ACME Threading

Casull

Casull

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I know this is not a simple question. But does anyone have any tips or pointers on cutting ACME style threads? Related to barrel threading for this purpose.
Thanks,
Rob

P.S. Anyone have a spare 55º Whiteworth thread guage they would sell? Not related to the ACME or square thread cutting obviously.
 
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I think I am making a mistake here in calling square threading ACME? The more I read, the more the two do not seem to be the same. And yes, it's regarding a P14/17 Enfield project idea but I see many actions have square threading by my books.
 
Enfields(P14's and M17's anyway) are square threads, 10tpi I think. Just need to make sure you have enough clearance on the leading edge of your tool to clear the helix angle. Otherwise you're in for a lot of rubbing (which in some cases might be a good thing:D ) and not a lot of cutting.
 
Rembo, in English please, you slipped into pro machinist there for a second.
Do you mean the concave area on the face of my cutter? Sorry, I know I have a lot to learn and I'm really not all that bright, ask any of my friends.
Rob
 
Casull said:
Rembo, in English please, you slipped into pro machinist there for a second.
Do you mean the concave area on the face of my cutter? Sorry, I know I have a lot to learn and I'm really not all that bright, ask any of my friends.
Rob
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A square thread is one of the most difficult threads to cut in the late and your lathe should be in good working order to get a good result. It is always easier to begin by using a V cutter to remove some of the material and then shave both sides of the thread flanks individually until the square thread is complete, better get lots of practice in before you attempt to work on a barrel.
The acme thread form has mostly replaced the square thread form.
 
Acme

Hopefully, you're well up to speed on the requirements necessary for cutting good, clean threads thanks to previous posts. If you're on the learning curve I agree with the advice to do a bunch of practice runs. I always liked the factory made carbide inserts in the thread form required but as you probably know it takes a fairly strong, steady lathe to be happy with them. We turned lots of square threads for pulp/paper industry but never Acme.

Have fun!

FM
 
Wow! Do I ever feel dumb! I said that Acme and square threads were the same. They are not. And no, I don't know of any action that uses acme threads.
Sorry for posting misinformation. And thanks to all who were so gentle in correcting me.
 
I watched a master thread my Swing barrel (same as P17). He started off by grinding an insert to suit the size of the thread (diamond wheel and surface grinder) and then cut about 2 thou per pass when actually threading. He then carefully put the insert away in case I bring the bloody thing back again.
 
The Acme thread form is a great thread and is kind of a marriage between square and "V". They are not commonly used firearms but certainly can be. Martin Hagn showed me a couple of Mauser take-down rifles which had been threaded Acme. His feeling was that this was a more durable thread than the 60 degree"V" for a take-down.
Acme threads are used on the leadscrews on most lathes. The Acme form allows for easier engagement by the half-nut than would a square thread while the steeper angle of the face of the thread makes for less spreading force than with a "V". A buttress thread would work as well or better but only in one direction.
The locking lugs and seats in a 1910 Ross are essentially an interupted buttress thread FWIW.
Cutting of square threads is accomplished in much the same manner as any other and there a various ways to do it.
One may grind the tool to a width of .051" (10tpi) then either feed in with the crossfeed or, setting the compound at 90 degrees, feed in with the compound and return the crossfeed to zero for each successive cut. An alternative method is to grind the tool to .050 or even .049, set the compound at zero degrees (parallel to the thread axis), feed in with the crossfeed to cut the thread to depth, then advance the cutter by .001" with the compound to gain clearance. In truth, this method is usually employed when you screw up grinding the cutter.
For lots of information on thread forms etc., have a look at a Machinery's handbook. All you ever need to know and then some! Regards, Bill
 
Leeper is correct as usuall. Square threads are not that uncommon on some older models of guns, Savage 1899's for example. Marlin 336's have square threads, except the .450 marlin model which has v threads. A lot of lever and single shot rifles use square threads for mounting their barrels. I just broke down 6 Remington rolling block barreled actions, all had square threads on the barrels-recievers.

In my expierience, you have to take smaller depths of cuts when cutting square threads (and acme's also). You can buy guages to grind your cutters to the proper t.p.i. in both square and acme models.

Bill is also correct about machinerys handbook, it is very handy to have around. If you are splurging and buying a new one, get the large format one, it is much easier to read.

Casull, if you are wondering what a butress thread is, the 98 mauser uses one in the end of the bolt for holding the cocking piece.
 
Folks,

Garands, M14s, M305s, etc are Acme thread on the barrel shank. It's incredibly common in industry, and not uncommon on firearms. It's a strong thread type, and easy to cut on a lathe. Carbide inserts (for cutting on lathe or mill) for virtually every size and style of Acme thread are available from most manufacturers.

Cheers,
Michael in Edmonton
 
Mike
Does the Garand not have a 10 T.P.I Square thread?
And I have never seen an Acme thread on a firearm. And what are the different “styles” of Acme thread you are talking about
 
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