[AT] Transmission oil, 90-wt? Now: drawings

[John Hall]

Seen it too many times of parts that are over toleranced. Especially the use 
of geometric tolerance. We have to read between the lines and figure out 
what matters and what doesn't a lot of times.

I'm a little confused when you said you're in favor of getting rid of 
dimensioned drawings. Do you mean paper drawings or cad drawings with no 
dimensions? We are seeing more and more solid models with literally no 
dimensions. We either charge for dimensioning or have the customer dimension 
them before we start. Heck, they even want us to quote parts lately without 
having dimesions on the print. My high school drafting teacher would go 
beserk on the junk some of these "engineers" put out. Our easiest to work 
for customers are the ones who put out "textbook" drawings. Even their 
prototypes bolt together and work teh first time. Revisions with these guys 
are generally minor.

Again to keep this tractor related, I'm impressed at the craftsmanship found 
on old machined parts. Running production on CNC machinery and holding .0005 
is one thing---to have done it 50+ years ago is another. It also surprises 
me to practically never see "screw-ups" where a hole got partially drilled 
in the wrong place or a tap broke and the part was salvaged. It seems to me 
they would have been more prone to let parts that would still work get 
shipped anyway.

One last thing on the paper drawings. There is a steakhouse about 20 miles 
from here that is in an old train depot. Naturally all decorations are train 
related. They have 2 huge assembly blueprints of locomotives. Absolute works 
of art in my opinion!! Now if the tractor companies ever decided to clear 
the vault........

John



----- Original Message ----- 
From: "Larry D. Goss" <rlgoss at evansville.net>
To: "'Antique tractor email discussion group'" 
<at at lists.antique-tractor.com>
Sent: Tuesday, September 05, 2006 8:33 PM
Subject: RE: [AT] Transmission oil, 90-wt? Now: drawings


> It's a little bit more fundamental than that, John.  The coordinated
> standards committees outlawed fractional tolerances, and in later
> modifications they eliminated "sheet tolerances" altogether. That also
> meant that implied tolerances were no longer allowed.  As a result, you
> have to specify the tolerance on every dimension on a part and you have
> to adhere to a hierarchy of tolerances based on guaranteeing
> interchangeability of parts.  My students used to think that if a little
> tolerancing is good, a lot ought to be better.  So they would specify
> everything to four-place decimals without realizing that they had just
> increased the production costs of the part by an order of magnitude or
> two (10 to 100 times the original cost) if it had a larger tolerance.
>
> The change isn't all bad.  With the proper application of linear
> tolerances, geometric tolerances, and statistical process control, we're
> seeing product life of engines, transmissions, and other major
> assemblies that far exceeds anything we could have reasonably expected
> 50 years ago.  Remember when Ford and Studebaker engines were basically
> worn out at forty or fifty thousand miles?  Now, it's not uncommon for
> an engine to go for over 200,000 miles without an overhaul and
> six-figure warrantees are fairly common.
>
> I must admit to being an advocate for getting rid of dimensioned
> drawings, John.  It became obvious to me when I was doing computer
> graphics for a large supplier to the AEC in 1969 that the real data
> resided in the computer program, not in the drawing.  It took 20 years
> for industries and standards organizations as a whole to recognize that,
> but in 1989 the unified professional societies made it official -- a
> drawing is no longer required of a part before it is manufactured, and
> the electronic database can be approved by a licensed engineer.
>
> But I too enjoy the look and feel of the old drawings.  They are an art
> form.  Just this week, I went through a closet full of materials that I
> used to treat with reverence, but that now has no utility -- a roll of
> tracing cloth from the Korean War era, a roll of drafting film, a roll
> of tracing vellum.  Bear and H. L. Staples stopped by on their way to
> Portland five years ago and I shipped all my drafting materials off with
> them -- thousands of dollars-worth of tools and equipment that was
> absolutely essential for engineering in a by-gone era but that now is
> archaic.  I have never shed a tear over letting go of it all, but like
> you, I still appreciate and value some prints of farm equipment from now
> defunct manufacturers.
>
> Larry
>