Necessity is the mother of annealing

[JR in TX]

After dulling a lathe tool bit, a bandsaw blade, and a hacksaw blade, I learned annealing: how to make hard metal softer. You heat things until red hot then let them cool slowly. Neat. I would appreciate any comments regarding details of this procedure, e.g., apparently the amount of carbon in the steel you are annealing determines the annealing temperature (dull red or cherry red). Evidently the more carbon steel contains the harder it is?
JR

[dkinzer]

Several pages on the subject of heat treating steel may be found at the link below (from Machinery's Handbook).

http://www.newmex.com/ebear/metal

[SGW]

Not quite that simple. In fact, the metallugry of steel is incredibly complicated. Other alloying elements have more influence on the annealing properties than does carbon. Those other elements are what gives high-speed steel its non-annealing qualities, A2 its air-hardening qualities, etc. I don't even pretend to know much about it. For "plain carbon steel" with more than about 0.50% carbon, however, it's basically correct that you anneal it by heating it up and letting it cool slowly, or harden it by heating it to its "critical temperature" (when it becomes non-magnetic) and cooling it rapidly.

[JR in TX]

Thanks for the input. How does one cut high speed steel, by the way? Or is this not something that can be done at the home shop level? I can certainly grind it -- as in resharpening drill bits, but how would it be cut or machined?--Not that I envision a need for me to do this.
JR

[lynnl]

I don't think you can cut HSS in the normal sense, ie w/saws, end mills, etc. .... maybe with EDM or Laser, or other exotic process. But I have shortened tool bits, e.g. for lathe boring bar bit. By grinding a groove around all 4 sides, then gripping it in a vise and giving it a heavy Ka Bonk with the Ka Bonker (as Thrud would say) it will break at the "dotted line". Even a 1/4 or 5/16 bit will require more than just a 'love tap'.
In doing that be sure to cover it w/a sturdy rag to contain any shrapnel that might fly off when it breaks. It's not what you'd call pleasant to do, but it works.

[Tel]

a cut-off wheel in a Dremel will slice thru' it like butter,

[lynnl]

But those cutoff wheels are really grinding their way thru aren't they?

Now that I think about it, while I don't have a Dremel, I have tried using one of the 3" cutoff wheels on a pneumatic cutoff tool, to cut my grooves for breaking the bit.
That didn't work too well. So I went back to my bench grinder to grind grooves to permit breaking it. Of course that's a thicker disk, probably 3/32" thk, maybe that was the difference.

[This message has been edited by lynnl (edited 07-25-2002).]

[JR in TX]

I wonder if a diamond cutoff type wheel would work. I think the Dremel wheels are ruby imbedded the last time I checked. Seems like with all the hard metal around someone would make a reasonably priced diamond cutoff wheel. You could cut a groove around it and then put the kibash on it with the blacksmith instrument.

[JasonW]

I just finish cutting some small 1/4" bits. I used my 3" cut off wheel on my pneumatic "muffler" cutter. The stuff cuts like butter. I was making some 2" dia follow bars for a cheap pipe bender. The bits could be no longer than 1" in order to make the 2" cut. The foot long aluminum stock was bolted to the carriage and the cutter was mounted in 1" drill rod. Started with HSS, but ended up using carbide bits with a thread cutting profile. I had a tough time getting some decent cuts, lots of gouging. RPM was around 800-1000, but my feed was too slow. After cranking up the feed, things went well. I used the follow bars to bend some 2" stainless steel tube. The cheap bender has two rollers that would kink the tube. The follow bars would minimize the pressure and help prevent kinks. I now have a stainless steel exhaust system for my truck for the same price as it would of cost for the rust prone mild steel system. Muffler( "Borla") is also SS. The mill came in handy for boring out the SS flanges I made. It looks like my tools are slowly starting to pay off.


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[Thrud]

JR

Do not use Diamond on any Ferrous metals unless you do not care about excessive wear of the Diamond tool! Diamond is ideal for non-ferrous and non-metallic applications. It reacts chemically with the Carbon in the ferrous metals and transfers to the ferrous metals - also affecting the properties of the metals. The proper super abrasive for Ferrous metals is CBN (Cubic Boron Nitride).

The Dremel cut of disks are either Aluminum Oxide or Silicon Carbide. The metal needs to be cooled frequently to prevent reduction in hardness - if you cannont touch it it is way to hot!

As far as Diamond saws go - any Lapidary shop can sell you Diamond cut-off wheels.

Optimum Cutting speeds for Diamond are normally 5-7,000 sfpm, CBN 7-9,000 sfpm. ALWAYS DOUBLE CHECK MAXIMUM SAFE SPEED ON ANY WHEELS OR POINTS YOU MAY INSTALL AND GO BY THE WHEEL'S MARKED MAXIMUM! Diamond or CBN Wheels mounted on grinders/toolgrinders need to be trued first and then the grinding face opened up according to MFG's instructions for best cutting action.

[doug931]

one thing that has not been adressed is how to slow down the cooling process. I have had good results burying the red hot metal in wood ashes overnight.

[Thrud]

What you can to is heat sand to 450 in an oven and then bury the piece in that. Make use you use clean dry sand - best to just buy a bag for $3. Silica dust works best because it is like flour and hold the heat better. Plus your chinchillas will love it - but not is it is at 450*F! (mmmm roast rat!)