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Building a New Lathe
vtsteam:
Definitely Andrew, what I was trying to say., last two posts The bore was dirty and irregular shaped if you go back to my original casting photos, necessarily -- it was a difficult casting to get everything right.
Because the bore is irregular and has hollows, I can't just get rid of the entire skin in one cleans swipe -- it will take removing another quarter inch of material to get completely rid of it. One small patch will dull HSS instantly.
But I also do think that this Zamak 12 is really recalcitrant anyway, by nature. You can get a good surface finish with carbide, but it's really tough on ordinary tools -- noticeably so on hacksaw blades and files. And chisels -- I did try chiseling off some of the flash. Nothing like as easy as even mild steel. I'd far rather hacksaw a 1/2" thick slab of steel, than the same size slab of Zamak. I think it's the combination of slipperiness, with high tensile strength, yet relatively soft qualities. It's both sticky and slick, and nothing less than a perfect edged tool tends to plow it to the side rather than chip it off. Or just slide over the cut. It is nothing like brass -- though you would think it's similar. The last thing you'd want is to stone back the inside edge of a drill. Cutting tool angles have to be more acute not to just ride over the cut.
vtsteam:
I was curious to see how much skin was left, so I decided to pull the bearing cap off and have a look. Quite a lot, since there were hollows in the core impression.
So I got out a Dremel and chucked up a carbide burr, and went at all the grainy looking areas I could find. When I put the cap back and resumed boring, I noticed a definite cutting improvement. I'm still sharpening the bit frequently, but not as much, and the cuts are a little deeper and more consistent, end to end.
Next improvement I'm contemplating is making a new 3/4" boring bar to replace the 5/8" one I started with. There wasn't clearance for anything bigger to start, but now that the bore is much larger I can move up in size. A larger bar will mean I have to also bore the pulley to fit it, but I judge there's enough hub to do that.
3/4" would be the limit for hardware store pulleys though.
Getting there.....
awemawson:
Can you not re-arrange so that the pulley is at one end, and just turn down the bar to suit the pulley bore ?
vtsteam:
I could. The pulley is located at the very end of the bar, now -- just a tiny bit ahead of the 60 degree tapered end that fits the center drilled hole in the tailstock ram blank. So yes, Andrew that would be do-able. Might take you up on that idea. :nrocks:
awemawson:
. . . .no charge . . . . :lol:
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