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andsaw for the Lathe

by Dennis HorlerBASICALLY A BANDSAW is a flexible saw blade

arranged to move downwards in a vertical plane.This is restrained by side and rear thrust devicesand held in tension by an adjustable tension wheel.It is essential that the blade runs true and doesnot wander when the work is applied. This isaccomplished by an angular setting device incor-porated on the shaft of the free running wheel.

For economy and space considerations themachine was built to operate on the bed of anM.L.7 lathe and was also provided with a choiceof speeds. It is worthwhile to slip two pieces of

cardboard between the base of the bandsaw andthe lathe shears; this will prevent any damage totheir surface.

T h e f r a m eIt is sound engineering practice to make all

frames as heavy as possible, so that all or mostvibration is absorbed. The frame was made of3/8 in. thick mild steel plate cut to shape as inFig. I. It was made in two pieces for convenience

of working. The bearing points were stiffened upeach side by welding 1/2 in. thick mild steel discsor bosses. The two members are held together bya 1/4 in. thick plate at each side and bolted through.The top member is extended at the front bywelding a bracket on the front edge to take thesaw guide assembly.

Two pieces of 1-1/2 in. x 2 in. angle were weldedto the lower frame member to form a clampingbracket to fit on the lathe shears. After cutting toshape, all rough edges should be cleaned up and theholes drilled as required. It is best to drill in the

lathe with the frame bolted to an angle plate on thecross-slide, thus ensuring that all holes are squareto the frame face. Before drilling the rivet holesin the angles at the base and the locating crossmember, make sure the frame is at right angles tothe lathe bed.

M a in s h a ft s a n d b e a r i n g b u s hHaving completed the frame, the shafts are the

next logical step. Fig. 2 shows all details. The

Below, left: The Bandsaw ready for use.

Below: The machine with the guards removed.

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FIG. I G.A. OF FRAME

BMS

15

Brass washer adjusting screw

I _, X check on assy2-1/2"x1/4"D silver FREE RUNNING BANDsteel bar WHEEL SHAFT BMS

Turn lubrication groove

DRIVE BEARING SHAFT ADJUSTING

BRASS SCREW BMS

F I G 2

Slots milled to suitsilver steel ba r

Retaining platessecuring to frameb y 2BA s c r e w s

UPPER WHEEL ANGULAR ADJUSTMENT

FIG 3

FlG 5

BRASS FIG. 4 WHEEL- -858 MODEL ENGINEER 6 September 1968

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c-_; 4, _, 34 , i,?ON ADJUJSTING SCREW

BMS

DETAILS OF THE BANDSAW

plywood. 2 o f f

Curved Sectionplast ic ty re

(Table edging)

-BOSS FOR DRIVE WHEEL

HEEL DET AI LS BMS

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main shaft consists of a shouldered length-of mildsteel with a hole drilled on the diameter at thelarge end for a split pin to secure the bandsaw

wheel. This should be drilled after marking offthrough the wheel boss to ensure sufficient endplay for free rotation. The main drive bearing isturned from phosphor-bronze, the outside being apress fit into the hole on the frame. The boreshould be reamed 7/16 in. dia. to fit the drive shaft.It is likely that the hole will close up after thebush is pressed into the frame; this can easily becorrected by reaming again.

The upper or free running shaft is also detailedin Fig. 2 and should present no difficulty. Theexploded view Fig. 3 shows the purpose of the

860

Above left: A close-upv i ew of thedrivemechanism.

Left: A view

of the thru strollers.

adjustment. This provides angular movement ofthe top band wheel in relation to the vertical planeof the blade. This ensures that the blade will runon the top of the curved surface of the wheel andremain there. The shaft is supported by the supportbar which is a length of silver steel; it is held inmilled recesses and kept in position by retainingplates and screws.

The band wheels, Fig. 4, are made up by gluingthicknesses of plywood together, making up a totalthickness of I in., and turning to 7-1/2 in. dia. Thecentre is drilled to take the bushes which are madeof mild steel for the drive wheel, and phosphor-bronze for the free running wheel at the top. Thedetails of the bushes are clearly indicated in thedrawing and an oil hole should be drilled at anangle from the outside face; when completed anoil groove should be scored across the inside of

the bore. The bushes are held in position bythree nuts and bolts spaced at 120 deg.; note thatthe clamping shoulders are dimensioned so that theplates make contact with the bushes before thewood in order to prevent movement. The mildsteel bush for the driving wheel is extended, thusallowing for a split pin to secure the wheel to theshaft.

The edges of the band wheels are completed withplastic trim, this is of curved section one side andflat the other and is sold for table edging. Thisis a must, the machine will not work with flatedges nor will it work if the wood edges are turnedto a curved shape due to lack of resilience. Theplastic trim should be cut at an angle where theoverlap occurs and stuck down without overlapwith Evostik.

Blad e t en s io n in g d ev iceThis is a free-running tyred wheel made from

plywood or fibre with a tyre of plastic trim. Thewheel is fitted on an adjustable bracket tensionedby a screw as detailed in Fig. 5. Since this wheel

revolves at high speed, it is fitted with a brassbush press fitted into the bore.

M a in d r i ve a s s e m b l yThe details are given in Fig. 6; the drive is

taken from the lathe chuck via a length of mildsteel to one side of a flexible coupling. If acoupling is not available a piece of heavy dutyhose-pipe about 2 in. long can be used. This isattached to the stub shaft that fits in the chuckand held with a Jubilee clip.

The other end is attached to the conduit andagain held by a Jubilee clip. The purpose of theflexible coupling is to relieve the lathe chuck of anyaxial or radial thrusts which may be imposed ifthe shaft centres are not in dead alignment.

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The various parts are machined as in Fig. 6;the main drive shaft should either be screw cutor tapped using the die in the tailstock holder.Similarly the hole in the frame should be threadedby using the tap in the chuck. This ensures thatthe shaft, when screwed up tight, will be square

with the face of the frame.The bushed pulley fits on the shaft and issecured by the 2 BA bolt and brass washer. Theconduit fitting (this was only used because it wasavailable and saved machining from stock) wasthen bolted to the pulley with two 1/4 in. bolts.The pulley boss should be turned off and the facecleaned up to receive the dome cover which wasalso machined. It may be necessary to put spacerwashers on the bolts between the pulley and thedome cover to give a little extra play. Beforepressing the bush into the pulley, two flats should

be filed or milled to give clearance for the fixingbolts.

A conduit nipple is screwed into the dome coverand locked with a nut, the short length of conduitis then screwed on and tightened. Next the shaftis turned to a tight fit into the conduit and fixedwith a split pin. The other end of this shaftcarries the flexible coupling or hose-pipe.

In order to keep the belt tight, which is ofcircular leather with a U fastener, a bushed

jockey pulley of any convenient size is fitted to abracket which is bolted to the frame. This istightened up at a suitable angle so that the pressureis applied to the belt and keeps it taut.

U p p e r b l a d e g u i d eGuides are required above and below the saw

table to offset the back and side thrusts producedwhen work is fed into the saw. This is shownas an exploded view in Fig. 7. The main supportis turned from 3/4 in. square steel bar to 1/2 in. dia.as shown; this fits into the holder welded to theframe. It is made adjustable to allow for height

variations over the work being sawn. A piece of7/8in. x1/8 in. b.m.s. is bent as shown and fixed tothe main support by two lengths of 1/4 in. BSFstudding to allow alignment with the blade in thevertical plane.

Take care when drilling the fixing holes for thebrass guide bars, these should be clamped up onthe bench with a short length of blade in position,together with a piece of 1/32 in. shim. The holescan then be drilled in this position; when the shimis removed the correct gap between the guides is

obtained. The back thrust is taken by a brassroller carried on a shaft fitted on the lower extensionwhich is twisted at right angles to the bent flatsteel holder. The shaft is threaded at each endand held in position by shake-proof nuts.

T a b l e s u p p o r t a n d l o w e r b l a d e g u i d e s

The table support serves two purposes, to supportthe table and also to hold the lower blade guides.Fig. 8 gives full details. The vertical member iswelded to a length of angle; this angle is drilled toreceive the table. Below this is a steel rod

shouldered at one end which carries a small lengthof angle mounted in a position behind the sawblade. This is located and fixed and the holes forthe side thrust roller shafts are marked off withthe saw blade in position. The saw blade shouldbe tensioned so that the band wheels grip theblade. Insert the piece of shim alongside the sawblade and place the rollers in position, either getsomeone to hold them or clamp up with a handvice. Now turn up a piece of steel so that it justfits the roller bore, turn the end to a point anduse as a centre punch to mark the hole centres

for the roller shafts. The holes can now be drilled,the shafts made and fitted in position. Note thatthe thickness of the rollers are less than the widthof the saw, and when in position the rollers areclear of the saw teeth. Since it is difficult at sucha small diameter to drill oil holes in the shafts, anoil groove is made inside the roller bore to retainand distribute the oil.

The back roller is mounted on a shaft with alarger end than the roller bore, and bolted up to ashoulder which allows free rotation and a littleend play. A lubrication hole is drilled through atan angle. This is bolted to a threaded bar, allowingmovement to line up with the rear of the sawblade. It should be fitted so that the roller justtouches the blade when the upper roller alsotouches : the working thrust is then shared betweenboth thrust rollers and gives the necessary supportat the working position of the blade.

It should be noted that the fixing holes on thevertical member for fixing to the main frame areelongated on one hole. This is to allow for anydiscrepancy in the centre markings for the band

wheels, and will also enable the table to be correctedif necessary to ensure vertical cuts.

T a b le a n d g u a r d

The table is simply a piece of 1/8 in. thick steelplate 8 in. square with a slot cut in the centre toreceive the saw blade. This slot is connected tothe side edge by a saw cut cleaned up with awarding file, alternatively cut with two hacksawblades, it will give the necessary width to allowthe band saw blade to be threaded. The tableis fixed to the angle support by means of twocountersunk 1/4 in. dia. Whitworth nuts and bolts.

The guard is a piece of plywood fitted with boltstapped into the machine, This could, however, be

Continued on page 852

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boiler on each side of the tug.Boilers and tubes were of iron and generally

lasted as long as the tug; the vessel might get asecondhand pair, but never a new set. Coalconsumption was heavy and owners often remarkedthat all the profits go up the funnel.

Boiler pressures varied between5

and 25 p.s.i.The simple lever and weight safety-valve couldeasily be tampered with and this was quitefrequent for short periods. When a little moresteam was required a shackle (always handy) wasplaced on the lever.

The old boilers rarely exploded but blows were frequent in shell and tubes. Temporarypatches were often applied to tide things over;these were known as one-eyed patches con-sisting of a nut, bolt and washer, liberally smearedwith red lead and tar.

I remember the case of an old tug steaming tothe breakers yard with two dozen one-eyedpatches on each boiler.

The wooden paddle tugs were essentially thesame, closely resembling each other; they variedin size only. The largest were the Seekers buteven the small ones also went over the bar tolook for a sailing ship when they had nothing elseto do.

Clipper stems, with or without bowsprits, werecommon to the very oldest tugs, then a veryinclined straight stem superseded them. Graduallythe inclination became less and less but they neverbecame vertical.

Tugs were steered by tiller at first, but later asteering wheel was placed forward of the enginehouse on deck; this alternative was generally usedfor long straight runs. In confined waters such asdocks, the tiller was more convenient, but it was

a very dangerous method though quick acting.The tow rope was a menace; many skippers wereknocked overboard or suffered broken legs.Finally, the steering position was taken to thecentre of the bridge plank over the casings; thiswas inconvenient when the very high spring tides

prevented the tug from passing under the SwingBridge at Newcastle. The funnels were cut forlowering but the primitive bridge screens toshelter the skipper were above the cut in thefunnel; this meant waiting for the tide to fall.

The first wooden tugs combined towing sailingships with ferrying, but the latter stopped in 1862when the regular ferry service was started by theTyne General Ferry Co. By this time industrywas in full swing and all its raw materials, coaland coke were carried by wooden wherries; theyalso carried the finished products to the regular

weekly boats established at the Newcastle Quay.There was abundant work until the First World

War after which this heavy traffic went on to theroads; tugs and wherries gradually died out.

One thing about paddle tugs eludes me: I cannotstate positively why they were so popular on theTyne; they existed in large numbers when allother rivers had discarded paddle tugs. No doubtthe private owners of the single-engined, woodenpaddle tugs lacked capital and the discards fromother rivers were to be had at reasonable prices, butthat did not apply to the company boats; thesewere iron tugs with twin, disconnecting side-leverengines. The fleets of these large vessels werepredominantly paddle tugs.

Screw tugs trickled here very slowly and mostof them were secondhand; I cannot account forthis very slow change over and probably nevershall be able to do so. q

BANDSAWCont inued f r o m p a g e 86 1

elaborated by making a hinged guard of plywoodto open as and when required.

P u t t i n g t o w o r k First of all, fit the blade over the wheels and

line up between the guides. Next adjust thetension wheel until the driving wheel will turnthe blade without slipping. Make sure the machineis lubricated, and with the lathe in back gear do a testrun. Carefully watch the blade to see if it trackscorrectly, if it runs to one side of the upper or lowerwheel, correct by making a small adjustment to theupper shaft. Having corrected the tracking, the bladeshould run smoothly and without side movement

on the wheels. Now put the lathe on higher speed

and make a test cut on 1/2 in. thick wood. If theblade tends to sag, increase the tension; if thickerwood, say up to 2 in. thick is to be cut, the tensionmay require to be increased more, but this thicknessshould not be difficult to cut. It should, of course,be appreciated that sharp curves cannot be cut in one go as they tend to twist the blade, but toywheels 2 or 3 in. dia. should present no difficulty.

Mate r i a l sAll materials used are easily obtainable. The

saw blade was obtained already as a loop 5 ft. 3-3/4 in.long, 1/4in. wide and with seven teeth per inch, butlengths can be obtained brazed up to suit individualrequirements. The blade used was obtained fromBurgess Products. q

852 MODEL ENG INEER 6 September 1968