Hex Broach Options?

[Stephen Kowski]

they may be expensive, but they are more or less a one time cost especially if you design with the mindset that you only have one or maybe two broaches, which simplifies things. If there is another team in the area you could possibly borrow it, or share the cost (just agree on a size head of time).

[geo]

We made a hex broach this year our of a harden steel rod for our 2 speed gearboxes. We used a surface grinder to make the hex shape on the rod. I would 've taken a picture of it if we didn't loose it...LOL

[Andrew Blair]

Originally Posted by geo

We made a hex broach this year our of a harden steel rod for our 2 speed gearboxes. We used a surface grinder to make the hex shape on the rod. I would 've taken a picture of it if we didn't loose it...LOL

I've heard of using a sharpened Allen wrench, after hardening it. Unfortunately, I doubt it would perfom on a high carbon or stainless steel.

[lupjohn]

Originally Posted by Andrew Blair

I've heard of using a sharpened Allen wrench, after hardening it. Unfortunately, I doubt it would perfom on a high carbon or stainless steel.

Andrew;
here is an article supporting your idea.
It is from the Home Shop Machinist, 2002 Sept.-Oct. Issue page 36
titled:
"Make Your Own Socket Head Fasteners with the Brinkerhoff Rotary Broach".

It is an interesting approach and does use a hex key that is sharpened and hardened. Unfortunately the magazine does not provide online copies of the article. Enjoy Larry Upjohn.

[Travis Covington]

If this is for a school or robotics project, how about calling all of the shops within a 1hr drive and asking them to wire EDM or broach the parts for you? I bet you'd be able to find someone to do it for free within a weeks time of when you call. That is a conservative estimate, too.

[Greg Perkins]

*cough* waterjet *cough*

If you can find a shop locally that has one that may be able to waterjet your parts for free, look into it. You might not always get the friendly shops, so another option would be www.dcwaterjet.com I believe you can have your gears dropshipped to them and they do the cutting.

[sanddrag]

I don't think I'd waterjet something like that. I'd be worried about the draft.

[Dick Linn]

Here's one possible way:

"Make up a fixture to hold the [item] you want to broach the hole in. Ideally the end should be vertical but horizontal will do. Take a good quality allen key
and cut the short end off it. Drill a small hole about 4mm diameter through the
key about 1/2 inch from one end - you'll see why later. Then heat the other end to bright yellow and quench in boiling water to get a superhard tip. Grind the end to get sharp cutting edges.

Drill the hole in the piece to be broached at the size across the flats of the
allen key. Make it a bit deeper than you need so there is somewhere for the
swarf to go although if you want a bar magnet in there you'll have a smaller
deep hole anyway which will be fine.

Now you need a guide for the allen key to run in. Take a piece of steel about
3/4 inch thick and drill a hole through it just smaller than the size across
the corners (not the flats) of the allen key. Then tap the allen key through it
and you have just broached your first hole. Mount this piece of steel so the
hole in it is central to the part to be broached. You now have a guide which
will keep the allen key bang on centre all the time.

Now just tap the allen key into the workpiece a bit at a time and pull back to
blow out swarf. If the allen key sticks then use a small tommy bar in the hole
you drilled through one end of it. If you want the broached hole to be as dead
to size as possible then do this. Heat the workpiece in a flame to 200 degrees
C or so until you have broached to full depth. This will expand the workpiece
and the broached hole will be a tad undersize when cool. Then let it cool and
contract again and take a final cut in one hit to the full depth.

It's a lot of messing about to make one hole but you'll get it dead true and
dead to size if you do it this way.

Dave Baker at Puma Race Engines (London - England) - specialist flow
development and engine work. ."

[sanddrag]

For that amount of work, I think I'd just buy a broach. And how do you grind the allen key without losing some dimension? Surely the end result would not be able to freely slide over a piece of hex stock like it would had it been done with a real broach.

[Dick Linn]

In this case, they were only grinding the end of the allen key. Think of it as a broach with one edge. Similar to a mortising chisel attachment for a drill press.

A clever machinist/toolmaker can do amazing things with rather simple machinery. In this case, the idea is to make a real broach. Even if you were to taper it and make several steps, it's really only the final step that makes much difference. Whether it will work or not depends on the precision of fit required.

[David Hoff]

This year our team faced the same decision. Spend the money and get a hex broach or find a different way of locking it to the shaft. We decided to spring for the broach because in the long run we will most likely use it several times over the next several years. They are expensive but we feel we will get our money out of it. If you think you won't use it more than once or twice then I probably wouldn't buy it.

[Not2B]

And here is the OTHER answer...

EBAY!!

I just searched for broach hex on ebay, and found a few. Just need to get lucky - but they can be found for cheap.