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lbhsbz
12-08-2010, 04:31 PM
Since I don't have any broaches, I've come up with what I think is a better way to prevent shafts/hubs from spinning independently of each other, and you can do it with basic mill tooling.

I simply use an endmill to remove a half round section of the hub, rather than a square section like you would with a broach, then cut the other half of the round into the shaft using a ball nose endmill. I've been using sections of welding rod for smaller "keys" or sections of drill rod/round stock for applications requiring larger sections. I've actually used 4 of these, positioned 90 apart to make a sort of splined slip yoke....and it worked very well. Of course, you are limited only by the length of your endmill.

Seems for high torque situations this would be advantageous as it involves none of the stress risers of the sharp angles on a keyway slot. Also, it would be tough to sheer something that's round. The only times I've seen this kind of "system" is when I've made it

I'm clearly missing something. What am I missing. Why isn't this more commonly used?

Paul Alciatore
12-08-2010, 04:39 PM
I believe this kind of key has been in use for many years. One of the handwheels on my SB lathe is keyed this way. It appears that it was assembled first with the wheel hub even with the end of the shaft and then the joint was drilled and a pin was inserted. No milling required.

John Stevenson
12-08-2010, 04:43 PM
Seems for high torque situations this would be advantageous as it involves none of the stress risers of the sharp angles on a keyway slot. Also, it would be tough to sheer something that's round. The only times I've seen this kind of "system" is when I've made it

I'm clearly missing something. What am I missing. Why isn't this more commonly used?

For light work it's fine but in high torque applications it rolls the circular key.

Had a largish rotor a while ago out of a motor generator, could have been a welder not sure as I only had the rotor.
This shaft was straight knurled and pressed into the rotor but the laminations had half rounds cut in them all round so the surface area was reduced by half ?? No idea why it was made like this.

When they started these things up they used to spin the shafts after a while. So because it had the half moons in which were 10mm in diameter I milled two groves the length of the shaft to match up with two opposing grooves with a 10mm ball nosed cutter.
Shaft was loctited and pressed back in with two 12 " lengths of 10mm steel rod as keys.

Lasted two weeks and shagged the inside of the rotor :( :(
Made a right mess of the shaft and rotor. Fortunately they had spares from dead motors, again with loose shafts so this time, re-knurl, send the rotor out to have two half round grooves converted to 10mm keyways, my slotter can only do 6" and these were 12" long.
Mill two proper keyways in the shaft, loctite and press in.
So far done about 6 or 7, never had one back

The Artful Bodger
12-08-2010, 04:45 PM
The thing about drilling the hole and putting in a pin is that I think you could only do that at the end of a shaft, I guess by milling a half round you fit a pulley (for example) anywhere along the shaft.

If you are going to use the drill method at the end of the shaft it is even better to tap the hole and screw a grub screw in, IMHO.

Ken_Shea
12-08-2010, 05:11 PM
If there is sufficient material, mill a small flat on the shaft, drill/tap the wheel and use a set screw tightened down on the flat, similar to what is done with end mill holders, they don't slip .

Carld
12-08-2010, 07:27 PM
I built about 5 stave cutting machines that used an 8" diameter x 12" long multi insert cutter head that had two 1/2" round keyways 180 deg apart. Making the shaft with two round keyways 180 deg apart was not easy. There could be no slop or misalignment. The depth of the pin and location of 180 had to be in tenths, not thousandths. As far as I know we never had a come back or failure.

If I were to use dowels to act as keys as you are I would press the pulley on the shaft and drill and ream for a round pin at the center line between the shaft and pulley. I would not try to do each separately because of the chance of error. When you use a round key there is no room for an error of even .001" because that will cause failure.

Actually what your doing is called a Dutch key and is usually a tapered pin but most the time is a drilled and tapped hole with an allen set screw in it.

GadgetBuilder
12-08-2010, 08:17 PM
You may have re-invented the "scotch key", see:
http://en.wikipedia.org/wiki/Key_%28engineering%29

Doozer
12-08-2010, 08:41 PM
http://www.ringfeder.com/Global/Images/Products/Ringfeder/Locking_Devices/Locking_Assemblies/RfN_7012.png Ringfeders are the ultimate solution. http://www.ringfeder.com/en/America/Products/RINGFEDER/?g=382 --Doozer

whitis
12-08-2010, 10:00 PM
I simply use an endmill to remove a half round section of the hub, rather than a square section like you would with a broach, then cut the other half of the round into the shaft using a ball nose endmill.

Using the same setup, cut a slot in the hub with a rounded, rather than flat, bottom. I.E. remove everything a broach would and plus a half moon. Then use a flat endmill instead of a ball nose on the other side. Now cut your key stock so it fits into that slot, filling in the half moon, or use regular size stock and plug the half moon so the key can't ride up and cut the half moon square. Be careful that you aren't removing too much material. You can also cut for a round top and bottom.

As John says, the round pin can roll or cause the hub to ride up over the key which can do things like split your hub or gall up the shaft/hub., out of balance, etc. Some parts will hold up better than others depending on the appropriateness of the key size, amount of material backing up the key, fit between hub and shaft, etc.

vpt
12-09-2010, 08:36 AM
I think you are doing something similar to how OMC outboard water impellers are keyed.

http://www.bassboatcentral.com/JohnRudeTips/BBC_photos_031.jpg