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Convert from LM8UU to "Sells-Mendel" style bearings?

Posted by Lenbok 
Convert from LM8UU to "Sells-Mendel" style bearings?
February 20, 2014 02:42AM
When I built my Mendel90, one of the things that I immediately noticed was that the carriage/bed motion is quite a lot noisier than my Sells Mendel. It may be that the LM8UU's were cheap ebay jobs, or maybe all LM8UU's are inherently noisier than the roller ball approach used on the Sells Mendel.

Anyway, I have a bunch of 624 bearings kicking around and I'm tossing around the idea of retrofitting them onto the X and Y carriages. For the X carriage, I am thinking of basing it off the OpenX carriage, and for the Y I'm hoping to make something that would be a drop in replacement for the current Y carriage bearing holders.

Sound like a silly idea?
Re: Convert from LM8UU to "Sells-Mendel" style bearings?
February 20, 2014 06:43AM
Rotary ball bearings have less friction because the balls are separated by a cage and are permanently engaged. Linear bearings have nothing to separate the balls so they rub with contra rotating surfaces. Also the balls return down a back channel and then have to squeeze between the shell and the bar against the preload pressure for the start of the next run. That makes them feel lumpy.

The sells bearings do work better but they fell out of favour in reprap due to the extra complexity, expense and setup required.

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