Hex Shafts and Bearings
 

We're potentially going to use hex drive shafts this year to get away from keys (that always seem to get lost at the worst times...).

I know other folks have used them. Can you run the hex shaft directly in the ball bearings without fear of point-loading the inner bearing race?

Re: Hex Shafts and Bearings
 

While it might be possible to do that for a while it is not a proper practice. Most teams turn down the ends of the hex shaft on a lathe so that it is round. There is also one other method which involves broaching bushings to the size of your hex and then putting that on the shaft to go in the bearing

Re: Hex Shafts and Bearings
 

I have always seen them turned down to round which is pretty easy with a 3 jaw chuck on a lathe, and some patients. If you are turning steel, it may be better to use HSS rather than carbide, because carbide will sometimes chip.

That being said, the point loading probably isn't a big worry to the bearing, but soft hex stock may yield at those points and thus be sloppy similar to a shaft that is several thousandths too small.

If you are switching over to hex, you will also want to have a broach and press to make custom interfaces.

If you only have a 4 jaw chuck for your lathe, some options might be:
Buy a 3 jaw (this could be cost prohibitive depending on lathe.

Make a round insert and then broach a hex. Cross drill and add a set screw.

Use square stock instead of hex. (you will also need a square broach). This does not seem to get used in FIRST as much so expect replacement parts to be custom.

Re: Hex Shafts and Bearings
 

Or if your lathe will take 5C collets, get a hex collet the right size.

Re: Hex Shafts and Bearings
 

http://www.chiefdelphi.com/forums/sh...aft+ bushings

check out page 2 of this thread paul and aj have some suggestions on hex shafts, especially post #26 from aj if you are worried about the point loading

Re: Hex Shafts and Bearings
 

hey im wondering what are the advantages to this switch? i'm confused on why you would change other than the the key getting lost at the worst time. which is why i always make sure we get extras :) .

Re: Hex Shafts and Bearings
 

A hex is superior to a key in pretty much every respect. You nailed one reason. No keys to lose. Another reason is that it's a pain is keys often don't fit into keyways easily, or over time the key can seize the wheel to the shaft (or sprocket or whatever you've keyed to a shaft). Keying a sprocket also introduces a major stress riser on the hub. Every sprocket failure we have ever had (and I believe the same is true for 968) occurred on the keyway of the sprocket.

Hexes mean assembly is way faster. They just slide on and off way more easily than any keyed interface I have ever used. It also is better at transmitting torque, as you have a vastly larger surface area to deliver the same amount of torque-this eliminates the stress riser associated with keyways.

If you have the ability to use hex shafts and hex broached gears/sprockets/wheels, it's an absolute no brainer, in my opinion.

Re: Hex Shafts and Bearings
 

I totally agree with Cory. One additional advantage is that the hex automatically centers the thing (gear, hub, sprocket) it is driving when torque is applied.

Andy B.

Re: Hex Shafts and Bearings
 

The method mentioned above is the cheapest and fastest way to pass a hex through a round bearing. Oversize your bearing id to accept a bronze bushing with suitable side wall. Then broach the bushing to use as a sleeve for carrying the hex.

You can also find something like this. Though I do not know of a source that stocks these.

Some notes about hex shaft from a former "hex only advocate." In applications where backlash and precision are a concern, say in an arm joint assembly, hex shafts can be less then desired. A broached hole is quite accurate, but hex stock has uncontrolled dimensions and may provide a loose fit.

Milling your own hex onto your shaft will allow you to control the fit precisely, but this requires more machining capability and diminishes the main 'ease of use' advantages.

For drivetrains, where lash is not a huge deal, hex is the way to go......

Also, precision ground keyed stock is readily available and keyway broaches are cheaper than hex broaches.

Good luck.

Re: Hex Shafts and Bearings
 

some of that shot over my head, but that makes sense

Re: Hex Shafts and Bearings
 

Hey, someone want to contact these folks and find out price/availability/sizes of their hex shaft adapters? Might be a cheap solution. :D

http://www.bnb-industries.com/Roller...%20Bearing.htm

See middle of page.

Stock Drive Products has round sleeves with a hex hole:

www.sdp-si.com/D790/PDF/D790C04023.pdf

Re: Hex Shafts and Bearings
 

Small Parts sells hexagonal sleeves, but they aren't cheap.

Re: Hex Shafts and Bearings
 

Does anyone know where to get a ball bearing with a hex in, like shown on aj's post. I was looking for a mcmaster number.

Thanks in advance.

Re: Hex Shafts and Bearings
 

The Small Parts item appears to have the same properties as the SDP-SI item that Dick linked just above. The SDP-SI item is priced much lower.

AndyMark sells a very nice hex hub for $15 each.

Now if someone would offer hex shafts that are turned down to 0.4995 inch on one end... :)

Re: Hex Shafts and Bearings
 

Some sweet poly bearings, but no 1/2 or 3/8 hex sizes:
https://qbcbearings.com/BuyRFQ/BallB_Plastic_FC.htm#

Re: Hex Shafts and Bearings
 

If any of you live near a community college that has a machining program, contact them and see if they will help with minor machining, such as rounding off the end of a hex shaft. Our local CC was delighted to help us put several of our #35 sprockets on a diet to save weight. They even gave me the mandrel they made in case we needed to do it again.

I've also had a local machine shop turn down some shafts for free.

Re: Hex Shafts and Bearings
 

Wouldn't it be cool if some small Indiana company would offer some bearing adapters and bearings for our applications?

Re: Hex Shafts and Bearings
 

Take a piece of appropriately sized aluminum tubing or bushing. Taper the end of a scrap of hex stock slightly, lube it and pound it through the aluminum tube, thus forming a hex. Spin it and use a file to turn down the outside until it is round and fits the bearing of your choice. Of course, that means using a bearing of sufficiently large size to leave enough material at the points of your homemade custom-forged hex adapter so it stays together. You could probably get it done with a wood lathe or drill press.

Re: Hex Shafts and Bearings
 

I think everyone is making this more difficult than it needs to be. While I understand these solutions are probably geared towards teams who do not have a lathe, the best and easiest way is to use a lathe and turn down the ends.

I would guess that 90%+ of FRC teams could find a machine shop willing to do so in less than an hour of calling up shops. Just for reference, when we do this it takes no more than maybe 5-8 minutes to face a shaft to length, and turn both ends down to fit into a bearing. So you're talking about maybe an hour tops to do all of the shafts in your drivetrain. I really don't think you'd have a difficult time finding a shop to do an hour of work for you (especially since it's all manual and involves virtually zero setup time).

Re: Hex Shafts and Bearings
 

Unless you want the bearings in the middle of the shaft.

Re: Hex Shafts and Bearings
 

I like your thinking. For example, it would be nice if the output sprockets in an AM Shifter could be hex broached instead of keyed or a smaller sized hex. To do that, the bearing in the gear that is between them and the dog would have to fit on a 1/2" hex shaft.

Re: Hex Shafts and Bearings
 

That is what i want, so i was thinking. What if you buy a bearing that has a 1 inch bore. Like this from mcmaster.com 60355K19. Then cnc or make a 1 inch bushing with a hex in the middle of it. Press fit the bushing into the bearing and try as hard as possible to not mess up the bearing. This way the sprockets and the gears can all be hexed @ the same size.

Or

Take the 1/2 inch hex and mill it down to a 3/8th's. Leaving a 1/2 inch circle for the bearing in the middle. I'll try to put up a drawing to illustrate what I mean. Sorry for the vagueness.

Re: Hex Shafts and Bearings
 

On the first point, standard hex stock is not real precise. It's going to be a pretty loose fit between the broached bushing and the hex shaft.

If you're machining a hex into round stock, it's a moot point. You want to do what I think you're saying in your second point, which is what 968/254 have done the last two years

Re: Hex Shafts and Bearings
 

Cory,

On the first part, we were going to have a 5 axis cnc make it. At our nearby college they have one. We have not been able to get our bits yet. We are still looking for clamps. But how has the second option worked for you.

-RC

Re: Hex Shafts and Bearings
 

I'm a bit confused. I don't really see how a 5 axis mill helps you. All you're doing is turning a plug and broaching a hole through the center. This is a manual lathe or 2 axis cnc lathe operation.

As for the way we do it, it works perfectly. It's more machining, but our shafts already require a live tooled lathe due to the non standard hex size, so really it's just a few minutes more run time.

Re: Hex Shafts and Bearings
 

I meant we needed a 5 axis for the shafts to be made (This part is my first suggestion). The bit isn't long enough on our regular CNC. So we take it down there. Hope that clears it up a bit.

Re: Hex Shafts and Bearings
 

A 5 axis machine, either mill or lathe, is overkill (in fact depending on the type, if it's a mill, you may not even be able to do it). You need a 4 axis mill or a 3 axis lathe.

Re: Hex Shafts and Bearings
 

We don't have a CNC lathe, I wish we did. But all we have is a 3 or 5 axis Mill.