Hex Shafts and Bearings

[Cory]

Originally Posted by bmarick

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 .

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.

[Andy Baker]

Originally Posted by Cory

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.

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.

[IndySam]

Originally Posted by Andy Baker

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.

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

[Dick Linn]

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.

[Cory]

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).

[IndySam]

Originally Posted by Cory

I thin 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).

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

[AustinSchuh]

Originally Posted by IndySam

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

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.

[R.C.]

Originally Posted by IndySam

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

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.

[Cory]

Originally Posted by rc_cola1323

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.

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

[R.C.]

Originally Posted by Cory

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

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

[Cory]

Originally Posted by rc_cola1323

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

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.

[R.C.]

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.

[Cory]

Originally Posted by rc_cola1323

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.

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.