I have a customer who wants me to make them a functional bat’leth
Sorry but steel plate will not work for something “functional”. First thing you hit with it, will bend it up nastily.
Also, if you are going use it, it needs to be hardened. You can’t harden mild steel as far as I know.
They use 1075 steel and send it out to be hardened then anneal it back a bit to shape.
I was planning on using something like this
https://www.metalsupermarkets.com/metals/tool-steel/
or this
https://www.metalsdepot.com/steel-products/high-strength-steel-plate/steel-plate-ar400f
which both come in plates, although I’m not certain if they are actual plate steel
Bru… you wrong.
The behavior of the metal is dependant on the alloy and the heat treat.
AR400 is a great choice for a sword like this. The only issue with it will be that the edge will not be hardened after you cut it with the plasma. You will need to reheat treat the edge of the sword for it to perform well.
I am a big fan of S7 and D2 tool steels as well.
6150 Spring steel should also work.
The tool steals and the spring steel will need to fully hardened after you are mostly done shaping them.
All that said I would probably go with the AR400 and not worry about the heat treat. I will be plenty hard for playing around in the back yard and if the customer wants you to make it harder you can.
Most tool steels are good, the ar400 not so much. YMMV
After alloy type, and how produced: Hot Rolled, Cold Rolled, Extruded, etc. basic definition of Sheet vs Plate: Sheet is under .1250", Plate is .1250" or larger. Others are specific types: bar, round, hex, rectangle, channel, box etc.
But if talking about sheet vs plate, it’s thickness.
I would expect the plasma heat would ruin the chance of holding an edge. Gotta grind that shape. How about CNC cut a rough shape and then grind it to final design?
Maybe someone here can go over the effects of localized heat and metallurgy. Not my strongest suit.
You are on correct, I would rought cut the piece, leaving at least 3/8 of an inch for a heat affected zone and remove that with grinding. I would then heat treat. How you heat treat fully will depend on what it is you are using for steel.
In theory you could use A36 & case harden it. I don’t think it would be worth it though.
Just remember that if you CNC plasma cut it, you will end up with a Decarburization likely in the HAZ. I don’t know a lot about it. From what Ive read, the plasmacut would be oversized so you can remove the area that has lower carbon content. Remember too much heat in this area is bad.
This is if you wanted to hold an edge
Pretty much this. I’d oversize the cut and grind down as others have said.
I don’t want to be the wet blanket here, but think about this project long and hard if the goal is truly a functional blade. You are talking about hundreds of dollars in material to start with, hours and hours of rough grinding, devising a way to heat treat it (we don’t even have a forge that can come close to getting something this large to the right temp., or quench, or etc…), or (probably better) sending it out to heat treat (which will be more money but has a vastly better chance of working), then you have final grinding, polishing, sharpening, final finishes… This world be a 15 part-er from Alex Steele and he’s a pro with a shop that puts our metal/blacksmithing capabilities to shame; he’d be the first to acknowledge that even with all that- it might not work.
All that said, if you decide to do it anyway, keep us posted! I’m super curious about how this’d turn out. As for materials, decide on an alloy and get some quotes on a piece that fits your dimensions. 768 square inches of 3/16 tool steel will be expensive and prices will likely vary fairly widely between suppliers.
While not as DMS-Makery, get material and have it water-jetted. No heat affected zone and can be cut to net since you’ll be grinding the edges and will allow sharpening.
How important is the ability to take an edge? If not, the HAZ isn’t as important. But I’m not sure about any heat discoloration, if any or how far that will extend.
Will be a cool project.
Go buy one at the Antique Mall in Denton. Every place like this seems to have one. 
all the making advice had been great. Does anyone know of a good place to actually get steel?
Call me crazy, but I don’t know if I’d want to be an accomplice for someone needing a ‘functional’ Bat’Leth. But I DO hope whoever uses it fights with honor.
Anybody else been watching Master of Arms? Some of the challenges involve the making of blades.
Let us all hope it’s not really intended to be ‘functional’. Perhaps he means as a functional prop?
It is legal now…
