Subject: Enco Mill and CCNC

From: [email-masked] (Daniel R. Mauch)
Date: Thu, 23 Mar 1995 03:15:35 GMT

I ahev taken my new Enco milling machineie the 8X36 and converted it to CNC 
using the Cimple Computer Numerical Control concepts previoulsly mentioned.
I got the X and the Z axis running beautifully but the Y axis stepper motor is 
weak. I'll try treplacing it tonight
	While testing the X axis I noticed that the number of steps required to move 
1 inch was not what it should have been. Using a 2-1 ratio timing pulley and a 
200 step per revoltution motor with the enco X axis 5TPI it should have taken 
4000 step per inch. After playing with it I found that it only took 3930 steps 
per inch. I used a 1" long drift dial indicator for my checks. It did the same 
using the computer to control it or the manual crank. This leads me to believe 
that the pitcch is off on the leadscrew. I have found that on other enco stuff 
such as the mill drill table. 
	Has anyone else found the leadscrew pitch to be off? BTW the Y axis was right 
on.

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From: [email-masked]
Date: 23 Mar 1995 04:14:41 GMT

>        Has anyone else found the leadscrew pitch to be off? BTW the Y axis was right 

Could your stepper motor be loosing/missing steps???  I have found that
too high of a move rate will cause missed steps, thus inacurate movement.
Also overloading can cause missed steps, as in too small of a power supply
or motor too small for application.

ED.
[email-masked]

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From: [email-masked] (Daniel R. Mauch)
Date: Fri, 24 Mar 1995 01:51:13 GMT

>or motor too small for application.

No. It is not losing steps. I manually turned the hand crank and found that 
turing the x axis dial .1 that the dial indicator moved .103.

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From: [email-masked] (Ron Ginger)
Date: Fri, 24 Mar 1995 18:51:48 LOCAL

In article <[email-masked]> [email-masked] (Daniel R. Mauch) writes:
>From: [email-masked] (Daniel R. Mauch)
>Subject: Re: Enco Mill and CCNC
>Date: Fri, 24 Mar 1995 01:51:13 GMT

>turing the x axis dial .1 that the dial indicator moved .103.

Are you sure of the dial indicator? Test it by holding it over a surface plate 
and measuring a block, which you can check with your mike.

Then of course, you have to believe your mike too :-)

Seriously, last night I was reading a MACHINISTS BEDSIDE READER, and he talks 
about the accuracy specs for Dial Indicators there, and according to Guy, they 
are only rated for about .5%, which is a half thou per rev. I know lots of 
people use Dials for long measurements, but they ought to be checked. Im going 
to do mine tonight, or next time I get into teh shop.

Ron Ginger
my signature is http://www.ultranet.com/~ginger

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From: [email-masked] (James Kirkpatrick)
Date: 24 Mar 95 08:12:38 MST

In article <[email-masked]>, [email-masked] writes:
|>
|>Could your stepper motor be loosing/missing steps???  I have found that
|>too high of a move rate will cause missed steps, thus inacurate movement.
|>Also overloading can cause missed steps, as in too small of a power supply
|>or motor too small for application.

This also points out the significant advantage of using a position sensor
and a closed-feedback loop, instead of the less-expensive open-loop design.
Missed steps would be noticed by the electronics, and retried.

Jim

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From: [email-masked] (Jonathan M. Elson)
Date: 23 Mar 1995 06:51:48 GMT

: Could your stepper motor be loosing/missing steps???  I have found that
: too high of a move rate will cause missed steps, thus inacurate movement.
: Also overloading can cause missed steps, as in too small of a power supply
: or motor too small for application.

Yes, but it moved TOO FAR!  It only took 3930 steps for 1", instead of 4000.
Well, checking the leadscrew should be easy.  Move in + direction to get
dial indicator to an even mark.  Make a mark with felt-tip pen on lead-screw.
Have computer move 1.000 inch in same direction.  You should see the pen 
mark move exactly 5 revolutions and return the pen mark to exactly the same
position.  If it doesn't, then the computer or motor is the problem.  If it
does, then the lead screw may well be off.  If the computer is the problem,
see if there is a software compensation for lead screw errors.  You probably
want to set error compensation to 1:1 unless an error is found.  3930 rings
a bell, however.  Isn't a Meter 39.3 inches long?  Could this be a china
import, with metric screws and calibrated dials on the handwheels patched
to show thousandths?  I've got their china 3-in-1 mill/drill/lathe that is
made that way, but I know about it.  So, maybe the screw is a 5mm thread,
not a 5 threads / inch. 5 turns gives 25mm, not 25.4mm=1".

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From: [email-masked] (Daniel R. Mauch)
Date: Sun, 26 Mar 1995 15:52:03 GMT

>Missed steps would be noticed by the electronics, and retried.

True but very expensive. Add at least $800 to the cost