Is This an Acme Thread or Something Else?

David2011

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When this shaft was handed to me I thought it was an Acme thread but on closer examination I'm not so sure. It lacks the distinctive flat valleys of Acme threads. It's off of the battleship USS Texas. I think it's off of a 1912 vintage 5" gun if dating the item helps any. The thread gauge is for standard Imperial V threads; 8 TPI. There does seem to be a progressively larger gap developing but is that because the threads don't match the gauge? The OD of the threads and shaft is .948". Does anyone recognize this thread?

IMG_E6992.JPG
 
Compare it to a Buttress thread profile.
I can't see well enough to tell whether the profile is correct.
 
It's not acme, or the angles would farther off from your gauge as well as having a flat bottom. What it is though I can't tell. (Other than interesting...) Do you know what its function is?

GsT
 
It appears to be a 60 degree profile. My first thought would be to make a 1" 8TPI test blank, then turn the diameter down to .948 and see how close it matches.
 
Since thread standards were pretty new at the time this was presumably made, it could be non-standard, an oddball standard, or perhaps a deviation to correct a recognized weakness?
The main difference between Seller's thread form and Whitworth's is that the tops and bottoms of the threads (the crests and roots) are flattened. The flattened roots was a bad choice. Such angular joins in metal concentrate stress, and the process of manufacture results in high stresses at the roots of threads anyway. The result is cracks and broken fasteners.

UNJ was created to fix the aforementioned issue with the USS (Seller's Standard).

A fascinating subject, really.

GsT
 
I've seen theads like that in plastic... the thread profile is for a thread with twice the actual TPI. Thus, shallow and fast.

In downhole tools we use stub acme all the time. It's just half depth acme threads. You get a strong thread in less wall thickness, but lose wear resistance and nut stretch resistance.

Sent from my SM-S911U using Tapatalk
 
Good question, what the heck is it?
As already mentioned, It's not Acme.

This is a pic of my lead screw on the lathe. Acme is squared off much more than your sample.
 

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There's a 55 degree Whitworth thread that looks similar to that.
 
It may be a modified Whitworth as epanzella mentioned. The US did some things in Whitworth around WWI to supply arms to Britain, so this might have that thread form. Do you have Whitworth thread gages to check and see if it is 55 or 60 degrees? If 55 degrees, then it is probably a 1” Whitworth shortened to 0.95” diameter.

 
I've seen theads like that in plastic... the thread profile is for a thread with twice the actual TPI. Thus, shallow and fast.

In downhole tools we use stub acme all the time. It's just half depth acme threads. You get a strong thread in less wall thickness, but lose wear resistance and nut stretch resistance.

Sent from my SM-S911U using Tapatalk
That sounds like API 8 Round.
 
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