View Full Version : Simple Thread rolling attachment for lathe

01-04-2006, 08:11 PM
I made this attachment to roll threads on the tail brace wires. The 3 legs are 1”x 8” x 1/8”. For the rollers I single point threaded some drill rod 32 T.P.I .700 dia. x .600 x .250dia. hole. Heat treated with a torch then oil quenched. Measured Rc 50. If I were to do it again I would make the rollers .650dia. as now they just barely do 3/16 x 32 tpi. without interfering with each other. Also I would make the holes 5/16ths for added stiffness. To make the rollers I started off by threading a 3” length of stock. I used a file to taper the first 5 threads then parted it to length. Filed the first 5 threads of the next roller then parted it to length and the same for the third one.
The rollers have about .065” end play on the pins to allow them to follow each other into the thread. The jaw pressure in the lathe was set using a 10-32 screw, then removed it with a screw driver. You have to add a bit more pressure, maybe a 1/16th turn on the chuck key. The end rod I was threading (.169”dia.) was tapered for about 3/8ths” to allow it to start. We either held it in a drill chuck in the tail stock or clamped in the tool post and hand fed it. Once it starts, it is self feeding so only a light hand pressure is required to overcome the drag. I tried using the half nut to feed it at 32tpi. But for some reason the rollers wouldn’t follow each other and it chewed up the thread. You may notice in one picture that I used a hose clamp on the end of the pins. This was to stop the pins from flaring too much. The jaw pressure and hose clamp had to be adjusted and fiddled with a bit to get the thread on size.
I was using a Hercus lathe, which is the same as a small South Bend, set at the slowest speed on belt drive, 356 rpm. The deformation speed of a material is about 3 times it’s cutting speed so it seemed to work much better than when we were going really slow in back gear. After it threaded for about 2 inches, the lathe was reversed and the rod backed out. It worked fine on some old steel tail brace wires but I haven’t tried it on stainless yet. When I do I will run some tensile tests and let you know the results.

01-04-2006, 08:18 PM
Sorry I should mention that the pictures are in Photo gallery

Steve Pierce
01-04-2006, 10:21 PM

Neat stuff. I would like to learn more about machining. Did a little in night school after I got my A&P. I keep looking at those Smithy machines.

01-04-2006, 10:51 PM
Thanks for posting the photo link Steve. I'm still playing around with the ins and outs of posting images. Re: machining. If you can find a small lathe at a decent price go for it you'll wonder how you ever got by without one.

jay cross
01-12-2006, 03:23 AM
Would you send me an e-mail. I liked your rig and I had a couple of questions about it.

01-12-2006, 08:41 PM
For what it is worth; I have left and right hand L M Fette thread rolling die heads and can roll 3/16 and 1/4" wires.

My stock is 10' long, 316 stainless steel, min tensile 95,000 on 3/16" and 105,000 on the 1/4"

3/16"- $1.00 per inch, 1/4"- $1.10 per inch (Includes threading, whatever your required length is).

We do charge a $15.00 packing fee to pack in a PVC tube container that the P.O. or others can't bend easily.

Material has certifications. We also sell the terminal ends (AN665-21L/R and AN665-34L/R).

We just did a set for an Arctic Tern in one day and shipped out same day. (That's if you are in a rush- no extra charge).

We currently have about 500 ft of each size in stock.

We don't do it all but we do some things others can't and we do it very well!


01-13-2006, 06:24 AM

Smithy combos: Pass.

From experinece, better machines available. get a dedicated lathe, and dedicated mill. You will be much happier.

Smithy works good up to about a 4" diameter, then it is not strong enough.

01-13-2006, 06:43 PM
Thanks for the info AV8R2.
I've put on file and will be in touch if my own system does not work out.