Hi Brett,
Thanks for your assistance. I changed the x and y pot/dir pins and as a result the keyboard up/down & left/right arrows changed their control to the other axis, but the original axes that are having the problems still have them. In other words, it looks like the inputs to the motors are OK, and the problem(s) are somewhere else. Any ideas?
Thanks again, Bob

Bob, could be anything from breakout board to power supply to drivers to motors or even axis binding. If you dont have a scope then it will just be a case of swapping things about physically until you can eliminate the problem. If you are using a breakout board then swap the step/Dir wires for X and Y and see if the problem follows, if it doesnt then move onto the drives etc etc.
Hood

ranphxaz,
Two things you said caught my ear.
-Buzzing sound - and they stall or don't move - reduce velocity and accel, which you did
 thus you kind of found a max and min range for you system - for now just set so they run.
 10 - 40 then use 15 or 20 for velocity, you need to just get them moving and don't worry about
 "how fast the table will go"
-clicking sound -  click-click-click ......or tap-tap-tap like someones taping with a pencil  on a board
 may indicate poor pulses, ( could be other things) maybe ringing on the pulse and in the last year there have been say 3 people wiith that problem.

RICH

Hi Hood,
I will try to bypass the BOB and see what happens. Part of the problem is that the guy who sold me the BOB won't respond to my questions so I don't know if there is a simple way to check that out. (Arturo Duncan @ cnc4pc.com, by the way).
Rich, I never really cared how fast the table ran, I just set things up so that the motors sounded good -- in the middle of their range. Since the problem I have tried speeding them up and slowing them down, but the sound (imagine a blender filled with gravel) gets worse in both directions. I have also tried adjusting the pulse debounce in both directions with no luck. The fact that it is happening with 2 of the 3 motors ought to be a clue, but I don't know how to read it. And it was working perfectly during its first real project, which it finished with no problem. Then when I tried to jog the Z higher to remove a clamp, it started. Weird.
Thanks again, Bob

There have been a lot of reported issues with the CNC4PC BOBs in the last while and a lot of these seem to be related to the optos. I believe they are socketed so can be replaced. Now I have never owned a CNC4PC BOB so dont really know how they are set up but if you could swap two of the optos around that may show if the problem lies with them.
Hood

I bypassed the BOB and it made no difference. My conclusion, therefore, is that it has to be the drive box, which is what I call the thing that Xylotex sent along with the stepper motors. It, I think, generates the pulses. I sent them an email yesterday and they haven't responded, but it's the weekend, so that may be the reason. Do yu think I'm right in thinking that it's the drive box?
Thanks, Bob

Certainly sounds like it is, what you could do is swap the wires around for  the motors and see if it follows them if it doesnt then it has to be the drives on the xylotex.
  I think the xylotex are 3 drives on one board which at first seems a good idea but the problem being if one drive packs up then the whole board is basically scrap, much better to have three seperate drives in my opinion. I suppose there may also be a chance that if one drive packs up it could cause damage to another one as they are all on the same board. It may not be the case as they may not share any common circuitry but I would guess otherwise.

Hood

I changed the ports/pins and that changed which motors were acting up. Wouldn't that tell me the same thing?
Bob

It could be the bob but it may be your PC. So if you have a scope and look at the signal
along the way you could possibly find the source.

BLENDER FILLED WITH GRAVEL SOUND
The sound of the stepper is a good tool. If a stepper gets hot ( maybe because of a current
setting ) it will sound and behave funny and hopefully noticed before that burnt smell is sensed.

Mrs stepper is getting a mr nice pulse and walking like a champ,
but some Kremlin dosn't care for mr nice pulse and also throws some pulses at mrs stepper, some hard, some soft, sporaticaly.
Now mrs stepper is still walking along and  the mr nice pulses are stronger and keep mrs stepper walking
along.
The Kremlin pulses are hitting mrs stepper somehwere during the walk and all they can do is
bonk against the stide.
The bad pulses give mrs stepper a ringing in her heart and can cause walking problems and sometimes even making her stop and sit down.

You really don't want the technical version!
RICH

OK, if I can get someone over here with a scope to look at the signal, where would I look and what would I expect to see?
The steppers didn't get too hot, and I also tried them after sitting for a few hours -- no difference.
Bob