624 bearings sets vs linear bearings???

I am part way into an Orca 3 build which uses ganged bearing sets instead of pla bearings. Recently, Orca 4 came out with linear bearings.

My questions is, did designers switch to simplify the complex build, or, are the linear bearings actually better?

Because linear bearings were common place when they first proposed the Orca design and they used 625 bearing sets anyway. Is it because it actually provides better precision? I would prefer whichever would give me the best print quality and question why they first went with roller bearings if linears were actually better.

Any comments or dialog? If this has already been discussed could someone point me to the thread.

tku in advance for any discussion or experiences.

Yzr1

Found this comment at one time from nophead:


The ball bearings on my Mendel have proved very durable but they do wear flats on the rods after about a year of continuous use. This wouldn't be a problem except that the rods wear more in the middle, which leads to inconsistent Z height eventually. You can turn the rods to put the flats underneath and get many more years life.

The linear bearings are mainly for simplification of the build.

I'm not sure they can compare to the 360° (3 bearings) and 180° (2 bearings) combined system in terms of precision and durability - would need someone with a lot of printing time using lm8uu to step up and report.

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Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.

I have run a machine with LM10UU bearings continuously for about a year and that doesn't show any sign of wear on the rods.

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[www.hydraraptor.blogspot.com]

Thank you to DeuxVis and Nophead for their initial response.

I would still welcome additional insight or experiences.

It's becoming clear that there are so many variables involved in a reprap that such a difference may be negligible. I do however think that at some point, one over the other would affect precision....

Edited 1 time(s). Last edit at 02/28/2012 03:16AM by Yzr1.

Bearing choice often comes down to availability and price instead of "best" design.
Gang bearings and linear bearings will both work if the correct bearing size is chosen for the design and installed correctly.

Anytime you have shafts and bearings you are going to have wear of either (and often both) the shaft or the bearing. You get
to chose which one you want to wear the most and the part that you want to wear should be the cheapest or easiest to replace.
If you put in a plastic shaft and have steel bearings, you are going to be changing out shafts. If you put in a steel shaft and
plastic bearings, you are going to be changing out bearings.

Precision with a bearing will come down to the size of the roller within the bearing. The smaller the roller (ball or cylinder) the higher the
precision. The precision issues with RepRap and others is in the drive system (motor, belts) instead of the bearings.

My personal choice is to use linear bearings. They cost me a little bit more, but I don't have to fuss with them as much.

Roller bearing carriages are a problematic construction. This is because to run smoothly, the bearing must push against the rod with correct pressure and run perfectly straight. When it's bolted into place with a bolt that goes through a hole in a printed part, the unevenness in the part tends to make the bearing move a tiny bit when it's tightened into place.

So there are two important adjustments for each bearing, the distance from the rod and the straightness of rolling, neither of which is actually adjustable in any reliable and controlled way.

Having rebuilt my printer that used roller bearing carriages (Orca v0.2) into one that uses linear bearings (Prusa I2) I can say that the linear bearings are a better design in almost every way. I don't understand why anyone would make a roller bearing design now that linear bearings are so cheaply and easily available.

Edited 1 time(s). Last edit at 03/07/2012 07:42AM by ttsalo.

Tku Ttsalo,

I thought the same. That is one reason it perplexed me. Why would they.