Making Square Broach

Mutt said:
Can I get some details on the use of boric acid to eliminate scale during HT? I scored a NICE Paragon heat treating oven and use it often pn O-1, A-2 and D-2, but would like to not have to deal with the scale as much as possible.
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Clickspring's videos are a much better source of that information than I am, he uses methylated spirits to form a paste which he can pack into wire baskets or specially made trays. The methylated spirits evaporate/burn off cleanly as the boric acid melts. I've also experimented with oil which is a bit stickier and adheres well enough to not need the basket/tray but the coverage isn't quite as good and the flames are a bit alarming if you're not expecting them (although they don't seem to cause a problem, just make sure you're doing this somewhere well ventilated).
 
Also,, I don't value my time, I value my cash. I would lihe to make my own 9mm square broach
Christian Poulsen said:
This is a top notch, step by step (excuse the puns!) video to making a broach....
...I have a variation (though not quite as fast or nice) of 2 broach's I made a few years ago due to stock and equipment at hand (Plus I am a lover of air hardening A2 and D2 tool steel):
All basically the same machining but milling D2 rounds to the square sizes needed then to the lathe using the compound for the gradual lead in...
But my home HT (no oven or wrap) just requires a torch (Oxy/Acty) with a "rosebud tip (or the biggest welding tip for "smalls") and air (compressor)...
...although there will be some scale and blistering....
I have some ceramic setters and half round lengths (for rounds) I dug out of the reclaim of my employer (before I retired) but some flat bricks work to make a Heat Treat "roofless house"
...Laying the finished broach (or whatever part) flat on a setter(s), I just torch (flame HT) the part evenly to critical temp. which for A2 and D2 is past a bright cherry red until you see a "flashing" in the steel (you can almost see the carbon globules "melting", and "shooting thru" the steel)...
...then, at that point of course, you have to freeze the part as fast as possible by blasting with the air nozzle evenly from all angles until it's completely cooled....
...but then, if there is no bead blaster** available, its all hand and flat steel table abraisive paper work, (to remove the "black" and any blistering) before using the torch to draw and temper the part back a little ("straw" color).... and your part will end at rc55-60
**= easy does it if with a bead blaster and hold (covering) the finishing square ends of the broach with the gloves where you should remove the scale by hand as the bead blaster will do some rounding of your sharp edges (the more you bead blast for looks, the more tiny edge radius on your sharp cutting edges)
...anyway, yoose' save over 120 bones' to make one yourself and I couldn't or/but could anyone here make one for less than this?:
http://www.mscdirect.com/product/details/00294264
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where can I find O-1, A-2 or W-1 square stock in 9mm? I need to make a square broach
 
I haven't checked specifically, but onlinemetals.com is a great resource for tool steel when you don't need a ton. (If you need a lot they're probably not as economical as buying more locally.)
 
onlinemetals.com has nothing in metric. Any one else?
 
T Bredehoft said:
Interesting Video. Wish I knew more about his heat treating. I'm used to a tiny oven and a torch, but what was that about Borax? and where do you get it? And what was his "container?"
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Borax is available in supermarkets as a washing aid. Borax is sodium tetraborate or the the sodium salt of boric acid and is not the same as boric acid. Boric acid used to be available in drugstores.
 
Another consideration that I have not seen in this discussion is how thick is the part to be broached? A broach should have several teeth engaged in the cut to keep it stable in the part being cut; if this cannot be accomplished with a broach, another method might be considered. I suspect that these gears used on musical instruments are fairly thin and MAY have punched holes. The punch could be piloted to insure concentricity.
 
Mutt said:
onlinemetals.com has nothing in metric. Any one else?
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Most tool steels are hot finish and usually a few thousands oversized. You want to buy it bigger than what you need, and machine it down to size you need before heat treat. I highly doubt you will find any sizes in metric in the USA. And be sure to allow material for cleanup after heat treat and grinding, if intend to grind it afterwards.
 
Buying something slightly oversize, I sorta figured that out after searching all the venues I knew about and found nothing in 9mm. I can get 3/8"square in any type I want and pretty cheap to. So I have a question about actually machining the broach.

In the video above, the guy takes the headstock of off that little lathe removed the bar that keeps the headstock indexed and turns it 3º.

I have a Grizzly 4003 lathe. Mine won't do that . So the question is: with my lathe, is it still possible to cut the 3ºcuts I will need to make?
 
Sure, pivot the compound to 3º, or would that be 1 1/2º? And hand crank each cut.
 
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