New threading tool

[KeithB]

I'm on a continuing quest to come up with the best way to cut threads quickly and accurately on a manual lathe. One way to do that is to use an expanding die head and the proper thread chasers. I'd bet that 99% of the threads I cut on a manual lathe are 5/8" diameter or smaller. Anything larger than that I can cut with a single point tool, so I determined that I needed a die head with that capacity. I found a used Rubometric (it's German) 9/16D die head on Ebay. I also found lots of used chasers on Ebay so I made sure when I bought an assortment that I got 1/2-20 and 3/8-24. Got a lot of other chasers also, but those two are the thread size on two products we make on the CNC lathe but could be made on a manual lathe.

The die head uses four chasers that can be changed out easily. In operation the die head is cocked, the rough/finish cut lever is flipped to the rough position and pushed on to the end of the rotating rod. The chasers cut and pull the die head forward. When the rear of the die head stops the front moves forward a short distance and then it automatically opens up. No need to stop or reverse the lathe spindle. Just push the die head back, recock it, flip the rough/finish cut lever to the finish position, and recut the thread to final size. The chasers cut the full profile including the top of the thread, so if the material is the proper size the thread crest is cut along with the flank and leaves no burr to be filed off. I threaded both ends of 32 3/8" rods (64 threads total) in about 2-1/2 hours. And I never even got out my thread file!

I needed a way to mount the die head to my lathe that would keep the head from rotating but allow it to move forward to a fixed repetitive location. The die head has a 5/8" straight shank. I made an adapter from a scrap piece of 4-1/4" aluminum round that would clamp on the OD of my tailstock quill. I also made a sliding sleeve that clamps onto the die head and that slides on a 5/8" rod that gets clamped into the tailstock adapter. Using this setup I can clamp my tailstock in place and control the length of threads. The die head moves forward until the slot in the sleeve hits a screw head in the shaft. The die head body stops moving forward and the die head front continues about 1/16" further before it trips and opens up.

The adapter to mount die head to tailstock quill.


Rubometric die head


Die head showing slots for chasers


Die head mounted on lathe




I'm really pleased with this tool, wish I'd bought one years ago!

 

[JWinAZ]

That is the way to thread! CNC is a wonderful thing, but many pre-cnc techniques are still useful and efficient.

 

[KeithB]

Right you are!

 

[smokeywolf]

They are fantastic. Only shortcoming is the limitation of how many inches of thread can be run on a shaft. yours is the spittin' image of mine. Brand name on mine is "Grand".

When I use mine, I mount directly into a Jacobs chuck in the tail-stock. I lock the quill, slide the tail-stock up to where the die head w/chasers is at the limit of desired thread, run the carriage back until it bumps the front of the tail-stock, lock down the carriage and the carriage acts as my deadstop.
The one caution to this setup is you have to be sure and add in the additional few thousandths of travel that takes place in the die head to trip the chaser release.
I also make sure that the ways where the tail-stock will be sliding are squeaky clean with a few fresh drops of way oil on them.

 

[KeithB]

I tried mounting the die head directly to the tailstock and letting the tail stock slide but ran into several problems. My lathe is a 15” Clausing and the tailstock is the size and weight of a medium size anvil. It exhausted me to slide it to change parts and it stripped the threads on aluminum, too much weight to drag along. That’s why I made the rod and sleeve mount.

 

[smokeywolf]

Taking that into consideration, your tooling is a real slick solution. I don't think I've ever used the geometric die head to run threads on aluminum. It was always stainless I had to thread. If I had to run a bunch of threads on titanium I'd single point down to .001" or .002" over, then finish with a button die.