Bronze Sleeve Bearings

Hello All,

I am working on redesigning an XY axis block for the Ultimaker style gantry system. I have been having trouble finding the same sleeve bearings that are used in the UM. I looked at the bearings at VXB but the cost kinda makes me cringe at $25. I was wondering if anyone has had any experience with the bearings in the bottom link or if they believe that these would work?

http://www.vxb.com/page/bearings/PROD/Kit8530

I was looking at using 8 of the bronze bearings that I found on McMaster (see the link below). Two per axis block at four axis blocks. The reason for using 2 per block is due to them being only 12mm long, whereas the UM bronze bearings are 30mm long. I know that more surface area touching the rod will mean more friction which also means more power is needed but two of these shorter sleeve bearings would help to distribute the forces applied to them.

http://www.mcmaster.com/#catalog/119/1128/=mq6v2h
(Product number: 6679K13 at www.mcmaster.com incase the link doesn't work)

I will post a picture of the XY axis block once I have it designed for the McMaster bearings.

I knocked out the design using 2 of the sleeve bearings. I shortened them to the 10mm instead of the 12mm long bearings.

I plan on using open ended belts instead of closed loop belts (its a larger design of an Ultimaker). In the top image the rectangles at the top of the object are for belts to feed into. The belts would loop through and be zip tied to themselves.

If anyone has any thoughts on the design please let me know!

Have you looked at sdp-si?
[sdp-si.com]

Edited 1 time(s). Last edit at 05/13/2013 09:59AM by akhlut.

---

- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

Iceman086 Wrote:
-------------------------------------------------------

> I know that more surface area touching the
> rod will mean more friction

Incorrect,

Surface Area has no bearing (haha pun) on friction.

It's a common misconception.
Friction is a result of force and a coefficient.
A pyramid block on it's base and pushed, has the exact same friction if it was balanced on it's point and pushed.

Force(friction) = Force(Normal to the contact) x Material Coefficient.

See, surface area isn't even part of the equation.

ShadowRam Wrote:
-------------------------------------------------------
> See, surface area isn't even part of the equation.

Friction due to weight won't change. But since bushings are usually a slightly tight fit, using more bushings results in a higher force against the rods which results in more friction.

ShadowRam Wrote:
-------------------------------------------------------
> Iceman086 Wrote:
> --------------------------------------------------
> -----
>
> > I know that more surface area touching the
> > rod will mean more friction
>
> Incorrect,
>
> Surface Area has no bearing (haha pun) on
> friction.
>
> It's a common misconception.
> Friction is a result of force and a coefficient.
> A pyramid block on it's base and pushed, has the
> exact same friction if it was balanced on it's
> point and pushed.
>
> Force(friction) = Force(Normal to the contact) x
> Material Coefficient.
>
> See, surface area isn't even part of the equation.

I wasn't aware of this. Thank you for the information. Part of the initial reason for 2 bearings per block was that my travel distance along the XY is about 1050mm. I can change the design to use 1 bearing pretty easily. I am considering getting a solid rod of the oil impregnated bronze and milling it down to about 1 inch long with an 8mm bore. The local hacker space has a mill that can do the job.

Otherwise I will likely go with a few of these Sintered Bronze 8mm x 14mm x 16mm.

I am still curious if anyone has had any experience with the McMaster part that I listed above.

Thank you to everyone for the information!

while friction is independant of the area of contact, there is other loss forces that are not.

especially with bushings, you can have sucker effects which are very dependant of the area in contact and especially of the smallest contact areas without micro scars. Which is why plain bushings works better with coarser smooth rods.
For sintered bushings, the smoother the rods, the lower grade of oil you need.

I plan on using 8mm precision rods from McMaster.

8mm x 1200mm Hardend Rods

PN: 6112k136

Edited 1 time(s). Last edit at 05/13/2013 05:36PM by Iceman086.

Iceman086: I'm headed in the same direction you are. I'd like to know how your combination of bushings and rods panned out for you.

If anyone else wants to point me towards part numbers, I'd be happy to hear it.

I'm thinking the same rod as above, but 10mm, and the Teflon-filled acetal press-fit bearing here: [sdp-si.com].

Ideal Newtonian friction is a function of only the normal force and the coefficient of friction. Usually measured with polished rigid pieces sliding over each other. Lubricants, surface imperfections, and deformation all make reality far more complex. Longer oil impregnated bushings will have somewhat higher drag because of the effects of the lubricating fluid's viscosity. Whether that increase is significant in this case, I have no idea.