RE: [CAD_CAM_EDM_DRO] Lengthening Digital Calipers

I have been thinking about using gauge blocks in a fixture on my Bridgeport
mill to allow for precise movements of the table. I've settled on what I am
going to do and should be able to hold tolerance to "gauge block precision"
with the method. No doubt this concept must be used by many already, however
in the process of figuring this out for myself, I realized something
probably also well known. Gauge blocks, when precise enough and when
properly used, allow an opportunity to fabricate instrument grade adapters
for things like calipers. If you have a good collection of gauge blocks, a
granite table and a height gauge, you may inspect the accuracy of any
adapter you fabricate and attach to your calipers. It also appears
potentially possible to make adapters which are slightly adjustable, so that
you may calibrate accuracy into measuring instruments and adapters you
fabricate. I am not a tool maker, but there are many on this list with much
more experience than I. I am sure they can make some very practical comments
about adapters for measuring instruments if that concept works for you.

While I am posing the obvious concept of adapters (to extend the range of
calipers), I'll take the opportunity to share my thoughts on gauge blocks
for precision movement of my mill table (likely useful on a lathe as well)
and open the topic for discussion so those with experience in this area can
offer some tips.

By mounting pairs of parallel precision ground round shafts to each axis of
my mill, with an adjustable sliding stop which may travel along the lengths
of the pairs of shafts, I can lay a stack of gauge blocks against the
parallel shafts, adjacent to the axis I wish to move in a precision manner.
By mounting a high precision (test) indicator on the table, I may move the
table the precise amount which equals the stack of gauge blocks. In place of
the two precision ground shafts, one may use a very long v-block, as the
shafts are used similar to a very long v-block. Long shafts appear to be
more practical over a long v-block for the extreme range of motion I am
interested in. Naturally for great distance, I will need a set of gauge
blocks to cover the distance I what to move. I will have to make some longer
gauge blocks to supplement my set to make this practical.

The horizontal axis of the mill is the easiest to apply this concept to. By
using the single t-slot on the side of the table kissing my belt buckle, I
can attach the test indicator in a manner such that at table 0.0000" the
test indicator reads zero. I next move the table to just short of where I
want it, slide the stylus of the indicator out of the way to clear the gauge
block stack I drop in, and complete the desired travel of the table until
the test indicator says I'm exactly where I want to be. The other axis of my
mill does not have a t-slot on the side and will require more stuff to
accomplish the same thing. Still, the project investment of time and
material is low for the precision I will end up with, so it seems worth the
time and trouble.

The table top version of this seems a little less interesting because the
setups are more difficult. The side mount setups may be left in place and
re-used without being re-setup. The precision of this may be especially
useful for boring holes. If (accurate) holes are placed for tooling balls in
a scrap plate mounted under or near the work piece on the table, accuracy
may be established on the table top where needed.

The project is actually not very difficult. My gauge blocks have a diameter
of 0.750" and will lay nicely on two 1/2" precision round shafts mounted
close to each other on each of two sides of the mill table. I could wipe the
chips out between measurements, but think I will cover the two sets of
shafts between measurements and/or when not in use.

David R. Howland

-----Original Message-----
From: bcollier@... [mailto:bcollier@...]
Sent: Wednesday, June 07, 2000 3:21 PM
To: CAD_CAM_EDM_DRO@egroups.com
Subject: [CAD_CAM_EDM_DRO] Lengthening Digital Calipers


Does anyone have info on making longer scales for the capacitor or
inductor type of digital calipers??

I vaugely remember something in Projects In Metal, the
Metalworking series of books, or Circuit Cellar. Any leads??


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