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vtsteam:
Nope, changed mind again. Not 1-1/2" square grid, but 1-3/8" by 1-1/2" rectangular grid. That will let me use 1" wide Tee bars instead of 1-1/8" -- an odd size.

I'm busy tapping 18 holes, now. Undecided whether to mill mill out steel Tee bars, or cast them in zamak. Since it's the weekend and I don't have the steel, and I'm an impatient cuss, probably the latter.

awemawson:
I suppose in the event of a calamity the Zamak could be a useful 'fuse-able link' and Tee bolts will pull though it rather than break something else.

vtsteam:
Well maybe not, Andrew -- it's stronger than cast iron, certainly in tension -- so not disadvantaged by most standard CI tee-slotted tables. Probably it would shear the 1/4" screws holding the tees down, as my own guess. They have a 3/4" bury in the table. Think a substance a little short of aluminum bronze, and you'll get a feel for it.

Of course I'm going to try to avoid inadvertent destructive testing! :zap: :beer:

I spent the day first tapping the holes, and then tuning up the cross slide. There were a lot of small details I'd left, and one forgotten step.

That last oversight was forgetting to run a hacksaw blade down the inside corner of the wear pads. :palm:

Because I'd milled this slide, rather than filed and scraped it, as I had my earlier lathe, Gingery book in hand, I had forgotten to do this. Y'see, no endmill, no matter how sharp and new is going to maintain a perfect inside corner. With square ways, you have to cut out the tiny radius a mill will leave, so the pads are separated and contact the ways properly. The Gingery way is just run a hacksaw blade in the corner at 45 degrees until there's a small slot.

Anyway I realized my oversight when I took the slide apart, and found a 1 thou shim on that side only. Weird to shim one side, if the whole thing was done at one setting in the mill. Well the corner radius was responsible, and as soon as I made the proper cut, the shim was no longer necessary. And of course the slide worked better, too!

Other tune-ups involved shortening the over-long gib screws, and fastening the cross slide leadscrew bearing in place with two flat-head screws. and squaring the slide to the ways.

The carriage now moves silky smooth, without wobble in any direction.

S. Heslop:
Are there any disadvantages with zamak? What I mean is, why isn't it used more.

vtsteam:
Simon, It's a real pain to machine, saw, file, or scrape. The only operation I've done with it that goes nicely, is tapping, for some reason. Boring holes is the worst. You need carbide for sand casting machining.

Now I know that hard machining qualities goes against the experience of other people, and maybe the alloy variety I've been making up is different than the variety they use. I dunno. But I believe my ZA-12 is correct. I'm using purchased virgin zinc ingots, and mixing in the right amount and type of aluminum (see the recipe, somewhere way back in this thread.)

I was using purchased ZA-2 earlier in the lathe construction (ie. years ago!) -- not mixing that myself -- and it seems to me that it was better/easier to work with than ZA-12. But I can't remember for sure.

The other negative thing is that it goes dull with age. I don't find that such a problem, as I intended to paint the lathe all along -- steel and iron rust, especially in the winter environment here, unless constantly used and oiled. Condensation does it. So it's just a different but similar problem.

And the ZA-12, at least, has huge shrinkage, when casting in sand. You really have to plan for that. It'll suck a hole right down the full length of a sprue. I'm thinking ZA-2 didn't do that as much. I'm going to have to try to do a comparison -- I think I have one ingot of ZA-2 left.

On the positive side, it is tremendously strong, solid, heavy, melts at the lowest temperature of the common structural metals, it's inexpensive, easy to cast (other then the shrinkage problem). I imagine it has excellent vibration damping qualities. It's very dense, but somehow, I dunno, "fluid" seeming

Oh also it's an excellent bearing material, unlike aluminum, or steel. So making lathe slides out of it is a really good choice, in my opinion. And the headstock feels massive and sturdy. My lathe is hard for me to even slide on the bench now, it's so heavy. The opposite of aluminum.

Well those are my experiences, anyway.

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