Bridgeport clone ball screw question

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sharab85

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Hello all,

I recently came across a deal too good to pass up on a Bridgeport clone that i believe is an ENCO.
I have been taking it apart to give it a thorough cleaning before I start using it. Well when I was unscrewing the X AXIS lead-screw I found out that it was actually a ball screw when I noticed all of the metal balls in the nut, well after some freaking out and some frantic forum searching I found out that I can re-pack the nut fairly easily. It looks like some of the balls are plastic or nylon but most of them are metal the metal ones are .124 and plastic ones are .1215. There where 19 plastic and 95 metal balls I did not think that I lost very many 3-8 at the most. My question is in what order should i load them 5 metal then 1 plastic or should I purchase new metal and plastic balls and do alternating like I have read about.

I included a pic of the Y axis lead-screw so you can see what it is supposed to look like.

Thank you for your help in advance with my rookie mistake.

photo (68).JPG photo 1.JPG photo 2.JPG photo 3.JPG
 
Do I need to post this question in a different section?

Thanks again!
 
I was afraid of that.

I guess I could take off the return tube off the other one and see what it looks like.

Thanks for getting back to me!
 
I've never had the chance to work on the ball setup so can't help much.
I do suspect the plastic balls are a cushion and probably need even placement between the steel balls as the steel ones take the load..
You could determine if the balls are carbon steel or stainless and get new ones.
Several companies sell packages of balls. Just give it a google and check for the diameter and material you need.
 
Well I took a peek at the ball screw that I did not screw up and it is indeed five metal balls then a plastic ball. Does that seem like an odd setup to you? I will try and reassemble the ball screw today or tomorrow.

Also, how many balls can you loose before you have to thing about buying a whole new set?


Thanks,

Shawn
 
I think you might be Ok if you are short 1 or 2 but after that you might run into trouble getting the balls to recirculate correctly. If you do decide to get new ones, measure the old ones very carefully. Bearing balls are sized in increments of .0001" or less and if you get the wrong size you may not get the preload on the screw back to where it was. Is there a way to adjust the spacing btween the nuts or is it fixed?
 
I believe there is a way to preload it. If you look at the picture I posted the black collar in the middle is threaded with a set screw, I am thinking I can adjust the preload buy unscrewing the collar against the other nut and then screwing down the set screw. Does that sound right?

Thanks again,


Shawn
 
Well, if the ratio is indeed 5 metal to 1 plastic, I'd say you either managed to loose one complete set of balls or you have all of them. I'd try to repack the nut to see if there is still a large gap left over once you run out of balls. Just make sure to REALLY clean them. Those races don't like grit or dirt. Also, when you put everything back together, make sure the alignment is really good. A ball screw is very strong along its axis, but they can't handle much of a side load. In effect, the axial loads are carried by all of the balls while radial loads will go in to only a couple of them. And once you get some surface damage on the nut or the scew, the whole unit can wind up eating itself up pretty fast. (Ask me how I know :) )

Anyways, good luck getting everything back in there. And I think you are right in that the preload can be adjusted by turning the nuts relative to each other. I just couldn't quite figure out how everything goes back toghther from you pictures.

Good Luck,
 
Well I got it back together and everything seems to be working the backlash is now .002 it was .001 but that is fine for me. Here is a pic of it all cleaned up, not bad for 450.00.



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