Ron, that blower housing was a lot of work. The scroll on the outside of both halves started out as a steel rod machined to the calculated taper using a taper attachment on my nine inch South Bend lathe. It was then sawn in half lengthwise, and each half bent to the involute on a steel plate using stop pins as a guide. The shape was bent hot with a lot of hammering to keep it flat against the plate. Each half was then sweat silver soldered to it's respective cover plate using sheet silver solder sandwiched between the parts. The inside of each half was machined to the involute shape using a ball shaped cutter. Of course the width and depth of this groove changes as you work around the scroll. The width was taken care of by simple manipulation of the X and Y axis of the mill table. The uniform change in depth was taken care of using left and right hand fixtures equipped with left and right hand jack screws under the plates. The screws were cut with a 6 threads to the inch pitch and with a rod welded to the plate, the fixture was rotated by hand for one complete turn. The rotation lifted the fixture into the cutter as the work was rotated, deepening the cut through the rotation. CNC would have made it a lot easier but I don't have the machinery to do it. Heck, I don't even own a DRO! The cooling fins on the outside are all silver soldered on using wire with a square cross section to mimic those on the full sized engine. I originally thought of making a wooden pattern and having the housing cast in aluminium, but it wouldn't have been any easier to do. I'm only building the one engine. The steel housing is a lot heavier than it should be, but then weight doesn't matter except for airplane engines anyway. I'm hoping this one never leaves the ground! The other techniques used on things like the crankcase, camshaft covers, etc, etc. are spelled out in my book on building the 270 Offy.