Acme thread in titanium

Jorgo · Jan 24, 2011

I'm thinking of cutting a acme thread in titanium (I don't know what grade it is it was a trade from a buddy to use my lathe). My question is will I have any success with a HSS tool or will I need to buy inserts. Time isn't an issue on this I could take all day to cut it as its a part for a peice of shop equipment. But will it be a long frustrating unsuccessful day with HSS.
Thanks for the advice,
Jordy

Finegrain · Jan 24, 2011

You might have MORE success with HSS than with carbide. Reason being is you can get a HSS cutter super-sharp, more so than carbide, and dull + Ti = Bad Day, as it'll work-harden on you and then you have scrap, and for Ti, expensive scrap. Just keep the speed way down (which you probably are already since it's single-pointing threads) and preferably put some lube on the cut, flood if possible.

Ti cuts nicely with slick-sharp HSS. It's when you start rubbing, or running too fast, that the trouble begins.

Regards.

Mike

Finegrain · Jan 24, 2011

Oh, and mind the steep helix angle on the typical Acme thread, and adjust the cutter accordingly, whether it's HSS or Carbide. Out-of-the-box, a threading insert won't necessarily have enough clearance to get itself out of the way of an Acme thread.

Regards.

Mike

Limy Sami · Jan 24, 2011

Shouldn't have any problem, the little Ti I've machined I've done with HSS at <> 40' min,......... I'd say think tool angles for soft steel but make sure it's sharp - as in 5X glass sharp.

Make sure the tools cutting and not rubbing or it will work harden, have plenty of coolant on the go, and keep you a troshin.

Edit - I never was quick on the draw

Metalcutter · Jan 24, 2011

The question I'd ask first, is Titanium a decent bearing surface?

Usually that's important if it becomes a working union.

Regards,

Stan-

Jorgo · Jan 24, 2011

Finegrain said:
Oh, and mind the steep helix angle on the typical Acme thread, and adjust the cutter accordingly, whether it's HSS or Carbide. Out-of-the-box, a threading insert won't necessarily have enough clearance to get itself out of the way of an Acme thread.

Regards.

Mike

Good advice I always do. That helix angle caught me more than once as an apprentice.
Jordy

Jorgo · Jan 24, 2011

Metalcutter said:
The question I'd ask first, is Titanium a decent bearing surface?

Usually that's important if it becomes a working union.

Regards,

Stan-

That thought crossed my mind. My plan is to mate this thread with a brass nut. Is that a good idea. Would a different nut material be better. I chose titanium for the thread for the hell of it and to try machining titanium. No other reason.

tdmidget · Jan 24, 2011

For manual machining of Ti, HSS will give a mirror finish.
Will it work? Yes, but why? Save it for an appropriate application and use steel. Make it easy on yourself.

FP4NC_Finster · Jan 24, 2011

Ti in general has pretty poor wear properties, most time if adjoining a moving surface of any material it's sleeved or wear plated.

Mike C. · Jan 24, 2011

Yup, titanium is actually a pretty soft metal. It's also VERY prone to galling and more flexible than steel. If you are making a leadscrew (sure what it sounds like), titanium would be about the last material to be considered. As sadi already, save this for making a really cool piece and use something like 4140ph.

Limy Sami · Jan 24, 2011

I can only agree, Ti is not something I machine for fun, and far too valuable to play around with

Jorgo · Jan 24, 2011

Mike C. said:
Yup, titanium is actually a pretty soft metal. It's also VERY prone to galling and more flexible than steel. If you are making a leadscrew (sure what it sounds like), titanium would be about the last material to be considered. As sadi already, save this for making a really cool piece and use something like 4140ph.

I was a little worried about flexibility. It is somewhat of a lead screw. I'm building a rolling machine and it'll be the screw that drives the "floating" (for lack of a better term) roll into the stock to put the first kink in it. I think I'll take your advice and go steel. Thanks for all your input guys. I'll post some pictures when I'm finished building it. Shouldn't be to long now. Gotta shuffle it between paying jobs and time with the wife.
Jordy

Mike C. · Jan 24, 2011

That would indeed be a real bad application for titanium. It's going to be under a lot of pressure while you are turning it in some cases (as you tighten to adjust to a smaller radius bend).... perfect recipe for galling. Threading it is really no trouble with HSS. I did an experimental 4mmx.05mm pitch thread on a ti bolt I had laying around. Came out even nicer then the brass parts I was making. Titanium is really not bad at all to work, on the OD. Single point threading and boring on the ID is not a problem. It's internal stuff where it gets nasty and evil. Drilling is not a lot of fun. Reaming or tapping are infuriating. It puts all the heat back into the tool, expands the tool until it rubs, work hardens and then galls to it.

tdmidget · Jan 24, 2011

And even on aircraft the acme threaded screws that operate control surfaces are steel.

Jorgo · Jan 24, 2011

Mike C. said:
It's internal stuff where it gets nasty and evil. Drilling is not a lot of fun. Reaming or tapping are infuriating. It puts all the heat back into the tool, expands the tool until it rubs, work hardens and then galls to it.

Boy that sounds nasty. I think I'll just stick with nice steel for as long as possible.
Jordy

maxh · Jan 24, 2011

A long time ago when I was first learning how to machine, I decided I wanted to design and build my own miniature lathe, and I was choosing exotics like Ti 6-4 and various stainless steels just for fun. I threaded a 1/4" rod of Ti (1/4-20 and ~5" long) for the compound lead screw.

It was a pretty dumb project, but I was young and had fun while learning to machine. I used my lathe once or twice after it was done; it wasn't that great. I know a LOT more these days, and I agree with the others here, Ti would be a bad choice for a lead screw.

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