attaching threaded rod to idler bearing ?

I am building a new Z axis, and I wanted to try attaching my z axis to my idler bearing by tigheneting a nut on both sides of the idler bearing.

So I am using a 10mm threaded rod, and a bearing with a 10mm inside diameter. and simply tighten a bolt against eiether side of the bearing to lock it in place.

It seems to spin very nicely when I move the motor by hand.

I also have access to a lathe, and I am wondering if there is any benefit to turning down the threaded rod so that it fits very snug inside an 8mm or smaller ID bearing vs. simply tightening the bearing to the rod via two nuts?

Any insight would be appreciated.

Using idler bearings on a reprap is generally considered a bad idea. Especially as your threaded rod is as thick as 10 mm.

Really, why? I don't understand this, I would intuitively think the exact opposite.

I think what JK's referring to is Z wobble being transferred to the x axis?

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Waitaki 3D Printer

There are two main reasons why idler bearings can be trouble. The first is that the threaded bar is never straight and when you constrain it even further with an idler the Z wobble becomes worse as it cannot float about. It was a major failing of my early delta robot and a reason why the Rostock with belt drive performed so much better.

In addition, if you measure the major diameter of the 10mm thread you will find it is much less than 10mm. When you bolt it up it is always eccentric in the hole. Machining down to 8mm is a much better idea, but you may still get problems as the threads on cheap bar are often "drunk", so a nut travelling along the thread does not move linearly, but wobbles about (Like a drunk hence why it is called such in engineering).

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Helium Frog Website

AVRkire Wrote:
-------------------------------------------------------
> I am building a new Z axis, and I wanted to try
> attaching my z axis to my idler bearing by
> tigheneting a nut on both sides of the idler
> bearing.
>
> So I am using a 10mm threaded rod, and a bearing
> with a 10mm inside diameter. and simply tighten a
> bolt against eiether side of the bearing to lock
> it in place.
>
> It seems to spin very nicely when I move the motor
> by hand.
>
> I also have access to a lathe, and I am wondering
> if there is any benefit to turning down the
> threaded rod so that it fits very snug inside an
> 8mm or smaller ID bearing vs. simply tightening
> the bearing to the rod via two nuts?
>
> Any insight would be appreciated.



If I was going to build this machine, I'd go with "Precision Acme Threaded Rod".:

[www.mscdirect.com]

Or, is there a reason you guys use plain/standard, theaded rod?


Not a bad price for this precision.....

Edited 1 time(s). Last edit at 10/20/2013 03:16AM by Metalmann.