CNC problems

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Shawn Wilson

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Dec 15, 2020, 7:01:13 PM12/15/20
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Hi all,
The CNC is down.  The X axis ball nut was grinding. I took it apart, never having dealt with ball nuts before, and spilled the bearings all over.  I am out of my element a bit. Can anyone help me ID what I need to replace this in the fastest way possible? The rubber circles are marked 1605.  I don't see any other markings on it.  
Thanks,
Shawn
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Joseph Baker

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Dec 16, 2020, 12:15:50 AM12/16/20
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Don't feel bad, those bearings look pretty rough, so you probably didn't shorten their life too significantly. You may still be able to clean them up and put the balls back if you can find them all. If you clean it really well, it may not be as rough as it looks in the picture.

This is the type of ball screw nut that you are looking for if you just want to replace it. Read or watch a YouTube video on how to install it without losing all the screws. Hope all is well back east!

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Shawn Wilson

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Dec 16, 2020, 6:39:23 AM12/16/20
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I think some of the balls are halfway to BC by now. I will see what that site offers for shipping options.  Thanks, Brandon!

Chris McDonald

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Dec 16, 2020, 7:23:10 AM12/16/20
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The balls may be a common size that a bike shop may have in stock. That will get you back up and running.

Generally the ball screw will wear out before the ball nut. So if you are replacing the ball nut, replace the screw too. It might be worth measuring the ball screw for wear using two precision pins and a micrometer. I’ve seen it done for other thread profiles. Might be worth searching YouTube for the exact process.

I have had good luck ordering from AliExpress and shipping with fedex. It usually around a week and still comes in at a lower price than buying  from a Canadian reseller. 

Chris 


Shawn Wilson

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Dec 16, 2020, 5:22:23 PM12/16/20
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Thanks Chris,
I had trouble finding the exact ball screw, so I just ordered the nut. Was supposed to be here by Friday,  but looks like it will be Monday or Tuesday.

Shawn Wilson

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Dec 21, 2020, 6:27:45 PM12/21/20
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So the first ball nut arrived.  I put it on the screw, but am surprised by how much torque I have to apply to turn it. I had suspected that I would be able to spin it and its inertia would keep it going.  Instead I have to hold the screw pretty firmly in order to move it at all.  Is this normal?  Also, the nut is a little longer than the original and there are 4 rubber things (gray) marked 1605 instead of the  3 (orange) on the original.  I am reluctant to install this as is.  Thoughts?

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Shawn Wilson

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Dec 21, 2020, 7:11:06 PM12/21/20
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So I put the machine back together and there is definitely a problem. That axis is super tight.  I am wondering if the following might be the issue:

When I put the nut on the screw, there were white threaded plastic pieces on each end. I think one went in a bit crooked (its set screws were tight as I put the nut on)  So I backed off the white pieces' set screws.  The pieces spun up and down nicely.  So I spun them back down into their recesses (not tight) and tightened the set screws.  But I wonder if, in putting the nut on with the white pieces set, I managed to crowd the balls, and if so, if reballing it would fix the issue.  I am reluctant to do this unless necessary,  though, as I am such a novice. Thoughts?

Joseph Baker

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Dec 21, 2020, 8:49:29 PM12/21/20
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I can't say for sure what the problem is based on this over email, but regardless of the problem, there should be no need to take the balls out. Ball screws feed the balls back through returns, so you shouldn't be able to crowd the bearings in a way that won't fix itself. 

It should definitely take minimal effort to spin it. If you have cleaned the screw well, the whole thing should spin very easily. 

I wish I was still in your province to come help in person. I do hope that this isn't a tolerance issue due to different manufacturers. 

Shawn Wilson

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Feb 18, 2021, 9:44:47 PMFeb 18
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Thanks for the help, everyone.  The second ball nut worked perfectly and the CNC is back up.

Jordan Edsall

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Feb 19, 2021, 7:38:39 AMFeb 19
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Awesome!

Thanks for doing that replacement Shawn.

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