Re: [Emc-users] Jogger wheel + switches

[Gene H. <gen...@ve...>]

On Friday 28 March 2008, Jason Cox wrote:
>I am going to give it a go soon., once I get my EMC2 back up and
>running. Im thinking of a single wheel and either momentry buttons of a
>4 pos slider to select the axis.
>Jason
>
I just played with both a 2.7 volt rated 50oz/in motor and a smaller one 
probably intended for a printer thats a 6 wire, marked 24 volts.

The 50 oz/in will not be usable without a very heavy knob to smooth out its 
magnetic detent action, it cogs so badly I can see it bouncing back and forth 
on the scope, which would probably confuse the heck out of an LM-339 unless 
it was setup with a volt of positive feedback or more, and that might make it 
miss a slow step or two.

The next one I grabbed was much smaller, a bronze bearing type about 3/4" 
thick and 1.5" OD, has a 24 volt label at 80 ohms and a small brass gear 
pressed on its shaft.  3 wires per coil, a detent you can feel but not very 
strong, nothing like the bigger motors clunk to the next position.

This motor generates a very nice 4 to 50 volt signal depending on how fast I 
spun it, and still makes over a volt as slow as my fingers can go, and the 
waveform is not nearly so distorted because its doing only 5% of the cogging 
the bigger motor does.  You could set an LM-339 up for 250 millivolts of 
positive feedback and I don't believe you would ever see or notice it missing 
a step.

A heavy knob/disk, with a finger dimple or hole to spin it with would make a 
very usable jogger dial IMO.  And 4 of those, with 2" knobs, would fit nicely 
in the project box I have.  I don't have 4 of them, but I think I know who to 
lean on to get some more of those.  And it will take longer to make the knobs 
that to wire it up I expect.

Humm, question, would you shield the edge of the knob except for a spot to lay 
a finger, or just use the finger hole to drive it all the time?  For motor 
longevity in a shop where it might get knocked around, I'm thinking of 
bracing the back and edges of the disk with some HDPE or some such.  Humm, 
make the knobs out of it too maybe, slick under a fingertip, I like that 
idea.  But chime in here folks & put in your own 2 cents.  Maybe someone else 
has an even better idea...

Like how about putting the joggers on the same side of the box as the real 
motors are on the machine?  That might help prevent grabbing the wrong dial 
when you are watching the machine and not your wandering fingers.

I also put the ball thrust bearings in the x drive today, and the backlash 
without adjusting the nut is now .0011".  I think I can machine an actually 
round hole now...  Just one problem though, I printed the bearing drawing 
from McMaster and used the listed measurements for the bearing, as it said it 
was 5.50 mm thick.  Tain't, they were 5.00 mm and I wound up boring one 
recess too deep.

The drawing is correct, the list above it was not.  I was also pleasantly 
surprised to find that one washer was sized to fit the shaft with a few 
microns clearance, and the other to fit the recess with several thou of shaft 
clearance, so with care one can make a pretty dirt proof assembly without 
needing seals.

The old fart does ramble on doesn't he. :-)
 
[...]

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Would you care to drift aimlessly in my direction?