I have been lurking here for years and just got around to getting my form 1 a few months ago. I saw a thread on here about threading titanium with a thread mill, but I need some pointers on doing it with a lathe. I am not very experienced with threading, especially inside threading, but I have successfully threaded some aluminum and stainless tube. I have a 12x24 bolton lathe with 1.5" thru hole. I want to thread 28 tpi. THe lowest speed it has is 75 rpm. I have a carbide threading tool. I dont currently have a flood cooling setup, but Im not against adding one if it is necessary. I have been spraying coolant or wd-40 from spray bottles or dripping magic tap on the material as I thread. I have found it easier to leave the half nuts engaged and stop the lathe and reverse it out of the cut than try to hit the mark every time.
Anyway. I would like to some tips on internal threading a tube. How deep should my passes be? Should I feed with the cross slide or 30* with the compound, or a combination.
Thanks.
Jarrod

jarrodl wrote:I have been lurking here for years and just got around to getting my form 1 a few months ago. I saw a thread on here about threading titanium with a thread mill, but I need some pointers on doing it with a lathe. I am not very experienced with threading, especially inside threading, but I have successfully threaded some aluminum and stainless tube. I have a 12x24 bolton lathe with 1.5" thru hole. I want to thread 28 tpi. THe lowest speed it has is 75 rpm. I have a carbide threading tool. I dont currently have a flood cooling setup, but Im not against adding one if it is necessary. I have been spraying coolant or wd-40 from spray bottles or dripping magic tap on the material as I thread. I have found it easier to leave the half nuts engaged and stop the lathe and reverse it out of the cut than try to hit the mark every time.
Anyway. I would like to some tips on internal threading a tube. How deep should my passes be? Should I feed with the cross slide or 30* with the compound, or a combination.
Thanks.
Jarrod

Compound at 29.5 or 30, feed with it. If you're using carbide full profile tooling (or not) you can take light cuts at the end using the crossfeed. I run about 5 thou a pass at first with a cleanup pass every 3rd pass or so at first then every pass at the end. My tools might be springier than yours though. Depending on how tight things feel at the end I may go down to 1 or 2 thou per pass.

Nothing wrong with leaving the half nuts engaged but it isn't my preference to do so. I use dykem before I start and as the crest starts to thin down I start checking for fitment. Those last few passes can go from too tight to fit, to sloppy in a hurry if you're not taking cleanup passes.

One thing I would recommend is, if you haven't already cut your tube to length, practice on an end of the same tube you're going to cut off. There are more than a couple threaded "rings" laying around my shop that were trial runs on the titanium tube I eventually used.

So, 7 .005"(on the compound) passes with cleanup along the way? What about coolant? Thanks.

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im in the same boat as OP, i just bought a lathe and some titanium tube for a 300BLK silencer, also in 28TPI.

ive never machined titanium, mostly aluminum, some steel.

The lathe i bought is a sherline, and it is mandatory to cut threads by hand by attaching a handwheel to the spindle and leaving the motor off.

what is a cleanup pass? not advancing the cross slide and tracing back over the same cut twice?

fishman wrote:im in the same boat as OP, i just bought a lathe and some titanium tube for a 300BLK silencer, also in 28TPI.

ive never machined titanium, mostly aluminum, some steel.

The lathe i bought is a sherline, and it is mandatory to cut threads by hand by attaching a handwheel to the spindle and leaving the motor off.

what is a cleanup pass? not advancing the cross slide and tracing back over the same cut twice?

Yep!

jarrodl wrote:So, 7 .005"(on the compound) passes with cleanup along the way? What about coolant? Thanks.

Only time I bothered with coolant while in back gear is during cutoff. TI doesn't seem to tear real bad or anything. However I'm using the sharpest hss I can hone which at 70 rpm is likely to work better than carbide inserts.

I feel like I've been cheating, I have been using a LH carbide threading tool and running the lathe in reverse at around 350 rpm with just Mobil 760 cutting oil it's been working great. Its also awesome when threading up to an internal shoulder

ETA: .005 per pass for the first 5, a clean up pass then .002-.003 until the thread fits

I cut my threads in back gears ( low RPM ) and use a heavy cutting oil ( Ridged or Oatey from Lowe's or Home Depot).
I use flip tip carbide and when I am getting near my final size I make two passes at the same depth to clean cut the threads.

Stub up the tool and make your set up rigid as possible ( no deflection ).

For muzzle threads I like to cut a plug gauge at the pitch diameter desired and use it accordingly. Dry titanium threads will gall so always have some oil or lube on the mating parts when test fitting. If a part starts to gall when screwing together STOP and give it a shot of Kroil or PB Blaster or they may not come apart pretty.

partsguy22 wrote:I feel like I've been cheating, I have been using a LH carbide threading tool and running the lathe in reverse at around 350 rpm with just Mobil 760 cutting oil it's been working great. Its also awesome when threading up to an internal shoulder

ETA: .005 per pass for the first 5, a clean up pass then .002-.003 until the thread fits

I can't/ won't trust myself to watch the thread dial and hit the half nuts when running at normal speeds. I've tried. It's scary lol

I won't lie I usally make 2 or 3 practice passes before I start it is a bit nerve wracking the first couple of times

You could do it at a lower speed I have done it as slow as 45 rpm...It just takes FOREVER ,or so it seems

I have also noticed carbide seems to cut better (better surface finish) at higher speeds

0101silent wrote:When I cut inside threads I keep the lathe unplugged and turn the chuck by hand. I set the compound at 30 degrees and feed in a few thousandths at a time. I've never cut titanium but if you turn the chuck by hand you will probably only need cutting fluid. I doubt that you'll generate much heat. Like propeine said practice a few times before you start the final piece.

Do you turn the chuck itself or do you use a crank? I have tried this a few times turning the chuck and it doesn't seem to cut, rather things just get bound up until the work piece is pushed out of the chuck or the threading tip breaks. Any tips on getting it to work by hand?

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I'd be around 1500 rpm for the muzzle attacent threads and 600 rpm for the cap/tube threads on the turning center. I'd probably be at 300 rpm for everything on the manual because that's as fast as I can reliably engage the half nut.

For internal threads turn your compound 29.5-30 degrees to the left (opposite of how you would for external threads). Feed both your compound and cross feed in past your work. Feed them both our until you just touch your work. Zero out both dials. Feed in a bit with the cross. Scroll your carriage to the point where your threads will end. Put a sharpie mark where your wiper meets your front v-way. Scroll the carriage back out of your work and feed your cross back out to zero. Feed out your compound .005", start the lathe and engage the half nut on any number (depending on the thread pitch, you can use different numbers but I always pick one and stick with it). When your wiper reaches the sharpie mark, simultaneously disengage the half nut and indeed the cross. Scroll the carriage out of the work. Check the pitch of the scratch down your bore. If the pitch is correct, zero your cross and out feed your compound and additional .010" and repeat. Continue this until you get your depth.

I'd make the external parts first using a thread mic or three wire method to gauge the pitch diameter. Use the external threads to gauge the internal threads.

I'm sure there's some great YouTube videos showing internal threading.

0101silent wrote:When I cut inside threads I keep the lathe unplugged and turn the chuck by hand. I set the compound at 30 degrees and feed in a few thousandths at a time. I've never cut titanium but if you turn the chuck by hand you will probably only need cutting fluid. I doubt that you'll generate much heat. Like propeine said practice a few times before you start the final piece.

What lathe are you using?

I made a crank handle for my Atlas 618 and
have cut threads as you. The hand crank does
make life easier.*


E.g.,
*<< https://www.youtube.com/watch?v=XMUY6ip14sM >>

<< http://www.deansphotographica.com/machi ... crank.html >>

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propeine wrote:I can't/ won't trust myself to watch the thread dial and hit the half nuts when running at normal speeds. I've tried. It's scary lol

I tend to tap my foot to the dial rotation like I'm keeping time with the (non existent) music. Works every time.

Stan1 wrote:

propeine wrote:I can't/ won't trust myself to watch the thread dial and hit the half nuts when running at normal speeds. I've tried. It's scary lol

I tend to tap my foot to the dial rotation like I'm keeping time with the (non existent) music. Works every time.

That actually makes a lot ot sense. Auditory clues/rhythm is much easier to track than that damn dial. I'll give it a go on something non essential. Thanks stan

I imagine everyone does this, but the way I cut threads up to a shoulder or into a blind hole is to set up a stationary dial indicator in a magnetic mount so the point will touch the carriage, and set it so it has 4-5 full rotations until the end of the cut, with the needle ending up straight up at 0. It's super easy to watch the dial turn with your peripheral vision 1 2 3 4 5 rotations-unlock-the-half-nuts-back-off-the-tool. You can cut at a decent speed and still hit the stop +-.002-.003 thou every time. Start the engagement far enough away from the work so in the rare case you don't tap your foot in time and catch the number perfectly so you have time to unlock and try again. Rhythm baby .

I feel for you guys, turning your lathe by hand. That's pretty rough.
I just practiced, practiced, practiced, until I felt confident enough to do it on a real part.
My lathe goes down to 55rpm.
I now thread at about 220rpm.
You have to give yourself some credit and go for it.

A trick that I learned for hitting the mark to engage the half nut is to keep back from the part quite a ways. When the mark gets close, lock the nut. If you missed, then you have room to open it up, back off a bit and try again. Once you get it right, allow the cut to be made, you just have to wait a bit longer for the tool to approach and engage the part.

bakerjw wrote:A trick that I learned for hitting the mark to engage the half nut is to keep back from the part quite a ways. When the mark gets close, lock the nut. If you missed, then you have room to open it up, back off a bit and try again. Once you get it right, allow the cut to be made, you just have to wait a bit longer for the tool to approach and engage the part.

This is what I do when threading at speed.

I like a 10-15% cobalt HSS that is very sharp.Lots of coolent to save my tooling edge.Lite passes with lots of cleanup cuts.I have carbide tooling but the usage cost is very high with smaller lathes.A little vibration and poof the edge is gone.
I have total confidence in my machines and ability.I will thread to a inside shoulder without a thread relief cut at high speed.Not recommended for those weak in heart.
This is a very fine inside threading tool:

I''ve only threaded one or two parts in titanium (Grade 2) with carbide tooling but they came out perfect on the first try. I don't do the 30° nonsense, just feed straight in. Speed is appr 100rpm with foot brake and locked half nuts.