# Acme Threads



## cfellows (Jan 24, 2012)

I had my first opportunity to tap a piece of brass today with acme 1/2 - 10 tpi threads. I have to say, it's not for the faint of heart or slight of build, at least not with the single pass tap I had. I had to back out and clean the tape about every half turn and the going got so tuff I had to use a large crescent wrench to turn it. Thought sure I was going to break off the tap. I'm guessing next time I'll break down and spend the money for a tandem tap which cuts the threads in two stages.







I'm adding a z-axis adjustment to my tool and cutter grinder. If there's any interest, I'll post some more pictures.

Chuck


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## doc1955 (Jan 24, 2012)

I've tapped acme that size before I seem to recall 3 taps and it was still tough I can imagine how 1 tap would be a bear to do.


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## Jasonb (Jan 24, 2012)

You could put the nut in the 4-jaw and screwcut most of the thread then just chase the final form with the tap.

J


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## tel (Jan 24, 2012)

That's certainly what I would have done, and have done in the past - Acme are no different to any other thread as far as screwcutting goes.


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## lathe nut (Jan 24, 2012)

Chuck, yes the progress, learned something about Acme taps already, thanks, Lathe Nut


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## Path (Jan 24, 2012)

Yes that would be great ... 

Looking forward to it.


Thanks, 

Pat H.


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## cfellows (Jan 24, 2012)

Jasonb  said:
			
		

> You could put the nut in the 4-jaw and screwcut most of the thread then just chase the final form with the tap.
> 
> J





			
				tel  said:
			
		

> That's certainly what I would have done, and have done in the past - Acme are no different to any other thread as far as screwcutting goes.



Aaah, I wish... My screw cutting abilities on the lathe are touch and go at best and that's on an outside cut. On a 1/2" inside thread, it gets more dicey. With an acme thread, the size and shape of the cutting tip changes with the thread size. Even less sure that I could grind an accurate cutting tool for that. Maybe someday I'll give it a go, but for now I just didn't feel up to it.

Chuck


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## tel (Jan 25, 2012)

The tool isn't at all hard to grind up - the angle through the series is a constant 29° - set your grinding rest to half of that and have at it, grind it down to almost a point and then gently bring the end back until the tip is a gnat's hair under the bottom dimension of the thread.


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## Jasonb (Jan 25, 2012)

As you will be cleaning up the profile with the tap the tool can be undersize and of approx profile, you are really only aiming to remove say 75% of the waste so the tap can go through easier and the screwcut rough profile will also guide the tap and help stop it going off line.

J


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## John Rudd (Jan 25, 2012)

Nice thread...( err. no pun intended..)

I've just acquired a shaping machine (havent actually got it yet and think it's a Perfecto... ) and am told the threads are damaged at the extremeties on the lead screw so I may have to make a new one..


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## rake60 (Jan 25, 2012)

Single point cutting of Acme threads can be made painless.

I grind the threading tool to a 29 degree included angle, but narrower than the 
finished thread. Set the compound parallel to the chuck and use the cross slide to
coax the cut deeper with each pass. When it starts to chatter, move the compound 
in and out slightly to relive the pressure on the tool. Then go back to the center to
take it deeper. You get the idea.

It's actually kind of fun to play with.

Rick


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