Bob Engelhardt wrote:
snip
Ed: in your description of your climate-controlled Metrology Lab, you
say that you measure to millionths. But you're making a *woodworking*
tool! Surely, this is overkill (?). Of course, woodworkers *are* nuts
and I'm sure that there is great appeal in a tool that is so precise.

Bob

Hi Bob,

Well, I do make more than just woodworking tools. But, your question
is a good one which has several answers. In short, there's some
marketing to be sure, but there's a lot of metrology here too.

1. Yes, woodworkers are nuts - but not without good reason. Almost
everything in their market is labeled "precision" and virtually nothing
is. In fact most of it is pure junk with absurdly bogus claims. And,
they really don't have the resources to explore the claims or test the
items. So, they are constantly frustrated because they never know why
all these precision things are letting them down. The "appeal" here is
being able to buy something from someone who is trustworthy and
capable. A guy who dabbles in millionths on a daily basis and has all
these instruments might just be that "someone".

2. The rule of "tens". A basic rule of thumb in metrology: you should
be measuring with an instrument which can resolve 10 times finer than
your spec. So, if you want to ensure tolerances of 0.010" (a fine
woodworking spec.), then you should be using instruments which can
resolve to 0.001". If I'm manufacturing instruments which will need to
resolve to 0.001", then I should be able to certify them to 0.0001".
Nobody is going work wood to these tolerances, but the measurement
instruments and standards need to be made to them. There are some
woodworking applications which require tolerances to 0.001". See:

http://www.ts-aligner.com/accuratemiters.htm

So, my angle blocks correspondingly have tolerances to a few tenths.
Why? Because you can't guarantee accuracy to 0.001" with an instrument
(or standard) which is also accurate to 0.001".

There are people who don't believe in the rule of tens. They feel it
is an overkill and that a 0.001"/div instrument can guarantee
tolerances to 0.001". They might also extrapolate "tenths" from
instruments which read in the thousandths. You won't find them making
anything for me!

3. I also have to compete with the $25 angle block sets from China
(which claim accuracy to within tenths). My angle blocks need to be
significantly better. They are definitely good enough for inspection
work in machine shops. Since I need to hold tenths, I need to be
measuring in millionths. Normally, I use the 10 millionths scale on
the Dia-Lectron to check them because that's what the rule of tens
dictates. My angle standards (Starrett LM angle gage blocks) go to
0.1u" - again, the rule of tens. So, there is no question or doubt
about the accuracy of my angle blocks.

Ed