Disadvantage of bearings in Sells Mendel

I've noticed wear in one of the x smooth rods in my Mendel (Sells) near one of the bearings. This has been puzzling me for months and I initially thought that it was due to a bad smooth rod. Cdnreprap was kind enough to replace it for free. But, I noticed the same thing happening to the replacement so I took a closer look. I found that the bearing nearest to the wear spot is not perfectly straight and parallel with the rod because the bolt holding it in place is not perpendicular to the x carriage. I'm going to try to fix this by adding a slightly bigger flat washer. If that doesn't work, then I guess it's time to print another x-carriage. I hope I can find one that's thin enough. But looking at the other bearings, I notice that there are similar wear spots on them but to a lesser extent. Considering that it's almost impossible to assure that the bearings are mounted straight on the printed parts, I think this poses a disadvantage to the design using standard bearings compared to bushings or linear bearings.

I have seen the same thing, and nophead has reported it as well. In my case the bearings on the y axis have worn "flat" spots on the smooth rod. I have now switched them out for lm8uu linear bearings instead, and the rods still work fine. The only thing is if the rod is rotated in a certain position, it makes a LOT of noise.

For an alternative x-carriage, may I suggest [reprap.org] I've been using it for more than a month, and it works very well. If you want to go with lm8uu bearings, Greg Frosts carriage also works very well: [github.com]

The bearing system on sells mendel works, but no it's not perfect and has disadvantages. Most people these days use one of the prusa style bushings.

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-Nudel
Blog with RepRap Comic

The open x-carriage would probably have the same problem although it would be easier to print and mount.

The lm8uu linear bearing solution sounds good. But is there a modifed x-carriage for the Sell's Mendel that uses them? I don't know if I can use the Prusa x-carriage on the Sells version. I couldn't find one.

How about the y-carriage? Can the Prusa y-carriage be used on a Sells? If so, the lm8uu mounts for the Prusa can be used.

The open x design relies on the quality of the printed parts, and doesn't have any adjustments like the sells mendel does. That means you can't over-tighten it and damage the rods, as long as the print is accurate. Though I have adjusted skew parts by softening the plastic with a lighter and bent them into shape for a tighter fit.

You can use the prusa mendel x-carriage on sells mendel, the smooth rod spacing is the same, by design. The only difference is the belt attachment which might need some work.

For the y carriage, I use [www.thingiverse.com] Here's a picture of it mounted on a sells mendel: [www.thingiverse.com] Notice the y smooth rod spacing on sells and prusa are different.

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-Nudel
Blog with RepRap Comic