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lgreen 11th December 2003 06:09 PM

Stupid Question- How To Use Ball Bearings?
 
Here is a stupid question. I want to set up a rotating shaft, to extend out through a front panel on my DIY preamp. I thought about using ball bearings. Here is a picture of what I am talking about:

http://members.shaw.ca/hiiq/bay/a_associated_12l3.jpg

1. Assuming I have a shaft that will fit inside these, doesn't it need to be tightened to the inner metal ring? I can't see how this would be done, any ideas how you do this?

2. Next I need to mount the outer section of the bearing so that the shaft is perpindicular to the front panel, and can extend through a predrilled hole in the front panel. How would I do this?

3. I've seen "pillow block" ball bearings which look like they are perfect for this task, but most of those have .5" bore or bigger, I'm looking for .25" (6.35 mm) bore, to fit in a tight space with a .25" shaft, these are just too large and bulky. Are there any other options that you can think of? These pillow block things are very nice but are much to large for my application. Ideally I'd like a super small one for a .25" shaft, any ideas?
Here is a pillow block

http://i6.ebayimg.com/02/i/00/fb/8f/36_1.JPG

sreten 11th December 2003 06:21 PM

As far as I know all you need is a plain plastic bearing.

You just drill and ream a hole in a flat piece of
plastic and attach it to the rear of your panel,
or a panel slightly behind the front panel.



:) sreten.

rwagter 11th December 2003 06:37 PM

The most elegant solution is a linear bearing:

http://www.wmberg.com/images/plinearbearings.jpg

it consist of very small balls within. Beware though, the ones sold on ebay <$15 are of no good quality. These bearings are $$$$$

Ralph

tiroth 11th December 2003 07:11 PM

I think you may be overengineering. I just drill a hole for the shaft to go through.

RHosch 11th December 2003 07:45 PM

Use a cheap nylon flange bearing instead. Drill a hole through the panel to match the outer diameter of the sleeve, maybe even a bit oversized... you don't want a tight fit on the shaft for this type of application. Push the bearing in from the outside such that the flange seats on the front face of the panel. Use some epoxy adhesive if the fit is loose.

This should provide for a smooth action when turning, and the flange provides a low-fricition face for the knob to rub against as well if needed in case you put too much pressure on it when turning.

Nylon flange bearings can be purchased from MSC or McMaster Carr (or, possibly, from stores like HD and Lowes as well) for just a dollar or so in 1/4" size.

jwb 11th December 2003 07:48 PM

Normally a shaft is pressed into a ball bearing. But, as the others said, a ball bearing is all wrong for this task. Just use a nylon sleeve, and if you don't like the fit you can use a permanent lubricant.

RHosch 11th December 2003 07:48 PM

BTW, you do not want to use linear ball bearings. Linear bearings are made for just that... a linear motion of the shaft. They are not designed for rotation, and in fact many are designed specifically to resist rotation. Turning a shaft in a linear ball bearing will wear quickly wear the shaft, the bearing, or both, and the "feel" of the turning motion will likely be about as smooth as a stick in a cement hole.

Teflon/Freelon lined linear bearings work very well for both rotational and linear motion, and that is their primary benefit. Much more expensive than standard nylon though, so I don't see any reason for using one in this application.

jwb 11th December 2003 08:14 PM

Speaking of Teflon, Delrin has a really nice feel in this application. You can buy it in raw form and cut and drill it yourself easily.

nemestra 11th December 2003 08:28 PM

Re: Stupid Question- How To Use Ball Bearings?
 
Quote:

Originally posted by lgreen
3. I've seen "pillow block" ball bearings which look like they are perfect for this task, but most of those have .5" bore or bigger, I'm looking for .25" (6.35 mm) bore, to fit in a tight space with a .25" shaft, these are just too large and bulky.
I don't know if bearings are the right way to go on this but if you are looking for small bearings then www.smallparts.com might be worth looking at.

James

purplepeople 11th December 2003 08:46 PM

2 Attachment(s)
You don't need ball bearings as a bushing will suffice. The easiest way to do this is to get a sheet of plastic. UHMW-PE, nylon and Delrin will all work in this regard. Use the same drill bit as the shaft diameter. If metric, then use metric bits. Using a hand drill will create the needed gap to make the rotation smooth. More looseness can be made by taking some fine sandpaper and rolling it into a stick and spinning it in the hole.

You can cut the sheet slightly smaller than your front panel (to fit inside the enclosure) and drill all the holes in the right places. Or you can make square blocks about 1/2" larger than your knob. Then drill 4 holes from the front and using small metal screws for an industrial look.

:)ensen


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