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Looking At An Atlas Lathe For Sale, First Purchase

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gearhead

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#1
I posted this in the General section, and it was suggested I post it here since it's an Atlas. I don't want to double-post, so I'll put the link in here. Many thanks to those in the know on Atlas lathes. I've only purchased one lathe prior and it turned out to be a dud. I'm shopping with better funds this time, and it would be a very bitter pill to swallow if I made the same mistake with more money (only spent $100 the first time).

Link: http://www.hobby-machinist.com/threads/considering-an-atlas-lathe-in-bedford-in.53949/#post-448073
 

wa5cab

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#2
gearhead,

Assuming that the subject is still open, the lathe that you are looking at is an Atlas model 3996 which is a 12x36 size lathe (12" [actually 12-1/4"] swing over the ways and a nominal 36" center to center distance (that means that if you put a dead center in the headstock spindle and one in the tailstock ram, and back the tailstock up to the end of the bed, the distance between the two points will be about 36". The nominal bed length measured along the front or rear way is 54". The CL ad is in error. And the person who said that he had an Atlas 10x48 lathe about the same age as the 3996 was wrong on two counts. An Atlas 10" with a 48" bed would be a 10x30. And the last Atlas 10" was made in 1957. The 3996 was made from late 1967 through March of 1981. From the serial number I would guess made late 1970 or early 1971.

The machine has Timken tapered roller bearings on the spindle. It is a 16-speed machine and has a Quick Change Gear Box and power cross feed. I bought mine new in 1981 and still have it.

The person who wrote that Zamak gears are pot metal was incorrect. Zamak is a die-cast Zinc alloy but contains no lead. The particular alloy used by Atlas is somewhat stronger than cast iron and most batches have held up well considering the age and operating hours on them.
 

markba633csi

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#3
Robert: I'm surprised to hear that Zamak is stronger than cast iron; how do you define stronger? Zamak is certainly softer than CI, I'm concerned the OP might think Zamak is the SAME as cast iron in all respects which would be incorrect.
Mark S.
 

gearhead

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#4
Robert,

Many, many thanks for all the details! I like the sound of this lathe more and more just as far as the basics of it go. I have been posting on social media looking for someone who knows an experienced machinist to see if they can look at it with me. I have been reading and watching videos about checking lathes, but that's really no substitute for having actual experience. It would be easy for me to buy one with bad ways or bearings if I got too excited and didn't know what I was looking at. By the way, how hard is it to get a milling attachment for these? I wouldn't mind one until the day arrives that I can afford a mill.

Mark's point is noted. I did not think Zamak was the same or better than cast iron. From what I have read, it is brittle, and that is why some people avoid these lathes. I understand that if something gets into the gears, that it can break or chip a Zamak tooth easier than cast iron, or such is what I've been lead to believe.
 

Rob

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#5
If you do a search on eBay for Atlas Lathe you will find several milling attachments as well as other parts. A lot of the items demand a premium and you can find them cheaper looking around on places like craigslist. Also you can still get support for a lot of the items from Clauseing which Atlas is the predecessor to. On a lot of the items they sell you can get new items cheaper than used off eBay.

On the strength of Zamak you will find that it wears very well. There are a lot of lathes out there that have been running for a long time with the original gears. My grandfather purchased my lathe new in the early 50's put a lot of hours on it. Several of the gears are original. I believe that over the years they have had a few batches of Zamak the was contaminated and that is what caused some of the parts to crumble.
 

BGHansen

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#6
Here are the basics on Zamak vs. Cast iron from Wikapedia:

Chart is for Zamak 2 which added some copper to the alloy (primarily zinc) to make it stronger. Yield strength (put a load on the part and it starts to permanently deform) - 52,000 psi. Ultimate tensile strength (when it breaks under load) - 58,000 psi. Depending on the cast iron, the yield strength (really the number we care about) - anywhere from 25,000 psi to 105,000 psi.

Another property is modulus of elasticity. It's the slope of the line when you plot stress vs. strain or basically load vs. deflection. Young's modulus for Zamak is 14,000,000 psi. Steels/iron are around 28,000,000 - 30,000,000 psi. That means a Zamak part will deflect about twice as the same part in steel or iron under the same load. But the point where they start to permanently deform could be the same depending on the type of cast iron.

I suspect Atlas used a lot of Zamak in strategic parts because of the melting point of 734 F instead of 2200 F for iron. It's a lot easier and cheaper to make a steel die and cast gears instead of cutting them individually. As Robert and others have noted, lots of Altas/Craftsman lathes and mills out there with Zamak gears that have held up really well. You'll see many posts here about broken gears (especially in the back gears) on lathes that are most likely steel, so no material is indestructible.

If you see a broken Zamak part, theoretically it's not a problem with the Zamak but a design/use problem. I have an Atlas MFB mill with a broken power feed gear box for the table. The mounting ears snapped off the box itself. My first thought was "I sure wish they'd have made that part out of steel"! However, looking at the material charts, it wouldn't have made a difference. The mounting ears were unbeknownst to me cracked when I bought the mill. One of these years I'll remake the box and reuse the guts, but will make the mounting ears more robust (thicker). I've seen ads on eBay for "repaired" gear boxes where the mounting ears were cracked, so I suspect there's a bit of a design issue with the gear box.

That Atlas lathe in Bedford looks to be a pretty good deal. It'll serve you well for many years if you work within its limits. I've read posts here where guys have taken something like 0.100" off the radius of steel on a lathe. I'm not in a rush to do anything and don't think I've ever taken a DOC deeper than 0.030" on the radius on a lathe turning steel, maybe 0.040" on aluminum; haven't broken one of my machines from use yet (Rockwell 10 x 36 lathe, Clausing 12 x 24 lathe and Grizzly 14 x 40 lathe). I might not be removing stock at the optimum rate, but I'm not a production shop getting paid by the minute. If I break something I have to fix it, so I chose to be a "sissy" and not push the machines to the breaking point. That Atlas lathe will treat you as well as you treat it!

Bruce

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markba633csi

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#7
Good info Bruce, thanks. I'm wondering if Zamak gears can be run dry, and how much worse the wear is compared to lubed. Zamak gears get really messy when slathered with grease or oil, as most every Atlas/Craftsman lathe owner knows.
Mark S.
 

gearhead

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#8
Thanks so much for the additional info, Bruce! It is greatly appreciated. I'm feeling much better armed in the knowledge department, but my experience is still nearly zero, and though I've been posting on social media and asking anyone likely for possible experienced help in looking it over, I've yet to find someone who can go look at it with me (and, yes, I am offering to pay them). So, still working on it. Might see it this weekend, but unsure at this time. I did make contact with two experienced machinists who said they'd never heard of Atlas, which I assume is due to the fact that it was more of a home lathe than a pro shop piece.
 

wa5cab

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#9
The Zamak grade supposedly used by Atlas was Zamak 5. It did allow making and selling the Atlas machines for a price that people in the 30's and 40's could afford. I was comparing it to gray cast iron. The bad rap for Zamak probably comes from several bad war-time batches which fell prey to Zinc Pest due supposedly to using Zinc of inadequate purity. Basically, if the gears in any Atlas built machine haven't fallen prey to Zinc pest by now, they aren't going to. Zamak has also been called "pot metal" (as a derogatory term mainly by those who don't like Atlas machines or their owners) which it isn't by definition as the percentage of lead allowed is minimal.

I would not run any metal gears dry unless the mating gear was something like nylon or linen based phenolic.

Between 22:00 Sunday and 07:00 Monday, I reduced a 3" diameter chunk of 4140 to about 1/4 its original weight with my Atlas machine and its Zamak gears. The pile of shavings in the drip tray weighs considerable more than the finished torque testing shaft. But it was the only suitable material that I could find Friday afternoon from which to make a part that had to be available for use on Monday. My feet still hurt!
 

wa5cab

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#10
Gearhead,

Most machinists still working today are too young to have been machinists when the last Atlas lathe was built. Their parents might not have been born when the last Atlas mill was built. Plus the company name was changed to Clausing in the 1960's, likely before they were born.
 

The Liberal Arts Garage

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#11
Robert: I'm surprised to hear that Zamak is stronger than cast iron; how do you define stronger? Zamak is certainly softer than CI, I'm concerned the OP might think Zamak is the SAME as cast iron in all respects which would be incorrect.
Mark S.
Remember that proper gears have "gentle mating" different
Strength quality required
 
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