Press fit hex into round hole?

[MinnesotaHSM]

What size round hole should I make in 6061 AL so I can press fit a 5/16-24 locknut into the hole. I want to be able to use the enclosing aluminum to spin on/off the nut and tighten it down.

Probably similar to a plastic knob with a metal insert. I don't want the nut slipping in the hole.

Are there different ways to achieve the same goal?

Thanks.

- T

[1-800miner]

How thick is the aluminum? Should be as thick as the nut.I think any torque or vibration and the aluminum will fail. Harbor Freight sells a nut riveter that installs nut into sheet metal just like a pop rivet.Someone may make them for heavier gauge material
What is the application? Maybe someone could throw in a different method if we knew what you are building.

[MinnesotaHSM]

The part is going to be made out of aluminum barstock so the hole will be as deep, and most likely, deeper than the locknut itself. The edge of the locknut will be flush to the edge of the hole.

I want to use a locknut because I want the locking capabilities of the locknut (as opposed to just tapping a hole). This isn't the type of application where locktite could be used.

My tunnel vision is pointing to using a locknut pressed into a hole, but the functionality needed is a 5/16-24 thread with locking capability. The part will be screwed on and off several times but it isn't a high torque application and the vibration requires it to be locked on.

Thanks.

- T

[Carld]

Unless you cut a hex recess in the aluminum shaft the nut will start slipping in the bore when you try to tighten the nut.

If the wall is thick enough you can use opposing set screws to tighten against the flats on the nut to retain the nut.

To determine the size hole to press the nut in measure across the high points on the nut and reduce the dimension by .050" and that leaves .025" on each side to press in. Then with the set screws locked against the nut it should work for a while until stress works it loose.

How thick is the wall going to be?

[MrSleepy]

My Modern Machine shop Handbook says a 5/16 locknut should be..

0.500 ins across the flats

0.552 ins across the corners.

I dont think you'll find a chart showing the exact dimensions for forcing a hex fit into ally ..so a few test runs may be needed..

You could try drills in the range from..

0.5 or 1/2 ins
0.5156 or 33/64
0.5313 or 17/32
0.5469 or 35/64

Rob

[Carld]

It's best to measure the nut your going to use because the maker may not use the standards in the book.

[airsmith282]

out side the box, iam thinking a counter sunk set screw to secure it and prevent it from ever spinning,

[JCHannum]

A wrap of momofilament line around the male threads will provide the same effect as a locknut. If you are concerned about the threads in the aluminum, use a Helicoil for the threads.

[saltmine]

I remember you when we were in kindergarten! You're that kid that kept pounding square blocks into round holes.

Why not just get a piece of 1/2" CRS Hex bar stock, bore a hole down the middle of it, and sharpen the corners....Presto! A hex broach!

[Evan]

For aluminum make the hole diameter the same as the dimension across the flats. For locking, use a Stover nut and grind the "corners" so the vertices of the flats are sharp and pound it in. A Stover nut is all metal and has a built in washer on one side so it won't go in too far.

One problem with press fits of steel into aluminum is that if it gets much warmer than the temp at which it was assembled the steel part will fall out.