ACME rod and multi start

[stern]

In my quest for info before building my CNC PCB router, I have come across some info someone gave me regarding the ACME drive screws. Seems many use multi start rod as its supposedly more efficient than standard single start (seems 10TPI isnt as good as 5TPI 2 start). I have used ACME rods before but really wasnt aware of multi start rods except some references in machine lead screws.
Now another problem pops up, are there rods as common and easy to get as standard single start ones, AND I also assume you cant use a normal nut tap for a multi-start rod (meaning I would need a special multi-start tap to make the matching nuts.).

Anyone have any info or used multi-start ACME ? any info would be a great help.

 

[Terrywerm]

I cut a two start thread once on a piece of rod that I had laying around. It was not ACME thread, but was standard 60* thread. I had read about multi-start threads and wanted to see if I could cut one. It wasn't bad, I think the hardest part was getting the second thread to start exactly 180* out from the first one, and even that wasn't too bad. As for double start taps or dies, I have no idea if such a thing is even made.

 

[stern]

Thanks for the info, as I need to do some reading up on this. Not sure if you could use a standard tap with a TPI based on what ever the rod TPI was divided by the # of starts (so a 10TPI double start rod would use a 5TPI nut, leaving one "thread run" empty). While I would like to get my lead screw as accurate as possible, I dont want to have to spend a ton to get the tools I need (btw, have NEVER cut a thread on my lathe and probably NEVER will. Its a PM1027 and I CANT get to the gear without moving the lathe, and have never tried to change the gears to try threading, just leave it for the finest feed for turning).
Since its only research I will do some digging and see what I can learn (like learning).

 

[rafe]

There are some good videos on threading dbl. on the lathe. I don't know if they make such a tap , but I think it's unlikely. I've never done a dbl. but don't see why I couldn't, if I had to.I enjoy threading on my lathe, not really hard but don't lose your focus..... I believe Tubalcain has that video up .....HTH

 

[stern]

Well after some digging I did find muti start rod is available (2, 3 even 5) and the taps are pretty easy to get too (although you miss a few heart beats when you see the price lol). Myself I would never even attempt threading one on the lathe (1, seems rolled ones are better with less metal stress than threaded, 2 never threaded anything on a lathe in my life, and even if I wanted to, the lathe would need to be dragged out to change the gear set up (didn't think of that when placing my lathe, no access to the side panel).

Going to do some more digging, as regardless of the method I choose I will BUY the rod and nuts (unless i use standard 1/2 10TPI rod, then I have taps). If I do buy other than 10TPI it will mean going up in dia, to 3/4 or even 1", but sure dont want to go bigger than 1" considering the small size of the project.