design question

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cambazz
Posts: 28
Joined: Fri Mar 18, 2011 1:58 pm

design question

Post by cambazz » Sun Nov 06, 2011 10:32 pm

Hello,

I am trying to make a gearbox. The question is, the rotating joints part of the gear, just snaps in, and there is no bearing or anything like that, so there is a lot of friction.
P1010468.JPG
P1010468.JPG (63 KiB) Viewed 5481 times
Putting a bearing like from a model helicopter there can be a solution, but using a bearing is too expensive.

how can i make my designs, so that when i need a rotating joint or rotating part - things go without friction?




Best Regards,
C.B.

William
Posts: 340
Joined: Tue Sep 21, 2010 12:02 am

Re: design question

Post by William » Mon Nov 07, 2011 5:10 am

That's a general materials science question isn't it? You'll always have some amount of friction.

If you want to smooth the plastic, you can try sanding it.

I've seen acetone bath as a way to smooth, but you'll lose structural integrity.

You can also use some type of filler, and then sand it smooth.

I have used brass sleeves as inserts for steel pins as axles. This tends to work out nicely, but probably too expensive, but I don't know your budget.

cambazz
Posts: 28
Joined: Fri Mar 18, 2011 1:58 pm

Re: design question

Post by cambazz » Mon Nov 07, 2011 11:52 am

Hello,

More then a material science question, this is a `where can i find what` question. I need a number of non-standard screws, nuts and bolts that I can not find in the general hardware store in istanbul.

I need especially brass sleeves as you said, and certain plastic/teflon screws/nuts/bolts.

What is a good online specialist fastener store that you guys can recomend?

Best

Madox
Posts: 441
Joined: Wed Sep 15, 2010 1:30 pm
Location: Sydney
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Re: design question

Post by Madox » Mon Nov 07, 2011 12:18 pm

Hi
What is your definition of too expensive? Budget?

I use bearings from http://www.lowpricerc.com/index.php?cPath=33
They can be as cheap as $1.24 for 5, or $0.248 ea

ETPDesign
Posts: 23
Joined: Sun Jun 26, 2011 10:22 pm

Re: design question

Post by ETPDesign » Mon Nov 07, 2011 2:00 pm

First of all, this is a prototype printer. It isn't really meant to do what you are asking by it's self.

That said, I would make the hubs over sized if they were the inner bearing surface and undersized if they are the outer bearing surface. Then, as a post process, I would machine them to have a better surface and more precise fit than the printer can provide. The ABS should provide a fair to good bearing surface for low speed operation. If this is for high speed use, I would most certainly add brass or bronze bushings to the bearing surface at the very least.

I know this depends upon the tools you have available. You will have to consider what is in your tool box to select the best method for your situation.

I can suggest several USA companies that are excellent resources for the various bit and bobs necessary to complete your project, however, I suspect someone more Euro-centric than I, can suggest sources that are closer and just as useful. As a reference here are some good US sources:

<http://www.smallparts.com/?tag=smallpar ... 19ztgj3i_e>
<http://www.aircraftspruce.com/catalog/h ... s35206.php>
<http://www.mcmaster.com/#>
<http://www1.mscdirect.com/cgi/nnsrhm>

Cheers

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