Acme thread - chatter in base of cut

I rarely cut steel without some type of cutting fluid or oil- it nearly always makes things go easier, gives a better finish and makes your tool last longer as well
 
Double check your gibs on the cross-slide and compound. If the cross-slide has a lock be sure it's tight. Also do you have much backlash in the cross and compound feed screws and nuts. If you do after you move in, reverse the screw until it takes out the back-lash. It's a pain. Or buy a new screw and nuts.

I leave the compound gib a bit tight too.
 
Hey! I'm in your backyard.

One thing that can really help when cutting is to make sure you have tailstock support. I ALSO have better luck cutting with HSS instead of Carbide, (though I grind my own on the surface grinder), and ALWAYS run pretty slow when cutting threads.

Then, as Richard says, make sure your lathe is pretty tight. Acme has pretty serious tool pressure compared to 60 degree threads, so you're always going to be fighting SOME resistance. That said, I've done 4 TPI threads (though in mild steel) with little problems.
 
Progress: Thank you all. I slowed the RPM to 180 and started the cuts at 2 1/2 thou and am finishing at 1 1/2 to 2 thou plus adding cutting oil. Even with these small feeds there is smoke and hefty material removed near the bottom I am currently 35 thou in and plan to finish at about 50 thou. Slow and steady with light cuts seem to be the trick.
 
I would put the tool on center. It’s probably rubbing more than cutting. I really like the full profile threading inserts.
 
You are doing better than me, I thread at about 60 RPM...........
 
Oil in a normal oil cn and just give it a squirt as it goes.

Put it in back gear and go as slow as it can.

No need for speed, going slow you can keep it cool and better see what is going on.

Lots easier to stop at end of cut.

Sent from my SM-G781V using Tapatalk
 
Jim F said:
You are doing better than me, I thread at about 60 RPM...........
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Me too. Usually as slow as I can get my lathe to go. For my lathe that is 100 RPM. At 4 TPI, that is moving pretty quick. Need to halve that speed to be comfortable. Takes a ton of attention to stop in the too short thread gutter!
 
Minimise the amount the tool is sticking out of the toolholder & have the compound slide retracted to bring the toolpost over the cross slide. These will help with rigidity.
p.s. the thread is not 10 pitch it is 10 tpi or 0.1 pitch.
 
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