A few thoughts, tips, pointers.
First of all, there's an excellent Yahoo! group devoted just to the Gingery books, machines, etc. You should definitely check out the Lindsay books (see link in step #1), and the Yahoo group: http://groups.yahoo.com/group/gingery_machines/.
There's a TON of good information and suggestions on the group. Some of the more popular ones seem to be: make the ways (a slab of 1/4" x 3" cold-rolled steel, on which the carriage (the main cutting-tool holder assembly) rides) thicker and thus sturdier; secure the ways to the bed with many more fasteners; and use a modified tool-post/toolholder. There are designs, photos, corrections, bills of materials, etc. (I'll try to add much of that information here, as I'm able.)
Secondly - the Gingery method mostly assumes using scrap aluminum. A few things I've learned:
(A) "Can you use beer/soda cans?" This is often referred to as "beercanium", or some similar funny term. The concensus I've seen, and have experimentally verified, is this: you can't really use JUST beer cans -- aluminum exposed to air instantly develops a thin layer of aluminum oxide (for fun, this is also. in crystalline form, basically ruby!). Beer cans are thin, with lots of surface area, so melting beer/soda cans alone just doesn't really work well (especially since melting tends to produce MORE oxidation.
HOWEVER -- if you melt some aluminum, such as window frames, pistons, etc. -- and THEN drop in some well-crushed and dried beer/soda cans, they'll contribute to the mix just fine.
SAFETY NOTE: if there's ANY moisture left in the cans, you are probably going to witness a SPECTACULAR explosion several milliseconds before losing your vision permanently. I'm not an expert, and if you follow my instructions, you'll probably DIE, be seriously maimed, or end up on some very, very pernicious mailing lists -- do NOT take ANYthing I say as anything other than potentially *very* dangerous activities. YOU HAVE BEEN WARNED.
(B) Using Metals Other Than Aluminum -- this is my personal choice. I cast a few parts out of Aluminum, then switched to a Zinc-Aluminum alloy (called Zamak, among other things).
Several reasons. (1) Zinc melts at MUCH lower temperatures, in the 700-degree range vs. 1,400 degrees for aluminum. (The common zinc-aluminum alloys also melt in the 700 degree range -- even though aluminum needs a higher temperature to melt, it's actually DISSOLVED in the zinc -- just as common table salt, with a VERY high melting temperature, DISSOLVES in room temperature water....).
This means you can melt zinc alloy over a propane flame -- like a barbecue or gas stove. Note: I would NOT recommend doing it on your kitchen stove. I've done this, but then you have to carry a 700+ degree pot of molten metal through your house and outside to where you have the mold. (If you try to pour molten zinc inside your house, you're insane -- just *melting* it inside is crazy enough.)
(2) Zinc alloys don't shrink nearly as much as aluminum -- so you can basically make a part prototype the size you want it to be, without calculating in shrinkage; and (3) Zinc alloys are nearly as strong as steel, in many respects.
WARNING -- the BIG drawback to zinc is this: THE FUMES ARE TOXIC. If you breathe a lot around melting zinc, and inhale a lot of the fumes, you're going to be very, very sick, and possibly die.
Now -- with lots of ventilation, and doing things outside, I understand it CAN be pretty safe. After all, gasoline fumes are toxic; so are toluene, turpentine, etc. -- and we're not utterly terrified of them. Just use some caution, mmmm'kay? And - read up on it a little.
One last note -- it's not the most economical source of zinc, but it's kind of fun, especially for small parts: you can simply use pennies. Since 1982, pennies are mostly just zinc. Look at http://www.gizmology.net/stovetop.htm
for more information. Seems to me it's about 2x as expensive as what I can buy scrap Zamak for, around here, but sometimes for small parts it's just easier.
That's all for now -- on to making the lathe!