Re: Hex shafts?
 

Coast does not stock any high strength aluminum.

The best place on the west coast for 7075 of any profile is Fry Steel, in our experience.

Tolerance on the hex is a constant battle for us as well. We either need to broach the mating piece multiple times or use a 3M deburring wheel to knock a little off the flats of the hex. We've tried using an oversized hex broach but it's unpredictable whether you end up with a nice fit or a sloppy fit and it does you no good when your mating piece came stock with a hex in it.

Re: Hex shafts?
 

Thanks for all the responses guys. But on buying the hex no where in Austin stocks hex in 7075 it's just 6061. But what were some problem y'all had with the 6061 hex? (sorry for the limited respons I am away from my comp. right now)

Re: Hex shafts?
 

http://www.onlinemetals.com/merchant...p=2&top_cat=60

Here's an online place to buy some 7075.

-RC

Re: Hex shafts?
 

During the middle of the 2010 season we switched our transmission output shafts from keyed to hex due to numerous keys sheared the previous three years. We will never go back to keys, and you will probably see us use hex in other applications also.

Actually, now that I think about it, we used a hex shaft on our custom worm gearbox this past year for the tower. No problems at all from the hex, but some other things in the gearbox were problems.

Re: Hex shafts?
 

Fry Steel will ship via UPS at quite reasonable rates.

Re: Hex shafts?
 

We have found that most fit problems with Hex shafts come at the corners. We always turn our hex shafts on a lathe to cut the corners off just a little and 90% of the time that fixes our fit problem.

Re: Hex shafts?
 

They bend and shear far too easily for our liking. We also managed to strip the hex of the shaft (!) in a drivetrain this year.

Re: Hex shafts?
 

This past year we used steel hex shafts in our drivetrain. normally I would use 2024 aluminum but weight wasn't an issue for us this year and the steel is very easy to slide bearings and hubs onto. Our 2010 robot had the aluminum and had no problems with bending or breaking going over the bumps.

Re: Hex shafts?
 

We have the same issues. We found that we can order various tolerances on the hex from McMaster last year. Beware what the fine print says when yoou order from them. Some of the hex they carry comes in as much as .005" over.

Also I have to agree with Paul that 90% of our issues are actually the corners caused by a worn broach.

We have almost exculsively used hex shafts since we first tried them in 2008 and I can't imagine going back. The y are just way too easy to make compared with keyway. If we key anything other than motors its a rare occurance these days.

Re: Hex shafts?
 

To elaborate, the material property that relates to strength in this case is called the yield stress. This is the point at which the material suffers a permanent bend. For things like a shaft, bent = no longer working properly.

Simplistically speaking, a shaft material with twice the yield stress will be able to take twice the load. This assumes that the size and support of the shaft remain the same. Changes to those are really important, but are a subject for another thread.

For some of the materials mentioned in this thread, here are the yield stresses as found at www.matweb.com

Aluminum - 2024-T351 - 290 MPa or 42000 psi
Aluminum - 6061-T6 - 255 MPa or 37000 psi
Aluminum 2011-T3 - 262 MPa or 38000 psi
Aluminum 7075-T6 - 462 MPa or 67000 psi
Steel 1018 - 370 MPa or 53700 psi
Steel 4140 - 675 MPa or 97900 psi

Be sure to compare the numbers for 7075 aluminum and 1018 steel to understand why folks are talking about 7075.

Re: Hex shafts?
 

How do you put bearings on hex shafts? Is there a good source for bearings with a hex ID or do you simply turn portions of the shaft down and put them in standard bearings?

Turning the shaft down seems like it would limit possible configurations by forcing you to put bearings only on the ends of the shaft. (e.g. It would be impossible to have a Wheel-Bearing-Bearing-Sprocket configuration as in many west coast drives.) Is there a way around this limitation or do you just live with it?

Re: Hex shafts?
 

AndyMark sells hex bearings

Re: Hex shafts?
 

Both. Andymark's hex bearings are a fairly recent thing which makes working with hex a lot easier.

Not simply. Some teams go from 1/2 hex -> 1/2 round -> 7/16 hex in order to put bearings in the middle of the shaft. Step hexing is pretty complex though.

Re: Hex shafts?
 

Who does that? Wouldn't it be significantly easier to install a sleeve instead? (I envision using a narrow needle bearing to make up for the added thickness of the sleeve—this would even work on an aluminum hex shaft, because the steel sleeve protects it against wear.) Even if you had to retain the sleeve to avoid sliding, it would still be far easier.

Re: Hex shafts?
 

254/968 have commonly done that. Its a super nice part and makes sense if you have the resources to do it.

http://www.chiefdelphi.com/media/img...3db741ff_l.jpg

Output shaft, but same concept.

973 last year was even able to have a student do it on manuals.

http://www.chiefdelphi.com/media/photos/35999

We (973/1323) even did the same setup for our arm this year. Its not that hard of a part, the output shafts are a bit trickier.

-RC