Inserting Steel Allen Socket in Aluminum? 1

[dtronvig]

I'm designing a small aluminum cam that will be turned with an allen wrench (or it could be a different cross-section). I'd like to have as small a socket as I can get away with--on the order of 5/32--for a given torque, without stripping the socket. I have vaguely heard of externally-splined steel allen-socket inserts that could be pressed into aluminum, but if they exist I haven't been able to find them or figure out what they would be called. If there is such a thing, what would you call it and where would you find it?

Thanks,
Drew

 

[MikeHalloran]

You call it an Allenut.

It's a hard double- height nut with internal double-hex wrenching feature and an external spline. You can use it as a free- spinning nut in a counterbored hole, or press it into a slightly smaller hole, turning it into an embedded thread insert. It would probably work okay for an application like yours.

http://www.mjvail.com/holokrome/dd_allenuts.html

Mike Halloran
Pembroke Pines, FL, USA

 

[dtronvig]

Hey Mike,

Looks good. I was picturing something with the socket running all the way through, but this should work, and it has the added advantage that it actually exists.

Thanks,
Drew

 

[tlee123]

Drew,

How about a Hollow Lock Socket Set Screw? Screw it in to a tapped hole. Secure with Loctite 680.

This will give you the socket running all the way through.

McMaster-Carr sells them.

Tom

 

[dtronvig]

Hey Tom,

Yeah, I like it! I haven't run the numbers enough to know whether the Loctite would be the weakest link, but if not there's always epoxy, or whatever. Nice glue joint, in any case.

Thanks,
Drew

 

[jistre]

dtronvig,

If you're only going to torque the cam in one direction, an approach to prevent the screw from moving relative to the cam may be to counterbore the hole for the insert along with use of the Loctite.

Have the through hole of the counterbore be large enough to accept the wrench you'll be using to turn the cam so that the through socket you desire is preserved. Then, tap the counterbore and finish with a bottoming tap to accept the set screw. If you choose the side of the cam that's counterbored correctly, you can design it so that when you load up the cam, you're trying to screw the insert down against the bottom of the counterbore and prevent its movement.

Of course, if you require it to be loaded in both directions, then you'll still be trying to unscrew it in one of the loading situations. However, I suspect that you'll find, given the size of the hex drive you're talking about, that you'll be able to choose a Loctite product that will give a standard Allen wrench a run for its money when used in a straight-forward through tap setup.

 

[dtronvig]

Hi Jistre,

The cam will actually be part of a latch, so it will have to be torqued in both directions. The main concern is that when some fool working the latch reaches the end of travel he'll keep on cranking, trying to get it even tighter. One of the advantages of the skinny Allen wrench would be to indicate how much torque can reasonably be applied. In a pinch, the wrench can just snap, which will be better than destroying the cam.

By the way, is there small-dimension hex rod stock that's significantly stronger in torque than a standard Allen wrench? Once I beef up the weakest link on the cam, the ideal thing would be to provide a high-strength Allen wrench end mounted on a torque-limiting clutch, so the operator can apply a high but limited torque. If he loses track of this specialized tool, he can still go find a regular Allen wrench. The torque will still be limited, at the expense of the ad-hoc wrench getting shorter.

Thanks,
Drew

 

[MikeHalloran]

You're not going to find much of anything that's stronger than an Allen key.

If you're contemplating _that_ much torque, maybe you need to consider sintered steel for the cam. That makes an insert unnecessary.





Mike Halloran
Pembroke Pines, FL, USA

 

[jistre]

If the part is thin enough, could you get a job shop to just laser cut the cam out of plate with the hex hole directly cut into the part?

If the bearing loads on the hex hole would be too high to allow direct cutting of the cam out of aluminum, would it be feasible to make the part out of steel to prevent the tool used to turn the cam scarring it?

 

[Broach]

The hex (or another shape) can be formed in your aluminum parts easily using rotary broaching. The rotary broaching toolholder can be set-up in any CNC machine so you should have no problem putting it into your part. The broaches for this tooling are quickly delivered (available in 1-2 days), and you can have any size hex from .050" up to 1".

See the tools at

http://www.slatertools.com

Also, see our rotary broaching showcase at

http://www.rotarybroaching.com

 

[dtronvig]

These are great ideas for strengthening the cam socket, and I'll study up on them.

I'm guessing that once I have any sort of steel socket the weakest link will be the shaft of the Allen wrench. At this point, I have to start fabricating and breaking some prototype parts. If a can't make the system strong enough I'll be back to bug you guys.

Thanks very much for all the suggestions,
Drew