David R. Birch wrote:
On 9/8/2011 6:38 AM, Jim Wilkins wrote:
wrote in message
...
...
Vancouver only had a limited choice. They were prepared to get them
from Wagner if I was prepared to wait 6 weeks and pay - $12 a disc!

Ontario has a slightly better choice and I was able to order 3" diam
3/16" discs for - $0.78 a disc!
...
If anyone can explain the economics of this feel free to enlighten me.

Michael Koblic,
Campbell River, BC

Perhaps you found someone who already had the right tooling left over
from a
previous job.

Welcome to the messy world of the build-or-buy decision that
confounds small
outfits developing new products. One of the reasons I first learned
machine
shop practice was to better understand production engineering. I
inventoried
the punch collection for the shop's Strippit press and tried not to
specify
hole sizes outside it. I wish electrical engineers would similarly
bother
themselves to learn the standard resistor values and tolerances
instead of
calling out 5K and expecting it exactly.

jsw

How about engineers who design for 1/16", 1/8" or 3/16" steel sheet
metal when the sheet metal industry uses 16ga(.059"), 11ga(.119") and
7ga(.180")?

David
That'll be effected by where in the world you get your supplies and the
materials concerned. In the UK I used to be able to buy 16swg sheet
steel (0.065") and it was, and now that is normally 1.5mm for steel and
it seems a lot of mills are rolling to bottom tolerance to get a few
more sheets out of a ton and I've seen it down to 1.4mm or just below.

A company I used to work for had a part with a spacer dimensioned at
0.065" and that was made from 16swg sheet and had not caused any problem
when made in the UK for many years but when it went to be made in China
they couldn't get it as the sheet thicknesses they used were either US
gauge or metric and not close enough.