Jerrod Miller

The first thing that popped into my mind (other than knife + school = cranky administration) was something involving an etch. If you limit your project to forge welded billets, that eliminates the "knives are dangerous, you can't bring that to school" aspect, and you can still turn them into knives later. Perhaps etching processes to yield a specific outcome in terms of resulting color or topography. You can test different alloys, different etchants (including concentrations), and/or different cycles (vary number of cycles, soak times, soak temperatures, etc.). Also keep in mind that etching can produce different colors before and after heat treat.

You are having the torch come in the side of the can, yes? Then presumably you have a drill to make the initial hole. Therefore, just use a slightly bigger drill bit to expand the current hole. The PoP and sand mix won't be great for the drill bit, but not that bad either. Light pressure should keep the plaster from cracking, but again, not a huge loss if it does.

Sounds like you need a little more of a gap around the torch head so it can suck more air in, or there is too much back pressure so you need more opening out the door of the forge. Also, the larger problem with the PoP and sand is that it isn't a refractory at all. Meaning it does not hold up to forging temperatures. It will start to crumble pretty quickly. Proper refractory materials are a little more expensive, but they last MUCH longer, and in that regard they are pretty cheap.

Just to put things in perspective on the safety side, OSHA has exposure limits on silica (as in sand/dirt) as 0.05 mg/m3, so if you are ever in a field with enough dust in the air to see it, you're likely over the limit. Now, this is for a time weighted (8 hour) exposure, and is for long term health consequences (silicosis). Point being, 35 mg is not a lot of material, but it is a lot if it is dust in the air. So the "don't grind it" advice is indeed spot on, but if you follow that you are not too likely to run into problems.

I've never even heard of this grinder project before, so I certainly am not an expert on it, but this thread on their forum has a zip file with all the parts. So if you want to have a shop make all the parts for you, then you send them all those drawings. There is a drawing for every part (19 drawings for the 19 parts). Though I didn't look too closely, so there may be some drawings that contain more than one part.

This^. I have had 9" thick tool steel castings waterjet before, so it can definitely be done, but if you choose a machinable steel, that is definitely the cheaper way to go. It may be best to just call out the material and let a machine shop supply their own. Say something like "4140 or similar", and "2 inch diameter, +/- 0.25 inch" (or whatever you are happy with). If you put a good note on the drawing explaining form, fit, and function, they may have a great piece of steel laying around that would save money that you would otherwise miss out on.

Yes, and this is done in a vacuum oven (which can also run at positive pressures). So if you are already heat treating in such an oven, when it is time to quench it you can't just open the door and pull it out, that will ruin your elements. You have to purge/fill the chamber with gas. Here they are telling you that you should back-fill the chamber with at least 2 bar to be effective enough.

Good points Alan. I should have added all that, but dropped the ball.

Heat it above critical and let it cool in still air. Keeping the blade in water will ensure you do not affect the temper there. Given the steel you have, it is going to need a lot of heat for a while to get maximum effect, but just above critical for just a couple seconds will still be a massive improvement.

Is this the one you were looking for?

This is a pretty common question. Check out some of the thread links in this search. You'll get lots of insight from many smiths on the forum.

That is exactly the setup I've done that with. I'm pretty sure it also works to submerge most of the part in water to act as a pretty good heat sink.

I was intending to melt the base metal with oxy/acetylene, too; a full bronze weld, not just a braze operation.

You need the proper balance of fuel and air, and then the proper quantity. Describe how much of each you are getting. Size of your propane orifice, pressure, etc. Also, do you have any flame coming out the door of your forge? If so, what does it look like? Is the steel scaling up really fast (assuming you can get it hot enough to)? This info will definitely help troubleshoot.

Considering he cast the piece, I would assume he still has scraps of the same. An oxy/acetylene torch or TIG welder should take care of it nicely with some filler. Pile it on, melt a puddle. enjoy.