Threading help

[plodder]

With 2 Form 1s in hand, it is time for the moment of truth between me and my trusty little Smithy 3 in one. I have run some practice threads on 6061 aluminum with mixed results, some pretty, some not so much. Here is the situation:
1. I am using 6061 aluminum for a .22 tube end cap, 416 stainless for a .300BLK tube end cap.
2. I plan to use American Standard Unified Thread, 24tpi.
(my Machinery's Handbook reports depth of sharp threads at .03608, depth of Internal threads .02255)
3. I plan to use a 60 degree straight carbide tipped bit for the external threads & a yet to be devised and ground 60 degree boring/threading bar for the internal threads.
(all of these plans subject to change via the input of you wise ones)

Questions:
1. How deep to cut the internal & external threads?...same for both aluminum and stainless?
2. Should I try to cut the threads completely in 1 pass, or take shallower multiple cuts?....same for both aluminum and stainless?

[BCJ]

I cut my threads .003 to .005 per pass depending on material. Cut your external threaded cap first and then use that as a thread gauge when cutting your internal threads.

[noscoe30]

If you use full profile inserts, that is all taken care of for you. You just cut until your major (or minor) is within tolerance.

The cost might be a bit steep for a diyer to get into but the finished result is incredible.

Also, you really need the higher SFM on aluminum and steel to get nice threads. Not sure if a manual lathe/operator is up to it. I thread 1/2-28 at 2000 rpm on steel fwiw.

[curtistactical]

I am not sure the steps you are taking to cut threads so here is a quick rundown. First set your tool post cross slide on 30 degrees and set the dial to zero, second touch off on the diameter and set the dial on your cross slide to zero. You will always return your cross slide to zero after each pass, you can back the cross slide out to return your tool then just crank it back to zero, you want to feed in with the tool post cross slide on 30 degrees so you are cutting with the front of the tool all the time, your finish will look much better. Start out with a .005 cut for the first pass then go .002/.003 a pass after that, as you get close to finish size take some free cuts without moving in to spring cut the thread, on 24tpi you will move the dial in a total of .030/.035 radially (.06/.07 diametrically) on 30 degrees to get the correct thread depth. One other trick is always start the threading dial on the same number not just even or odd this will cut a more accurate thread.

[CMV]

Posted this a few times but here is an economical tool that does both internal & external threads:

http://www.mesatool.com/products/threading-tools/

I use the 1/2" one on a BXA toolpost (middle one, left column). Cuts nice threads & the inserts last a long time unless you crash the tool. Comes with 2 inserts, each with 2 cutting faces.

When I was learning & practicing threading I found layout fluid (Dykem) very helpful. Esp with finer pitch threads, it makes it a lot easier to see what's going on with each pass & you see you're at the right depth when there is just a hairline of blue left on the crown - I had a real hard time trusting the dials (still do somewhat - I'd suck flying IFR). Go at 50 or 60 RPM - whatever your slowest speed is. You can cut your entire thread at that speed and then take a final spring pass or two at a higher speed and get the same surface finish as cutting the entire way at higher speed. For the Al you will probably be happy without a higher speed spring pass to finish. For the stainless, you will probably need two higher speed spring passes (I always do at least) but nothing insane - 220-300rpm should suffice. Anyway, if you're like I was, it will take a lot of practice to get comfortable threading at higher speeds.

For Al I just use WD40 as a lubricant. For anything else, I use a mix of tap magic & anti-seize & apply with an acid brush. Messy, but works well. You can't use the layout fluid method with the antiseize+cutting fluid mix.

Lastly, consider 7075 Al in place of 6061. Costs a little more but still inexpensive compared to a lot of material. Much stronger and machines even easier. Definitely use 6061 (or CRS) for practice, fixtures, sacrificial stuff, etc.

[Bendersquint]

If you use full profile inserts, that is all taken care of for you. You just cut until your major (or minor) is within tolerance.

The cost might be a bit steep for a diyer to get into but the finished result is incredible.

Also, you really need the higher SFM on aluminum and steel to get nice threads. Not sure if a manual lathe/operator is up to it. I thread 1/2-28 at 2000 rpm on steel fwiw.

I daily thread everything from aluminum to titanium to stainless and run from 200-500rpm and get perfect threads everytime.

You don't need speed just a nice rigid setup and quality inserts.

[cal50]

If you try to cut threads in one pass you will not have any threads....

I like running slow rpm ( back gears) and light cuts / multiple passes. If you are using a carbide tool or insert be sure to stop your threading pass the same each pass. Nothing worse than letting the tool travel past your cut threads into heavy material and chip your insert. Slow spindle speeds are easier to control the tool and retraction unless you have a thread relief.

[Historian]

I found that for specially small and delicate pieces
I thread by hand cranking the spindle of my antique
Atlas 618 lathe.

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

<< http://www.bedroom-workshop.com/tools-l ... crank.html >>

<< http://www.toolsandmods.com/docs/ralph_ ... rank_3.pdf >>

I find that at the end of each cut I can crank back the tool, crank in reverse direction,
feed in, and crank again.

Ultimate control for an eternally primitive amateur. But satisfying.