How to machine a 56 Rockwell lead screw

[bgolash]

Hi Group

I need to machine the ends of my Thomson lead screw. I just
checked the screw with a file. It seems the screw is hardened
to a 56 Rockwell. I`ve heard some people machine the screw without
annealing. I have a small south bend lathe ..I`ve machined some
hard stuff before but the progress was too slow. Can I run the piece
in the lathe at slow speed and use a Mapp touch to anneal the screw.
Is warping or distorting the screw a problem.? How hot do I have to
get the screw to anneal it. Sorry for all the questions.

Thanks for the help.
Regards barry

[BigDaddyG]

Barry,
Your on the right track! I also use Thompson Ball Screws. Without getting into too much detail, just use a trial and error to get to the final results. Without being able to measure the heat on the surface, I can't tell you how hot I make mine. I heat "the crap" out of them, then turn. As for warping and distorting the screw, I have not had any problems yet. As with any process, take your time, use common sense and good machining process and you will do just fine.
Regards,
Glen

[ViperTX]

Let me know what you find out...I suspect that you want to keep whatever you don't want to heat up as cool as possible....wet rag comes to mind....and use a carbide bit (insert) for the machining. I believe ball screws are just case hardened (surface only).

[HuFlungDung]

So long as you apply heat only on the end, which subsequently gets machined, warpage is irrelevant, because you will machine it straight anyways (won't you? )

The screw was likely tempered after hardening at 400 degrees F (perhaps), so you'll need to take it up higher than that. You don't have to go all the way with a full anneal (1500 degrees, orange color). Probably up to 1000 would suffice. This would be shortly after the part turns almost colorless. Use a 1000° templestick to check the temp.

And yes, wrap the adjacent section of the screw in a wet rag to keep it from annealing, if you think the ballnut will run up that far.

[Swede]

I've machined these without annealing with a 1HP lathe, no problems. Get through the "threads" where it is surface hardened, and once in the core it behaves like any carbon steel, meaning that while not exceptionally hard, it is tough and stringy. I recommend sharp carbide to get through the case, then you may want to switch to a tool (HSS is fine) with a small radius and a bit of extra top rake. This will reduce cutting pressures and allow for a finer, more even cut.

This link may help, although it shows a ground screw rather than a Thompson. Both have behaved similarly. Good luck!

http://www.5bears.com/cnc16.htm

[Kmed]

Another way to tackle this if you are uneasy about machining it, is to set up a dremel with a grinding wheel attached to the lathe and ease it in with a grinding stone. Then do a finish cut with your lathe. I machine tool steels daily on my lathe and just use a slow speed and lots of coolant and tian coated insert bits. No worse than stainless. Just be carefull as many lead srews are air hardinging steel and if you dont catch them hot, they get even harder. For the acme screws I turn regularly, 400 rpm or so, moderate feed, and light cut works wonders.

[BT1]

I recon Mother in law's are a lot harder, just get in to it!