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Paul Alciatore
11-10-2004, 02:40 PM
The thread (no pun intended) on the threading dial has got me wondering. A little while back I made a set of rollers for a tubing cutter that produced a 1/16" groove in aluminum tubing. It worked better than I had dared to hope and the O ring fit perfectly.

So now I am wondering if rollers could be made to fit a sizzors type knurling tool that would allow me to roll threads in a lathe. It seems to me that if you had two rollers with the desired pitch and thread form that you could roll it onto a part just like you do knurling. Of course, you would need left hand threads on the rollers to do a right hand thread on the part. And the rollers would have to be hardened.

I doubt that this is a new idea. Has it been done? Any problems with it? Seems like it would make a stronger thread than cutting. And would be easier to control? Or not? Does anyone sell such rollers? In sizes that fit standard knurling tools?

Any experience or thoughts?

Paul A.

Alistair Hosie
11-10-2004, 02:55 PM
It sounds feasable but I wonder why it has not been done before must be a hitch somewhere.Alistair

nheng
11-10-2004, 03:06 PM
It's sort of the female equivalent of thread forming taps. You might want one roller with the thread form and the other one flat to distribute the forming pressure though. Two threaded rollers might be difficult to "sync up".
Den

Paul Alciatore
11-10-2004, 04:35 PM
Yea Den, but I don't know if it would work with one roller trying to make a vee and the other trying to flatten it.

Paul A.

JRouche
11-10-2004, 04:37 PM
I would think it would take more than just two rollers. I'm thinking twenty or so very small ones (1/4").

Just "pushing" the rollers, sideways across the material would be what you are doing unless the tool would swivel a certain amount of degrees for various thread pitches.

Now with the multitude of wheels and clamping pressure the machine would have to be up to the task, very stout in re: to torque and stiffness.

For example, look at the pipe threading machines made by Ridgid.

http://www.ridgid.com/Tools/1224-Threading-Machine/index.htm

The drive train is very powerful re: rotational torque, also quite slow. And those use "blades" to cut the thread. To roll-yer-own you would need even more torque.

But,,,,I like it, build it and we will come, err, I mean follow. JRouche.

nheng
11-10-2004, 04:55 PM
How about a single roller in a standard knurl size, with the full thread cut into it (for finer pitches only on smaller machines).

If the carriage were stationary, this roller would want to travel along the work at the pitch rate but with the leadscrew engaged, it would rotate and form the thread along the part. I seem to be having a mental block as to whether or not this is correct though http://bbs.homeshopmachinist.net//wink.gif

If a single vee roller were used and tilted, then it seems like the 60 degree point would have to be altered to compensate for the helix angle tilt.

I suppose there are a number of ways to accomplish it, or to at least have fun trying! It might help to look at the thread rolling process and try to emulate it.

Den

Dr. Rob
11-10-2004, 05:19 PM
It does work, very quickly and easily. Thread-knurl wheel tools of yesteryear were available (didn't somebody post a pic of some a while back, or was that the PM board?) and just recently I was at the technical trade fair, and found a company that supplies wheeled threading dies. They look almost like normal dies, but have three thread-rolling wheels annularly disposed around the center axis. Like a very small cat's-paw steady rest. They intention is to use them in for example a tailstock die head. The manufacturer touted less torque, less heat, less wear, less time and low cost as some of the benefits. They weren't very expensive, either.

Don't recall the name, but have the brochure someplace. Can find it tomorrow.

brunneng
11-10-2004, 07:10 PM
Here's some links for thread rolling heads and some theory stuff.

http://www.findarticles.com/p/articles/mi_m3101/is_4_76/ai_108197879
http://www.namco-tooling.demon.co.uk/index.htm
http://class.et.byu.edu/mfg130/processes/descriptions/deformation/threadrolling.htm

It looks like the dies are self syncing in that they just slip into alignment. Since the metal grain flows to shape instead of being sheared you have a much higher fatigue strength. Plus since you aren't removing material it takes 27% less material to roll a 3/8"-16 UNC-2A thread. (quoted from site)

They also say it's generally done at high speeds - like 2300 rpm (varies by pitch) and takes a seconds. So it's used a lot on cnc but not so much on manual because of the speed.

Also the material has to have good plasticity. You wouldn't roll cast iron.

kevin

Paul Alciatore
11-10-2004, 10:21 PM
I knew it couldn't be a new idea.

And I think it would make it easy to thread right up to a shoulder.

Now to find a source for the rollers.

Thanks for the replys.

Paul A.

ulav8r
11-11-2004, 12:35 AM
It is done a lot. Reed Machinery(split off from Reed-Rico) sells the head and rollers. There are several others. The head has two spindles the rolls ride on. The rolls are keyed to the spindles and the spindles are geared together to keep the rolls in time with each other. In a screw machine the rpm is usually controlled to the limitations of the cutting tools, not the thread system.

The spacing between the rolls is adjustable to control the diameter of the thread. The blank to be threaded is turned to the pitch diameter of the thread needed. The rolls are specific the the thread diameter, the same as a tap, although you can adjust the tolerance of fit. In a multi-spindle screw machine the head feeds from the side of the shaft, same as a cut off tool. The tool travels just past center by .002-.005, then retracts. The maximum length of the thread is determined by the width of the die. On a 10 second cycle time the rolls are in contact with the part for less than 2 seconds.

The rolled thread is stronger than a cut thread, and is usually smoother when adjusted properly.

JohnnyHopper
11-11-2004, 01:11 AM
I know this is a shameless plug, but I found one of these in a crate of junk that was purged as clutter and left by a dumpster.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=3851556281&ssPageName=STRK:MESE:IT

I don't even have a lathe, much less a CNC one so eBay gets it http://bbs.homeshopmachinist.net//smile.gif

wierdscience
11-11-2004, 08:36 AM
Hill-Acme has been making them for years,they fir either the tailstock or in the turret. They show up on Ebay from time to time,but still hold their price,plus the rolls are like $175-200 a set if memory serves.

Paul Alciatore
11-11-2004, 12:44 PM
So it seems to be a good idea on CNC bun not necessairly for a manual machine. As I see it, the problem is that if the rollers are bigger than the thread you are rolling, then there is a feed involved and it is not the same feed that you would use for cutting a thread. Whole new set of problems. And you would still have to stop when you reach a shoulder.

JohnnyH,

On your auction item, the left hand threads on the rollers are not odd or strange. You want a left hand thread on the roller to make a right hand thread on the work. That much I figured out early in the process.

Paul A.

JohnnyHopper
11-11-2004, 01:52 PM
Paul A - You give me too much credit. I read the "LH" on the dies when I called them left handed. I did not actually try to look at the dies and follw the direction of their thread pattern and then interpolate their function http://bbs.homeshopmachinist.net//wink.gif