port face holes were then marked out on the surface plate using the height gauge. The holes
were marked relative to the top end face. So this face was placed on the surface plate. The top end
face is the one faced at the same time as the ‘Cylinder’ was bored. As stated previously this was
done to ensure it is perpendicular and that the piston will run true.
November 20, 2014
33 The Cylinder
The ‘Cylinder’ was then set up on the vertical slide. Packing was used to ensure the port face was
square to the chuck. Then each of the holes was centre drilled and then drilled to depth.
Each of the sets of holes, both those in the end faces and those on the port face were then tapped
on the bench. Due to the shallow depth of the holes it was necessary to grind the end of the tap flat
to allow the tap to thread to the full depth of the hole.
Once these operations were complete the whole ‘Cylinder’ Sub Assembly could be trial assembled.
This allowed both the ‘Cylinder’ and ‘Baseplate’ assemblies to be brought together for trial
assembly. This can be seen in the figures below.
Figure 69 – ‘Cylinder’ Sub-Assembly
Figure 70 – ‘Cylinder’ and ‘Baseplate’ Assembled
34 The Stuart Half Beam Engine
November 20, 2014
The Eccentric Sheave and the Eccentric Strap The Eccentric Sheave is machined from a piece of cast iron round bar that is supplied in the kit. The
cast iron is used as it will run smoothly on the gun metal material supplied for the eccentric strap.
The bar was mounted in the 4-jaw chuck and ‘clocked in’ to run concentrically. The part was turned
to the OD which is a general tolerance along a length longer than that of the part. The two
concentric features that form the bearing surfaces were then machined to the ‘f8’ tolerance. The
length of first feature includes the length of the both the bearing surface and the boss to be
machined eccentrically.
The second bearing surface forms the location rib. The length and location of the second bearing
surface has to ensure the thickness of the location rib is within tolerance and that the bearing
surface is long enough to get the whole part from the bar. See Figure 71 below.
Figure 71 – Turning the ‘Eccentric Sheave’ Bearing Surfaces Figure 72 - Machining ‘Eccentric Sheave’ boss
The part was then decentred in the 4-jaw chuck. A dial test indicator was used to ensure that the
boss would be machined with the correct offset. It should be remembered that the offset is half of
the full scale deflection indicated. This allows us to position the part with a reasonable degree of
precision with a 10um DTI. The boss was then machined to diameter and length. The bore was
centre drilled and then drilled out to 11.5mm before finally reaming the hole to achieve the ф12 H7
tolerance required.
The part was then be parted off from the stock
and mounted in a 3-jaw chuck by the boss
feature. Shim material was used to protect the
finished surfaces from being ‘marred’ by chuck
jaws. The part was then faced to length and the
small boss feature machined. The part was
removed from the lathe and mounted in the mill
to drill and tap the 5BA securing screw.
Figure 73 – The ‘Eccentric Sheave’ machined to size
November 20, 2014
35 The Eccentric Sheave and the Eccentric Strap
The ‘Eccentric Strap’ is machined from a bronze extrusion. The stock, as supplied was measured and
the machining allowances were marked on the part and the drawing. The first step is to bore the two
2.5mm clearance holes that will be used to join the two halves of the strap together. These are
located on the approximate centre line of the part to allow an even amount of stock removal from
the front and rear faces. The strap can then be removed from the vertical slide and sawn along the
line marking that is part of the extrusion. The joining faces were checked and the two mating faces
were machined so that the lugs were nominally 6mm thick.
Figure 74 – The ‘Eccentric Strap’ Reassembled Figure 75 – Facing the rear of the ‘Eccentric Strap’
The part was then bolted together using the 5BA screws that come with the kit. The centre of the
parts was then marked out and the part set up in the 4-Jaw chuck. The rear face of the component
was set facing away from the chuck and this surface was machined to size. The rear surface now
becomes the datum and the part is then drilled and bored out to size. The diameter 27mm H7 bore
was checked against the eccentric to ensure it would run smoothly. The retaining groove that keeps
the ‘Eccentric Sheave’ in place was then machined.
Figure 76 – The ‘Eccentric Strap’ Bored Figure 77 – Milling the rebate the ‘Eccentric Strap’
The part was then revered in the chuck and re-centred and the front face machined to size. The part
was then moved to the milling machine. The part was clamped to the machine table and the rebate
for the area that connects to the ‘Eccentric Rod’ was produced. The two holes were then added to
suit the holes drilled into the ‘Eccentric Rod’. This operation was left until the assembly to ensure
that the parts were correctly integrated.
36 The Stuart Half Beam Engine
November 20, 2014
The Eccentric Rod and Eccentric Clevis Both the ‘Eccentric Rod’ and the ‘Eccentric Clevis’ are produced from carbon steel flat bar stock that
is supplied with the kit. The length of the rod according to the model is 116mm long. However, I
have decided to finish this part once the remainder of the assembly is complete so that I can be sure
to set the length correctly. However, the three holes at the valve end of the part can be marked out
and then drilled at 2.6mm diameter for the pair that connect to the ‘Eccentric Clevis’ and drilled and
reamed for the 3.0mm diameter H7 hole, that connects to the valve gear. In addition to this, the
radius was formed at the end by filing.
Figure 78 – The ‘Eccentric Rod’ and ‘Eccentric Clevis’ Figure 79 – The ‘Eccentric Rod’ and ‘Eccentric Strap’
The ‘Eccentric Clevis’ is slightly more complex, in that the position of the holes and the bend are
quite critical. The first stage was to bend the part to provide a 6mm offset. This was hard to do to
sub millimetre accuracy but I was happy with the 7mm offset I achieved. The 3mm diameter H7 hole
was then drilled and reamed and by aligning this to the 3mm hole in the ‘Eccentric Rod’ the radii
could be filed to match and the holes could then be marked through and any adjustments required
to the ‘Eccentric Clevis’ could be made.
With the connection to the ‘Valve Lever’ complete, the length of the ‘Eccentric Rod’ could be
assessed on the full assembly. The 116mm length appeared correct and so the part was cut to length
and the connection drilled to the ‘Eccentric Sheave’. The part was then ready for assembly to the
‘Crank Shaft’.
<Picture of the Eccentric Assy after >
November 20, 2014
37 The Flywheel
The Flywheel The ‘Flywheel’ casting is one of the larger castings to be machined. The flash and other casting marks
were removed with a file and the part measured and the depth of cuts determined for each of the
surfaces. The casting was mounted in the 4-jaw chuck with the jaws set to clamp on the internal
surface of the rim of the flywheel.
Figure 80 – Centring the ‘Flywheel’ Figure 81 – Machining the ‘Flywheel’ Boss
The wheel was centred and the run out reduced on the central boss and the lip to around 300um on
the cast surface. The first operation was to face and turn the boss to size before drilling and reaming
the 12mm H7 diameter hole for the ‘Crank Shaft’. The hole was initially centre drilled then drilled
through at 6mm diameter and then 11.8mm diameter before reaming.
The next step, whilst the ‘Flywheel’ was held in the 4-jaw chuck was to face and turn the outer rim.
By machining this in one setting ensured that both the boss feature and the rim of the ‘Flywheel’
remained concentric.
Figure 82 – Keeping the Boss and Rim concentric Figure 83 – The ‘Flywheel’ mounted on a mandrel
After these operations were completed, I machined a mandrel from some 18mm diameter carbon
steel stock. In fact it was the other end of the mandrel that I had machined for the Stuart 10V
‘Flyweel’. The mandrel was turned to a 12mm g6 diameter and terminated with an M8 thread to
secure the ‘Flywheel’.
The mandrel was mounted in the 3-jaw chuck and the ‘Flywheel’ was secured against the shoulder
with the un-machined parts facing towards the tool post. As the lathe was spun up the ‘Flywheel’
could be seen to be running true. The second boss feature was then faced and turned to size and the
last face of the rim was faced to bring the ‘Flywheel’ rim to width. Care had to be taken with the
38 The Stuart Half Beam Engine
November 20, 2014
spindle speed as the tool was liable to chatter. I reduced both the speed and the feed for the final
cut and the finish was good.
Figure 84 – The mandrel used to machine the ‘Flywheel’
The last operation was to drill and tape the retaining screw in the ‘Flywheel’ boss the hole was
drilled with a pistol drill and tapped by hand on the bench.
Figure 85 – The finished ‘Flywheel’
November 20, 2014
39 The Flywheel
The Beam Support
The ‘Beam Support’ is supplied as a casting and requires finishing in a similar way to the ‘A-Frames’.
Initially the part was supported by a parallel and clamped to the table of the borer. The two faces
were machined to allow the relief pattern to be polished at a later date and to bring the part to the
correct thickness. The bottom edge was then milled to provide a reference edge and the inner
surfaces of the yolk were cleaned up.
Figure 86 – Machining the ‘Bean Support’ Figure 87 – Removing the file marks
The outer edges were then filed smooth to remove the features left over from the casting process.
The bulk of the material was removed with a second cut file. A needle file was used to remove the
marks left by the file and then the edges were treated with progressively finer grades of wet and dry.
This was done on the surface plate top maintain the square edge of the part. A small amount of oil
was used to improve the finish.
Figure 88 – The finished ‘Beam Support’
Finally the two faces were polished with wet and dry and a small amount of oil to remove the
machining marks and bring the surfaces to an even finish ready for polishing for polishing.
40 The Stuart Half Beam Engine
November 20, 2014
The Beam This rather simple looking casting along with the ‘steam chest’ caused me the most difficulty in
machining to a satisfactory state. I started off by cleaning up the outer flanged surfaces with a file.
There were a couple of small features left from the casting process that needed to be removed and
the whole of the outer ‘rim’ of the beam needed to be cleaned up ready for polishing. I started with
a second cut file before moving to a needle file and then to wet and dry laid on the surface plate
with a small amount of oil.
Figure 89 – Dressing the Flanged surfaces of the ‘Beam’
The beam was then supported on parallels and clamped to the borer table. The bosses and rim of
the flanged edge brought to the correct thickness. The four holes were then marked out on the
surface plate with the Vernier height gauge.
Figure 90 – Milling the faces of the ‘Beam’
I then drilled the 3mm and 12mm diameter holes undersize, 2.5mm and 10mm respectively. I
removed the beam from the table and to my horror, the holes, whilst central on one side were off
centre by a large amount on the other!
After stopping and some careful consideration I thought about scrapping the ‘Beam’ and buying a
new casting. However, I first decided to find out what had gone wrong. It transpired that the bosses
November 20, 2014
41 The Beam
cast into the face of each side of the beam were not in aligned to one another. Would a new casting
be any different?
I decided to try to recover the ‘Beam’. I mounted the beam on the vertical slide mounted to the
cross slide of the lathe and aligned the 10mm diameter bore to the axis of the machine. I then drilled
and reamed this hole to the 12mm size and checked the concentricity of the hole to the cast boss. A
minor correction was made to the cast boss using a small Dremel type grinder.
The vertical slide was replaced on the cross slide by the rotary table fitted with a 4”, 3 jaw chuck. The
chuck was ‘clocked in’ so that its axis of the rotary table was aligned with the axis of the lathe
spindle. The ‘Beam’ was then mounted to the rotary table chuck via the mandrel produced for the
‘Flywheel’. The part was then orientated using the rotary table and the lathe cross slide and the
3mm holes were carefully and slowly milled into the part using a slot drill.
This ensured that the 3mm holes were reasonably parallel to the main 12mm diameter hole. On
inspection the hole that interfaces to the connecting rod was still not central to the cast boss feature
on one side. So I decided to machine a larger hole, slightly offset to minimise the decentre on both
sides. This worked and required only a small amount of correcting or the cast feature with the small
Dremel type Grinder and needle files.
To correct for the now over-size hole I machined a small brass sleeve insert which also acts as a
bearing. This will hopefully be obscured by tines of the connecting rod. All in all I am happy that I
managed to save the ‘Beam’ from the scrap pile. Unfortunately, I neglected to take any photographs
of this process as my mind was elsewhere.
This whole episode reminds me that I should not be complacent and I should double check
everything before making a cut!
<Picture of the Beam after >
42 The Stuart Half Beam Engine
November 20, 2014
The Connecting Rod and Big End Sleeve Bearing The material for the ‘Connecting Rod’ is supplied as a flat bar of 5/8” (15.8mm) x 1/2” (12.7mm)
section. The first step was to mount the stock into the 4-jaw chuck and ‘clock in’ so that it ran true
about the axis. Both ends were then faced and centre drilled for the subsequent turning operations.
The main features, the big end, little end and bottom of the yolk were marked out and centre
punched and drilled through with pilot drills. The waste material in the yolk was then chain drilled to
remove the majority of the material before machining a slot which will eventually form that feature.
Figure 91 – The ‘Connecting Rod’ drilled
The ‘Connecting Rod’ was then clamped to the table and supported on a pair of aluminium plates to
allow the cutter to go through to the full depth without damaging the table. The rotary table allows
the length of the stock to be ‘clocked in’ very easily. The cutter was then touched on and brought
into position. Initially an 8mm slot drill cutter was used to
remove the majority of the material and the slot was
finished with a 10mm diameter cutter to bring the width
of the slot forming the yolk to size.
The part was then removed from the table and deburred.
The width and shape of the big end and the width of the
tines of the yolk and the circular features around the small
ends were then marked out on the surface plate
Figure 92 – Machining the Slot for the yolk Figure 93 – Marking out the other features
November 20, 2014
43 The Connecting Rod and Big End Sleeve Bearing
The ‘Connecting Rod’ was then clamped to the vertical slide that was mounted on the cross slide of
the lathe so that the big end pilot hole could be opened out to size. A 9.8mm diameter drill was
used, followed by a 10mm diameter reamer to bring the hole to size.
Figure 94 – Drilling the ‘Connecting Rod’ Big End Figure 95 – Reaming the ‘Connecting Rod’ Big End
The part was then mounted between centres. The top slide was adjusted using a DTI to machine a
taper of 1 in 30. This will be used to machine the ‘fish bellied’ effect. The tool was aligned to the
portion to be machined and the diameter was reduced down to 8mm using the saddle.
Figure 96 – The ‘Connecting Rod’ between centres Figure 97 – Machining the ‘Connecting Rod’
The taper was then machined into the central portion. The top slide was then repositioned to
machine the taper in the other direction and complete the ‘fish bellied’ effect. The surface was then
polished with progressively finer grades of ‘wet and dry’ paper to remove the tool marks and make a
smooth uniform finish.
The ‘Connecting Rod’ was then clamped to the table of the borer and big end machined down to the
size. The end was then sawn off and the radii filed to shape. See the figures below.
Figure 98 – The ‘Connecting Rod’ filed to shape Figure 99 – The ‘Connecting Rod’
44 The Stuart Half Beam Engine
November 20, 2014
The ‘Connecting Rod’ was then set up on the borer so that the tines could be machined down to size.
Sufficient material was left to form the radii at the end of the tines. Once the tines had been
machined to the correct width the job of carefully filing the radii at the end began. A combination of
round files and needle files were used. The end was then removed and the part finished.
Figure 100 – The ‘Connecting Rod’ radii being finished
The ‘Big End Sleeve’ is a relatively simple component but the outside and inside diameters are
controlled by limits and fits. The part was machined from a piece of Phosphor Bronze. The outside
diameter was turned to size and the inside diameter drilled and reamed. The ‘Big End Sleeve’ was
then parted from the stock at length. It was then deburred and trial fitted to the assembly.
Figure 101 – The ‘Big End Sleeve’ drilled and reamed
November 20, 2014
45 The Pulley
The Pulley The pulley casting was actually missing from the kit of parts when I received it. However, Stuart’
were very helpful and once we told them it was omitted from the kit, they happily posted one
through. The part was carefully surveyed and the depth of cuts required to machine the part to the
final dimensions were calculated. It was then mounted in the 4-jaw chuck by the larger of the
diameters and centred using a ‘DTI’ to minimise the ‘run-out’ in the boss portion. The boss and the
near side face of the pulley were faced and then brought to final size. The boss was then centre
drilled, and the bore for the main crank shaft, drilled to ф11.5mm before it was then reamed to
ф12mm H7.
Figure 102 – Drilling the ‘Pulley’ Bore Figure 103 – Turing and facing the ‘Pulley’
The part was then reversed and mounted in a 3-Jaw chuck. Thin shim material was used to protect
the finished surfaces from being ‘marred’ by chuck jaws. The part was then faced to length and the
outside diameter of the part brought to size. A series of 3 groove features were then machined in to
the outer surface. Chamfers were then added to break each of the sharp edges. Lastly the 5BA hole
was drilled and tapped into the boss.
Figure 104 – Finished ‘Pulley’
46 The Stuart Half Beam Engine
November 20, 2014
The Assembly & Finishing The parts were trial assembled in their sub-assemblies as time went on. These were then integrated
into the main assembly to ensure they would fit. At each stage some fitting work was required to
ensure the parts operated together and run true. With the completion of the bulk of the parts the
final trial assembly and integration could begin. The components on the ‘Crank Shaft’ such as the
‘Pulley’, ‘Eccentric’ and ‘Flywheel’ needed fitting to the shaft. The positions were set and I found that
there were small gaps. So, I machined a number of spacers from Delrin to ensure the ‘Crank Shaft’
did not wander as it was driven.
Figure 105 – The ‘Valve Gear’ Assembled. Figure 106 – The ‘Beam’ and ‘Crank Shaft’ Assembled.
In addition to this the smaller bearing components and the valve gear required adjusting so that the
timing was correct. A small amount of fettling was required to ensure that the valve operation was
satisfactory and was relatively free of friction. The assembly was then ‘run’ using an electric drill.
November 20, 2014
47 The Assembly & Finishing
Figure 107 – The Trial Assembly Completed
The next step was to finish the oak base and begin the finishing processes for each of the parts. Both
the ‘Baseplate’ and the ‘Pedestal’ were fixed down using custom screws made from hex-bar to
fasten the engine to the oak support base assembly. The engine was then stripped down and each of
the parts cleaned, painted and polished as required ensuring a pleasing finish.
