Recycling & rehardening HSS

[Dr. Rob]

Sometimes I have the need for special cutting tools, which I make myself. Tool steel is nice, but I've been wondering if I could use the HSS from say, a drill shank (unhardened) to make say, a special tap, and harden it myself. Or, maybe use an expended thread die, soften it, work it, and re-harden it.

Obviously this can be done; the question is, how well does it work? Which hardening parameters are applied? Does it just become brittle? Or not as hard as it used to be? Crappy in some other way?

[SGW]

HSS needs fairly precise heat treatment. It's quite difficult to anneal HSS; it needs a closely-controlled heating and cooling cycle. I'm not sure you can do anything that would be satisfactory in a home shop, but give it a try! Look up the heat treatment specs and see how close you can come.

You could certainly make a tool and take it to a commercial heat-treat facility though, and have them harden it. A local shop here will take work "off the street" and as long as you're willing to wait until they have a batch of the same stuff going through the oven, the price is fairly reasonable. You might want to check around.

For home shop work, ordinary tool steel is much more practical. As long as you keep from overheating it in use, I think it's just as satisfactory as HSS.

[This message has been edited by SGW (edited 12-13-2002).]

[halfnut]

As SGW says. Plus I'll add that those drill shanks might not be HSS, some are welded on 1144 or such.

HSS drill rod is available if you really need it, then the hardening process might be a problem. Hardening temperatures are rather high, 2225f for M2 for instance. That's hot, D2 quenches at 1850f, hotter than blazes, takes the old furnace at work quite a while to get up there compared to doing A6 at 1550.

The carpenter book says this about annealing M2. The steel should either be packed in a suitable container, using a neutral packing compound, or placed in a controlled atmosphere furnace. Heat uniformly to 1550/1600 degF and cool very slowly in the furnace at a rate not more that 20 degF per hour until the furnace is black.

I'm afraid even after this process the results won't be as good as using unhardened virgin steel. Got to be grain growth problems.

O1 is good stuff, it works for specials, just don't run it fast. In fact run it good and slow. Old feller I used to work for used to keep carbon steel drill bits around. I had to be careful not to use these, I'd burn them up. He claimed he could drill harder stuff with these bits. One can, since high carbon steel does harden to a higher hardness than HSS, but you have to run them dead slow.

[This message has been edited by halfnut (edited 12-13-2002).]

[Thrud]

Dr. Rob:
What ever grabs your snappy/wallet. You can recycle to a point. I Keep dead carbide inserts or shanks from endmills/drills for future use. I have far more carbide than HSS, the carbide can be brazed on to steel tools and just ground with diamond tools. No Heat Treating, and they cut like crazy. That being said, I also have HSS in the various flavours and even carve hunks of T-15 out of great big mangled surplus endmills with diamond saws. One man's junk is a Scotsman's gold - that's my story and I am sticking to it.

[This message has been edited by Thrud (edited 12-13-2002).]

[Uncle Dunc]

With a toolpost grinder, you could make a tap out of HSS without annealing it.

[Dr. Rob]

Well, I lied a little...Really, I was looking for a suitable source of chunks from which I might make gear hobs. This means round, diameter 1"+, machinable, and very hard. Now, if I were only cutting brass or something it might do well with any old tool steel, but I'll be making gears of SS or Ti, you see.
Now, I have in fact already bought hobs, but the future need may arise for one for a small job of slightly different pitch, so I thought I'd ask.
But if I were cutting a slightly nicer material, the rules above is what goes, then?

[This message has been edited by Dr. Rob (edited 12-14-2002).]

[SGW]

Tool steel. Tool steel can be made harder than HSS. It can take a keener edge than HSS. The biggest drawback to tool steel is that it can't stand up to heat the way HSS does, so you need slower speeds/feeds or coolant or both.
If you want the best out of tool steel you'll have to get it heat treated at a commercial heat treat shop. Although tool steel is pretty tolerant and you can do an "okay" heat treatment of tool steel in your basement, a commercial shop will do better.

[Dr. Rob]

Really...I didn't know that. Thanks, SGW. Do you have any particular species to recommend? I don't mind at all taking it to a hardening place. It would be worth it.

PS I live overseas, so words like D2 and 1144 don't mean much without some kind of DIN or ASTMA info beside it. I have Brady's, if that helps.
What, by the way, is the stuff Englishmen call Silver Steel?

[Rich Carlstedt]

Dr Rob
"Silver Steel" is what Americans call "Drill Rod" and I believe it refers to the oil hardening type, which we call O-1 (most common).
Gets its name from the shiney (precision ground) surface and of course in all diameters so you can make drills or tools out of it.
We also get "Drill Rod" in air hardening (A-1)and water hardening(W-1)types.

[SGW]

For a gear hob I'd guess you would want an oil-hardening steel. It warps less than water-hardening. Air hardening warps even less than oil hardening, but probably isn't necessary. Beyond that, I'm not sure. If I get a chance I'll see if I can find some more specific recommendations for what to use for something like a gear hob. There may be considerations of wear resistance, shock resistance, etc. that come into the equation. I bet a general-purpose oil hardening steel would be okay though.