# Atlas Half Nuts OEM vs Brass



## Wildman326 (May 18, 2021)

I have a 12X36 101.07403 Atlas lathe that I have to push the lever all the way down to make it engage.

I’ve seen the half nuts for sale on eBay.

Are the brass ones worth the extra $30?


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## jocat54 (May 18, 2021)

I have no knowledge of the Atlas lathe, but I think the brass ones would be worth it.
The stock gears are made of zamack zinc alloy and are much softer than steel, so I am assuming that the half nuts are also made from zamack


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## Ulma Doctor (May 19, 2021)

the OEM half nuts are Zamak.
Zamak was chosen to minimize post formation machining, it casts very well and has moderate wear and strength characteristics
Bronze or Delrin may be very well suited materials to construct half nuts from

brass would be a step up from Zamak
i would become religious about lubrication of the feedscrew if/when you swap to brass- for longevity of the screw as well as the half nuts

there is another part inside the apron that helps to engage the half nuts.
i cannot recall its proper name, but it it connected to the engagement lever and runs transverse across the apron.
it has a couple half circle channels cut into actuator face that is distal in proximity to the engagement handle
these half circles can become worn and no longer move the half nuts as efficiently.
as a result, the travel between open and closed diminishes with the wear in the system


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## wa5cab (May 19, 2021)

The factory name for the part that Mike is describing is "Scroll".  The normally visible half nut engaging lever is mounted on the outer end of the scroll shaft.  The other three parts of the mechanism that are subject to wear are the Guide and the two studs.

I disagree that brass half nuts are superior to or will outlast the OEM Zamak ones.  On average, both materials will wear at about the same rate.  There are two reasons that all of the after market halfnuts are made of brass instead of Zamak V - they can make unsubstantiated claims that their brass product is superior to the Zamak V OEM ones, and they couldn't machine them out of Zamak V if they wanted to because AFAIK no one markets Zamak V bar stock.  There is a third reason why no one makes them out of Naval Bronze which is that they would be too expensive to compete.  In general, the brass ones tend to ba a little more expensive than OEM, which they get around by claiming that their brass ones will outlast the OEM ones.  Or by depending upon their customers not knowing that the OEM ones are still available.


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## markba633csi (May 19, 2021)

Would naval bronze be superior to regular bronze or zamak? I would think a leaded bronze like SAE 660 would be a good choice
-Mark


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## Wildman326 (May 19, 2021)

Thank you very much for all the replies and information. I ordered the OEM half nuts. I’ll have to look at the scroll when I take it apart to see how much wear they have.


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## wrat (May 19, 2021)

Just agreeing with Robert D. on a different note.
Lathes have half-nuts.  They're made of all kinds of materials for all kinds of reasons.
The Atlas used Zamak.  Low power.  Low speeds.  Low loads.  Works fine.  Zinc is a good lubricant, which is why we put it in certain motor oils.
The original equipment Zamak lasted longer than i've been alive, probably with dubious upkeep.  How do I improve on that?
Brass?  Not really.
But if I get another Zamak, and took care of things, it will only last another generation and then some.  If I got another Zamak and a spare, I'd have the half-nuts covered for my great-grandchildren.  That'll do,.


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## benmychree (May 19, 2021)

In my opinion, cast iron is the best material for half nuts, evidenced by the fact that all lathes, other than Atlas use it for half nuts.


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## Ulma Doctor (May 19, 2021)

after having personal experience rebuilding an Atlas TH42, zamak is junk 
you can keep the low grade stuff


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## benmychree (May 19, 2021)

Ulma Doctor said:


> after having personal experience rebuilding an Atlas TH42, zamak is junk
> you can keep the low grade stuff


AMEN!


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## wa5cab (May 20, 2021)

If you two had your way, there would be no Atlas machines around for you to denigrate as the company would not have survived.  

Making the half nuts and many other parts out of cast iron would be fine, but the price would be or have been 3x to 5x the cost of the Zamak V ones.  That market was already sewn up by SB, with no room for another player.  And we would not be having this repeat argument.  So if you have nothing positive to add to the discussion, please take your comments elsewhere.  They will not be tolerated here nor anywhere else on this site.


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## wa5cab (May 20, 2021)

markba633csi said:


> Would naval bronze be superior to regular bronze or zamak? I would think a leaded bronze like SAE 660 would be a good choice





markba633csi said:


> -Mark


I wasn't able within a few minutes to find a reasonable definition of the term "naval bronze".  So I don't know and will withdraw the comment.  But I would suspect that your comment on SAE 660 is probably correct but that the parts cost would be increased again over brass as it will be for brass versus Zamak V.  But for different reasons.


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## Larry$ (May 20, 2021)

Zamack was used because it is reasonably strong, easy to cast and cheap. A good choice for the intended market.


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## Ulma Doctor (May 20, 2021)

for the record, i impugned the material, not the machine.


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## benmychree (May 20, 2021)

Ulma Doctor said:


> for the record, i impugned the material, not the machine.


And I merely agreed---


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## markba633csi (May 20, 2021)

For the record, I have found Atlas lathes to be quite capable within their limitations- the gears have never been a significant problem other than being somewhat messy, so I run them nearly dry.  They seem to be self-lubricating to a certain extent, I suspect due to the zinc and copper content
-Mark


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## benmychree (May 20, 2021)

Larry$ said:


> Zamack was used because it is reasonably strong, easy to cast and cheap. A good choice for the intended market.


Zamac or Zamak is an acronym for an alloy of zinc, magnesium, aluminum and copper; both spellings are commonly used, but I'd think Zamac is more proper, as it represents the correct spelling of the ingredients.
Brass is not a very good bearing metal, it can wear rapidly under pressure, naval bronze would be better, and sae 660 (bearing bronze) probably better yet, but cast iron , I think is better yet, as it is porous and can take up oil, and it works well against moving steel parts without galling, and is long wearing.


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## Bi11Hudson (May 20, 2021)

benmychree said:


> Zamac or Zamak is an acronym for an alloy of zinc, magnesium, aluminum and copper; both spellings are commonly used, but I'd think Zamac is more proper, as it represents the correct spelling of the ingredients.
> Brass is not a very good bearing metal, it can wear rapidly under pressure, naval bronze would be better, and sae 660 (bearing bronze) probably better yet, but cast iron , I think is better yet, as it is porous and can take up oil, and it works well against moving steel parts without galling, and is long wearing.


The "K" in the word ZAMAK is from the German word for copper, being where the alloy was first used. That from a history from Atlas. . .  I won't comment on brass being used for the half nuts. I have used it for other "screw followers" where it seems to last about as long as ZAMAK, give or take depending on how well it is maintained.

Iron has many advantages, as described above. But one of many(?) reasons it is not used for lead screw followers is to maintain the "purity" of the lead screw. I don't know the proper word for purity but lead screws are one of the central issues on a "screw cutting lathe". Their accuracy is central to the work, without which the machine is just a "lathe".

By making the half nuts softer than the lead screw, all (or most) wear is on the followers, the half nuts. The lead screw cannot be easily replaced, nor is it an inexpensive repair. The followers are a cheap and fairly easy to replace. When the machine goes "out of tolerance" on the followers, there is the option to relagate the machine to non-critical work until the repairs can be accomplished. When the lead screw wears out, cutting is also affected and takes much longer to correct. It has been protocol for many generations to protect the accuracy of the lead screw at whatever the cost. Using iron for lead screw followers, to me, would be a sign of poor design.

.


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## benmychree (May 20, 2021)

Bi11Hudson said:


> The "K" in the word ZAMAK is from the German word for copper, being where the alloy was first used. That from a history from Atlas. . .  I won't comment on brass being used for the half nuts. I have used it for other "screw followers" where it seems to last about as long as ZAMAK, give or take depending on how well it is maintained.
> 
> Iron has many advantages, as described above. But one of many(?) reasons it is not used for lead screw followers is to maintain the "purity" of the lead screw. I don't know the proper word for purity but lead screws are one of the central issues on a "screw cutting lathe". Their accuracy is central to the work, without which the machine is just a "lathe".
> 
> ...


But, we must note that nearly every lathe made in relatively modern times , other than Atlas, has used cast iron half nuts, this is a fact.  The only other material that I have ever heard of was from an old friend that had an ancient lathe that had babbit half nuts, poured in place, I saw it once, it was about 36" + swing, can't remember who made it.  May have been a McCabe.


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## wa5cab (May 22, 2021)

OK, benmy, that is more than enough Atlas bashing for the year.  It may be a fact that every other brand of lathe except Atlas made between 1935 and 1955 used cast iron that had to be fully machined from bar and cost about 3X what the Atlas ones did and didn't work any better than the Zamak ones.  It is also a fact that during that time frame, Atlas produced and sold about as many machines total as the sum of the production of the next three or four competitors.  And it is also a fact that out of Atlas and the three or four competitors, Atlas is the only one that you can still pick up a phone and order most of the parts for if you want to restore one to factory new condition.

Otherwise, I think that this thread has outlived its usefulness.


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