Threaded rod through ball bearings

[Madison]

My gut tells me running threaded rod as a live axle on a drive is a bad idea, but I'm curious if any folks have hands-on experience with this or some words of wisdom about what the pitfalls may be.

It's entirely possible to avoid using threaded rod through the bearings, but it'd simplify things a lot and make me a much happier person if it were an acceptable alternative.

Okay, so.. go!

[Aren_Hill]

i think that if you lock the threaded rod to the id of the bearing somehow you'll be fine and it would eliminate some interesting looking wear patterns

[Billfred]

I can't speak on live axles, but 1293 used threaded rod as a dead axle on a total of 16 different wheels over the past two seasons (two on Ockham, six on Chomp, and then double that for their practice robots). I can count the number of problems we had with it on zero fingers.

[capnrmorgan]

Team 1882 is thinking of threaded rod as well. We think we may fit threaded rod inside 1/2 od tubing to make a long bushing that the wheel rides on (dead axle). This will fit inside the 1/2 id bushing and lock the side rails with nylon lock nuts outside. We could modify this to be a live axle as well. This will be the first time we try this so it will be a wait and see at this point. Good luck with the 2007 season.

[Madison]

Originally Posted by Billfred

I can't speak on live axles, but 1293 used threaded rod as a dead axle on a total of 16 different wheels over the past two seasons (two on Ockham, six on Chomp, and then double that for their practice robots). I can count the number of problems we had with it on zero fingers.

I suppose it makes little difference if the bearings are riding in the wheels or in the frame.

Coupling nuts are a small miracle, by the way.

McMaster-Carr doesn't carry studs of convenient length, so I was resigned to assigning some poor student to threading steel rod with a die, but if we can cheat a bit and use rod that's threaded along its whole length, that'll save me from the dishonor of assigning more kids to sweatshop duty.

[Andrew Blair]

If you used large enough diameter rod, and assuming you only need threads on one side of the rod, you could turn the rod down and fit it to a smaller bearing. 1/2" threaded rod could easily be modified to fit 3/8" bearings.

[Gabe]

Originally Posted by Andrew Blair

If you used large enough diameter rod, and assuming you only need threads on one side of the rod, you could turn the rod down and fit it to a smaller bearing. 1/2" threaded rod could easily be modified to fit 3/8" bearings.

For you people that don't have access to a lathe, mount the threaded rod in a drill press and then file away while it's spinning.

[Madison]

Here's a cross-section of the drive arrangement I'm considering.

The dark gray rod is the axle; potentially a steel, 3/8-16 threaded rod. It runs through two bearings, shown in white near the center, and has a cantilevered sprocket on one end and a wheel on the other. Threaded onto each end is a 1/2" hex coupling nut. The ends of the axle are drilled and tapped to accept left-handed screws which'll hold plates against the wheel and sprocket to prevent them from backing off.

I was looking specifically at Grade B7 threaded rod available from McMaster-Carr -- part no. 98750A068.

[Rob2713g]

We've successfully used rod with jus threaded ends for axles. Although they did not transmit power. I believe we bought then at either Lowe’s or Home Depot. Good Luck!

[Gabe]

Thread a bronze or steel bushing and this goes onto the rod to offer a smooth shaft for the ball bearings to ride on. All it requires is increasing the inside diameter of the bearings.

[MrForbes]

looks to me like you are actually planning on using ball bearings, not roller bearings?

As long as the inner races of the bearings are clamped tightly to the spacers, using the threaded rod and nuts to hold it all together, it should be ok....

[Madison]

Originally Posted by squirrel

looks to me like you are actually planning on using ball bearings, not roller bearings?

As long as the inner races of the bearings are clamped tightly to the spacers, using the threaded rod and nuts to hold it all together, it should be ok....

Yep. I associate "ball bearings" with the balls alone and not the whole bearing, so I've always called them roller bearings. It's fixed now.

[MrForbes]

OK, I work on cars a lot, they have both types, and there is a big difference between roller and ball bearings....so I'm kind of picky about the terminology.

[hallk]

Originally Posted by M. Krass

McMaster-Carr doesn't carry studs of convenient length, so I was resigned to assigning some poor student to threading steel rod with a die, but if we can cheat a bit and use rod that's threaded along its whole length, that'll save me from the dishonor of assigning more kids to sweatshop duty.

If you can't find the right length at McMaster, you might want to try calling your local Ace hardware stores. Numerous times they have had odd ball size/ threads. But it won't be listed online, you will need to call local stores.

[Not2B]

We did alot of our rollers for the ball system last year out of threaded rod. We didn't want to, but we didn't have a lathe, and it was taking too much time threading the ends of solid shaft. So we went with threaded rod. It was a bad idea. Most issues you wouldn't see (we had nuts that tightened as time went on, binding the system), but we did cut into the bearings with the thread.

Good luck!