Tolerance of Ultimaker 688 2RS Bearings and 8mm Rods

[3drockstar 0]

Hey guys,

 

I'm about to build a Ultimaker Clone with aluminum profiles. Everything works pretty good beside of the X- and Y-Axis. I've ordered "normal" 688-2RS flanged bearings and 8mm steel rods with the tolerance h6 from here: Link

Know they fit to each other as press fit (don't know if this is the right translation for Presspassung). That means that I need tools like a hammer to fit the bearings with the rods. In the assembly manual from ultimaker 2 the bearings and rods fit as match fit (Spielpassung). So I don't need tools to put in the bearings into the rods. In the books I've read that I need a H7 Bearings that fits with a h6 rod. But I can't find at any supplier the tolerance of the bearings to see if this is a H7. Now my question is, how did ultimaker solved this problem? At the Specs of the rods and bearings there aren't any tolerance written inside. I can't imagine, that they use special bearings .. I think the solution is in the tolerance of the rods?!

 

Kind regards

3D_Rockstar

[Torgeir 248]

Hi 3D_Rockstar,

 

I can confirm you're on the right track, -it's about the tolerances of the rod's!

 

Thanks

Torgeir

[3drockstar 0]

Hi Torgeir,

do you know which tolerance the rods of the UM2 are? And do someone knows which tolerance normal bearings have?

 

Greetz

3D_Rockstar

 

 

Edited August 1, 2020 by 3drockstar

[Torgeir 248]

Hi,

 

Do not know the tolerance Ultimaker use, however -it might be h6(?).

 

If you use this producers shaft, you'll have the best there is:

https://us.misumi-ec.com/vona2/detail/110302634310/

 

You may also order bearing/linear bearing from them, -expensive but high quality.

 

Thanks

Torgeir

 

 

[3drockstar 0]

Hi Torgeir,
thank you for the reply. If you go to the page of misumi, there you have to choose the tolerance (f8, g6, h5) too. Therefore I think it is necessary to know one of the tolerance (bearings or rods) to calculate the other. I think if I spend enough money, I could buy the right fitting with expensive rods and Bearings (the one with given tolerance for example SKF start with each 5€ and above). But I think that it should be possible to solve it with standard bearings too. But I don't find nothing on the internet about that?! And I didn't find other topics where someone would change the rods of the Ultimaker with self made once.

 

Kind regards

3D_Rockstar

 

[UlrichC-DE 111]

Theoretically you can measure the Ultimaker shafts, then you know everything you need to know.

 

 

Let me guess (Because mechanical engineering is mechanical engineering and not tinkering)
The printer is metric ISO and not a Chinese wonder weapon.

Shafts H6(?)
Bearings H7(?) (german Presspassung)
Slide bearing G7(?) (german Gleitpassung)

 

You can get this stuff pretty good in Germany. You just have to use German words.
Geschliffene Wellen
Gleitlager
Wälzlager

 

Greetings from Germany / Schnitzel / Bratwurst / You understand 😉

Edited August 2, 2020 by UlrichC-DE

[Smithy 1,144]

5 hours ago, UlrichC-DE said:

Greetings from Germany / Schnitzel / Bratwurst

Bratwurst yes ok, but Schnitzel is ours not yours 😀 greetings from Austria

[3drockstar 0]

Haha,

good example.. when you put a bratwurst (=rod) in the bun (open bearing) then it is a sliding fit. When you have to put everything in your mouth then it becomes a pressfit. Now I understand the difference 😉.

 

But seriously...

Now I have bought a professional rod h6 and it don't fits without tools in the bearings. In the assembly manual from UM2 it fits without bearings. The right constellation that I've read is H7 (for the bearings) and h6 for the rods. But the standard bearings aren't H7, because I have a h6 rod it I can't assemble it with the bearings. Maybe Ultimaker has a build in special bearing H7. But this would be very expensive in comparison with standard bearings. Therefore I don't think that's the solution.

 

Funnily I've found so much topics discuss this problem, but without solutions. That's a secret in the 3D industry 😉

 

 

Edited August 2, 2020 by 3drockstar

[UlrichC-DE 111]

6 hours ago, Smithy said:

Bratwurst yes ok, but Schnitzel is ours not yours 😀 greetings from Austria

Touché. I usually say Schwarzwald and Bratwurst. I don't know what got into me. 😁

 

 

6 hours ago, 3drockstar said:

Funnily I've found so much topics discuss this problem, but without solutions. That's a secret in the 3D industry 😉

 

 

I think the problem you described has sometimes another cause.

 

When I buy bearings from FAG SKF JKF etc. they usually fit without force on a H6 shaft.
Of course the shaft ends must not be crushed. But this happens when sawing, grinding and cutting.
The bearing must not be cooler than the shaft. Because of the thermal expansion.

 

If you buy the bearings in packs of 10 and 100 from Ebay/Amazon, you sometimes have to use tools for mounting the bearings.
This is then really the pure tolerance.

 

I can't imagine Ultimaker buying their bearings on Amazon/Ebay.
 But with the famous printers that are available in kit form, this is standard.

 

In short: I claim Ultimaker has normal H7 bearings. But doesn't use the cheapest B-goods.

The open secret is. Many 3D-printers are assembled from scrap and B-goods. Therefore, these parts are often offered as DIY and spare parts.

Quality costs money. The market of cheap bearings exists in fact only for private individuals and in the DIY sector. The for others such a cheap shaft bearing offers no advantage. In the assembly such bearings are too expensive.
The bearing costs nothing, but the assembly takes 10 minutes, which is 7 EUR per bearing. That times a hundred thousand and you can have bearings manufactured for the price.

 

If such an inexpensive bearing breaks down because it does not fit properly, it costs real money.

Another truth. You can copy any printer. The printers have no secrets for technicians. The problem is, it doesn't make it any cheaper on the bottom line. (At least not if you want to do it right.)

 

 

[3drockstar 0]

Hi UlrichC-DE,

thank you for the explanation and the example with the diy kits. I think I have to verify the solution with professional bearings with H7. Because the rod is a professional one. If that's the solution I'm fine. My goal is to build a good and not a cheap printer. I would only avoid buying expensive parts that aren't necessary. In that case (and in other topics I've read) I found out that it is essentially buying high quality bearings. Thanks a lot.

 

Greetz 3D_Rockstar