Linear bearing upgrade options?

Hi there

I was wondering if anyone had any experience with upgrading chinease linear bearings?

On current machine I have 20mm supported rails and the LM20UUOP type bearings, they perform well but there is quite a lot of variance between them, as in some feel smooth and others are gritty and notchy. I have tried various settings of "preload" by tightening the grub screws on the housings but for the bad bearings this just makes them worse.

I have seen the top ball type units sold from marchantdice that have a much higher load rating and seem better quality

http://www.worldofcnc.com/products/tk-uuop

Has anyone got any experance with these and if they might improve smoothness or accuracy ??

Joe

They can feel like that if the number of balls is too low or too high. You might want to count how many balls per circuit are in each bearing for comparison.
An easy way is to look at the gap left when you bunch them together using a toothpick or similar.

I will have a look tomorrow, if there is to many or not enough balls surely it's not going to be practical to put another one in? Or is this possible ?

Do you think the more expensive bearings will be worth the money and actualy improve anything , I am a little sceptical but wondered if anyone had any experance

Joe, I'd think that the MD ones (and most that you get here in the UK) are also of Chinese descent/origin.....

The problem could be also the shaft. There are some super nice plain Frelon bearing blocks from PBC Linear and similar, but if your shaft is not ok the result will be short life.
Check their tech info. But as i see it you need brand bearing, plain or ball, if you expect a real upgrade

I counted the balls and there was one missing on one of the races but that was the smooth one!! Who would have thought that!

I think that there is to many things I would like to improve and by just upgrading the bearings that probably isn't going to do it and may well be a waste of an investment. I am probably going to upgrade to a hiwin RG type rail in the future and larger better quality ballscrews but that investment will have to wait a bit longer

I have checked the shafts and they are all prefect as far as I can see and measure but there are only limited screws holding the rail to the aluminum profile which is a sorce of flex as well as the bearing

I took some pictures so you can see the machine anyway but thanks for your help guys !

Just upgrading the rails would give you an enormous improvement. Looking at the pics the screws seem fine are they 1610 x and y and 1605 for Z ..Clive

Nice looking little machine Joe, like the housing too. What do you make out of interest?

Yes the enclosure is a good thing to have, the machine and all its electronics are in the enclosure and then I have storage space in the bottom.

I cut mainly aluminum, plastics, modelling foam and wood, a real mixture really . It can machine steel but I try to avoid it when I can.

all the ball screws are 1605 from linearmotionbearings and they seam accurate but I can get up to 0.09mm of "backlash" or flex when I push and pull on the machine, but the accuracy/repeatability of actual parts is more like 0.03mm which is really good. I am thinking of upgrading to a branded 20mm screw which should give me a bit more rigidity.

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Originally Posted by Joe

all the ball screws are 1605 from linearmotionbearings and they seam accurate but I can get up to 0.09mm of "backlash" or flex when I push and pull on the machine

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If you actually mean backlash, then 0.09mm is a sign of the ballscrews being damaged, however it sounds like you mean flex in the machine? If that's the case then better rails is one way to help with that.

Quote:

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Originally Posted by Joe

I am thinking of upgrading to a branded 20mm screw which should give me a bit more rigidity.

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You don't need a larger diameter screw - it will only slow things down. The load rating and stiffness of 16mm ballscrews is plenty for the size of your machine.

Yes I don't mean backlash as such I mean machine flex around the screw , so cumulative error between the screw support, ballnut and housing ect.

I wasnt sure about a larger screw and if it would actually improve things, but your right the extra mass will definitely kill acceleration.