Dimensioning
01/28/09
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Working Assembly Drawing
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Dimensioning of Holes
Counter Bored
Holes are shown
as concentric
circles in the plan
view, and
dimensioned
using the
standard symbols
Dimensioning of Holes
Countersunk holes
are dimensioned by
Callout the diameter
of the thru hole, the
diameter of the to of
the counter sink and
the included angle of
the countersink.
Spot Faced Holes
The symbols for
spot faced holes are
the same used for
countersunk holes.
Conventional Breaks
These are used to shorten very long objects
that have the same cross section throughout
or a uniform taper.
Cylindrical object are “broken” with a “S”
shape
Rectangular and other non-cylindrical object
are “broken” with a jagged heavy weight
irregular line, (.6mm), always drawn freehand.
Conventional Breaks
The length of these parts will not be
shown to scale, but will be dimensioned
as if the break was not there.
Dimensioning of Chamfers
Dimensioning of Knurl Finishes
A knurl is a roughened surface intended to provide a better hand grip or press fit between two parts
Coordinate Dimensioning
The use of Coordinate or baseline dimenions
eliminates the effect of “accumulation of
tolerances”, and is useful to the machinist
using a positioning table.
Tabular Dimensions
Used to show dimensions of similar parts, tabular dimension reduce the number of drawings required for a series of nearly identical parts
Mating Parts
In instances where a feature on a part
must fit into or onto another part. The
“mating dimension” must be identified.
Mating Parts
Mating Dimensions
Most often the dimensions of the mating
features will not be the same, and a
factor will be added to the dimension to
allow for the type of fit intended by the
Designer, (clearance, interference,
etc…)
The Cad Technician must choose the
dimensions keeping the type of fit and
tolerances in mind.
Key Ways
The dimensions for standard key ways are found in The Machinists Handbook
The distance from the center of the recess to the edge and the width of the recess are always provided.
The distance from the bottom of the shaft to the bottom of the keyway is always provided, rather then depth of the recess
Key Ways
Machine Pattern and Forging Dimensions
Parts that are machined from castings, will have a set of dimensions that the casting pattern maker will work from, and a set of dimensions that the machinist will work from.
When the part is not complicated enough to require two drawings, the dimensions for pattern maker and the machinist may be included on the same drawing.
Since the machinist will refer to the drawing more often then the pattern maker the drawing should be arranged in a manner that is convenient for the machinist.
Machine and Pattern Dimensions
Forged and Machined Parts
Separate drawings are typically created
for the forged part detail and the
machined part details.
Finish Marks
A Finish mark is used to identify those
surface that are to be machined or
finished, (as on a casting of forged part)
To the diemaker or pattern maker it
indicates that additional material should be
provided to allow for finishing.
If a part is to be finished on all faces a
note such as FINISH ALL OVER would be
used rather than the finish symbol
Finish Marks
Finish marks are only shown on the
edge view of a finished surface, and are
repeated in all views that show the
finished edge..
If a part is to be finished on all surfaces,
the notation “Finish All Over” or “FAO”
should be used in lieu of a Finish Mark
Finish Marks
Surface Finishes
The need for higher performance power
transmission components and other
devices that can withstand heavy loads
and high speeds has increased the need
for accurate control of surface finishes
Surface Finishes
The surface finish symbol alone is not
enough to specify a finish for a high
performance component.
Symbols for Surface Texture, Lay, and
Roughness are used to dimension
surface finish.
Surface Finish Symbols
Surface Finish Specifications
Lay Symbols
Surface Roughness
Designations
Process Range of Roughness
in Microinches
Range of
Roughness in
Micrometers
Flame
Cutting
500 – 1000 12.5 - 25
Milling 32 – 250 .80 – 6.3
Grinding 4 – 63 .10 – 1.63
Electro
Polish
4 – 32 .10 -.80
Welds
Welding Symbols
Most Commonly used welds
Fillet
Bevel
V Grove
V Grove Butt Welds
Bevel and Butt Welds