Mach3 Backlash Compensation Pm45CNC

[Jamespvill]

Hello Folks!

I am trying to make up for the about 1 thou of backlash in my X and Y through Mach's backlash compensation. The problem is that It simply isn't applying any sort of compensation for me! I've got the Backlash box checked and values applied to my X and Y.

I am running a Pm45CNC for what it's worth.

Any ideas folks?

I've got about .0008 backlash on my X and about .0015 on my Y. The tiny little flats on my OD circle cuts are just staring into my soul, laughing at me and mocking me for playing with a big, bad CNC machine. That simply won't do my friends!

Thanks gentlemen!

 

[JimDawson]

Just as an experiment, see what happens when you double the compensation values. Also try a negative value if Mach3 will accept it, just to see the result.

I think the real problem is that even though the compensation is being applied, it is being applied at the end of the travel and the table momentarily stops and that is where the little flat is coming from. I suspect the only real way to get rid of the problem is to eliminate the backlash mechanically.

 

[Jamespvill]

Just as an experiment, see what happens when you double the compensation values. Also try a negative value if Mach3 will accept it, just to see the result.

I think the real problem is that even though the compensation is being applied, it is being applied at the end of the travel and the table momentarily stops and that is where the little flat is coming from. I suspect the only real way to get rid of the problem is to eliminate the backlash mechanically.

Hi Jim,

I've doubled and decupled the values, doesn't seem to change anything, it's as if the backlash compensation is just broken on my mach!

I should specify with the flats: I have always gotten those when I run OD circles, thats what led me to research fixing my backlash- thus to Mach's backlash compensation. I am measuring my backlash with a last-word before I run a program and It's simply not applying no matter the value I enter.

 

[JimDawson]

The only other thing I can think of is to set the backlash comp speed higher. The default value is 20%, maybe try 80% or 100%.

 

[Jamespvill]

I've tried a few different speeds with no additional luck. Perhaps some software somewhere is not compatible...

 

[JimDawson]

Well, I took a look at the documentation, it was painful, :lmao:when all else fails dig the instructions out of the trash. I think I found out why it seems to have no effect.

http://www.machsupport.com/wp-content/uploads/2013/02/Mach3Mill_Install_Config.pdf

5.6.3 Configure Backlash:

''The Config>Backlash dialog shown in Figure 5-24 lets you provide an estimate of the distance the
axis must back up to ensure any backlash is taken up when the final “forward” movement is made.

You can also specify the speed at which this movement is to be made.
Mach3 will attempt to compensate for backlash in axis drive mechanisms by attempting to approach
each required coordinate from the same direction. While this is useful in applications like drilling or
boring, it cannot overcome problems with the machine in continuous cutting where changes in direction occur.

Also note:
• These settings are used only when backlash compensation is enabled by the checkbox.
• Consider backlash compensation as a “last resort” when the mechanical design of your machine
cannot be improved. Using it will generally disable the “constant velocity” features at corners.
• Mach3 is not able to fully honor the axis acceleration parameters when compensating for backlash,
so stepper systems will generally have to be detuned to avoid risk of lost steps''

 

[bladehunter]

One thought, did you check the backlash at a single point along the travel or did you try several different points along the travel, also having the gibs too tight can throw things out a bit ?

I found this out after chasing a backlash issue.

 

[Jamespvill]

Well, I took a look at the documentation, it was painful, :lmao:when all else fails dig the instructions out of the trash. I think I found out why it seems to have no effect.

Jim, Your the man! Thank you for powering through the literature.

What Is sad is the fact that I never even thought to look in the Instructions...

When I found videos about the backlash compensation, it showed the backlash compensation quickly taking up the backlash then moving at regular speed while running a part. I'm glad you pulled that up! Many thanks!

I'm still gonna do some tinkering. I contacted Newfangled Solutions and they told me to contact the manufacturer of my external motion device and see if it supports backlash compensation. Sent an email off to Precision Matthews to see if he could point me in the right direction.

Hopefully the CNC Gods are kind to me and give me exactly what I want.

On a side-note, what is a reasonable amount of backlash anyway? My Y is the most at right around .0015.

Anywho, thanks for the continued suggestions, all are very appreciated!

 

[Jamespvill]

One thought, did you check the backlash at a single point along the travel or did you try several different points along the travel, also having the gibs too tight can throw things out a bit ?

I found this out after chasing a backlash issue.

Backlash was checked a few times about 3 inches apart, the results were all consistent. It's funny you mention the gibs, I was tinkering and tightened them up more and the backlash increased by .5 thou...."Oh Crap, Go back!!" anic:

I have a PM923 which is just about the exact the same machine, just manual and with a few bells and whistles. I am able to adjust the backlash with the brass (bronze?) backlash nut. Would a CNC have anything like that? I can't seem to find anything similar on the CNC.

 

[bladehunter]

You should be able to tell what motion controller you are using from within Mach3. It should be noted in the installed plugins dialogue.

What kind of cable is used from the PC to your machine ?