Hi Jon, you could make it out of plate. But I didn't have any 1" thick plate. And more important to me, this time I wanted to use a better bearing pair than steel on steel. The Gingery lathe used aluminum and steel on steel for the slides. They work, but can be bettered. Bronze, brass and cast iron make good bearing pairs with steel. But I can't cast iron until warmer weather arrives here, and I didn't want to cast brass or bronze for this particular part, and wasn't sure I could with the small furnace (well found out I could later today as an experiment).
I bought some Zamac ZA-2 for experimenting and building some small engines via lost foam casting last fall, and chose that particular alloy because I knew it had good bearing properties. It's not the usual choice for hobby greensand casters, but I wanted to try it.
Since I already had it, It seemed like a good choice here on the tailstock base. It's extremely tough (much higher tensile strength than cast iron in fact). Zamac and other zinc based alloys are commonly used in die-cast parts, which has given it a bad name, but those castings are usually very thin (often 1/8" or less) because it is so strong. In that thickness it can be shattered with a sharp blow. Because it is so thin, it's cheaap and used for mass produced products.
But it is a completely different material when cast into a heavy piece like this 1'" thick tailstock base. In a proper thickness, it's extremely tough, takes a great machine finish and in this case is a good bearing material. Very hard wearing, too. Seemed like a good idea under the tailstock.
Just how tough this stuff is was brought home to me when I spilled a small amount onto the ground today. it immediately ran down the slight grade. When cool I picked the splash up, and it was just a thin sheet of material. about 1 inch wide, 8" long, and less than 1/16" thick. I tried to bend it in half to break it into pieces, but I absolutely couldn't. If it had been cast aluminum, no problem. I put it in the vise and using vicegrip pliers, got it to bend double, but it still wouldn't break. I can only imagine what a 1" slab would be like.
It is also quite difficult to file -- it is fairly slippery, and also very tough at the same time. steel files much easier. Progress is really slow with zamac. This means it has very good wear properties.
Anyway a hard wearing, high strength, nice machining, good bearing material, which just happened to be on-hand, seemed like it was right for the job. So I used it.!
