Heat Treating O1 Tool Steel Lathe Bits

[epanzella]

I made a dummy barrel stub for a smokeless muzzle loader build so I could have a dress rehersal on fitting the barrel to the action (Savage) and the breech plug to the barrel. As none of my internal bits were small enough to fit the bore, I made a boring bar and an internal threading bit from O1 tool steel. To harden them I heated the bits red hot until they were no longer magnetic using Oxy/acet and then quenched them in oil. I tempered them in an oil bath at 300 degrees F for 30 minutes. The tempering bath was the same one I used for quenching and was held @ 300 DegF via a propane stove and a thermometer normally used for lead bullet casting. When I heated them I did only the cutting end and about 1 inch down the shaft. It went pretty quickly, probably under 2 minutes but I didn't time it. Boring the hole started OK but then didn't sound right so I switched to another boring tool that I inherited from a toolmaker. It worked better than mine. When threading the hole, my 60 degree bit worked great at first but then I noticed on my xslide mounted DI that I was going past the target value for DOC but the thread was still too small. I took out the cutter and resharpened it, then reacquired the thread. It started cutting great again and the thread came out perfect. Do lathe bits made with O1 tool steel dull this quickly or did I not do the heat treatment and subsequent tempering properly? I did file test it and the file just skated across the surface. I can think of 3 possible reasons for my problem but maybe the more experienced members can see this more clearly. They are as follows;

1. Heat treating not done correctly, or slow enough, or long enough?

2. Tempering not done correctly, or maybe shouldn't have been done at all?

3. When I was turning the OD at 1000rpm with carbide, at one point some sparks flew out of the cut. It didn't hurt the cutter and the finish was perfect. Could there be some inclusions in the steel that wouldn't hurt carbide but would dull an O1 threading bit?

Below are some pix.

 

[T Bredehoft]

One point to remember, O1 is not HSS. Perhaps if you ran the threading slooooly, the tip would last for an entire thread. Just a guess. You might try not drawing the bit after hardening, or only drawing the shank.

 

[epanzella]

One point to remember, O1 is not HSS. Perhaps if you ran the threading slooooly, the tip would last for an entire thread. Just a guess. You might try not drawing the bit after hardening, or only drawing the shank.

I ran the threading at 70 rpm, the slowest my lathe will go. I was threading near an internal shoulder so I stopped the spindle about 50 thou short and threaded the last bit by turning the chuck with the chuck key. Some people say (on the instanetz) that O1 lathe bits should be tempered or they'll shatter and others say not to. I only heat treated the last inch of the tool so the shank was still ductile.

 

[george wilson]

The oil should need be heated for the quench. Just use room temperature for the oil quench.

The lathe needs to run as slow as possible for carbon steel cutting tools. I make special cutters from 01 or W1 frequently. I used to make all of the wire drawing dies for making bracelets,and molded wires for PGA trophies. I made all of them from carbon steel. They were intricate,and had to be filed into shape,sometimes using needle files. I used these cutters for fly cutters,cutting across 1" wide blocks of annealed 01 in the horizontal mill at low RPM's. They worked just fine. Later,the dies were also hardened.

 

[Karl_T]

I heat like you do then quench in oil. Don't temper, but what you did would help a bit if anything.

I would suspect your cutting edge. If things aren't just right, carbon steel dulls right away. Did you grind or stone after hardening to get a real keen edge? How about rake and relief angles?

Karl

 

[randyc]

How about using the shank that you've already made but grinding the end off and silver-soldering a small length of HSS to the end - maybe in a milled slot for location and security ? Start with a 1/4 square HSS tool and grind it to rough shape before soldering then finish grind. Just a thought -

 

[epanzella]

Like I said in my orig post the threading bit worked great for a while (6 or 8 passes) then got dull. I then took it out and sanded the top surface on a disc sander. I honed it briefly on a diamond stone as well. I had to raise my tool holder to comp for the material removed by the sander. When I reaquired the thread it once again cut great. The fact that it works well when sharpened is telling me it has clearance. It just doesn't seem to be hard enough. Can I just heat it and quench it again without tempering or do I have to anneal it first?

 

[epanzella]

duplicate post

 

[rgray]

I may have this wrong. I'm thinking you're not tempering unless the part comes down to 150 deg or so then goes into the tempering oven....My understanding was this was a necessary step. ...Using it full hard is not a good idea I don't think...I believe results will vary widely with the torch method....over cooked....under cooked....I did some hardening that way in the past and my results were never like they are now since I built an oven........ Ray C's oven build got me going on building one and a book he got "Heat treatment, selection, and application of tool steels" by William E. Bryson.....I fine invaluable.

 

[Baithog]

It has been many years since I did much heat treating, but my guess is that you didn't get it fully hardened in the first place. There is always a risk of decarb when torch hardening. The flame must be neutral to carbon rich. Excess O2 pulls carbon out of the surface, making it softer than intended. Temperature must be high enough, but not too high or you loose carbon again. Light cherry (more like an orange to me) in a dimly lit room. Bright light can mask the true color. The soak time must be sufficient to fully transform the steel. I saw some place a while back that an 1/8" knife blade needed at least 7 minutes. This is where I used to screw up. I get too impatient. Quench at room temperature, preferably with agitation. You have to get it into the quench before it cools too much and starts to convert. That's sometimes hard to do with little things like pins. The steel also has to cool fast enough so that it doesn't start to convert to its softer state. I always cooled it to the point that I could hold it in my hand. Knife temper is 375-400. The guy I knew that made knives used to do it in the kitchen oven and soak it a couple of hours.

Torch hardening is a pain. That's why people that do a lot of it have ovens.

I had better luck with A2. I never had any problem getting the stuff hard. Annealing A2 without a proper furnace was another matter. The stuff just loved being hard.