If someone close to you has a D-bit grinder it would be better to grind the hex on 10mm HSS. I'm a bit far from you at 12,000 miles away!! The beer currency does sound good though!! By the way, no drawing??

DH

You could make a jig up and mill them in the lathe .

All you need is some hex bar with a hole drilled and reamed through it to accept the blank broach and a couple of decent grub screws to lock it in , if your toolpost is big enough to accept the hex bar mount it up in there and set the toolpost to the 91 deg you need then mount a milling cutter up in the chuck .

If your toolpost is not big enough you could set it all up on an angle plate on the lathe cross slide and set the angle plate to the 91 deg . You would have to set up some fences or stops on the angle plate also

The hex bar holder becomes your indexing device as well ,

You could also leave the a few thou oversize and then set up a grinding wheel in the chuck and use that to give them a final sharpen up after hardening .

Ian.

Some allen head screws ape punched rather than rotary broached. You can use a cut-off from an allen key as the punch. It helps to leave the head of the bolt a litle tall. A shallow counterbore matching the across-corners dimension of the key will aid in centering the punch. Machine off the extra height after punching. The pilot hole should be about 5% over across-flats dimension.

Sam

Why not have a go at making your rotary broach following the ideas of mike's workshop?
http://mikesworkshop.weebly.com/rotary-broaching.html

Doesn't look too involved.

Dave
The Emerald Isle

Meths. I hope your manufacture of the broaches in the lathe works out, but I'd be willing to make them as it's on my "have a go" list anyway.

Seeing we are having such cold winter weather here a bit west of Sydney (18deg C !) I thought I'd hang out in the nice warm workshop and make/post a simpler method of rotary broaching for home use. The test was the 5mm size which fitted on a piece of 1/4" HSS round. The form was ground on a D-bit grinder which has been very handy for this type of work. As I have one of those little Myford ML7 lathes in the corner of the workshop (it was a project a couple of years ago to save it from the scrapper!! A great little machine but rarely used in my workshop) I used that as the OP indicates it is Aluminium alloy he will be using so it didn't require a heavier machine.

A short piece of 12mm silver steel (mild would do) was used to house the broach one end with a 1/4" blind hole. The other end has a No. 3 centre drill hole for centre support. The tailstock is offset to give about the 1 deg taper on the broach form but not more than the taper. The hole was drilled 5.1mm dia, as another poster suggested with a small 1mm deep counterbore of 5.8mm dia. to guide the point A bit of lube on the form and some on the centre, speed set at slow high range and presto, wind the tailstock spindle forward steadily and you have a nice 5mm hex for the key to fit. Suggest making the broach 5.1mm A.F.

Edited By D Hanna on 06/07/2017 09:15:49

Only if you fiddle around with methods deemed to be "the only way"!! A DTI either held by it's tail or even a magnetic base attached to chuck face, rotate stylus around tailstock centre or bore of taper and read front to back until zero difference. Forget what reading is at top as "mostly" the tailstock will be a wee bit high unless it's worn through misuse. A couple of minutes should have it back in alignment. Trial cutting in most cases has whiskers on it unless the lathe bed has other problems!!

Don't forget to post your results.

Regards from OZ

DH

To centre tailstock quickly. Put accurate centres in head- and tail-stock tapers. Bring TS up to HS trapping a thin pience of shim/razor blade/thin steel rule in between. Adjust TS until shim etc is perpendicular to lathe axis seen from above. Done. Simples.

I created a space for a brass gib, just rectangular, not angled, and it made the task much easier.