Mike BR

I’m far from an expert, but ductile iron is designed specifically to be less brittle, which could be important in that application. I’ve never heard about any downside to using it instead of gray cast.

If the ram slowly descends when you release the flywheel, it’s probably working as it should. If not, I’d first try applying some light oil to the threads at the top of the screw box and see if that loosens things up. If not, apart from the guides, check the connection between the ram and the end of the screw. Mine has something like a ball joint held by a split collar that threads into the top of the ram — this sometimes requires adjustment or lubrication. Of course, you might want to disassemble and clean even if a little oil loosens it up. And that’s mandatory if there’s grit in the threads.

It's also an important distinction that your body eliminates zinc readily. Any exposure to cadmium or lead is a bad thing, because those metals build up in your body. But occasional exposure to zinc that doesn't cause acute symptoms also doesn't (in all probability) cause you long-term harm.

I built a two-wheel grinder similar to the one from Grizzly. It doesn’t have a very big footprint. But I don’t make knives, so can’t say much about the pluses and minuses for that kind of use.

I'd take a good look at belts before deciding on a grinder. 2X72 is the de facto standard, and there's better selection and likely better prices (keeping in mind that at 72" belt will last 70% longer than a 42", all other things being equal). If you're doing much grinding, a couple of hundred dollars savings on a smaller grinder could disappear pretty quickly in abrasive costs.

Cast iron is a brittle material, meaning that it normally breaks rather than permanently deforming when it reaches its yield stress. But like every material except maybe kryptonite, it does deflect under stress -- how else would you clamp the table to the column? And brazing it will put it under stress. Very possibly not enough to matter, but my advice is don't try to find that out unless you have to. (Though in the worst case, you might be able to come up with a way to drill the brass back out )

A drill press isn’t really a precision machine, but I’d be worried about the brass pulling the table out of flat as it cools and contracts. (Bondo should be strong enough to keep the oil out of the holes.) If you do braze, I’d avoid grinding, to limit the amount of base metal you remove.

Cool paperclips! 3/16 is quite likely cold rolled; if you annealed first, it might bend smoothly cold.

Many common alloy steels would improve hardenabiliy, permitting the face to be hardened to a greater depth. But that would depend on the specific alloy and heat treatment technique, and might well not make a practical difference in any event.

I don't believe I've ever seen another leg vise that had bolted-on jaws. I'd give at least even odds that some had a brainstorm and added them on (or that they were intended for a special application). Taking them off will change the degree of opening at which the jaws are parallel, but that might be either a plus or a minus depending on the stock you work. The biggest possible issue would be if the jaws themselves are soft, but using jaw plates would help protect them even then. If they're hard, there's no reason to use jaw plates unless needed to protect your stock

Even my cheap machinist/shop vises have the liners let in so the bottom rests on a (part thickness) shelf that forms part of the jaw itself.

Or you could just send the rack to me. I'm sure the sun would look right here on East coast.

You’ve really got to keep your eye on it.

There are lots of options. You could leave a port in one or both doors and cut a piece of firebrick to plug it up when you use the top port. Or just build and see what happens. In theory you could have cold air entering through the ends and coming out the top with the exhaust. But that might never happen in practice

A lot of forges have openings in the doors so you can put the end (or even the middle) of a bar in without opening the door itself. If you add those -- and I find them quite useful -- you should think about also adding a way to block them off.