[JTillotson]

Short question: Does anyone know or have access to a procedure for replacing the y axis ball screw?

Long version:
I have an 1100 series 3 that I purchased last summer used. This is my first cnc machine; I'm just getting into cnc knifemaking from doing it by hand. I was getting a lot of chatter regardless of speed and feed adjustments. This led me down a path of servicing the power draw bar and then checking lost motion. I was within spec on the x axis. The Y axis was taking about .0045" as displayed in path pilot to go .001" as measured by a dial test indicator even after repeated measurements in different places. I would step in .0001 increments with the ballscrew moving but no motion of the table, then almost seem to go back a tick, then finally move. This is with the y axis gib screws loosened.

After a bit of reading online and you tube videos, I made the decision to replace the ball screw, thinking that the ball screw fit to the ball screw nut was loose, and that replacing it would be a surefire way to fix the problem. In retrospect after more reading, I wish I had also checked to see if the base had some torsion in it before going down that road.

Well now I've learned that when you remove the ball screw nut from the ball screw a LOT of ball bearings and little parts fall out. I had been counting on being able to remove the ball screw nut to allow me to re-insert the new ball screw through the holes in the base casting in the back of the machine. Now I know I can't take the ball screw nut off so I came up with the idea of lifting the machine, putting it on blocks, then I would be able to reach up underneath with the new ball screw. Well there isn't enough room to get it in.

I figure there has to be a reasonable way to do this that I am just not figuring out.

[R.DesJardin]

I built an open top table to set the machine on. Then installed a new nut/ball screw assembly. I put a top on the table and use it for storage. All good.

[mountaindew]

Been looking at doing this for a while. Major problem I have is it come from factory this way. I have little confidence replacing the ball screw will improve it. Does the quality of the ball screws vary that much? Is the new ball screw going to be better or worse then what is in the machine now? I don't want to end up with a worse problem as detailed above. You wont find any videos on this because its way outside their wheel house. A couple people around here have dissembled their machines and have shown some pictures that's about it. I was going to pull that machine off stand and place on 4x4 stand, but reading your post has me re-thinking that also . Another problem I have is there are a number of people that all see this in their y axis only. I guess next step is to expose the y axis mechanical, put some indicators on everything that moves and figure out exactly where the problem is.

[syscore]

Been looking at doing this for a while. Major problem I have is it come from factory this way. I have little confidence replacing the ball screw will improve it. Does the quality of the ball screws vary that much? Is the new ball screw going to be better or worse then what is in the machine now? I don't want to end up with a worse problem as detailed above. You wont find any videos on this because its way outside their wheel house. A couple people around here have dissembled their machines and have shown some pictures that's about it. I was going to pull that machine off stand and place on 4x4 stand, but reading your post has me re-thinking that also . Another problem I have is there are a number of people that all see this in their y axis only. I guess next step is to expose the y axis mechanical, put some indicators on everything that moves and figure out exactly where the problem is.

You also have 0.0045" of play in the Y-Axis? From the factory?

Can you go in from the top by removing the Table and X-Axis first?

https://www.youtube.com/watch?v=EchELgqGz-c

[popspipes]

I built an open top table to set the machine on. Then installed a new nut/ball screw assembly. I put a top on the table and use it for storage. All good.

Did this fix the backlash problem after installing the new ballscrew? The reason I ask is I am wondering about the replacements quality?? I dont want to fix a problem with the same problem again.
I am wondering if I need to send it to one of the places that rebuild them?

[mountaindew]

You also have 0.0045" of play in the Y-Axis? From the factory?

Can you go in from the top by removing the Table and X-Axis first?

No I have about 0.0016+ with half that on x, and z axis. Still very noticeable.


I would rather complete this from the top and never lift machine off the stand. My lift system is marginal and I am not convinced I could do all the work safely.

My problem is like Mike, not clear if this will make a difference!

[SCzEngrgGroup]

Have you adjusted the gibs for minimal backlash? Are you sure it's getting properly lubricated? The best you can reasonable expect, on average, is close to +/-0.001", so replacing the screws because you see 0.0015" seems a bit silly. I expect the problem is elsewhere. In correct gib adjustment, and/or poor lubrication can EASILY cause much worse backlash than you're seeing, and is far more likely than a bad screw.

Regards,
Ray L.

[syscore]

Have you adjusted the gibs for minimal backlash? Are you sure it's getting properly lubricated? The best you can reasonable expect, on average, is close to +/-0.001", so replacing the screws because you see 0.0015" seems a bit silly. I expect the problem is elsewhere. In correct gib adjustment, and/or poor lubrication can EASILY cause much worse backlash than you're seeing, and is far more likely than a bad screw.

Regards,
Ray L.

The OP had 0.0045". I agree though, replacing a ball screw for 0.0016" would not be worth it. Unfortunately, in the OP's case, I think he is already committed to replacing the ball screw, since the balls fell out. I would replace a ball screw for 0.0045", if I knew for sure that the ball screw was the fault. Moutaindew is correct though, he should have troubleshot it first. Kind of late for that now. I would also check the contact bearings on the end of the ball screw. Anyways, at this point the OP should go through the whole thing.

[mountaindew]

Have you adjusted the gibs for minimal backlash? Are you sure it's getting properly lubricated? The best you can reasonable expect, on average, is close to +/-0.001", so replacing the screws because you see 0.0015" seems a bit silly. I expect the problem is elsewhere. In correct gib adjustment, and/or poor lubrication can EASILY cause much worse backlash than you're seeing, and is far more likely than a bad screw.

Regards,
Ray L.

Reading this tells me I need to re visit all of the above.
Base twist,gib adjustment,anular bearing assembly adjustment. Lube is only thing I have no concern
As noted in another thread these numbers are easy to see when setting offsets, annoying to me because they very from x to y.

[R.DesJardin]

Did this fix the backlash problem after installing the new ballscrew? The reason I ask is I am wondering about the replacements quality?? I dont want to fix a problem with the same problem again.
I am wondering if I need to send it to one of the places that rebuild them?

It was another issue. Nothing to do with backlash.

[Djstorm100]

It was another issue. Nothing to do with backlash.

What was the "other issue"


If your reach your hand on the ball screw (x and z at least) if you have oil, you are good? I typically will lower the head and squirt some oil on the z ball screw and slowly reference that axis.

[mountaindew]

Copy/ Pasted from different thread!

The screws used by Tormach have a spec of <=0.0005" backlash. That is as good as you get without spending far more money on the screws than the machine is worth. Realistically, that, along with the other error sources inherent in any machine in this class, means your best-case average error will be no better than +/-0.001". That is simply reality. Add in poor gib adjustment, poor lubrication, less-than-optimal toolpaths and machining strategies, and your actual results can be much worse.

The chances of the ballscrew itself being responsible for 0.0045" backlash are slim and none. In all the years I've been messing with CNC machines, I have never seen a ballscrew with that much wear. If it did happen, simply turning the screw by hand would tell you in a heartbeat what the problem was. I can all but guarantee the OP is barking up the wrong tree entirely, and replacing the screw will be a complete waste of time and money.

Here is a simple test to prove my point: Lock the saddle in a fixed position, by cranking down on the gib adjusting screw so the saddle CANNOT be moved at all. Now see how far the Y ballscrew can be rotated by hand. If the ballscrew is the source of the problem, you'll be able to turn it quite a bit - at least aboutt 8 degrees. I would be willing to bet you can barely turn it at all - no more than 2 degrees. Once you've done that, you can start looking for the REAL problem...

Regards,
Ray L.




I often forget almost everything you do can affect something else. Last time I adjusted the machine and cleaned it, I was not thinking. I must have tightened the bolts holding the machine down to the base without checking the base for twist or if it changed from before. I loosened all the bolts relaxing the base casting and I guess it relieved some tension and binding I had put into it . This improved what was bugging me and returned it back to the specs I had noted down over years of use.
Going to tune this with some shimming and leveling, then adjust gibs and should be good to go. Some of the smallest things can bite you when working with these tools.

[R.DesJardin]

What was the "other issue"

Nothing to do with the reliability or accuracy of the PCNC1100. Let's just let it go please and thank you.

[Djstorm100]

Nothing to do with the reliability or accuracy of the PCNC1100. Let's just let it go please and thank you.

I was asking a genuine a question. What's with the butthurt?

[R.DesJardin]

I was asking a genuine a question. What's with the butthurt?

Ha, not butt hurt at all. Lol. Just trying to keep the thread on topic. Too often rabbit holes topics take over on here. It was my own created problem, has nothing to do with Tormach maintenance.

[popspipes]

Near as I can tell the ballscrew has to come out thru the front of the machine, I tried to move it thru the back after removing the stepper adapter screws, there is a double wall in the casting and it wont let the screw move out the back of the machine. I am going to have to lift the machine off the stand or cut a hole in the top of the stand to access the screws and oil line, I just want to add a tee in the oil line to the ballscrew so I can suplement the oiling of it. The backlash isnt bad enough to cause chatter, I am just concerned about the metal flecks on the ballscrew and more oil cant hurt it.....

edit: I did install magnets to secure the way covers so it isnt too much trouble to access the ballscrew for oiling, seems to work OK...........

[Engineerable]

Short question: Does anyone know or have access to a procedure for replacing the y axis ball screw?

Did you try to use Backlash Compensation to get rid of the free motion?
https://youtu.be/XjQlK82avtA
And
https://youtu.be/ZzgsUcI43SM