Hex Broaching?

[AdamHeard]

You might want to check if a local college or shop has a pull broaching machine. Cal Poly (the school I attend) has a few, and is willing to let us use them. I've yet to do so though, as we have a line of push broaches in our shop which have worked adequately for us so far.

[ChuckDickerson]

Originally Posted by NickE

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.

Picture please? Sounds like a great idea!

[AdamHeard]

Originally Posted by DeepWater

Picture please? Sounds like a great idea!

It's pretty simple, imagine making a new end to your press that has a hole 1" deep in it that the end of the broach sits in.

[Alan Ing]

Cory,

To be specific, a .505" hex rotary broach with a 1/2" shank runs about $70 from Slater Tools, when I asked for a .500" hex rotary broach, they quoted about $80 and about 1-2 day turnaround.

There are basically two kinds of rotary broach holders, Swiss type which are non-adjustable and the regular adjustable type. Since you plan to use it in a Haas milling center, you might want to consider the Swiss type. I asked the salesperson what the advantages were between the two. The Swiss type is smaller and has more clearance (it is round) whereas the adjustable has a wide base that could cause clearance problems since you will be spinning the tool holder rather than spinning your material. Adjustable ones are nice if you have a non-standard broach with a different length. You can only use standard length broaches in Swiss type holders and are limited to a max of 1/2" shank broaches.

Last year, I tried to use it on a bridgeport type vertical mill and failed miserably. I ended up having to retram the mill and gave up. We went back to our push broach which didn't always cut perpendicular no matter how hard we tried.

Of course your Haas is quite a bit stiffer. I would not expect a problem providing you adequately clamp your work piece.

This past summer, I decided to give it another try and placed the rotary broach in the tailstock of our lathe. Surprise, it was so easy and I felt like an idiot for not trying it earlier!

According to the slater tools chart, it takes about 600-700 pounds of thrust to rotary broach a 1/2" hex in aluminum.

Because rotary broaches are driven by the work piece, the hex can have a slight twist. One work around, is to reverse the spindle half way through the piece to reverse the twist. Rotary broaches don't care about spindle direction for cutting.

I'll let you know how it works out for us.

[Andy Baker]

Originally Posted by polygon

This is a great thread, and I'm wondering if you have any more observations about the broaches. Has anyone run the broaching tools on a Bridgeport? Check out this video:
http://www.youtube.com/watch?v=uTsPXFy7Xx0
Also, you might consider Polygon Solutions as a pricing option.

Polygon,

Thank you for the information. It seems that your company's services and tools could be an asset to many FRC teams. That is a great video, as I have not seen broaching done in this way before.

Sincerely,
Andy Baker

[Alan Anderson]

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.

[polygon]

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

[nick_sheets]

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[nick_sheets]

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.

[Cory]

Originally Posted by nick_sheets

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.

[nick_sheets]

Originally Posted by Cory

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?

Thanks!

[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.