TOS FNK machine rebuild and ballscrew help request

[mung]

I am starting to try and work out what I should do about backlash in a machine I have just got for a hobby rebuild.

Does anyone know how to adjust ballscrews to remove backlash on this type of machine???

I have attached a few photos.

I will be doing a build log over the next couple of months as I progress with the installation of new servos and emc2 controller.

[Woody111]

Hope you got this cheap!! Looks like it was abused send the ballscrew out to a rebuilder and plan on putting in new bearings. While you have it down give it a good cleaning and some TLC. Good Luck

[mung]

Originally Posted by Woody111 Hope you got this cheap!! Looks like it was abused send the ballscrew out to a rebuilder and plan on putting in new bearings. While you have it down give it a good cleaning and some TLC. Good Luck

how can you tell it has been abused??

[mung]

I stripped down the ballscrew and it looks very strange over a 30mm section of the screw there are rough cracked edges to the ball groove.

Has anyone seen this sort of damage to ballscrew before??

It almost looks like corosion, but then I wondered it the ball screw is chrome plated??

I think maybe the plate is chipped away?

I am going to try phoning round ballscrew specialists for advice next week.

Unfortunately I have virtually no budget for repairs.

I will clean and test all the ball bearings over the weekend and maybe look into getting oversize ballbearings to remove the backlash but maybe the damage means the screw is a write off??

[Ark1]

Hate to tell you but this ball screw has been abused. The location of where the nut was without wipers allows ingestion of chips that just do not have a clearance to go through the ball screw nut. Unless this screw is reground and has larger balls installed you will not be able to obtain Zero lash.

Email Gary Higgins of Zap Automation he sells new screws and nuts in the UK. This screw looks to be over an 1" in diameter. You will be looking at more that $700USD to replace it and the nut.

The Acme screw on my TOS FN20 was shot. I replaced it with a ballscrew from Gary and was very please with the replacement and tolerance of the machining.

Ark1.

[mung]

Unfortunately i have had a nightmare with internet connection today and only now have been able to get back online, so I have not made any enquirys about ballscrews with suppliers and repairers.

Hopefully will do that tomorrow if I can get online.

I did make a few more photos and a rough sketch of the ballscrew for reference.

It looks like a 32mm diameter screw with 5mm pitch and most of the balls seem fairly well shot to pieces I have photographed the worst ones I could find.

[Ark1]

You aren't fibbin us and showin us a bag of buck shot?

Go to Zap Automation's web site, I think he goes up to 32 MM.

Look through my build log, you can see the new ball screw and the adapter I made up to install in my milling machine to replace the Acme screw that it came with. That should give you an idea or two on where to start.

Ark1.

[mung]

Some more photos take at the weekend.

So far have:
1) got a general feeling of what is where on the machine
2) mounted the servo controllers in the cabinet
3) tested the Z axis quill ball screw backlash
4) tested the X axis backlash, removed and cleaned ball screw
5) tested the Y axis backlash, removed and cleaned ball screw
6) emptied and cleaned sump
7) traced the motor terminals and switch leads on the head
8) set up a pc with emc2 linux
9) purchased some L type belts for the servos
10) made a mounting plate for the servo for the Y axis

[mung]

From testing of the ball screws I have very roughly found:

Z axis) 0.07mm
X axis) 0.12mm
Y axis) totally shot to pieces, 0.5mm or more

The tests were only over a small portion of the middle of the screw so really don't give a full idea of any wear but I think that I may try to change the ball bearings in the X axis, leave the Z axis as is, and the Y axis definitely needs replacing.

I have stripped down the X axis and all the balls in it look very clean and the screw thread and nut look good also.

I have not made a fully inspection of the stripped screw yet and will soak everything in parafin and test all the bearings with a micrometer.

What is the normal procedure for testing ball screw back lash?
What sort of back lash would be considered ideal for a mill like this?

[Ark1]

Normally set up a dial guage on the axis to be tested to a solid part of the machine and then move the axis by hand in one direction then zero the guage. Now use mechanical force to move it in the opposite direction and see how much the dial indicator shows for back lash. You should be able to find a location that you can use a pry bar to move the table. Depending on the Machine's size I would expect less than .001" If the dial guage goes to let's say .003" and you release the tension from the pry bar and it goes back. 001" Then that is tension from the bar bending part of the machine or ball screw. You may find that an end thrust bearing is worn and may need adjustment or replacement. Judging by the ball bearings of the ball screw, which look more like lead shot. Don't be surpised that the end thrust bearings could need replacement.

Ark1.