Molding knives

If the furnace is good for 1750F, I'd give A2 a shot. It's inexpensive, relatively easy to work, dead simple to harden, and dimensionally stable in heat treat. McMaster has the SS tool wrap in small rolls ($20-30) and small bags (as low as $2 ea). Or you can pack the part in cast iron borings in a suitable container. Worst case is you may have to touch up the edge to remove any decarburized suface.

My biggest concern with A2 for short runs is whether the edge will get hot enough in use to draw the hardness back. As long as it doesn't exceed 450F, which seems unlikely if the cutters are sharp and you're milling pine or the like, I'd expect it to work OK.

For longer runs abrasion resistance is probably more important than hardness. There's a huge difference in the abrasion resistance of something like M4 compared to A2 at equal Rockwell hardness.

Ned Simmons

Ned Simmons

How about buying hardened stock and carefully grinding it without destroying it's temper.

Thanks Ned,

snip

I guess I just wan't thinking about McMaster, the stainless bags are just the right size. Can they be reused once or tweice? Would you use the oversize (.015" over the nominal .250") material and surface grind or will the pieces come out clean?

Heat treat regimen something like: 1750 for 10 minutes, air cool on a brick, temper at (??) for 10 minutes, cool on a brick???

I can't see the temp being a huge issue. The molder has power feed, very little chance of just sitting in one spot and rubbing.

Yep!!, the first pieces I need are all pine. If it works, there are several runs of cherry in the plans. THAT stuff is ABRASIVE!! But still relatively short runs, no more than low hundreds of feet.

In order to quench the part you need to get it out of the bag quickly, otherwise the bag may prevent the part from cooling at the proper rate. I suppose you could get the bags large enough that you could snip off the sealed end, leaving enough for another use, but in my experience the foil takes a beating at A2 temps. You also want to minimize the amount of air in the bag, so an oversize bag is less than ideal. Wrapping the part in brown paper helps to consume any oxygen in the bag and also helps to prevent the part sticking to the foil.

If you seal the bag or foil pack carefully and use the paper wrap you shouldn't see much decarb, certainly nowhere near .015 inch.

The usual recommendation is "cool in still air". I'd avoid setting the part on anything that would tend to cause uneven cooling and increase the chance of internal stresses and distortion. If you can put a hole in one corner you could fish the part out of the foil with a wire hook and hang to cool. However you decide to handle the part, it's a good idea to do a practice run cold, perhaps with aluminum foil. You don't want to be scrambling for another pair of pliers while the part is cooling in the bag.

More heat treat info, including tempering temperatures, here...

If you're going to make it yourself I'd stick with the simplest steels that are most forgiving to work with. That would be 5160 or 1080,

No. Annealed steel will be way too soft.

If you wanted to go to all the trouble... you could theoretically build a sealed box, place your blade inside, spray a bunch of WD40 and weld it shut. You put that whole thing in the oven... when the WD40 combusts it burns the oxygen in the box and you've got a controlled environment. But you've also caused yourself a lot of new issues... Foil is much easier.

If you use one of the simple steels I mentioned before, it is actually possible to harden just the edge using nothing but an oxy-fuel torch and a quench tank. You can see a video of this process here:

John P.

I was a custom knifemaker for 15 years, did some bookbinding knives, woodworking knives and carving tools, did dies for leather welt splitters, did all kinds of crazy stuff.

I completely endorse both of Ned's posts, he is right on the money from my point of view. I think A2 is probably the sweetest spot in terms of relative ease of use, relative ease of availability, good result etc etc. Heat treating foil is great stuff. One thing to watch for in heat treating A2 is that there are two tempering temperatures that give quite good toughness, while most of the range between yields markedly less toughness. I'm away from my technical references, but i believe a two hour draw at 430 F, cool, then second two hour draw at 430 will be close to optimal. Sub-zero after the hardening would be good, but is not absolutely mandatory.

Adam Smith Midland, ON

I stopped to check on the heat treat oven, found out that there is a "lifetime" supply of the foil in the cabinet next to the oven. :)

I just took a look at the toughness chart. Wow! is there a valley > I was a custom knifemaker for 15 years, did some bookbinding knives,