Mike BR

Mystery steel could also crack because air cooling was fast enough to harden it in places (thinner sections, or where it contacts a cooling rack or something). If you're talking about a once-in-a-lifetime fish, maybe temper to 300C or so after normalizing.

Come to think of it, you could just use a tube about the same diameter as the blower outlet that continued across the top of the hood and ended just short of the window opening at the back. That would recreate a “venturi” burner inlet. You might need to add a horizontal length of stovepipe extending out the window to improve the flow.

I've made a system with a blower feeding about a 2" nozzle inside a 6" flue/duct (in other words set up much more like a venturi/ejector burner, but on a large scale). It improved the draft, but the bathroom fan blower I had wasn't really sufficient. I'd worry with your set up that the air from the blower would slow (and the pressure increase) when it hit the opening at the top of the hood. Then it might not "know" to continue out through the window, and too much might end up blowing back down into the hood. There's only one way to find out, I guess. Another possibility with your general configuration might be a true venturi -- something like a 6" vent from the blower that narrows down to 4" in a short section directly above the hood, with a lengthwise slot along the bottom to suck in air from the hood. That could take a lot of experimenting to get right, though.

Iceland is definitely spoiled for hot water. The guide also talked about his reaction when he moved to Copenhagen and first stuck his toe in a 60-degree swimming pool. (I was reacting more to the Shakers squeezing out the last bit of energy from what flowed their way.)

Pretty impressive roller (and story). But I think you've just snuffed out my last hope of ever getting my shop cleaned up (grin). Maybe I'm getting more efficient, though. Last winter I used up the last bit of steel from my old water heater -- and the "new" one promptly failed. I was in Iceland last month, and the guide was talking about how they'd drill a geothermal well and run the water through the radiators in the house, then to a hot tub in the back yard, then through coils under the driveway . . . . (These days they mostly have municipal systems with central heat exchangers and recirculating fluid.)

Assuming you'll be attaching a rubber hose to the shut-off valve at the bottom, I'd say the most important thing is to support the valve somehow, so the hose isn't hanging off the copper tubes. Apart from that, I like the "loops" version better, because there are two less sets of threads, and the loops will help relieve stress on the fittings if there's some flex in the system. But the other version should work fine too.

If necessary, you could cut around the shank with a small hole saw or a plug cutter, and glue in a wooden plug. It sounds like the bolt sheared because it was “wedged” into the wood too tightly, and might be hard to back out even if it were intact.

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.