Threaded rod through ball bearings
 

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!

Re: Threaded rod through roller bearings
 

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

Re: Threaded rod through roller bearings
 

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.

Re: Threaded rod through roller bearings
 

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.

Re: Threaded rod through roller bearings
 

The following are some thoughts, where if I'm understanding you correctly, you're asking about using a "live" threaded rod with a wheel fixed to the end, running through a roller bearing.

Assuming the roller bearing is running on the threaded rod itself....
As you may already know, roller bearings are designed to run on hardened "smooth" shafts. Being that the threaded rod is most likely not hardened, and obviously not smooth, I would suggest it be avoided, as there will most likely be bearing issues.

Regardless of whether or not the roller bearing is running on the threaded rod...
You'll have a pretty high stress concentration at the "v" of the threads (since you'll have a cantilevered load), so depending upon the diameter of the threaded rod, the distance from the bearing, and the load, you'll possibly cause fatigue failure of the threaded rod (since it's a live axle).

While it may work at first, it then becomes a question of how long. If it were me, and I had an alternative (which you stated you do), I would not risk my drive train.

Maybe I'm a bit conservative, but that's my 0.02.

Re: Threaded rod through roller bearings
 

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.

Re: Threaded rod through roller bearings
 

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.

Re: Threaded rod through roller 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.

Re: Threaded rod through roller bearings
 

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.

Re: Threaded rod through roller bearings
 

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!

Re: Threaded rod through roller bearings
 

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.

Re: Threaded rod through roller bearings
 

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....

Re: Threaded rod through roller bearings
 

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.

Re: Threaded rod through ball bearings
 

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.

Re: Threaded rod through roller bearings
 

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.