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Re: Drafting ?

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Posted By<" ">Randy Kimball on August 31, 2002 at 12:15:13:

In Reply to: Drafting ? posted bySteve on August 30, 2002 at 12:40:30:

Two answers, a comment, and some don't.
1. Go to you local library and ask for high school
drafting text books, these will give you the best
and quickest results on drafting protocal.
2. You mentioned that you are using shops to produce
your work now, ask them for comments and see if they
have any non-controled examples of prints they like.

comment: All engineers have quite a few quirks they
like to use as poetic right in their prints. CAD products
are doing worlds of good in the dirrection of making
us all more uniform. The best teacher of BP form and
style is experience. But, your vendor doing the work is
by far the best source, after all he/she is the one that
neeeds to be able to extract the data needed to produce your
design from the BP. If you satisfy them, you have achieved
your goal, right?

Some hints from common mistakes I see every day:

a. Do not require a tight tolerance where it is not needed.
This means drop off some of those numbers to the right of the dec. point
if they aren't required in that portion.

b. Be sure your dims. are from a reasonable and useful location point
or portion of the rest of the part body. In other words be sure you dim. from
the place that is functional, and from a location that is manufacturable.

c. Don't stack dims. In other words dim from one side or end.
Do not dim. from a dim to a dim to a dim. This stacks the tolerances and
will result in a part that is out of your tolerance needs but is still
in the tolerances you allowed in the BP. The scrap part is yours. Also, with the
use of CNC equipment becoming standard dims. from one side and end are by far
easier to program from. Your vendor will love it.a

d. Do not dim the same portion more than once. Often an engineer
will give a dim. to an area from two different places or in two views
causing the manufactur to be trapped, guess, or call the engineer
for clearification. Frequently these double dims. conflect in size or tolerance.

Closing comment:

I prefer a main view, at least one end view, a top view, AND always
an ISO view. ISO views make grasping that first mental concept
of what the part looks like 50 times faster. AND often completely
prevents those many times when a manufactur gets started with
the wrong mental vision of the part and quotes it wrong or has
to start over OR delivers a part that is correct of your print BUT
is not the part you intended, this can happen. If you've drawn it poorly,
you bought it.

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