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marbles
06-02-2013, 11:30 AM
Hi,

Hopefully this question will have a simple answer or a link.

I bought a c5 ballscrew and bearing blocks. The bearings are too tight for the shaft, or so it would seem.

The bearings ID is only a fraction smaller than that off the shaft. Am I supposed to mill, heat or freeze the shaft or bearings to get them on?

How do I get these part to sit together?

Thanks

JAZZCNC
06-02-2013, 11:52 AM
It's not uncommon for the bearings to be tight fit and need some slight pressure or cleaning up with fine emery paper.
Really the bearing ID shouldn't be less than the the shaft if anything fractionally more but I suspect this down to your measuring equipment. It's much harder to measure the ID than the OD without correct measuring device.!

I would just clean the shaft with solvent then lightly lube and try again. Maybe a little clean up of shaft with emery paper depending on surface finish.?
Chances are that's all that will be needed.
If you want to try the Shaft in freeze and bearings on Radiator/oven job then it will make it bit easier but be careful it's not too tight and binding when on. If it still won't go after this then don't force it because some things wrong.!!

Good luck.

marbles
06-02-2013, 12:15 PM
Thanks for reply,

I'll try a clean up first. Your right that the calipers can be out but I do think the shaft is bigger than the bearings. I also noticed that on the shaft to motor coupling, neither hole is the right diameter for either the ballscrew or motor shaft. I'll post the measurements later and see if that helps explain the situation. Hopefully a cleanup and emery will work however :)

Gary
06-02-2013, 12:29 PM
The tolerance on the machined end of the ballscrew should be between -0.008 and -0.015mm.
This is a tight tolerance to achieve on a lathe and would normally be ground.
if it is too tight, i suggest using the method Jazz mentioned, or putting it on the lathe and use a fine emery cloth to take it down slightly.


Thanks for reply,

I'll try a clean up first. Your right that the calipers can be out but I do think the shaft is bigger than the bearings. I also noticed that on the shaft to motor coupling, neither hole is the right diameter for either the ballscrew or motor shaft. I'll post the measurements later and see if that helps explain the situation. Hopefully a cleanup and emery will work however :)

Jonathan
06-02-2013, 01:38 PM
or putting it on the lathe and use a fine emery cloth to take it down slightly.

That's probably the best option - I have to do it all the time to ballscrews from Chai. Freezing the ballscrew and/or heating the bearings can get it to slide on to the shaft, but you risk there being too muck friction which may stop you being able to pre-load the angular contact bearings since they require a 'just sliding' fit.

marbles
06-02-2013, 08:16 PM
Hi, i measure both ends of the ballscrew rod. What do you think about the emery on this, should I just buy new bearings? maybe worth mentioning that the bearings are 6000zz and 6001zz.

A
Ballscrew rod end 9.99mm OD
the bearing ID 9.95,

the other end

B
ballscrew 11.97mm OD
bearing ID is 11.87mm

ptjw7uk
07-02-2013, 12:24 PM
Thats strange 6000zz should be 10.00 mm bore and the 6001zz should be 12.00 bore.
I suggest you just emery the ends of the screw or try new bearings.
Never found bearings to be that undersize.

Peter

Jonathan
07-02-2013, 12:35 PM
There is definitely an error in the way you're measuring the bearing bores as the tolerances on bearing dimensions is very tight - a few micrometers at this size.
More worryingly, why are you using deep groove (6000 series) bearings on a ballscrew, not angular contact bearings? If you get the bearings you have to fit they will probably only last a few months since they're not designed to tolerate axial loads. Angular contact bearings are, so you need to get a pair of 7200 and 7201 bearings and the appropriate mount for them, or double row bearings may be acceptable (5200, 5201).

Gary
07-02-2013, 12:35 PM
It is more likely the verniers are not accurate.


Thats strange 6000zz should be 10.00 mm bore and the 6001zz should be 12.00 bore.
I suggest you just emery the ends of the screw or try new bearings.
Never found bearings to be that undersize.

Peter

m_c
07-02-2013, 01:05 PM
As Gary says, far more likely the verniers are out. I've got a couple pair where the internal jaws are out (one set by about 0.5mm!), so if I'm using them, I zero them against a micrometer set to the required size.

One day I'll be able to afford a full set of internal micrometers...

Gary
07-02-2013, 01:17 PM
Cheap verniers are renowned to be inaccurate.

JAZZCNC
07-02-2013, 02:05 PM
Defiantly will be the measuring. You can not accurately measure internal dimensions using verniers, you can't really accurately measure the shaft with verniers you need micrometers for both.

But like Jonathan says your using the wrong bearings any way so do your self a favour and get the right ones. They still won't fit if shaft dimensions are off but they will be correct for when they do.!

marbles
09-02-2013, 05:06 PM
Correct!! It must be that one side of the vernier jaws is out as I have to reverse them to measure the inside and out. Thanks for all the advice, much appreciated.

A bit of emery and on the bearings went. Worth asking the question thought as i'd not done this before and I didnt want to jam them on.

I wonder now if the retaining nut with the grub screw at the top of the twin bearing unit is enough to hold that lot, would a second nut be useful and if so where can I get one in the UK?