Question about Bearings?
 

If I mount a steal shaft to a piece of aluminum through a 1/4 inch whole, and the shaft spins pretty fast and often(say for like a roller to grab balls), is it nessisary to use a ball bearing? Thanks for the help.

Re: Question about Bearings?
 

Not necessary, but HIGHLY recommended. The steel shaft would quickly open up the hole in the aluminum plate, then things just get worse from there.

Re: Question about Bearings?
 

That was my thought, but I just didn't know if it would be a problem. Thanks for the answer.

Re: Question about Bearings?
 

There are lots of other options that might work better than steel on aluminum (but worse than a ball bearing). How thick is the plate that you're going through? You might be able to use a bronze or plastic sleeve bearing (bushing) if it's thick enough. Otherwise, you could bolt a piece of hard plastic to the aluminum, make a large hole in the aluminum for clearance, and drill a slightly oversized (e.g. 0.01 in larger) hole in the plastic for your shaft.

Depending on the specifics of the situation (how accurate everything is, how heavily loaded the shaft is, how much you intend to use it, etc.) you might even be able to get away with running it as you described—lubrication would be a very good idea, in that case (use grease).

Re: Question about Bearings?
 

For the application depending on shaft speed and loading you could get away with an oilite bushing as well. Roller element bearings aren't always necessary.

Edit: Remember steel and aluminum are a galvanic couple and will likely corrode during shipping, so at a minimum a bushing is recommended for this.

Re: Question about Bearings?
 

Search mcmaster.com for "sleeve bearings". That should work for your application.

Re: Question about Bearings?
 

In automotive engines, most overhead camshafts ride directly in holes in the aluminum head, and the aluminum lasts for a long, long time. The trick? lubrication. Since you can't have oil dripping from your robot, you probably need a bushing or bearing. Which you use probably depends on load, speed, thickness of the mounting surface, and other stuff that we don't know, but you do know.

Re: Question about Bearings?
 

IGUS makes some really nice bushings for small holes like this.
You would most likely want a flanged plain bearing. Or McMaster sells plastic and bronze bushings either of which would work, and be lighter than a ball bearing.

Re: Question about Bearings?
 

While you might be able to get by with a plain hole (if properly dimensioned and finished), you'd be well advised to consider an oil-impregnated bronze bearing. They are very inexpensive in the small sizes - well under a dollar. There are a number of 1/4" inside diameter bearings of varying lengths for 50 to 75 cents each here:

http://www1.mscdirect.com/CGI/NNPDFF?PMPAGE=3670