Finding Aluminum Axle

[Dale]

I've been looking high and low for an internet source for solid aluminum rod that's the right OD to use with normal steel sprockets. Most aluminum rod seems to be sized right at the outside diameter indicated or even a little bigger. For example .5" rod will be somewhere in the .500 to .503 range. The problem is most of our 1/2" sprockets tend to have holes that are around .498" . They are just enough too small that they'd won't slide over the aluminum rod. Steel rod seems to work fine as does (expensive) coated aluminum from igus. Our 5/8" sprockets and aluminum have the same problem.

Any thoughts as to where to find aluminum stock the right diameter? We'd rather not have to bore out every sprocket or turn down every rod!

[Cory]

You can buy precision ground rod that is undersize up to a couple thousandths. McMaster should carry it.

[artdutra04]

McMaster-Carr is a great place to look for practically everything that exists under the sun - and their shipping can only be described as light speed.

Also, if the difference is only a few thousandths, why not just just use some Emory cloth and sand it down? Yeah, it can be a pain sometimes (chucking it into a drill, turning it on, and holding the Emory cloth to the axle works ), but on applications like fitting sprockets on axles, I'd rather err towards tight, press fits than loose, sloppy fits.

[vivek16]

Originally Posted by artdutra04

McMaster-Carr is a great place to look for practically everything that exists under the sun - and their shipping can only be described as light speed.

Also, if the difference is only a few thousandths, why not just just use some Emory cloth and sand it down? Yeah, it can be a pain sometimes (chucking it into a drill, turning it on, and holding the Emory cloth to the axle works ), but on applications like fitting sprockets on axles, I'd rather err towards tight, press fits than loose, sloppy fits.

What he said. Precision rod is probably going to be too loose. I would sand it down until it works just barely.

p.s. Just wondering but why aluminum axle?

[Cory]

I think the best answer here is buy a 0.501 reamer, and start buying precision ground 0.500" shafting.

[Kyle Love]

Originally Posted by Cory

I think the best answer here is buy a 0.501 reamer, and start buying precision ground 0.500" shafting.

Amen.

[Dale]

Thanks for the ideas. So far I haven't found anyplace, McMaster included, that sells precision ground aluminum from McMaster-Carr that's .498" except igus. I've been able to get .500 +- .002 but then we end up rummaging around through the stock and finding some that works and some that doesn't.

We do a lot of pre-season building of 90lb or so robots to get new members up to speed. These are often students who have never done much metal work. I'd like to be able to hand them a rod that I know it will work wiothout a bunch of fiddling on their part. During the competition season we'd rather not have to ream out all our sprockets and bearings. It just seems like it should be easy to find off the shelf material for this but...

As to why Aluminum? It's easier to cut keyways into and, of course, it's lighter. Since we keep the widths short we've never had a problem with it bending, especially at 5/8". On a six wheel robot it can save a significant amount of weight.

Just want to make sure I'm not missing something!

[kramarczyk]

Stated briefly... Our experience with keyways in 5/8 aluminum igus shafting was, well, less than desirable.

[Karthik]

Originally Posted by Dale

Thanks for the ideas. So far I haven't found anyplace, McMaster included, that sells precision ground aluminum from McMaster-Carr that's .498" except igus. I've been able to get .500 +- .002 but then we end up rummaging around through the stock and finding some that works and some that doesn't.

Try McMaster Catalogue page 1046 for aluminum precision shafts.

[Kevin Sevcik]

Might I also recommend the fully keyed aluminum shaft found at McMaster on catalog page 1053? I mean, just to save you the annoyance of keying your own shafts and all that. The 1/2" diameter is -.0005 to -.0025, so there's some odds that it'll fit your stock sprockets, or you can ream them as suggested above to get them perfect. But .498 is a weird ID for a finished bore sprocket anyways. Martin Sprockets specs +.001 to +.000 for a 1/2" finished bore, so any finished bore sprockets from McMaster should be fine. So I'm kinda curious where your undersized bore sprockets are coming from. If only to avoid them.

[IndySam]

Your freezer can be your friend.

[DonRotolo]

Originally Posted by Cory

I think the best answer here is buy a 0.501 reamer, and start buying precision ground 0.500" shafting.

Ream out a bearing race? These are generally quite hard and un-reamable.

[Cory]

Originally Posted by Don Rotolo

Ream out a bearing race? These are generally quite hard and un-reamable.

Why would you do that? I meant ream the sprocket, since it's the undersized object here... With the accuracy of whatever measuring tools you may have on hand, if your bearing isn't reading dead on 0.500" on the ID, you're buying bad parts.

[MrForbes]

Originally Posted by Dale

As to why Aluminum? It's easier to cut keyways into and, of course, it's lighter. Since we keep the widths short we've never had a problem with it bending, especially at 5/8". On a six wheel robot it can save a significant amount of weight.

Just want to make sure I'm not missing something!

I can think of better places to save weight, as live axles are one of the highest stressed parts of the robot. They also sit very low, so the "extra" weight of steel is in a good place.

I was talking about live axle design ideas with my son when he discovered the Banebots wheels, and it looks like 1/2" keyed steel shaft would be the way to go. 6 axles 4" long will save you almost a pound if you make them of aluminum instead of steel....is it really that significant?

[AdamHeard]

Originally Posted by squirrel

I can think of better places to save weight, as live axles are one of the highest stressed parts of the robot. They also sit very low, so the "extra" weight of steel is in a good place.

I was talking about live axle design ideas with my son when he discovered the Banebots wheels, and it looks like 1/2" keyed steel shaft would be the way to go. 6 axles 4" long will save you almost a pound if you make them of aluminum instead of steel....is it really that significant?

There are allows of aluminum (7068, 7075) that are plenty strong to handle the job of being live axles.

Saving an entire pound is very significant; and it can easily lead to having a lower CG than keeping that pound in the shafts.