[Rich05]

I need to cut a small square or hex pocket in the inside of a 9mm shaft, so the shaft can be held with an allen wrench.

I do not have a fancy machine for this any good ideas? I have a mill and lathe.

Thanks R

[Geof]

One work around is to simply tap the end and use Loctite to lock in a socket head cap screw with a head less than 9 mm; 10-32 would be suitable.

If the shaft is not hardened you can use and Allen key as a broach to make a shallow hex.

You have to grind the end of a good quality Allen key perfectly flat to create a cutting edge.

Drill a hole about midway in diameter between the across flat dimension of the key and the across corner dimension in the end of the shaft about 1-1/2 Allen sizes deep, and drill a hole the same size as the across corner dimension about 1/2 the Allen key size deep.

Grip the shaft in the lathe chuck and the sharpened Allen key in a drill chuck in the tailstock.

Use the tailstock to push the key into the hole to broach the hex.

The larger hole acts as a guide hole making it easier to line things up.

If it is too difficult to push it in a do the broaching make the small hole larger; making this larger reduces the amount of hex created and reduces the amount of torque that can be applied to the shaft with an Allen in the hex; there is a compromise here between what it is possible to make and how well it works.

The Allen key of course will be tight in the hole it has broached so it is a good idea to use a pair of Imperial and Metric sizes that are close; use the large one for the broach and the other to turn the shaft. 7/32 is slightly larger than 5.5mm so that may be suitable for a 9mm shaft.

[Rich05]

"Use the tailstock to push the key into the hole to broach the hex." how hard do i need to push it, do I use a tool to do this?

very interesting so the edge of a sharp allen wrench will actually cut the hole out?

would a cheap arbor press be a better choice I need about 1/8" hex hole max in Stainless or mild steel. and not very deep. shaft is about 6 inch in length total. what ton capicity would you recomend if so.

[Geof]

"Use the tailstock to push the key into the hole to broach the hex." how hard do i need to push it, do I use a tool to do this?

very interesting so the edge of a sharp allen wrench will actually cut the hole out?

If you cannot push the key in just using the handwheel on the tailstock make the hole bigger.

[DareBee]

I broach them similar to Geof (why is it a am always following you up ol'boy and usually a half hour late).
Only I grind the hex on an HSS blank (Allen key is not hard enough IMO) and I HOLLOW grind the end to produce a positive shearing action.
I usually only drill a pilot hole the size of the flats for a small broach like that and the tailstock will easily push the broach in.
As with all broaching operations use good quality cutting/tapping oil.

[Geof]

.... (Allen key is not hard enough IMO)....

I guess really I should have said 'cold formed' not broach, broaching is a cutting operation and my way is more a squishing operation.

[peter@slater]

What size hex are your after? and what is the material of the shaft?

[DareBee]

I guess really I should have said 'cold formed' not broach, broaching is a cutting operation and my way is more a squishing operation.

Yeah
I can see that.
What I mentioned actually broaches, leaves little curls of material in the bottom just like some of the cheaper cap screws on the market.
BTW don't forget to start with your hole, like 1/4" deeper than finished depth required.

[Geof]

And I guess my way is more analogous to the high quality cap screws which are forged, all I lack is temperature.

Maybe I am wrong though, are they hot forged or cold headed?

[Mike Stevenson]

And I guess my way is more analogous to the high quality cap screws which are forged, all I lack is temperature.

Maybe I am wrong though, are they hot forged or cold headed?

They're "hot headed"

[Rich05]

What size hex are your after? and what is the material of the shaft?

5/8" stainless steel rod with 1/8" allen wrench

[Geof]

5/8" stainless steel rod with 1/8" allen wrench

Your first post read; I need to cut a small square or hex pocket in the inside of a 9mm shaft, so the shaft can be held with an allen wrench.


5/8" is a lot bigger than 9mm and makes the problem trivial.

Get some 8-32 socket head stainless steel cap screws.

Cut the heads off.

Bore a hole slightly smaller than the head in the end of the shaft; if you look at the head you will see they are knurled and have a smooth ring, make the hole about the size of this ring.

Push the head into the hole.

[Rich05]

Push the head into the hole.

very cool idea.

sorry that was a typo .. i meant 5/16.

[peter@slater]

You could also get a 1/8" hex rotary broach, #306-127($49). This will give you sharp corners. Usually you need a broach holder, but it sounds like you could just push it in for a few pieces. 'DareBee' was right, "don't forget to start with your hole, like 1/4" deeper than finished depth required." You will need some room in the bottom of the hole for the chip to curl into. They're in stock with most rotary broach suppliers.

[HIRAH]

i've broached 1/4" hex into steel a bit.
spot drill for a pretty chamfer, drill just under the flats of the id hex,
undercut with a key cutter so you dont have that ugly mess at the bottom, endmill to size, and broach with a hex.
we use ground hexes. we also drill a thru hole to help the air escape.

[SQT18MS]

There are tool to do this with you know

But the allen key works just fine, you could even drill the hole a little larger than the allen key are on the flats.

I have the tool to do this on large series, its like a coned allankey in HSS and its out of senter but its angled too so that the allan like HSS tap hits the senter anyway. I usaly rut the tool at 250 to 400 rpm i mild steel. (ST52-3)

If its just one or two parts I would go for the allan key tric

[MFassler]

you could do it the old school way and watts drill it,or edm it or broach it the list goes on.