Shop Made Broaches

[Fabrickator]

As I wind down on one project (Super Bowl Trophy), I always find myself thinking about the next one. I was browsing the web a few weeks ago and found something very interesting that I decided to make. The major components are many hexagons and pentagons that would be around 5/8". They are like window frames with the shape not only on the OD but also the ID. The OD is easy to make, but the ID is the problem. I searched for pre-shaped tubing to no avail and contacted several aluminum extruders, but the cost/quantities were out of the question. So I figured that the only practical way to do it is with a broach.

I looked into purchasing store bought, straight broaches but they were out of the question at $220 for the hexagon, and one of the major suppliers wanted $799 for a custom-made pentagon broach! I could buy a rotary broach set-up but it's too expensive. I could also make one, but it's really not the proper tool for this project because of the limited depth and the quantity I have to make. So I studied my 21st Edition Machinery's Handbook and decided to attempt to make my own broaches from scratch. I'll be machining the window pieces in aluminum so it won't be like cutting steel.

I started with the hexagon by turning a series of incremental sizes in a .625" piece of cold rolled steel bar stock, increasing the depth of cut by .010" per cutter with a .500" pitch. I then mounted it in the rotary table and cut the land width and a clearance angle of 3 degrees. I returned to the lathe to cut a radius in the gullet. I did some fine tuning on the rake angle and then heat treated it. I was a bit anxious when making the first cut but it went through the aluminum like butter producing a very nice hexagon hole. NOTE: The pic is not the finished broach, I cut a lot more clearance for chips in front of the cutters but failed to get a pic at this time.

View attachment 87543

With the success of the hexagon broach behind me now, I began making the pentagon broach. I included a few extra cutters because the the cuts will be larger with a pentagon shape. After successfully producing a test piece I'm now ready to move on to the the real thing.



Stay tuned.

Rick

 

[Uglydog]

This is really cool!
I've not even considered doing such a thing.
I don't see any mention of grinding.
Was everything cut and then HT?
Direct from the oven to broaching?
CR? But, then you were cutting aluminum.
That makes sense.

I keep looking at Dumont Broaching sets.
The bushings are relatively easy, the broaches are intimidating.
I've got plenty of O1 plate laying around.
Hmmmmm.

Daryl
MN

 

[Fabrickator]

This is really cool!
I've not even considered doing such a thing.
I don't see any mention of grinding.
Was everything cut and then HT?
Direct from the oven to broaching?
CR? But, then you were cutting aluminum.
That makes sense.

I keep looking at Dumont Broaching sets.
The bushings are relatively easy, the broaches are intimidating.
I've got plenty of O1 plate laying around.
Hmmmmm.

Daryl
MN

Daryl,

Yeah, I used CR because I was only cutting alum. If you were going to be cutting a bunch of steel, the M Handbook recommends HSS. Of course, if you could grind all of the cutting surfaces it would probably last much longer for cutting steel. I just used carbide tooling to cut all surfaces and it's pretty sharp. Then I HT'd it by bringing it up to dull cherry and quenched it in oil. I only made one cut, but it showed no signs of wear and produced good chips.

I'd say if you have a need to do some broaching, give it a try. I think that you could machine a keyway broach with HSS and HT it. Make a bushing and some shims. The key is too make the increments really, really small, like .002 -.004" and a sharp tool, good fitting bushing and some cutting oil. Check the Handbook, it's all in there.

Rick

 

[Earl]

Very clever and innovative solution. Thanks for sharing. Sometimes even if we could afford something, we feel that it seems more valuable to the seller than it is to us. I wonder how many of those broaches I would have made before i got one to work?

Earl

 

[rmack898]

Nice job Rick, I've considered making both square and hex broaches for one time use on several projects but always found an alternate work around. I'd still like to make a square broach for an upcoming project though. Can you go into a little more detail of how you cut the relief angle on the rotary table? I'm not sure how you did that.

 

[Fabrickator]

So were talking about the same thing here's a basic pic from Wiki.



The clearance angle Y was cut on the RT by jacking up the RT 1/8", to find the std center height of my tail stock, which produced about a 3 degree angle, per the Machinery's Handbook specs for aluminum.

The the pitch, P was about 1" tooth to tooth.

The width of the land, L pretty much comes together at the required clearance angle.

The gullet (depth), D was is experimental and not called out in the Handbook. The idea is too provide enough volume to handle the chips.

The rake of the teeth, (the unidentifiable icon), was made with a carbide o-ring tool (1/8" radius)that I have. I ran it down into the gullet at a 10* compound/with the tool holder at about 30*, to undercut the flat face of the cutter. The broach also needs an inside, gullet radius to curl away the chips and this cutter happened to provide both an adequate rake and radius and it left nice, sharp edges in one pass. Sometimes you just get lucky.

As was stated in my last post, the pic is not the finished product as I hogged out much more area in front of the cutters for chip clearance and narrowed the Lands to about 3/16".

I'm sure theses tools could be made much more professionally, but they're good enough for what I'm doing.

Hope this helps.

Rick

 

[Fabrickator]

WOW, where did the time go. Kitchen remodel, Xmas, Out of Town company and back to work.

I finally finished machining the Pentagon broach and heat treated it. I'm making the aluminum blanks now to broach out the hexagons and pentagons IDs. Once they're done, I can move on the real project that I'm making all f this for, a DNA lamp/sculpture. I've seen it done in Super Scale in a few parts of the world, in a University and a museum, but I want one for my living room shelf.

I plan on making it about 12-15" tall and mount on an LED, rotating lighted base like used for jewelry. It should cast out some nice, colored light beams if it turns out as planned.