This is probably an ignorant question but one that I need to ask. Is Zamak magnetic. I've read where some Atlas mk ll lathes had headstocks made from zamak. Would a magnet stick to a zamak headstock?
No a Magnet will not stick to Zamak however depending on how strong the magnet is it might have the capability to "grab" some other component of the headstock that Is Magnetic into its field of attraction which may give the zamak the "appearance" of being somewhat Magnetic only because its between the magnet and a magnetic material!
Zamak is non-magnetic. And yes, the last several hundred Atlas 6" MK2's had Zamak headstocks and legs. Although some are known to have survived, more didn't. That mistake as much as anything else caused production to cease. I understand that some repair kits with the previous version cast iron headstocks and legs were either supplied or sold. It isn't known whether they were supplied at no charge or not.
It's actually pretty durable if made with a high degree of purity- if not, it can develop a problem called "zinc pest" which causes it to deteriorate. It is not suitable for such things as headstock castings, as Atlas discovered, but for gears it gives a fairly good service life / cost ratio
Actually, Zamak 5, aside from about three known instances of them using what turned out to be contaminated Zinc, has held up pretty well. On my 3996 (the newest 12" currently known), after 38 years, none of the gears nor the half nuts really need replacing. But there is one thing that all of the nay-sayers ignore. And that is that there are more Atlas machines still around today in either working or restorable condition than at least the next three or four more expensive US badges combined. That we know of, between 1932 and 1981, Atlas built a total of 267,034 metal lathes of 6", 9", 10" and 12" swing. The actual figure is probably approaching 300.000. Atlas started out to build metal lathes that were more affordable than the then competition and still be capable of turning out useful work. And for about half a century, they did just that. So we can do without comments like the one in post #6.
Let me also clarify my statement about headstock castings: A strong enough casting could be made but not a simple substitution of zamak for cast iron using essentially the same mold- additional webbing and thickness would be required in the part but it would have required a re-design. Didn't happen.
As an aside, it is amazing how strong some of the rare earth magnets are. I just bought a phone holder that actually sticks to my granite counter top. I assume there is some iron in the granite. You would never notice this except with very strong magnet.
You guys have hit on a very good point. When the part is well designed, Zamack is a viable choice. It is commonly used to cast precision tolerance parts and, if it is heavy enough to handle the load, it does just fine. The cross slide and compound leadscrew nuts on my Emco Super 11 are made from Zamack and they are adjustable for backlash and smooth as silk - ZERO backlash - and have stood the test of time on many Emco lathes. Some CNC ballscrew nuts are also cast from Zamack because they can be made with great precision. Not a bad material; just sub-optimal design and/or application.
Zinc, Aluminium, Magnesium, Kupher (?, German for copper) Many products were made with Zamak. I have numerous models made of it. Depending on the manufacturer, meaning quality of the alloy and cleanliness of the molds, it is a solid and reliable alloy.
As stated above, there are several factors involved in the longevity. One not covered by younger readers is that Trichloroethane, 1,1,1, Tech was used for many years as a replacement for carbon tetrachloride. It has been outlawed for a long time. The issue is that when used on Zamak, it turns the metal to dust. Quite literaly... ... This applies to any aluminium compound, not just zamak. Ask any Navy pilot (especially A-10s) from the post Viet Nam period what happens. It clouds plexiglas too.(acrylics)
I have a Craftsman 12X36, which is the same as an Atlas 10" machine. The gears are all zamak, and in very good condition. The lathe dates from the (early?) '50s and the gears seem original. I did replace a couple, but they were from abuse of the QC threading box, not decomposition.
I also have had three (3) UniMat DB-200s. They date from the late '50s, at best. Two have held up well, one was a basket case. They have been passed on, no threading gears... ... The entire machine was cast of zamak. Well, the ways and handwheel knobs were steel. The rest was zamak. I recognized what had happened to the rotton one and eventually took it off the guy's hands, for very little.
In answer to the original question, Zamak has -no- magnetic properties. It is almost as strong as grey iron castings. If the section is increased. For gears it's a perfect solution. For a headstock and the like, not so much unless it is redisigned. The big advantage, in Atlas' case, was that when the gear was extracted from the mold, it was, quite literaly, ready to use. During the WW-2 era, it was very useful for instruments where magnetic deviation was critical. Both in aircraft and in ships. Ever seen "minesweeper" tools, of bronze?
I have, somewhere, a detailed chemical analysis of the material. But it is rather long and I see no need to post a "filler" unless asked. Many older machines that have been "serviced" with chlorinated solvents look good on the showroom /photographs but fall apart a year or two later. Carbon Tet does the same, just not as quickly.
I use a carburator cleaner that is isopropyl based to clean my castings. If it is safe for carburators (zamak) it should be safe for my models.