View Full Version : This broach is killing me!! Help!!!

Bob Quale
03-05-2003, 09:15 AM
I need to make a 5/16 square broach. I bought a 8'' long HSS cutter and tried to grind it, but was unable to keep the corners of the cutting wheel sharp enough to form the front of the teeth. Then I thought I would use O-1 and make it on the lathe where I could use a sharp cutter for better profiles and heat treat. It is between centers but I'm getting too much chatter for the nice finish I want.

Maybe I should go back to the HSS cutter blank and cut my releafs with a cut off wheel and finish with a regular wheel?

Mabe rough it in O-1 on the lathe, heat treat and finish grind it?

Help. How would you do it?

This is a good, hard project and it's personal now, buying a broach is out of the question!!!

Thanks Bob

03-05-2003, 09:49 AM
Hold the blank in a 4 jaw chuck instead of between centers. Only let enough of the blank stick out of the chuck to do one relief at a time.

Bob Quale
03-05-2003, 10:02 AM

Would you use the HSS cuter blank and grind it or the O-1 on the lathe?


03-05-2003, 05:12 PM
I know exactly what you mean when you say it's "personal now".

I've nevered tried to make a square broach, but a regular keyway broach yes. It looked nice until I tried to use it. I think a blunt screw driver would have done a better job at cutting. Half way through it was binding to the point where it was useless.

Unlike single point cutters, you have to be very careful with the rake and clearance angle. Here's a link which should give you some pointers.

Broach design (http://members.rogers.com/rotate/Broach/Broach.jpg)

I think you'll have better control using a milling machine than a lathe. I would use O-1, instead of trying to grind a HSS.

Good luck, and let us know how it turned out.


Bob Quale
03-05-2003, 05:24 PM

I like your link! The hook or face angle is said to be 0-15 degrees. The machinist ref calls for 10-15 degrees. What do you think would be a good bet? I'm thinking maybe the 15 degree?

Also, when you did your broch did you do a final grinding after heat treating? or did you heat treat and use it?

Thanks Bob

03-05-2003, 05:44 PM

If the work is mild steel, I would definitely use 15 degree angle.

Unless you have means to grind it in a machine, I wouldn't grind it after heat treating. More often than not, I find that grinding tools free hand make it worst, but that's probably just me. I wouldn't do more than deburr the tips with a fine stone.


Bob Quale
03-05-2003, 06:01 PM

I'm planning on using it on W-1 for some tool holders I made.

I have an old OD grinder I might try to grind it with. But I will try it without grinding and after heat treating first!

A shaper uses a face angle of 0 for steel. It sure would be easy to make. What are the applications of different angles? I assume steeper is for softer materials?

03-05-2003, 10:24 PM
I made a 7/16 square broach the other day the first thing to consider is if you want a full square or round with square holes.This determines the length.Also you have to start with a square blank and taper it down to 5/16"od on the start end.what I did was to start with a o-1 square rod and taper as stated before(mine started at 9"oal and tapered down to 7/16"od round over 7-1/2")I chucked the work piece and center drilled both ends,then I chucked the first 1"and completed the tapering,I then steped off the tooth spacing(.250"on mine)then with a thin parting blade I parted in for each tooth until the cut witnessed round on the square portion of the work piece.I then ground a HSS threading tool(60'profile)set it and the topslide at 90'degrees to the work and then swung the top slide over to 45'degrees then I fed the tool in from the opposite side of the parting cut and into the face of the finished tooth(done very slowly of course)Then after I had completed the broach I placed it on end in side of a length of pipe to heat treat.I was able to use this broach to broach out some 1" long holes in 12L14 material with no trouble(I didn't even grind it)I don't know how deep the holes you are doing are but I also made a 3/16" "set" from Hss tool bits by taking four blanks and grinding the corners round to produce a four piece set where each one got a little less round and more square as they went.I also produced a concave on the end doing the cutting with a small mounted stone the broaching I did in the mill with the spindle locked by pushing the cutter trough with the quill handle,each cutter took out a little more until it was finally square these where much easier to make than the single pass model(about 30min.)and did just as good for a depth of about 1/2".

[This message has been edited by wierdscience (edited 03-05-2003).]

Al Messer
03-06-2003, 12:16 AM
Can you make key way broaches the same way? I need to broach some internal key ways that are 3/8" by 1/8" by 6 inches long and are 180 degrees apart.

03-06-2003, 12:32 AM
If I undertand this correctly you want to make square holes in W-1?

Don't even bother. First time you try to harden it it will crack and fail at the corners of the hole. Any heat treating house will tell you the same thing - do not even bother. You are better off using A-2 as it is less likely to fail. Same thing goes for W-1 and threaded holes - waste of time. A-2 can be hardened with no failures on threads if you use a sacrificial threaded plug in the threaded hole (full threaded length). The plug allows even heating a high temperature antiseize should be sparingly apply to the threads and the excess wiped off.

Bob Quale
03-06-2003, 09:30 AM
The part I want to broach is already made from W-1, but will not be heat treated. It just needs to be broached. The W-1 was something I had around so it was handy.