Author Topic: Can't get rid of 4th axis backlash! Do you recognise this table?  (Read 6244 times)

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Offline Tj256

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Hey guys!

I finally set up my MaxNC 4th axis. I noticed it had a severe amount of backlash, and trying to apply manual pressure to rotate the table compresses the black motor coupling and moves the table 10 degrees! I did play around with Mach's backlash settings but it's so bad that I probably won't be able to fix this one in software.

Since MaxNC is kauput and I can't ask them, Does anyone recognise this table? I am trying to locate any instructions for adjusting it. Surely there's got to be a way to adjust this thing. It does have 2 set screws in it but they don't seem to do much but cause things to bind when tightened.

Offline Tweakie.CNC

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Re: Can't get rid of 4th axis backlash! Do you recognise this table?
« Reply #1 on: June 28, 2011, 10:43:34 AM »
That looks like the RG Tools 100mm rotary (made in China) which has been converted to CNC by unknown. I really don't think this model had any adjustment at all.
In fitting the stepper the thrust bearing for the worm seems to have been removed and you are just relying on the coupling to take the load, perhaps modifying the motor mounting method and refitting a thrust bearing would go a long way towards improving things.

Not much help really.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline Tj256

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Re: Can't get rid of 4th axis backlash! Do you recognise this table?
« Reply #2 on: June 28, 2011, 11:39:23 AM »
Thanks! I did think that maybe the backlash was entirely caused by that silly coupling. I'm probably going to just goup up some epoxy in it tonight and see if making it ridged helps at all. The fact that when I grab the table and rotate it causes the shaft to move toward the motor and compress the coupling can't be helping at all.

I'll let you know if that does anything. "It can't get any worse" (tm)

:)

Offline Tweakie.CNC

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Re: Can't get rid of 4th axis backlash! Do you recognise this table?
« Reply #3 on: June 28, 2011, 11:42:51 AM »
Not sure if making the flexi-coupling rigid is a good idea but I will find out in the morning then  ;D

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline Tj256

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Re: Can't get rid of 4th axis backlash! Do you recognise this table?
« Reply #4 on: June 28, 2011, 11:54:03 AM »
By the way, I'm a big fan of your icon/avatar.

Offline Tj256

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Re: Can't get rid of 4th axis backlash! Do you recognise this table?
« Reply #5 on: June 29, 2011, 08:25:54 AM »
You were right! Not such a great idea. But once I made the coupling rigid, the backlash went completely away. The reason you don't want to do this is because the motor is slightly off axis and binds after rotating a small amount.

I'll have to figure out if I can get ahold of a coupling that flexes but doesn't compress, or maybe make the motor holes a bit bigger so it centers itself relative to the shaft it's driving.

The bigger question for me: Why the heck did MaxNC ship this thing to me in such a broken state? Surely they knew this would never work :(

Thanks again!

Offline Tweakie.CNC

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Re: Can't get rid of 4th axis backlash! Do you recognise this table?
« Reply #6 on: June 29, 2011, 11:09:47 AM »
Quote
The bigger question for me: Why the heck did MaxNC ship this thing to me in such a broken state? Surely they knew this would never work

Perhaps because they knew they were going on an extended fishing trip.

Some of the flexi-couplers, which have a plastic insert, may not compress to the same degree but still allow slight misalignment

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline Overloaded

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Re: Can't get rid of 4th axis backlash! Do you recognise this table?
« Reply #7 on: June 29, 2011, 03:13:43 PM »
What you might be overlooking is that the motor bearings will then be forced to take on all of the longitudinal force of the worm shaft from the table.
Not good.
There should be a thrust collar of some sort for the worm shaft, if only held in place by setscrews.
Where there's a will, theres a way.
Russ

Offline Overloaded

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Re: Can't get rid of 4th axis backlash! Do you recognise this table?
« Reply #8 on: June 29, 2011, 03:22:11 PM »
Whatever backlash is in the gearing, you will have to live with I guess.
What I am referring to is removing all end play from the input shaft.
Maybe a spacer ???? and / or shims under this cover. ????
Russ

Offline TramAlot

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Re: Can't get rid of 4th axis backlash! Do you recognise this table?
« Reply #9 on: June 30, 2011, 03:11:55 PM »
Most tables let u mesh the worm tightly/tighter or just drill the mounting holes for lash. I use / sherline type setups, there collar is solid. The bigger motor / driver the better.....

Sully