Hex Broach Options?

[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.

[Veselin Kolev]

Go to a waterjet shop.
Ask them to demo their waterjet.
By cutting some 1/2" hexes in 1" steel.
And ask if you can keep it as a souvenier.
Proceed.

[ajlapp]

buy a 3/8" hex and go!

$130 is not all that expensive if you consider all of your options. if you buy the right size, a size that will fit all your applications then that one broach will probably last you your entire life.

as long as you use the broach correctly and feed it plenty of high quality lube then you'll be fine.

we do a lot of broaching in our lathe. put the material in the chuck and the broach in the tailstock......lock, crank, broach. very simple.

no more keys, no more trantorqu......just cheap hexagon stock.

our 3/8" hex broach is going strong after hundreds of broachings.

[Paul Copioli]

We use 3/8" (used in kit transmission, too), 1/2", and 3/4" (used in kit transmission, too). We added the 1/2" to our arsenal this year to drive the shooter wheels.

The 3/4" was expensive (like $400), but the 1/2" and 3/8" are less than one night at the Omni. These broaches will last you a very long time. We do not use keys anymore, just hex broaches and very cheap hex stock.

This solution is a very reliable and maintenance friendly design.

[Pat Fairbank]

Pardon my ignorance, but for those teams that use hex shaft, what's the standard practice for when it comes to putting bearings on a hex shaft?

[Paul Copioli]

For us, the beauty of using the metric system (whenever possible) is that 10mm bearings work great with 3/8" hex (look at kit tranny hex shafts). 1/2" work great with 12mm or 14mm bearings. 3/4" work with 20mm bearings. I can show you pictures and cross sections when I get more time.

[Ed Sparks]

I solved this problem once by buying these and welding them to some sprockets. It worked very well. They are available from Small Parts .

[Cory]

Originally Posted by Pat Fairbank

Pardon my ignorance, but for those teams that use hex shaft, what's the standard practice for when it comes to putting bearings on a hex shaft?

We turn down the ends of the shaft to fit it through a smaller bearing than the hex.