Acme Threading

You will probably need a bigger tap handle. I've seen one or two tandem taps broken when hand tapping, they snap right between the roughing and finishing sections. Be sure to do this in the mill with a pilot in the quill.
 
I would just give the single point lathe threading a try in a piece of junk brass. If it worked, it could come in useful in the future. When I tried acme threading for the first time, I did not practice but went straight to the cross slide nut which I had put a lot of time in to. It worked pretty well even though I made the same mistake that Abom79 made in his video. I watched the video and made the mistake anyway. Fortunately, I was able to recover as soon as I heard the squeak.
 
Here's a thread of me cutting a 7/8" x 6 ACME thread into a CRS bushing. I don't recall having any issues other than pucker factor of of a fast-moving carriage. My Grizzly's minimum speed is 70 RPM, so at 6 threads per inch it's moving about 12" every minute or an inch every 5 seconds.

All you'll need is a boring bar and a HSS bit for grinding the profile. It helps to have an Acme thread for getting the 29 deg. correct and the tip width. Other than that, it's no different than conventional 60 degree threading.

Bruce



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Potd - Project Of The Day- What Did You Do In Your Shop Today?

A while back I got stupid and jammed up my power feed on my South Bend lathe. In my panic to unstick it, I broke the screw head off the apron screw. I know this is a left hand thread screw , so I thought if I drill a small whole in the center of it the piece would come out of the clutch shaft...
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ericc said:
It worked pretty well even though I made the same mistake that Abom79 made in his video. I watched the video and made the mistake anyway. Fortunately, I was able to recover as soon as I heard the squeak.
Click to expand...

What mistake did you/Abom make?
 
devils4ever said:
What mistake did you/Abom make?
Click to expand...

Watch the video and watch the second video in which Abom fixes the mistake. It has to do with underestimating the front clearance angle due to the thread helix angle. I cut a junk credit card to the correct angle to make a gauge, reground the tool, and finished successfully.
 
I did it! Tonight I tapped my first Acme thread. It was just about as hard as I thought. The first part (roughing) of the tandem tap was the hardest. The last part (finishing) was a lot easier. I thought the tap might break on the initial threading. I had to switch from my Starrett 91B tap wrench to my 91D tap wrench after starting the thread in the mill to gain more torque. I used lots of cutting fluid, but it was still rough going. I'm not sure I'd want to tap anything too much bigger in steel. I tried to reverse the tap many times to clear the chips, but it was a lot harder going in reverse than going forward. The end result is satisfying though.



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So, I'm just about done with my drill press vise. One of the final steps is to add a handle to the end of the Acme threaded rod.

I want to add a cylindrical metal piece on the end to beef it up so I can add a thin rod to turn. I have a 11/32" (0.34375") reamer that I plan to use on the cylindrical steel piece and press it on the turned down Acme threaded rod. I have a 2 ton Arbor press for this.

So, I'm wondering how much of an interference fit is needed? 2-3 tenths?

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devils4ever said:
So, I'm just about done with my drill press vise. One of the final steps is to add a handle to the end of the Acme threaded rod.

I want to add a cylindrical metal piece on the end to beef it up so I can add a thin rod to turn. I have a 11/32" (0.34375") reamer that I plan to use on the cylindrical steel piece and press it on the turned down Acme threaded rod. I have a 2 ton Arbor press for this.

So, I'm wondering how much of an interference fit is needed? 2-3 tenths?
Click to expand...

Assuming the "tommy bar" passes thru both pieces, yes that would be fine.
 
Your reamer is likely to cut oversize so be aware. Roll pins can be used in situations like this. Or tapered pins. If you do use a press fit pin you can always add some Loctite if it is a little loose fitting.

Ted
 
I finished my drill press vise and I'm very pleased on how it turned out. I learned on a lot on this project which was one of the main goals. I worked with Acme threads for the first time and tapped the steel with some effort.

I was able to press fit the end of the rod with a bushing to allow a beefer rod to be used to turn the screw. The interference fit was a little intimidating since I had trouble accurately measuring the reamed hole with my telescoping snap gauges. I was able to press the bushing on the turned down rod on my 2 ton arbor press without much difficulty.

Thanks for everyone's input!

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