Transcript Slide 1

Engineering Drawing:
a machine shop perspective
Presented by Angus Macpherson
What makes a good drawing?
 It should clearly describe the part.
 The dimensions should match the intent of the part
Basic Information Included in a Drawing
 Projected Views:
show as many sides
as required for completeness.
 Cross Sections: the preferred way to show internal features.
 Title Block: should include part name/number, type of material,
number of parts required and the name of the designer.
Do not use default settings blindly.
If the function requires different units or more or
less precision adjust accordingly.
Producing drawings requires time and thought.
Whipping out a complex drawing in
15 minutes is not something to brag about.
Drawings produced by more than one person
should be consistent as to units and style.
Use either metric or inch units, not both.
Very often the outside shape merely supports the features
and is dimensionally irrelevant.
Precise dimensions should only be applied where required,
i.e. to features ( hole patterns, slots, shoulders etc.)
Basic Dimensions
Always include the overall length, width and height
Avoid hard conversion of
metric and inch dimensions.
Where possible use standard sizes
 Materials such as flat bar, round bar and shafting,
sheet, plate, pipe, tube and structural shapes are all
supplied in inch dimensions.
 Fasteners (screws, bolts and nuts etc.) and bearings
are supplied in both systems.
Milling cutters are usually inch sizes.
For clarity, spread details and dimensions over multiple sheets.
However, the relationship between the sheets should be clearly
indicated.
All dimensions relevant to a particular detail should be contained on
the sheet.
How you draw it, can greatly effect how
much time is required to make it.
Typical bearing block
Difficult to machine, many
operations
The same bearing block
through bored with
retaining rings.
Much simpler and quicker
to machine
Show co-ordinates for arc centres
Holes are always dimensioned by Diameter
Fillets and arcs are always dimensioned by Radius
Arc
Fillet
Hole
Unless otherwise specified, holes are
assumed to be plain and through the part
You get what you ask for.
½.50
.532
nc -–44holes
holestyp.
typ.
Avoid chain dimensions
General tolerances are applied by machinist where
specific tolerances are absent on a drawing
Inches:
X.XX ± 0.01
X.XXX ± 0.001
X.XXXX ± 0.0001
Metric:
X.X ± 0.1
X.XX ± 0.01
Tolerances
There are two types of tolerances:
Dimensional and Geometric Position
Parts that are left and right handed should
be placed on separate sheets
Just because you can draw it, does not mean it can be built.
If there is any doubt, ask!
What is wrong with this drawing?
The part is lost in the dimensions
What is wrong with this drawing?
•The part is too small on the page.
•Dimensions are crowded and confusing.
What is wrong with this drawing?
Outside diameter is missing
Conclusion
Before starting the drawing consider if there is a
simpler way to make the part.
If you are not sure, check with the person who will
possibly have to make the part.
Use standard shapes and sizes wherever possible.
The drawing should clearly describe what is required.
The drawing should be large enough to be easily
understood
If necessary draw the part on multiple sheets.
Left hand and right hand parts should be on separate
sheets.
Dimensions should match the intent of the part.
Choose the units, either metric or inches, not both.
Avoid hard conversions.
Start by dimensioning the overall dimensions, then
dimension the features.
Avoid chain dimensions wherever possible.
Use decimals sparingly, the more digits after the point
the longer it will take to manufacture the part.
Only call for precision where it is required.
Holes should be dimensioned with diameter.
The way you dimension a hole determines the kind of
hole you get.
Where more than one person is making the drawings,
ensure that all the drawings are consistent in units and
sequencing.
Before submitting drawings to your report, ask yourself the
following:
Does the drawing clearly show what I want unambiguously.
Are all the dimensions there.
Have I indicated the material.
Have I indicated how many parts I need.
Have I indicated which holes are threaded and which holes
are plain.
Have I discussed any of this with the techs.