Improving single point thread quality?

ErichKeane said:
You CAN buy HSS insert tooling, which I hear good things about (@davidpbest can probably give you the best hints as our resident insert guy!), OR you can buy pre-ground HSS tooling that is pretty darn good, and probably just needs dressing every once in a while.
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When I need to thread slowly, I use an indexable “On Edge” threading tool (yours is the “Lay Down“ type), and HSS inserts from AR Warner. Here is a link to one version of that tool, and the HSS inserts that go with it.

www.arwarnerco.com

Kit #18 1/2 inch Threader NV

www.arwarnerco.com
 
I would practice with what you have rather than running out and replacing your threading tools. You lathe should be rigid enough to just use the cross slide so you do not have any issues with threading angles. I have been using laydown (Carmex A16ER or IR AG60 which has a wider pitch range of 8-48) with good results in a wide range of materials. When using the cross slide I zero the dial when the tip just touches the OD, then advance it 0.01" per pass until close to target, then take the last pass at target and then a spring pass. I use to thread at around 120 RPM in steel, but now thread on upwards of 300+ RPM in steel and 500-600 RPM softer metals since I do not need to worry about the stopping position. On edge HSS may work better at lower SFM's, I previously used on edge TPMC/TNMC used years ago, they were horrible and constantly broke. Switching to the Carmex lay down I am still on the same insert after years of use.

If I am doing a deeper thread pitch then I will be more aggressive on my first passes.

Example of threading passes:
 

Attachments

  • Threading Tool Speeds & Feeds.pdf
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Look up "thread relief" and try to incorporate one whenever possible.
 
I use the same technique Mark (@mksj) does, but of course I have a proximity stop system like he demonstrates - it really takes the pucker factor out of threading to a shoulder. If you're nervous about cutting to a shoulder, having a thread relief landing zone is helpful, and will ensure you aren't stopping a carbide cutter "in the groove" which will often fracture the insert. Also, if you're worried about overshooting and don't have a proximity stop, you can always employ a carriage stop. And like Mark, I prefer the laydown inserts like you have been using, and I don't advance the cut with the compound angled, but instead drive in perpendicular to the spindle axis on successive cuts using the cross slide. But there have been situations with 304 where the OnEdge type with HSS inserts makes a cleaner cut because it has less tendency to work harden the material. With stainless, once the work hardens, getting a decent thread cut on successive passes is challenging - often the threads tear and leave a nasty finish.
 
Other than an ELS or a CNC lathe , you could go with a trav-a-dial on a lathe to aid in threading . Easy to watch a dial or indicator vs. a DRO . After years or doing it for awhile , you'll get comfortable and you won't even think about threading into a relief . You'll just do it . :) Thread looks alot better now btw .
 
As I have stated ever so many times, I was taught to set the compound at 30 degrees off the cross feed center line, and when I went to work everyone in the shop (with 7 lathes) set the compound at 30 degrees, all competent journeyman machinists, Rather than black oil, I use TapMagic, as it promotes free cutting more than black sulphurized oil, and makes observing the threading operation easier, and I agree that 100 RPM may be too slow, carbide does not like slow cutting speeds. Personally, I would be using HSS; I use the form ground Aloris threading tools.
 
benmychree said:
set the compound at 30 degrees off the cross feed center line
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As a person who's read that ever so many times, I can verify that it's not as clear as one might imagine..to everyone. Lol
OP I think that solved your problem, yeah? Looks good from here!
 
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