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My dad machines little resistive elements for a customer of his. These
are generally under 1" dia and we run multiples of up to 8 at a time on
a custom pallet setup. We've tried using G92 to set offsets for each
nest, no subroutines; G92 with subroutines; G91 with and without
subroutines; and if a particular job is going to show lost steps, it
doesn't seem to matter how we approach it. Some parts do not lose steps.
Each part will show a different pattern of lost steps. The pallet base
has a .500 dia hole that we indicate from to establish datum, all
pallets and all programming is referenced from this hole. It's real easy
to drop an indicator in and check for lost steps.
For example, one particular part run in multiples of 8 parts per pallet
might show .0013 lost in X and .0003 lost in Y every for every pallet
load. With the tolerances on this job, Dad can let this accumulate over
two pallets before having to rezero. This is so consistent that he
stopped checking after every two pallets and simply would jog X.0026
Y.0006 and rezero. After running several hundred parts, he'd check with
the indicator after the last two pallet loads and be off exactly
.0026/.0006. (I don't recall exactly the sign (+/-) of the error or
corrections, but the numbers are real close to what he runs into)
This is with a program that does not use G92, it's done with geometry in
a subroutine, we move to a set entry point, enter the subroutine, enter
G91 and machine features, then back to G90 and exit the subroutine.
We lose NO steps in the Z axis.

From: Jon Anderson <janders@...>

Dan Mauch wrote:

On the Ah-Ha software there can be a problem. I had one customer that had

2 amp drivers and ran into a problem with lost steps. We finally figured

that there is a timimng set up in the ah-ha set menu. We increased the

and the prblem went away.

Dan,

If you ever happen to remember what parameter it was you changed, could
you let me know? I'd be eternally grateful.
While I feel it's software, there are too many people using Ah-ha
commercially for this to not have a fix. It's just finding that fix....

Thanks,

Jon

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From: "Tim Goldstein" <timg@...>

Jon,

I am sure you said, but what are you using for a controller? How many amps
are you running to the motors and at what voltage? What is the volt & amp
rating of your motors? What is the max feed rate you are trying to achieve?

I think you can safely assume your lost steps are not due to the software

this point. From my playing with a number of software products I have

well come to the conclusion that if you are having lost steps it is not the
software that is usually at fault. Do you have lost steps even at very slow
feeds or are the lost steps most common at fast rates? The torque curve on

stepper falls off very rapidly with increasing RPM, so if you try to go too
quickly you can easily get to the point of having too little torque to get
the job done even with very large motors (actually, lager motors tend to
drop off in torque faster than small ones and turn less RPMs). You can also
have a problem if you have a very slow acceleration rate and your motor

a harmonic in the ramp up. Often if you increase the acceleration you can
get past the troublesome RPM without losing a step.

A problem I had that drove me crazy was phantom steps. It seems that RF off
the drive circuitry was inducing a signal into the step wiring on one of my
axis. It was manifesting as lost steps when it really was unwanted steps. I
ended up curing this by shielding the wires in a wrap of aluminum foil and
grounding it at one end. Maybe you could also use ferrite filters?? (can

of you electronic gurus help explain if this would be a useful method? Jon,
Mo, ?)

I am sure with the help of people on the list we can figure out why you are
losing steps and get it fixed.


Tim
[Denver, CO]

-----Original Message-----
From: Jon Anderson [mailto:janders@...]
Sent: Tuesday, June 15, 1999 7:10 PM
To: CAD_CAM_EDM_DRO@...
Subject: Re: [CAD_CAM_EDM_DRO] MaxNC modifications


From: Jon Anderson <janders@...>

Andrew Werby wrote:

[What is the advantage to using Aha software on the MaxNC, over

using their

supplied software?]

Stock setup way too wimpy and slow. While I'm sort of playing around
with my MAX,
I do use it in my business, and my dad uses it a lot (learning CNC in
his 70's!)
for some commercial work he does. We needed more performance. Tried the
step/direction
version with Cyberpak drivers and MAE motors and found we were losing
steps. Bought
the PacSci motors (from Bill Griffin, used, he has no more...), still
losing steps.
Bought Compumotor drivers (brand new, obs stock) from a motion control
outfit in
Florida (can dig up the name and URL), still losing steps.
Tried Ah-ha software both to try and cure lost steps, and for a better
interface, better
handling of radius comp, and the ability to search directories for files
and not have
to dump out of the program just to look up a filename. Still losing
steps btw, and have not
had time to dig deeper.

[Were these easy to mount, or did you need to machine new

mounting plates?

Plates use existing holes in MAXNC. Motor attaches to standoffs to
accommodate
helical couplers.

[Where did these come from? Are they what Aha recommends?]

Ah-ha was the last item purchased, I'm sure they'd prefer we had bought
their whole
setup. Maybe we should have...

motor mount plates with preloaded ball bearings to
handle thrust loads,
[Were these something you purchased or built from scratch? ]

Fabricated the plates and the shaft. Leadscrew attaches to the shaft
same as stock on the MAX.
Screw side has hex for wrench, other side has 5/16 nylock nut to adjust
play in bearings.

BS&A ActiveCam nuts and 16 pitch screws,
[Are these ball-screws, or is this an anti-backlash modification to
standard screws?]

Acme screws, and an attempt to cure backlash. Mostly successful. Nut
screws into 1/4" AL
plate that in turn is screwed to saddle. These nuts are available in
V-thread, so you
could fit them to the stock screws EXCEPT that they mount outside the
saddle so screws
must be extended or you lose travel.

[Do you think they would fit a stock zero-backlash nut?]

(referring to the Thomson econo ball screws) No, probably not. If one
wanted to play with
ball sizes, one could probably get down to little or no backlash. For
the size machine you
are thinking about, you will want the larger 5/8 screws that Dan
mentioned. The small screws
over long lengths can whip at higher rpm, and buckle under compression.
They would be fairly easy to adapt to the MAXNC and could be fitted to a
Sherline if one had
access to a full size mill for the modifications. Would be very tight
however. These little
ballscrews might also work well to CNC a smaller lathe. The sample I got
is useless for any
CNC testing as it's too short, but I'm going to purchase a longer screw
and two nuts to play
with.

Control systems? Heck, wish I knew. Still having minor lost step
problems. Wish I had a local
expert that could come over and tell me what I've done wrong...
For econo linear bearings in a router application, personally I think
I'd look around for some
surplus Thomson ball bushings and fully supported rails.

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