Re: MaxNC modifications

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 at
this point. From my playing with a number of software products I have pretty
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 a
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 hits
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 one
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@onelist.com
> 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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