Half bearings for the extruder drive screw - How do they work?

Should be a fairly simple question to answer:
How do the half bearings placed in the screw-holder work? Do they rotate with the screw within the screw-holder? Or does the drive screw rotate within the bearings? That is, do the bearings themselves move?

[I'm asking because I'm designing a bootstrap extruder and it might be better if I use rectangular prisms of brass/etc with holes drilled in them, and then cut in half, to use as the half bearings; the square part would contact the screw holder, and the half cylinder hole would be where the screw goes. If the bearing is supposed to move within the screw holder, however, this wouldn't work, as the squareness would stop it from rotating independent of the holder.]

Thanks!

Joshua Merchant Wrote:
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> it might be better if I use rectangular prisms of brass/etc with holes drilled in > them, and then cut in half, to use as the half bearings

That's what I did. It works fine for me.

Bearings don't move - I think they're just round because you can get brass bar like that.

EDIT: had this thread open a while before I responded, whoops. Forrest got there first.

Edited 1 time(s). Last edit at 07/20/2008 01:56AM by Kyle Corbitt.

Forrest Higgs Wrote:
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> Joshua Merchant Wrote:
> --------------------------------------------------
> -----
> > it might be better if I use rectangular prisms
> of brass/etc with holes drilled in > them, and
> then cut in half, to use as the half bearings
>
> That's what I did. It works fine for me.


Wonderful! I love it when my options are expanded. Makes things so much easier.
Thanks!

Kyle Corbitt Wrote:
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> Bearings don't move - I think they're just round
> because you can get brass bar like that.

Ah. Well, I'm hoping that the option for using a squared bearing will increase the number of materials that I can use, which decreases cost and complexity (theoretically).

Edit, in response to Kyle's edit:
Heh, I was replying to his post when you posted.

Edited 2 time(s). Last edit at 07/20/2008 02:00AM by Joshua Merchant.

I used stacks of halved washers held in place with CAPA as I didn't have easy access to any brass tubing, it worked pretty well, haven't had any trouble with them.

Sorry, maybe this is going to be a dumb question, but maybe not

ptfe is known to have a very low friction,

isn't it possible to machine the halfbearing from the same piece of rod we use for the extruder insulation?

'sid

While PTFE is very slick, it's not hugely strong and you can cut it pretty easily. While it might be nice if you could line your bushing with PTFE I doubt you could make the whole thing from it successfully.

yeah, spray lining the half bearings and the channel on the other half of the extruder would be sweet! Make the GM3 strain a lot less.

Demented

sid Wrote:
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> Sorry, maybe this is going to be a dumb question,
> but maybe not
>
> ptfe is known to have a very low friction,
>
> isn't it possible to machine the halfbearing from
> the same piece of rod we use for the extruder
> insulation?

Well I tried something like this. I drilled a hole and then cut the shape I needed with a sharp knive. Works very well we already printed a screw holder part with the new ptfe bearings

[reprap.soup.io]
[reprap.soup.io]


greetings
wizard23
[reprap.soup.io]

Edited 1 time(s). Last edit at 08/29/2008 05:22AM by wizard23.