Ignoramus3537 wrote:

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.

i

i

For all of the holes, you should be spotting them with the short
flex-free center drill to get started on center without wander. You also
need to plunge the center drill down solidly to start which also helps
ensure it doesn't wander. After center drilling switch to regular drill
bits, but work your way up to the final hole size in a few steps if it's
a larger hole. If you really want a good hole, you drill up to a size a
few thou short of the final size and then ream to final size.