S7 & Plasma Cutter

TLR

TLR

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Oct 5, 1998
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So I sourced the S7 for some tomahawks and was graciously sent a slightly larger piece then I requested which is great in that I can actually fit in an extra, the bad is that it's to big for my bandsaw at this point. I have a friend with a cnc plasma table but I've never had him use it for my knife steel because of the heat zone it would create and I'm concerned that with that heat it may warp the steel slightly.

Any insight?
Should I expect warpage on a 3/8" piece?
Since S7 is air hardening would the heat affected zone end up being to tough for me to cut/grind off?
Any one have any idea what the heat zone would be? 1//16"? 1/8? More?

Trying to see if there's someone local with a waterjet but coming up empty so far. I'd consider sending it off but don't know the cost would work out for 3 pieces.

Thanks.
 
I have wondered this too. I have a hobby plasma cutter (out for repair right now so I can't experiment) and have thought about using it to cut out profiles. The blank could always be full annealed after cutting it out if you have the equipment for that.
 
"Hobby plasma cutter"

H'mmmmm What would that be exactly. I'm intrigued by that. I may need one of those.

Syn
 
Warp should not be a problem, and the HAZ can be ground off with good belts. Allow 1/16"+-1/8" extra in the profiles for the HAZ in 3/8" thick steel.
S7 does not get extremely hard, but it sure is tough. Great for hawks and hard use choppers. HT is the same as A2. I'd soak those thick blades for 30 minutes at 1725-1750F. The as-quenched hardness is only Rc59. A 400F temper will drop it to Rc57, and 500F to Rc55. Cryo helps a bit, but isn't necessary for most uses. Do it between the tempers to reduce RA.

Annealing S7 needs a programmable oven:
A. Heat to 1550F (840C), hold 2 hours, slow cool 50F (30C)/hour maximum) to 1000F (540C), air cool.
OR
B. Heat to 1550F (840C), hold 2 hours, cool to 1400F (760C), hold 4 hours, air cool to room temperature.
 
Thanks bladsmith.

That answers my questions and makes this something I could attempt. This is definitely outside of my ability but I have a friend heading back to Afghanistan and told him I'd attempt this for him. He's on a Chinook team and wants something to cut his way out of a downed chopper. Interestingly they have supplied tools to do just that but they are stamped mild steel and he doesn't trust them.

I'm having the HT done by Peter's. Looking at 57 for the head and 40 for the handle.
 
I would have them harden the whole thing for Rc57 if he will be using it to cut miscellaneous things and as a last ditch defense weapon, or maybe Rc53-55 would be better for something that is to be used for chopping metal and fiberglass.
If Peter's doesn't do the differential temper, you can do it yourself after it gets back. Draw the handle with a torch to around 1000F. Do it in a darkened room with the axe head in a bucket of wet sand. The color you want is just beyond black...barely a dull dark red glow.

A Horse Stall Matting handle ( just glue and pin it in place) that is over-wrapped with 1" wide leather or rubber strip ( think golf club handle) would be a strong and shock distributing handle for a crash axe.
 
Why would you have me do it rather then them? Just curious.
 
I was just saying I didn't know if they do differential tempers. I never had a need, so I never asked Brad. If they do it, by all means let them.
 
OK just curious. I did call and he said it would be no problem. I wasn't sure if they would either. Thanks again for the input and advice!
 
Everything sounds great.

I'm curious to see how the RC comes out and what temps/methods were used.

I use a lot of S7, I think you will really like it.
 
I have a combo tig, plasma, arc welder from Purifion. It works really well, excepting I had to send it back for warranty work. The arc and tig work as well as the miller units I used. Reliability is a question though. From what I read the early units had a faulty component on the board, and once replaced with the newer one they are reliable. If starting over, I would likely buy a Hobart, which have great reviews, but are a few hundred bucks more expensive.
 
I cut all my blades out with a plasma, about 35 now with no warping, 2 out of 3/8" d-2 with no warping (even in the thinner stock sizes)
But like bladsmth said there is a heat affected zone about 1/16 which is murder on belts when profiling but definitely worth the convenience, you can cut out a big knife in less than a min.
Once you get familiar with the operation of a plasma cutter they are awesome.
Also if cutting out by hand leave yourself at least 1/8 - 3/16 extra for bad touch angle and cutting wobble.

post a pic
 
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Ah, good, they have 4140. That's what I was more interested in. I figured if they carried S7 they might have 4140 as well. Thanks! PM on its way.
 
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