Messages

11

General Mach Discussion / Re: Problem with Backlash...

« on: November 19, 2010, 03:30:14 PM »

Rich,

Yea, its painful and as Mach is, unless the uncompensated axis goes really slowly, there is no way to avoid the sudden stop in that axis. I've tried to draw what I mean. Does this make sense to you?



1) without backlash, X axis almost constant speed, slows a bit for the Z axis to get up to speed
2) with Mach3 backlash, when Z changes direction, X suddenly stops whilst Z changes and does comp, the X suddenly starts again
3) how it could be, X predicts it has to stop (look ahead) so ramps down, Z does its thing, X ramps up again. All done together so exact profile is followed and no instant acels required.

Woody.

12

General Mach Discussion / Re: Problem with Backlash...

« on: November 18, 2010, 04:29:27 PM »

Jeff,

Yes, completely agree, but there are different ways of stopping.

It knows it has to stop the non-affected axis. It should ramp down to a stop, then the other axis gets compensated, then they both should start off with acceleration. Of course, this means CV is not possible, but that may be better than loosing steps?

At the moment Mach just bangs the unaffected axis to a stop, compensates the problem axis gently then and bangs the other back to the velocity again.

Unless I'm wrong, reading other threads it seems there is a solution being considered and I'm wondering if / when that will be implemented.

Woody.

13

General Mach Discussion / Re: Problem with Backlash...

« on: November 18, 2010, 07:49:58 AM »

Claude,

I have exaclty the same issue with my mill. I'm using the latest lockdown vn...40. I am cutting a profile using X axis and Z axis with a round part in the A axis. The X axis moves along the part and Z goes up and down to give the right profile on the part. A then rotates half a degree for the next part of the profile and x moves back the other way.

I have 0.05mm backlash in X and Z that is not normally an issue but for this part it is, so I turned on backlash comp and set up each axis distance, shuttle time and velocity and all is fine with each axis.

BUT, as you say, when one axis is moving along smoothly (x) at 0.3M/min and then the other (z) changes direction the X axis suddenly stops to wait for the Z axis to complete its compensation, then suddenly X carries on at the same rate.

From what I have read in other threads, this sudden stop is possibly because the backlash comp is not within the Mach3 "trajectory planner" - it just stops motion, adds the compensation regarding the adjustments set and starts it up again. This is very hard for stepper motors as, with a heavy X axis, it will possibly/probably loose steps. There is no respect for the (de)acceleration or any other setting for the axis that is having to wait for the other axis compensation.

So, it is possible to adjust the way the compensated axis behaves (as Rich explains well) and to get that smooth and not loose steps but other axis are abruptly interupted. Luckily my mill is small and it just about copes with it, but it is painful to watch and I'm sure will loose steps under heavy load one day.

Rich, Hood, Brian, Art, may I ask if my understanding is correct or have I missed a magic setting somewhere? If correct, are there any plans to get backlash inside the trajectory planner so it can work with all axes smoothly and be more stepper friendly?

Or, any advise to improve the situation for the "not compensated" axis motion?

Thanks!

Woody.

14

General Mach Discussion / Re: Huge Threading Problem Help

« on: October 27, 2010, 12:35:50 AM »

What is interesting here is Cartierusm stated no spindle speed with Vn .40, just 7rpm, that is exactly what I got. When Vn.32 was tried looks like it was sucessful.

I`ve tried vn.20 and spindle speed is ok, vn.40 no spindle speed,no matter what the debounce or M3. I now need to try V.32, but I`m 6000miles from my workshop at the moment so that will have to wait! Anyone got spindle speed with Vn.40 and parallel port? Can you share your relevant "Turn" settings please!

Thanks, Woody.

15

General Mach Discussion / Re: Spindle DRO not working in Mach3 Turn

« on: October 17, 2010, 05:02:54 PM »

I have a similar problem but for a different reason perhaps. I have a simple, single LPT set up with a home made breakout board and a single index pulse. With Mach3 R3.042.020 Turn, this works fine and I see a stable and accurate spindle speed from 50 to 2000rpm and I can thread well (given the known limitations of this version).

However, I updated to Mach3 R3.042.040 for the threading corrections and now I have no spindle speed in the DRO or in the Turn Diagnostics. Back to version 020 and its fine. I've tried to read up on this and read Rich's pdf but can't see where I've got it wrong.

I know there have been quite a few changes between vn 020 and vn 040, can anyone help me with why I would loose spindle speed? Is there a setting or approach I need to change to get this working? I can see the index pulse in diagnostics when I turn the spindle by hand but over 50rpm its gone. I've tried with turn diags enabled and without, which made no difference.

Is the new driver approach compatible with Win2000 and 1GHz P4 machine? Everything else seems fine and Mill works great as does my MPG with Turn and Mill at vn 040, just no Speed reading and presumably, no threading!

Thanks,

Woody.

16

Show"N"Tell ( Your Machines) / Re: CNC CONVERSION - 6" ATLAS LATHE

« on: September 28, 2009, 07:11:34 AM »

Hi Rich,

Correct me if I am wrong, but I thought Art had spent quite some time looking into this and found that some PC's have timing issues in the way Mach3 spits out Z movement for threading?

What happened with all that work? Did version .29 implement a different means of generating timing that overcame this issue? It may be worth trying version .29 just in case. Change log doesn't list it.

On my ORAC I have a really old, but seemingly good NEC 1Ghz PC and using the parallel port, single index and version .23 (I think) and I get no variation in pitch that I can measure, certainly up to 100mm length. Lines up with a rule perfectly the whole length and functions as a thread. Lucky perhaps. Deep cuts though are a no-no on that version, otherwise the X axis goes crazy (but never the Z for me). I've not tried vn 29 yet as I don't seem to have the timing issues.

Woody.

17

General Mach Discussion / Re: Turn G3 feedrate problem

« on: May 09, 2009, 11:20:24 AM »

Hi Melee,

I think Mach3 may use G99 differently looking at the Mach3Turn manual, G95 is feed per rev and G99 is "R point level return after canned cycles" whatever that means! Page 10.10.

By the way, are you using Mach3 R3.042.027? Maybe worth trying because a number of turn related problems have been fixed, including a driver error in threading. I wonder if that also affected your issue?

Cheers,

Woody.

18

General Mach Discussion / Re: Turn G3 feedrate problem

« on: May 09, 2009, 05:48:52 AM »

Hi there,

I usually work in G95 mode (feed per rev) as I'm more used to that in the lathe, and I've not had this problem with G2 or G3. But I'm a bit paranoid and set the F on every non "G0" line as attached. Does this file show the feed problem on your setup?

One thing I did notice just once, Mach3 got the feedrate completely wrong on one line (G1) (much too fast, but not G0 fast), then the next line was extremely slow, after that it was OK. Code was fine as far as I could tell.

Do you still get the problem in G95 mode?  Also, I'm not sure how to get a feel for feed per min when turning. Why would you use that in the lathe? If no spindle speed feedback?

Regards,

Woody.

19

General Mach Discussion / Re: Problems threading on the lathe

« on: April 22, 2009, 04:17:49 AM »

Hi Art,

Thanks for all this work. My ORAC had an index and 60 (I think) slot wheel which I replaced for a single slot wheel for use with Mach3.

(BTW, I've not experienced any noticable pitch error with my setup so far but only tried up to 30mm long threads - the fit felt perfect along their length in a nut. I must be lucky with my old Pentium 3, 1.0 GHz, win2k, NEC PC... My RPM is rock steady (when not cutting).)

The benefit of a single slot was I could re-start a thread easily and shave a little more off to fit, so long as I did not shut the machine down. If you do away with the index, I think that would be impossible? Or at least difficult?

I like the idea of multiple slots to ensure a perfect thread pitch but also an index for re-starting. Trouble is, I only have one input available for the spindle unless I disconnect something else...

If you can make these things optional, I think that would be a good way forward so that the user can decide the compromises.

Just thoughts!

Regards,

Woody.

20

General Mach Discussion / Re: Problems threading on the lathe

« on: March 17, 2009, 12:39:29 PM »

Great news, looking forward to trying the fix