Both Y axis ball screws on my Woodworker have between .005" - .006" of backlash. I feel this is causing rigidity issues. Are there any means to eliminate or reduce said backlash?
Have you checked the ball screw hex nuts to make sure they are tight against the washer?
Some in the forum have reported that this reduced backlash, but warned that there is a very small window between overly tight (ball screw locking up) and too loose (washer loose/backlash).
Yep…had indicator on end of ball screw at the nut end. No movement there. Thanks for asking.
How are you determining/measuring the degree of backlash?
You know its funny, I have measured all my ball screws for B/L and find little to no backlash, less than .0015 which I thought to be better than expected for rolled ball screws.
Pat
Wow. Wish I only had .0015 b/l. Here’s how I measured mine. Setting up my 1" dial indicator on the X gantry block parallel and close to the Y ball screw, I gently rocked the X gantry back and forth by hand. The indicator showed .005" backlash on one screw and .006" on the other. All connections within the screws and gantries are tight with no indicated end play on the end of screws opposite the motors. Controller was powered on preventing the screws from turning while checking the backlash.
I just set up an indicator off a very heavy steel plate and touched anywhere in the direction I moved, then I moved the axis .100 back and forth, it always came back to the original spot, I also pushed on the axis and got the same result.
Thanks, pat
Aw yes…,forgot to mention that I also had magnetic base on steel plate clamped to the machine table. Was able to get indicator stem set against gantry to show actual reading in line with the ball screw.
I have read in some manufacturers documents that rolled ball screw tolerances are given per 300 mm. For one C7 I looked up it was +/- 50 micron (~0.002"). I think there are also differences in quality of rolled ball screws within the same grade.
I tested my axes a long time ago with a small NC program I got from Masso support. It ran each axis in its pos/neg direction several times varying the travel each time. I did not detect any backlash using my 0.01mm dial indicator. I think this method may be preferable than any physical pushing and pully of the frame/components as there is a fair amount of flex in the overall machine that could be contributing to the movement on the dial. Also, when I recently tested the deflection of my Woodworker X50 I recorded the dial so that I could more accurately review the dial readings - I was using 0.002 mm increments so it really helped.
I think if you want to test just the nut to isolate and measure just that error, you would attach(carefully) the magnetic base to the actal ball screw, and place the dial test indicator on the ball nut flange. Then push and pull the gantry block with attached ball screw nut.
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Good info there. Thanks.
I guess what I am trying to establish through this forum is whether or not my ball screw looseness is typical of the Onefinity. I am considering replacing my ball screws with the expectation that it will improve rigidity. However, I don’t want the expense and work involved in changing them if new units are not considerably tighter.
Pretty sure replacing the ball screws will not affect rigidity at all, maybe reduce back lash but that would be all.
Pat
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Perhaps I am wrong here, but having looseness (backlash) in both ball screws would allow for back and forth motion creating a loss of rigidity? Would this also not cause unnecessary vibrations and chatter while cutting?
I guess it might be a terminology thing with me, for me rigidity is how much flex you get in the structure of the machine, if you have the indicator on the machine when checking back lash with the z axis in the middle of the machine you can easily push it around .005-.008, for me this is rigidity and really compared to milling machines this is not very rigid, for wood and aluminum ( with light cutting on finish passes in aluminum) it works very good.
Backlash is looseness much like if you have loose spindle bearings or worn thrust bearings, causes chatter and bad finishes.
Thanks, Pat
Yes, exactly… it’s the backlash issue I want to remove in order to hopefully reduce chatter when cutting hardwoods. Just not sure that new ball screws would be any tighter than what I have. Am hopeful that someone on here has done ball screws replacement and can tell me whether or not it tightened things up enough to reduce chatter. Would be nice if these ball nuts had some adjustability to reduce backlash, but then that defeats their purpose in the first place. Ball screws equals very minimal backlash as I understand it.
OK my 2 cents worth again, rolled ball screws are not all that precise, ground screws would be much more accurate.
I believe I got lucky on my machine.
I have in the past when I wanted a metal cutting CNC that I built have zero backlash to a little preload, bought oversize balls and replace the balls in the nuts. it was a hit and miss till I went too tight then backed off a little, I did end up with near perfect rolled thread ball screws.
The balls can be bought in very small diameter increments, .0001 ( tenths) and are not very expensive.
Baltec - Home is where I got mine
Pat
I’d say that’s more like 2000 cents worth. Very good info indeed. And very helpful I might add. Am now thinking I might order just ball nuts and see if they tighten things up, as I now realize the balls are probably the weak link in keeping backlash in check. Maybe I’ll get lucky and won’t need to buy a bunch of various sized balls. Thanks again.
May I encourage you to record the results of your testing method and results both before and after - should you choose to replace your ball nut with another stock replacement - as it would be interesting for us to compare the data.
I became interested in your question, so I just did a quick set up - see photo - trying to isolate just the ‘play’ in the ball nut. When applying 50N of force to the Y axis block, there was about 30 microns of movement.
Earlier, to satisfy my own curiosity (and to gather empirical data), I investigated the amount of deflection I could achieve at 3 different locations on my Woodworker X50. Without getting in to too much detail, When looking at my scatter plots I found that (in my testing up to 50N push/or pull):
- the greatest deflection, not surprisingly was at the endmill (in my case I have ISO20 ATC toolholders, measured at the collet/endmill) with a range of 110-210 microns at 50N
- the deflection varied in the X and Y axis direction
- adding the 3rd rail reduced deflection in all tests and directions of applied force
- the force/deflection curves remained linear (for my test force range)
I have been mostly interested in machining aluminum, and have had great results (for me) using effective and conservative cut parameters and toolpaths. After collecting my deflection data, I used a few programs I collected to look at (theoretical) cut forces for the spindle I have and the chip loads I usually aim for. From my machine and machining data, it seems to confirm that I am able to keep deflection in a range where it has limited impact on the quality of my cuts.
Absolutely I will record my procedure and results both before and after. Probably won’t do the replacement until the new year. Many projects to do still. Will post results here as well. As a side note, maybe Onefinity will have X50 rails for Y axis at some point. These 1610 ball screws are not up to the task, in my opinion. Mine always seemed to groan and creek compared to the smoother sound of the 1616 screws on my X rail, and no discernable backlash there.
I actually went the other way on my Woodworker, and got the 10mm pitch for the X50. I do not typically need/use high travel speeds and accelerations, so with the lower pitch I get high mechanical resolution as well as torque.
I know many people, perhaps with more experience or different use cases, travel and machine a lot faster than I do. For them, especially if 3D carves are commonly done, I can see the advantage of higher pitch ball screws.
I think a good test for rigidity is this one .
But ball screw backlash is something different. I don’t know why you want to replace the ball screws.
I would adjust their play:
For the rest, I would agree to Tom
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