Making of encoder mounting plates requires several accurately drilled
holes. I already made one plate and it seems to work, but I had some
problems/issues with placing holes precisely.

The material is brass (it was a great idea to use brass).

I calulated all hole positions using a spreadsheet. See "Encoder
Mounts" sheet he

http://spreadsheets.google.com/pub?k...en&output=html

To fit it over a 17mm motor shaft, I had to drill a 43/64
hole. (17.065mm).

I do not know of any way how I could drill that hole precisely, with a
huge (comparatively) MT3 drill bit, as any drill bit would wander away
at least somewhat, I think.

So what I did was, I drilled the 17mm hole aproximately where it
should be. Then, with DRO, I located the center of the hole and then
moved to what should be a point (0,0), based on the calculated
position of the center of the hole. (kind of a backwards thinking
process).

For smaller holes, all I did was start them with a center drill and
then drill with a drill bit.

It actually seems to have worked, as the encoder works just fine.

When making that mounting plate, I realized that there is a lot to
precision drilling, and want to ask now if anyone knows tricks for
drilling precise holes. I have two more plates to make.

The required precision for locating encoder base is 0.01". (which is
not that bad).

On a related note: to bolt the base to the motor, I had to drill four
holes for the mounting bolts. How can I precisely measure the distance
between holes. I tried using a caliper and it worked, obviously, but I
can not be totally sure how accurate I was. I would measure the
distance between two points in holes closest to one another, then
farthest, and average the two. But it felt that there was a lot of
wiggle room in those measurements. SEM has a manual for the motors in
question and it specifies the distance, but based on what I drilled,
the distance is slightly wrong. (the motors were made 20 years ago).,
I was lucky that I drilled the holes slightly oversize. For the next
pair of plates, I would really like to drill to-size holes in the
right place.

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