Recently, some friends and I have begun making our own knives, along with our sons. So far, we have done 4" fixed-blades, and used the charcoal-in-a-chimney method for heat treating. Well, now we would like to try our hand at large choppers, but these will no longer fit in the chimney. Any suggestions on an economical method for a DIY heat treat on 10-18" blades? TIA.

You might try to find a used (or even new, they are not that expensive) farrier's forge. You would have to get a thermocouple sensor for accurate heat, or learn to gauge heat by color, but they will certainly get the heat you need. Plus, if you want to start hammer forming rather than grinding, you can do that as well.

I believe that Grumpy Biker built a home made forge from firebrick a propane burner and welded angle iron from an internet plan.

I'm probably picking up a welder this week, so if you needed to weld framing, I could help with that.

Assuming you are using a grinding belt now, what are you using?

I've always wanted to make a couple of knives.