Hex Broaching?

[,4lex S.]

For the last while I have been wondering how to broach hex holes in parts inexpensively, and can't seem to find an answer. All the rotary broaching tools I can find seem like they would be quite expensive to purchase/maintain.

What method do most FRC teams use to get this job done?

[R.C.]

There is a startup cost to broaching.

You have to buy an Arbor Press and Broaches.

We have a 10 ton press from harbor freight and then we bought a 3/8ths and 1/2 hex broach. Arbor was about $200 and then the broaches were donated via sponsor.

-RC

[Doug G]

Originally Posted by rc_cola1323

There is a startup cost to broaching.

You have to buy an Arbor Press and Broaches.

We have a 10 ton press from harbor freight and then we bought a 3/8ths and 1/2 hex broach. Arbor was about $200 and then the broaches were donated via sponsor.

-RC

We too got our 1/2" broach donated about 5 years ago. If you want to save yourself some dough, contact a DuMont Sales Rep and beg. We agreed to put their name on our robot and sent them a nice picture plaque at the end of the season.

[Bob Bonczyk]

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

[Brandon Holley]

Originally Posted by Bob Bonczyk

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

That sounds pretty cool. Have any pictures/details?

-Brando

[nick_sheets]

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?

Nick!

[sanddrag]

Originally Posted by nick_sheets

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?

Nick!

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

[Brandon Holley]

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.

-Brando

[Gray Adams]

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.

[artdutra04]

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).

[kajeevan]

We started hex broaching last year. Our mentor purchased 2 hex broaches, 3/8'' and 1/2'' out of a catalog (don't know which sorry) for around $150-$250 a piece. Must say well worth it.

[,4lex S.]

Thanks for the prompt replies.

Apparently I was searching in all the wrong places, as soon as I input into McMaster I got a quote of about $200 for a 1/2" hex broach. Is there a minimum recommended press size in order to do this kind of work (probably for aluminium applications only)?

[NickE]

Originally Posted by ,4lex S.

Apparently I was searching in all the wrong places, as soon as I input into McMaster I got a quote of about $200 for a 1/2" hex broach. Is there a minimum recommended press size in order to do this kind of work (probably for aluminium applications only)?

It really all depends on how thick the material you plan on broaching is.

If I recall correctly, we use a 5 ton arbor press with our 1/2" and 3/8" broaches. It starts to get pretty hard to broach as you approach 1" thickness in Aluminum.

The biggest problem that we encounter with broaching is getting the broach perfectly perpendicular to the part. This season we built a fixture which is pressed onto the square ram of the press. This piece has a hole in it (about 1" deep, i believe) which is a slip fit for the broach. This ensures that the broach is held perfectly vertical in reference to the press, allowing for straight cuts.

[sanddrag]

We have a standard 1/2" McMaster push broach which we use in our ~3 ton arbor press in a pinch, when we need to do something in-house. It works well enough, but this is about as small of a press as I'd go for this. The pinion in the press has since let a couple teeth go.

A pull broach would be the best in terms of perpendicularity and whatnot, but these are usually found only in specialty broaching shops.

You can also broach in a very large lathe or horizontal milling machine, if you have access to one of those. And when I say very large, I mean >2000lbs. I would fear it could damage a smaller machine. A press is the definite way to go if using a broaching shop is out of the question. I think a larger arbor press would be preferable over a hydraulic press in this application, for the better feel for things. On an arbor press you'll know when something is wrong.

Just be careful to never drop the broach! Best to have a box with a pillow or something under the press. Don't trust yourself to hang onto it / catch it.

Also, remember to use lots of oil!

[Alan Ing]

Hex broaches are expensive. Following 254's and 968's lead, we have been hex broaching much of our hubs for various things for the past 3 years. One problem that we have always had is that it is sometimes tough to get the broach to cut perpendicular. Our arbor press is a bit on the small side, I think its a 2 ton press. We ususually start the broach on a lathe using the tailstock as a ram, and then finish up on the press. Even then, sometimes the broach runs crooked. This year, we are going to try rotary broaching. The holder itself is very expensive, up to $700 new. But the broaches themselves are about $60 - $80 (half the cost of a push broach). They are usually used on cnc lathes, but can be used on manual ones. I bought a used holder on ebay sometime ago. I think it was about $150. There is a guy who makes and sells his own branded swiss type holder on ebay for $200. Might be the way to go. The nice thing about rotary broaching is that it is much more likely to be perpendicular since it is cut on the lathe. It also can broach blindholes. check out www.slatertools.com and watch the video you can just buy the broaches from them and then buy a holder on ebay to save a ton of money. I would not suggest this for smaller lathes. I consider our 13" and 14" lathes about the smallest I'd want to try this on.

I already broached a 7/16" hex in some aluminum for fun and it was surprisingly a lot easier than I thought it would be. Next week I'll try a 1/2" hex and report back if anyone is interested. The only thing I don't like, is that rotary broaches are a bit oversized. A 1/2" hex broach is actually .505" this is to account for wear, but for $10 more you can have them grind a broach to .500" if you can wait a couple of days. We will just cut our hex shafts a bit larger.