[H.O]

Hi John,
I'm sorry for making you repeat yourself but are you saying that if you run something like:

M98 P123 L100
M30
O123
G0 X10
G0 X0
M99

The X-axis does not drift but when running arcs both axis drifts?

What if you run:

M98 P123 L100
M30
O123
G0 X10 Z10
G0 X0 Y0
M99

I was thinking that perhaps the voltage of the step- and/or dir signals are marginal but if that's the case you should've seen the error on single axis moves as well.

Does the VSDEPI buffer the LPT-ports output signals?

Crosstalk, as Tero mentioned, sounds like a possible cause (not very likely but who knows at this point). If the ribbon cable you mentioned is carrying step and direction signals and you're prepared to "sacrifice" that cable try splitting the individual conductors, separating them as much as possible.

However, I think it's more likely to be crosstalk in the DB25 cable. Do you have another one? Preferably a shorter one, perhaps even from another manufacturer.

You say that you've tried to reverse the active low setting for the DIR signal, but have you tried doing it with the step-signal. Having the wrong "polarity" could screw up the timing and make it step the wrong way. However, that too should've showed itself on single axis moves as well.

Interesting problem, I don't claim to have the solution just thinking out loud. Good luck and please keep us posted!

/Henrik.

[theshed]

Hi

Your first G code is almost exactly what I have been using as a test word for word except that I used L50 and had a 50mm move. When I test the two axis together I gave programmed a G2 move followed by an opposite G3 move to make an "S" shape. I have also run a diagonal move with both axis and as far as I recall that resulted in the error.

I have changed the parallel port cable from a 3M cable to a 2M cable with no change. However I am wondering........my pc is a little industrial panel unit. I have it mounted in a metal cabinet. I have a short cable inside the cabinet - say 200mm I then have a D connector through the cabinet to pick up the main cable down to the drive. I can try a direct connection this evening and see it the short cable is the issue. I did solder up the short cable myself and that is rarely great!

[theshed]

Another few hours of testing later.....A rapid 200x X0 Z0 to X24 Z24 program i.e with both axis moving did not result in any error. It is just circles so far. As I write this it dawns on me that I should try both axis moving but at different speeds.....back to the shed!

[Xerxes]

So if reversing didn't change physical drifting direction, then the problem is not probably in step/dir signal but in encoder signal. As Henrik pointed out, you might also try inverting step pulse polarity just in case.

There is one thing you can still do to enhance encoder signal quality: connect 120 ohm resistors between + and - output pairs of encoder (from A+ to A-, B+ to B-) to the D-sub 15 connector end. Resistors properly terminate the lines and helps especially in long cables.

[TSJ]

I have been following the thread with some interest as I plan a system very similar with similar hardware. Has there been a resolution to this problem?

[theshed]

Yes!!!!! At last I have got it working properly. I am 99% certain that it is the multiplier. I changed the multiplier to the only setting I had not used 1x and low and behold the errors disappeared like magic - it is now perfect although as my PC is a little old and my encoders 2000 line I can only run at 600mm per min - I can live with that.

A very helpful guy on the Mach3 support site suggested that the multiplier might be the culprit but as I had used every setting except no setting at all I did not try it out.

The only reason that I am not 100% is that I put a small shield between the transformer and drive - I do not think that could have been the issue or it would have affected not only arcs.

All is well that ends well - although I did nearly burn the dammed thing when terminating the encoders had no effect..... that bit of rewiring took days.....

[Xerxes]

I'm glad to hear about success! If any trouble starts bothering, just post here