Reply with QuoteHow many hours on it you think? I'd check the bearings on the end of the screw as well, it's not uncommon for those to loosen up and lose their preload.
Z axis backlash of around 0.2mm could it be a worn ballnut ?
Years ago I purchased a conversion kit for the Seig SX2 from cncfusion, installed it and made a few alterations as the kit out of the box had a few issues. Once these were sorted the machine has chugged along quite well for years.
Until this week. I decided to making a mounting and install a new motor that would crank the spindle up to 20krpm, That part is working a treat however what I have suddenly found is that each pass the tool seems to be dropping very slightly. I put the dial gauge on and found that there seems to be around 0.2mm of backlash.
The Ball Nutt has Thompson on it and other than that there are no other markings. cncfusion seem to be no longer around and I am not sure as to how to find out what the ball nut is, do I need to replace the entire nut or can i just repack it with larger balls. I have tried to adjust the backlash out using the backlash adjustment in Mach3 but that seems to come with its own issues where the unit almost dwells at one position where it is compensating for the backlash and I am no longer getting a nice clean cut.
The X and Y are still working perfectly with no backlash.
Any suggestions as to how to deal with this issue would be most welcomed.
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Re: Z axis backlash of around 0.2mm could it be a worn ballnut ?
How many hours on it you think? I'd check the bearings on the end of the screw as well, it's not uncommon for those to loosen up and lose their preload.
Re: Z axis backlash of around 0.2mm could it be a worn ballnut ?
Hopefully you don't mean spinning the stock spindle 20,000 RPM , that won't work for long.I decided to making a mounting and install a new motor that would crank the spindle up to 20krpm
If the error isn't greater than commanded position +/- backlash maybe you're on to the problem. If it's greater than that start looking further.what I have suddenly found is that each pass the tool seems to be dropping very slightly.
cncfusion used to repack with larger balls for an extra fee. Worth a try.do I need to replace the entire nut or can i just repack it with larger balls
Last edited by cyclestart; 10-26-2018 at 04:04 PM. Reason: spelling
Anyone who says "It only goes together one way" has no imagination.
Re: Z axis backlash of around 0.2mm could it be a worn ballnut ?
Lol, Yes and No, I have replaced the original spindle and upgraded the bearings, IIRCC the original bearings were only rated at about 6K RPM, the ones I installed were some time back were rated from memory about 30K.Originally Posted by cyclestart
It ran for about 4 hours with no issues, then put the original motor back in for some heavier work.
It may not be that, the error does not seem to be constant and seems to vary between 0.22 and 0.13If the error isn't greater than commanded position +/- backlash maybe you're on to the problem. If it's greater than that start looking further.
When cutting a 3D relief from the outside to the inside the passes seem to get progressively deeper.
I ordered my kit with the oversize bearings to start with as they recommended that was a better option.cncfusion used to repack with larger balls for an extra fee. Worth a try.
Re: Z axis backlash of around 0.2mm could it be a worn ballnut ?
I will strip them down again, I did check them and they seemed OK but I an now starting to wonder if this is not the issue due to what appears to be a slight inconsistency in the backlash.
I shudder to think how many hours is has on it, I built the unit about 5 years ago, due to the low spindle speed and the reliefs I have used it for it was not uncommon for the thing to run for 17 hours at a time especially when using 0.1 engraving tools in brass.
Re: Z axis backlash of around 0.2mm could it be a worn ballnut ?
Well, that is something not to be amused about!!!
So I replaces both Z axis shaft bearings and just for a near future upgrade ordered a couple of thrust bearings in as loading two normal bearings on the sides does not seem to be the right way to do things.
Still had the same issue so stripped the Thompson RC0605 ball nut, some 69 bearings in all. After releasing all the balls I discovered a heap of what appears to be glitter inside. Now keep in mind that I mostly use my machine for Plastic and Brass. It is quite rare for me to cut steel although I have put a small amount of aluminium through it. the "Glitter" seems to be really really hard and quite small chips, If i did not know any better I would swear it was flaked chrome but this would mean that the Bearings supplied would have been Chrome Plated ones and not high quality balls.
Surely not, I did not find any brass coloured glitter so I think it s safe to say that its not something I have cut.
Re: Z axis backlash of around 0.2mm could it be a worn ballnut ?
Great news...!! i repacked the ball nut with 3.175mm chrome steel balls, added what appeared to be 2 missing balls in accordance to the Thompson manual and its working a treat.
Now the backlash is less than 0.004mm Possibly even better than that as I had the dial gauge set up, jogged the head backward and forward until I could just see the needle move left or right then checked the readings on Mach3.
What i found interesting is that there is NO binding at all, I suspect this is because ALL of the bearings are in the housing and there are none missing, When i first got the kit there was always a bearing binding nose so I suspect this is the reason for that. I am going to order in some new bearings for the X and Y and repack them as well.
I'm going to
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