Turning Square Threads

Found it: page 1584 of the 23 Ed. of the Handbook. 10-degree Modified Square Thread. I knew it existed but could not recall the name. That's what I would specify if I thought I needed a square thread and was specifying both the shaft and the nut.
 
In robotics I would imagine the shaft and nut would see a lot of use for motion control, unlike a one time nut and bolt arrangement that is used for a fastener. Look at the lead screw on most lathes.
 
John Hasler said:
Found it: page 1584 of the 23 Ed. of the Handbook. 10-degree Modified Square Thread. I knew it existed but could not recall the name. That's what I would specify if I thought I needed a square thread and was specifying both the shaft and the nut.
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LeBlonde Machine Tool made a special lead screw used on some of their heavy duty lathes and gun boring lathes that had a one pitch thread. It had a depth of .250" and a root width of .470", and flank angles of either 5 or 10 degrees. The leadscrew was made in three diameters of 2.500, 3.000, and 4.000". We cut the threads on a thread mill and single pointed the half nuts on a lathe capable of cutting a one pitch thread. The aluminum bronze nuts were around 15" long. Think that wasn't fun threading!
Ken
 
I've cut a lot of square threads using a hss tool I ground up on a surface grinder. I also "cheat" a little. I rough the threads out with a standard V thread tool, and then finish them with the square tool. That eliminates a lot of the chip load and makes a smoother thread.
 
Not having the MH at home, from memory a square thread is exactly as described.
A 1 1/2-4 thread would look like this I believe, .25 lead, .125 at the crest and root and a minor diameter of 1.25, I may well be wrong.
If correct however this will present a formidable turning challenge if done in an engine lathe over a considerable length, say more then 10 diameters, that will be a LOT of tool in the work at any given time.

Give it a try and see how it works, note that you will need 5° minimum + clearance on the leading edge of the tool. Good Luck
112_4squarethread_zpslfgganfs.jpg

112_4squarethread_zpslfgganfs.jpg
 
There's a lot of down hole oilfield equipment out there that uses a 4 pitch modified square threads and other various thread pitches, including Metric, and it's not trapezoid either. And they are mostly left hand. That allows you to "get off" of the tool by right hand torque. The leading flank is at 0 degree and trailing flank 5 degrees. Sometimes we would make the trailing flank up to 45 degrees.

Edit: Got that backwards, the trailing flank was nearly always 0 degrees or 90 deg to the thread axis. And the leading edges of the thread were at an angle from 5 degrees to 45 degrees.
Ken
 
One could also grind a slightly narrow high speed or cobalt tool with back rake and side rake so it only cuts on the leading edge and end.
Then set the compound to the correct angle and remove most of the metal. I've done that once before on a lathe that wasn't rigid enough
to simply single point the thread.
 
Why was ACME thread invented? Is it easier to cut or does it wear better?
 
Main reason-Acme and the similar threads are far stronger than a 60deg thread form of same size.
Acme and similar threads are better for transmitting motion and better centralize components to the thread center.
 
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