Mach3 Backlash Compensation Pm45CNC

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.
 
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 ?
Click to expand...

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.
 
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

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.
Click to expand...


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? :))
 
JimDawson said:
Also make sure that the leadscrew end play is zero, the leadscrew support bearings should be preloaded a bit.
Click to expand...

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
 
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.
 
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
 
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.
Click to expand...

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?
 
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
Click to expand...

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! :))
 
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.
 
You must log in or register to reply here.
Back
Top