# Mach3 Backlash Compensation Pm45CNC



## Jamespvill (Jan 28, 2015)

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!


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## JimDawson (Jan 28, 2015)

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.


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## Jamespvill (Jan 28, 2015)

JimDawson said:


> 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.


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## JimDawson (Jan 28, 2015)

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%.


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## Jamespvill (Jan 28, 2015)

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


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## JimDawson (Jan 28, 2015)

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''


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## bladehunter (Jan 28, 2015)

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.


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## Jamespvill (Jan 28, 2015)

JimDawson said:


> 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!


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## Jamespvill (Jan 28, 2015)

bladehunter said:


> 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.


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## bladehunter (Jan 29, 2015)

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 ?


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## JimDawson (Jan 29, 2015)

Some machines have dual ballnuts that can be tightened against each other to set the preload.  I have heard of people replacing bearings in the ball nuts that are about 0.001 or so larger than the original to correct the backlash.  I'm guessing yours are somewhere in the 1/8 - 3/16 inch range.  The only way you can find out what balls are in yours is to actually measure them.

See this thread by countryguy http://www.hobby-machinist.com/show...ng-replacement?p=239269&viewfull=1#post239269

Also make sure that the leadscrew end play is zero, the leadscrew support bearings should be preloaded a bit.

I really don't think you have a software problem, pretty sure it's mechanical.  0.0015 seems like quite a bit on a CNC machine, ideal would be zero.  This is why I am such a fan of putting the of putting the position feedback device on the load, that way any leadscrew backlash is automatically compensated for.


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## Jamespvill (Jan 29, 2015)

bladehunter said:


> 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 ?



The motion controller is a Jamen, as far as I know. The plugin specifically is entitled "JNC-40M-Ver1.26". The PM45CNC uses a printer cable.


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## Jamespvill (Jan 29, 2015)

JimDawson said:


> Some machines have dual ballnuts that can be tightened against each other to set the preload.  I have heard of people replacing bearings in the ball nuts that are about 0.001 or so larger than the original to correct the backlash.  I'm guessing yours are somewhere in the 1/8 - 3/16 inch range.  The only way you can find out what balls are in yours is to actually measure them.
> 
> See this thread by countryguy http://www.hobby-machinist.com/show...ng-replacement?p=239269&viewfull=1#post239269
> 
> ...




Okay, I'll see what I can see. Thanks for the link to that thread.

I would preferably like to fix the physical source of the backlash, so we'll see how that goes. I have a pretty bad track record with tinkering around with bearings though! I did go through and take the motor mounts and motors off to make sure everything looked right. I dared not delve any deeper than that for fear of getting myself in over my head! Nonetheless, I am learning a few new things and that is what it is all about, right? )


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## jbolt (Jan 29, 2015)

JimDawson said:


> Also make sure that the leadscrew end play is zero, the leadscrew support bearings should be preloaded a bit.



This would be my first suspect. The AC bearings at the fixed end are probably not matched and may require some shimming to get the preload right. I would also check if the AC bearings are orientated correctly.

Bob has some good info on eliminating backlash. http://www.cnccookbook.com/CCBacklash1.htm

Jay


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## Jamespvill (Jan 29, 2015)

At the risk of sounding stupid...Leadscrew end play?


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## JimDawson (Jan 29, 2015)

Movement back and forth in the bearings or supports.

Check this with an indicator base on the table, and the plunger on the end of the leadscrew.  There should be no indicator movement as you screw the leadscrew in and out.


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## Bishop (Jan 29, 2015)

I would try backing off the gib screws and checking the backlash again. I solved a backlash issue the other day by doing this, the gibs need to apply a slight pressure to hold the bed, they don't need to be tight. At the same time I lapped the gib on a surface plate and honed the dovetails with a stone. I had tried the backlash compensation in Mach3 but then decided to find the source instead. Mach3 does need to be restarted when you select the backlash compensation applied box. 

Shawn


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## Jamespvill (Jan 30, 2015)

JimDawson said:


> Movement back and forth in the bearings or supports.
> 
> Check this with an indicator base on the table, and the plunger on the end of the leadscrew.  There should be no indicator movement as you screw the leadscrew in and out.



So what I can tell I don't have any noticeable leadscrew endplay...this is assuming that I measured it properly of course. It would probably behoove me to toss a picture up of how I am measuring it.

I pulled the motor off and was turning the leadscrew by hand, I set up a indicator and it was obvious that the backlash is there. 

So my next question....Am I going to have to remove my table to properly access all the goodies?


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## Jamespvill (Jan 30, 2015)

Bishop said:


> I would try backing off the gib screws and checking the backlash again. I solved a backlash issue the other day by doing this, the gibs need to apply a slight pressure to hold the bed, they don't need to be tight. At the same time I lapped the gib on a surface plate and honed the dovetails with a stone. I had tried the backlash compensation in Mach3 but then decided to find the source instead. Mach3 does need to be restarted when you select the backlash compensation applied box.
> 
> Shawn



I've tried quite a few different tightnesses for the gibs, from completely loose to overly tight my backlash only changed ~.0005 . 

I've also restarted Mach whenever I make an adjustment. I was also hoping that maybe it only applied when I actually ran a part, unfortunately it still didn't kick in. Perhaps I'm completely missing something...Probably am! )


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## bladehunter (Jan 30, 2015)

From what Ive gathered backlash usually doesn't have any affect with a motion controller. Usually there's a config program for the motion controller.

Found a link a Jamen manual http://api.viglink.com/api/click?fo...aring. Free file hosting. File upload. Fil...

I had a quick look and it's your typical lack luster Chinese manual. Talks about a USB connection from PC to Controller.

Might pay to have a look see around cnczone if you haven't already.


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## JimDawson (Jan 30, 2015)

Jamespvill said:


> So what I can tell I don't have any noticeable leadscrew endplay...this is assuming that I measured it properly of course. It would probably behoove me to toss a picture up of how I am measuring it.
> 
> I pulled the motor off and was turning the leadscrew by hand, I set up a indicator and it was obvious that the backlash is there.
> 
> So my next question....Am I going to have to remove my table to properly access all the goodies?




A picture would be helpful.

It really sounds like the ballscrew/ballnut interface is a bit loose.  If you only have a single ballnut, then the only fix is to take a look at the bearings like countryguy did.  Another option is to add a second ballnut if there is enough room to stuff it in there.

I'm afraid that removing the table is in your future.


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## Jamespvill (Feb 1, 2015)

bladehunter said:


> From what Ive gathered backlash usually doesn't have any affect with a motion controller. Usually there's a config program for the motion controller.
> 
> Found a link a Jamen manual
> 
> ...



Nothing quite as fun as reading a "well" translated manual!

 Thanks for that link! I took to the New-Fangled Solutions forum also, they looked over my XML and couldn't find anything awry. I did find out that I am running a pirated license though! I had thought it was just the demo version of mach that came with the controller software...but nope! I'm thinking maybe that might be hanging up somewhere and giving me issues with the backlash compensation. So I'm gonna grab a legitimate paid license in a bit and see where that takes me.


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## Jamespvill (Feb 1, 2015)

JimDawson said:


> A picture would be helpful.
> 
> It really sounds like the ballscrew/ballnut interface is a bit loose.  If you only have a single ballnut, then the only fix is to take a look at the bearings like countryguy did.  Another option is to add a second ballnut if there is enough room to stuff it in there.
> 
> I'm afraid that removing the table is in your future.



Thanks for all the help Jim! I am going to put off pulling things apart for another week or so. I have a small batch of parts to run and want to get those out of the way first. 

But don't you worry, I am sure I will be back with some form of bearings or ballnut question...Perhaps somewhere along the lines of, "So I snapped my ballscrew in half, Can I JB weld it back together?" :lmao:


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## bladehunter (Feb 1, 2015)

Jamespvill said:


> Nothing quite as fun as reading a "well" translated manual!
> 
> Thanks for that link! I took to the New-Fangled Solutions forum also, they looked over my XML and couldn't find anything awry. I did find out that I am running a pirated license though! I had thought it was just the demo version of mach that came with the controller software...but nope! I'm thinking maybe that might be hanging up somewhere and giving me issues with the backlash compensation. So I'm gonna grab a legitimate paid license in a bit and see where that takes me.



Gee that sounds somewhat dodgy. Did you get it from a dealer ?

As for the snapped ballscrew...plasticine is usually the go for half\half and flour and water for any other situation.:rofl:


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## Jamespvill (Feb 1, 2015)

bladehunter said:


> Gee that sounds somewhat dodgy. Did you get it from a dealer ?
> 
> As for the snapped ballscrew...plasticine is usually the go for half\half and flour and water for any other situation.:rofl:




The gentleman that informed me that it was a pirated version also mentioned that it is a very common thing for controllers out of China, they just send a disk with the drivers and with a pirated version of Mach. I don't understand why they don't just send a demo from Mach's website. Mach's "demo" offer is about as good as it gets. 

I'm glad I've got a few options for the snapped ballscew! Wouldn't want to have to go strait to the old stick welder, would we? )


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## salut_max (Oct 26, 2019)

[QUOTE = "Jamespvill, должность: 271202, участник: 29512»]
Джентльмен, который сообщил мне, что это пиратская версия, также упомянул, что это очень распространенная вещь для контролеров из Китая, они просто посылают диск с драйверами и с пиратской версией Маха. Я не понимаю, почему они не просто отправляют демо с сайта Маха. "Демо" предложение Маха примерно так же хорошо, как и получается.

Я рад, что у меня есть несколько вариантов для сломанного мяча! Не хотелось бы идти прямо к старому сварщику палочек, не так ли? )
[/ QUOTE]
Hi, did you manage to enable backlash compensation in mach3 with JNC-40M?


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## Boswell (Oct 26, 2019)

I could never get the backlash compensation to work with the JNC-40M board. I suspect that the board does not support it. Once I moved to the smoothstepper, It was not problem to enable.


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## salut_max (Oct 26, 2019)

[QUOTE = "Босвелл, должность: 691331, участник: 30083"]
Я никогда не мог получить компенсацию люфта для работы с платой JNC-40M. Я подозреваю, что плата не поддерживает это. Как только я перешел на сглаживатель, включить его было не проблема.
[/ QUOTE]
Хорошо, спасибо, я мучил эту доску в течение недели, вероятно. почему доска должна поддерживать если функция в mach3? плата просто переводчик того, что посылает mach3 к моторам, странно. возможно что-то в плагине не включено китайцами и функция не работает ..


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