[martin_05]

I am working on a design that consists of the following:

1/4 steel inch shaft sliding in 1/4 inch hole in aluminum.

The shaft has external retaining rings to limit motion from end to end.
It will have to be turned to cut grooves for the rings.

The hole is 0.750in long.

There are two of these shafts running parallel to each other and about 1.6 inches apart. Both guide holes are in the same block of aluminum.

I want to be smart in material and size selection in order to avoid this thing being more complicated (and expensive) than it needs to be.

First would be material selection for the rod. It will have to be cut and grooved, which means that it can't be hardened steel shafting. I don't want to turn something to 0.250, I want to stick with stock sizes. What are the range of diameters one might get if I specify nominal 1/4 steel rod?

Now, the holes need to allow for a smooth sliding action. Motion is slow. No need for bearings. This is basically a clamping mechanism. I want to make it so that hole manufacturing isn't anything special. If the rod is undersized a little maybe I can specify a 0.250 drilled hole. My guess is that it is more reasonable to go with an F drill and get a 0.257 hole. This might allow for tolerances in both the rod diameter and the center-to-center distances between the holes.

What are best practices when dealing with something this simple: A 1/4 rod sliding in a 1/4 hole. Simple, but not so if you look at the details of making the thing.

Thanks!

-Martin

[RomanLini]

In computer printers they use an oversized hole, with a pressed in or pop-in (sprung) plastic sleeve bearing. Then the steel shaft slides or rotates inside the plastic bearing. If you check the Asian suppliers you can probably find those pop-in plastic bearings to suit all common shaft sizes, and I would expect them to be extremely cheap in quantity.

They may also be able to supply your shafts, cut to length and grooved for take a external circlip.

Another option might be to not use an aluminium block but to bore the two holes in a block of slippery plastic.

[RICHARD ZASTROW]

Turned, ground and polished round rod is a catalog item at most steel suppliers.(TG&P) You could cut to length and cut the grooves.

Dick Z

[martin_05]

In computer printers they use an oversized hole, with a pressed in or pop-in (sprung) plastic sleeve bearing. Then the steel shaft slides or rotates inside the plastic bearing. If you check the Asian suppliers you can probably find those pop-in plastic bearings to suit all common shaft sizes, and I would expect them to be extremely cheap in quantity.

They may also be able to supply your shafts, cut to length and grooved for take a external circlip.

Another option might be to not use an aluminium block but to bore the two holes in a block of slippery plastic.

I don't really know of any Asian suppliers that you can buy from that would be the equivalent of MSC, for example. Can you provide any links to such suppliers?

[packrat]

I think this is what he means; Nyliner Product Catalog

McMaster-Carr used to carry them, plus almost any bearing supply.

[martin_05]

I think this is what he means; Nyliner Product Catalog

McMaster-Carr used to carry them, plus almost any bearing supply.

Very interesting, thanks.

[plasmamatt]

If it is just a clamping device you probably don't need any real close tolerances. I think I would just start with a piece of C1018 1/4" dia. round. You may even have to turn the shaft just slighly to accomodate a slip fit. C1018 turns very easy and it is also very common. If this was a location with quite a bit of motion you may want to consider the Igus brand of plastic bearings. I have used these in one particular fairly high load design and they work great. The steel actually wears more than the plastic.