Hex Broaching?

Polygon, if you were a bit less faux-subtle about your motives here, you’d likely be a bit better received. Try again, and present yourself as a company with a product rather than apparently pretending to be a disinterested party. Most of us are engineers by inclination, and we like straightforwardness.

Well said sir. My apologies, and thank you for the advice. I hope to be more helpful in the future.

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We are looking to broach through 1.75" aluminum, does anyone have a recommendation on what size arbor press to get? We recently had a sposnor donate 1/2" Hex broaches.

The short answer is that’s not going to work very well at all.

You’re only supposed to go 2-2.5xD on a hex broach. Any longer than that and you’ll get excessive wear and require massive amounts of force. You will need a 5 ton press and it will not be easy at all.

What is this for? Some type of hub? You probably don’t need a full 1.75" of engagement and could counterbore your part to allow a more reasonable hex length.

Thanks COry for the reply, it would be a hub for a plastic wheel we got from our sponsor. Its about 1.5" long with a nub. Its a 1" od plug with a 1/2" bore.

Would you counterbore one side to .577" or similar and have the hex be 1.5" long? What would you suggest?


We made our own 1/2 hex broach years ago and it works just fine.

That sounds pretty cool. Have any pictures/details?


Hi guys,

Our team is making our FIRST (haha get it!) westcoast drive. We bought an arbor press and broaches a long time ago, but we can’t seem to get a perfect broach… We have had this problem buying from FIRST suppliers as well. What is the best way to get perfectly hexd parts? When I mean perfect, I mean no wobble?


Start it in a lathe, finish it in an arbor press.

Obviously you need to ensure that the broach is kept perpendicular to the part’s face for the entirety of the broaching process. Hex broaches take some patience to get through, but taking your time will go a long way in helping out.

If you have a lathe- you can simply start the part there and move it to the arbor press to finish to get a nice straight broach. If you do not have open access to a lathe, you can try this:

I’ve had success making jigs and guides for broaches. Essentially I just machined a part that had a large face to mate against the part I was broaching. I drill and broach the guide to same size I was broaching my new part. I carefully feed the broach through the guide, lined up the hex properly, and put the whole stack together on the press and then began broaching my new part slowly, especially in the first few teeth.

Also make sure you are liberally lubricating the part you are broaching as well as the broach itself.


Start it on a lathe if you can. If you can’t, just constantly take 5 or so steps back and check how straight it looks from a distance (from multiple view points as well), and adjust as necessary.

Also, don’t stack multiple parts and broach them together. It may work sometimes, but we had a bad experience when a machinist in the NASA trailer at CMP tried it. They broached all 4 gears at the same time, they ended up crooked, and we had to have them weld it shut and try again.

Similar to Brandon’s post, I’ve had success with a jig that holds the broach colinear with the arbor press ram. Here’s a simple mockup of this idea:

The square inset in the top fits over the end of the ram. The small hole on the front face is for a 1/4-20 or similar size set screw to hold the adapter onto the ram (you can also use a thumbscrew or similar fastener to mount/remove it).

The through hole in the bottom is a reamed hole that provides a very tight clearance fit around the shank of the broach. The tighter this clearance fit, the more accurate the broach alignment will be. When properly machined with tight tolerances, this adapter can be used to quickly and accurately hex broach objects in one operation (no need to start on a lathe).