david.s30
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Re: Replacement bearings recommendation

Mon Feb 13, 2017 11:02 pm

I wanted to update my X,Y,Z-axis rods lengths to achieve quieter and smoother performance. My understanding is the rods and bearings are the thing to replace. So far after researching today i think I found a decent choice for replacement bearings and rods. Can the community confirm my BOM before I hit the purchase button.

https://us.misumi-ec.com/vona2/detail/1 ... tCode=LMU8
https://us.misumi-ec.com/vona2/detail/1 ... e=SFJ8-320
https://us.misumi-ec.com/vona2/detail/1 ... e=SFJ8-330
https://us.misumi-ec.com/vona2/detail/1 ... e=SFJ8-370

If my research is correct the appropriate lengths rods are:
Smallest smooth rod: 8mm x 320mm
Middle smooth rod: 8mm x 330mm
Longest smooth rod: 8mm x 370mm

wirlybird
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Re: Replacement bearings recommendation

Mon Feb 13, 2017 11:17 pm

I did the PSFU8- rods and the LMU-N8 bearings. No regrets so far.

david.s30
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Re: Replacement bearings recommendation

Mon Feb 13, 2017 11:59 pm

I had the PSFU8- rods and the LMU-N8 in the cart, then I spoke with the engineers and he mentioned the PSFU is a h5 tolerance and "You need a g6 tolerance to use with Misumi linear ball bushings". I figure he knows what hes talking about. Hows the play, give, slop, etc on the PSFU8- rods and the LMU-N8? are the bearings and rod supposed to be tight or have a little glide to them?

david.s30
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Re: Replacement bearings recommendation

Tue Feb 14, 2017 12:11 am

Also can you confirm the lengths? Thanks

Smallest smooth rod: 8mm x 320mm
Middle smooth rod: 8mm x 330mm
Longest smooth rod: 8mm x 370mm

ales.f
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Re: Replacement bearings recommendation

Sun Feb 19, 2017 1:35 am

david.s30: did you order the Misumi rods indicated in your previous post? I am thinking of getting those rods along with the LMU-N8 bearings.

david.s30
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Re: Replacement bearings recommendation

Sun Feb 19, 2017 10:25 pm

After a long email conversation with an Engineer at Misumi, I ended up getting LMU8 G6 Linear Bearings and SFJ8 h6 Linear shafts.

I struggled because it seems everyone is getting the LMU-N8 and PSFU8 rods as mentioned by other people an they are working. I'm no expert but after talking to the Engineer he said the LMU-N8 Linear Bearings are an G6 tolerance and the PSFU8 rods are an h5 tolerance according to iso standings. He said they would work but "Our linear bushings can work with an h5 shaft. However, there will be some that are too tight to the nominal value, so that the bushing will not slide on the shaft properly."
LMU-8 is with a seal and LMU-N8 is without the seal. I'm not sure how the seal will affect the linear motion, but my environment could be prone to dust so I wanted the Linear bearing sealed. I figured I would trust the engineer and give it a try, if the linear motion isn't as smooth and quiet as the original Linear bearing and rod, I can just use the LMU-8 Linear Bearing and order a PSFU8 rod and bite the cost of the rods. I also never got any firm confirmation from any source on the correct Linear Shafts sizes, so Im praying my research is correct sizes. I'm supposed to get my Prusa on 2/21 and will probably build it on 2/25, so ill let the forum know how it goes.

So my complete order was
12 x LMU-8 Linear bearings
2 x SFJ8-320 Linear Shaft
2 x SFJ8-370 Linear Shaft
2 x SFJ8-330 Linear Shaft
About $140 US.

For reference Lowercase letters are for shafts (h5) while uppercase for holes (G6).

patrizio.b
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Re: Replacement bearings recommendation

Mon Feb 20, 2017 8:15 pm

Just to confirm your statements:
http://uk.misumi-ec.com/pdf/fa/2014/P1_ ... F04_EN.pdf

LMU8 / SFJ8 is indeed the most effective solution (although not the most "silent" or "cheap").

ales.f
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Re: Replacement bearings recommendation

Wed Feb 22, 2017 5:56 am

Excellent. Please let us know how it went, especially the lengths of the rods. My Prusa will probably come sometime in April, so I have enough time to do research and order the parts.

ken.f2
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Re: Replacement bearings recommendation

Fri Feb 24, 2017 1:21 am

Has anyone tried Matthew's O-ring suggestion (pg7) on Drylin bearings? I like the O-ring idea because they insulate the bearing from the plate.

Ken

ales.f
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Re: Replacement bearings recommendation

Sun Mar 12, 2017 2:35 am

Hi david.s30

Have you built your printer yet? Did the Misumi rods work?

Thank you,
Ales

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