Which bearings do not require modifications for X-axis?  

Re: Which bearings do not require modifications for X-axis?

So in research the forum threads:
http://shop.prusa3d.com/forum/original-prusa-i3-mk2-f23/replacement-bearings-recommendation-t2085-s30.html

- I just upgraded my bearings to the IGUS RJ4JP-01-08, I bought them on Ebay for $21 for 6. Shipping from IGUS was super expensive since I live in Hawaii, but the vendor from Ebay gave me free shipping.

Here are my first impressions:
1. They are a perfect match for the original Prusa bearings. I installed them and they fit like a glove in the X and Z carriages.

Re: Which bearings do not require modifications for X-axis?

However, the Igus may not be the best fit for the Y-axis, but there are adapters:

http://www.thingiverse.com/thing:1930525

Re: Which bearings do not require modifications for X-axis?

Also, some users are having issues with the Igus Drylin RJ4JP-01-08

update:
i'm back to the standard ball bearings and steel rods at all axis.
the igus DryLin's may reduce the noise, but the higher friction caused several problems. one of them is the slight skew of the heatbed (described above) another one is the effect that at the x-axis some fast movements of the x-stepper are not successful... due to the required additional force.
you can see the effect on the printing (layer shift in x-direction) at the attached picture.

so at least in "silent mode" (my default setting) the RJ4JP-01-08 are not suitable for me.

Re: Which bearings do not require modifications for X-axis?

To use RJ4JP you have to find the right tightening of the zip-ties and you need a perfectly square frame. Just check previous threads, the topic has been covered tens of times.

Re: Which bearings do not require modifications for X-axis?

Thanks for the pointer. There almost needs to be a FAQ or Wiki format just for this topic, in searching the forums I found:
http://shop.prusa3d.com/forum/improvements-f14/upgrade-recommendations-during-initial-build--t2754.html#p21837

Ancient wolf, let me recap. You'll have three problems with igus bearings:
1) they are more tight and allow less tolerance;
2) the plastic part is compression dependent;
3) their performance is weight/load dependent (only relevant for y).

Let's focus on problems 1 and 2 for now.

RJ4JP-01-08 with zip ties will work as long as you have a decently aligned X/Y axis (to mitigate problem 1) AND they are correctly tightened (that is, "not too much" - to solve problem 2 and further mitigate problem 1). The trick is to tighten the zip ties with the right strength just to keep them in place, and although not "measurable" it is rather easy to do in practice - just have many zip-ties spares to learn and do it with the rods in place. Once tightening is right, it usually helps to glue the bearings to the zip ties to avoid rotation and linear shift while still keeping the needed out-of-axis movements. Just a drop a glue, so you will be able to remove and reuse it in the future. I tell you that it is way simpler to waste 20 zip ties doing that alone in your working room than trying to be professional with a webcam pointed at you.

RJZM-01-08 will indeed solve problem 2 by design, but problem is that for some reasons you'll be going to use printed adapters to mount them instead of zip-ties. Maybe for X there are modified parts which still use zip-ties, but i've not tried them. So you will have to solve/mitigate problem 1 entirely by assembly accuracy, because the bearings will be fixed in place. My opinion, in this world that I admit is rather new for me, is that many expert machinists have experiences based on precisely machined equipment, that is not the case of this printer, which is entirely held in place by zip-ties and cost-saving design solutions. I mean, just look at how the frame is fixed or how the X is supposed to be kept straight. So, ok for the RJZM-01-08 to avoid problem 2, but if you have experience with small tolerances, i assure you that it is way more simple to find the right zip-tie tightening than to have the entire rest of the printer perfectly aligned to support a bearing that is firmly attached to its carriage. (...and +0.5mm; you may think that's the only drawback, but look at the feet and at the Y endstop and you'll find more problems there).

After tinkering with all of these, i'm now with zip tied RJ4JP-01-08 for X/Y and LM8UU on Z. Should i ever develop a printer to be sold with the same market talk of the Prusa's printers, i would use neither of the above, but RJZUM-03-08 for all instead of cheap LM8UU and proper mounts instead of zip ties - that would solve problems 1 and 2 and just put OCD to sleep.

BTW, if you want to solve problem 3 (e.g., you print heavy things) or just want an higher quality hardware with no specific noise requirements, go for higher end linear bearings such as misumi etc.