Chatter Marks on Single Point Threads

[Bob Korves]

I will have to check out the gear train to the lead screw on my Chinese 13x40 lathe. I know I have changed speeds while threading before, multiple times, but did not have a problem. I don't suppose my luck could be that good, but it is still worth checking. The more we understand the details of how our machines work, the better.

 

[MSD0]

Tool is not dull, however it is of course possible that the insert geometry isn't good for what I'm doing.

What would you consider an acceptable depth of cut? I usually do .002" radial DOC on steel and .004 on aluminum. Pure radial feed.

Have you tried infeeding with the compound set to 29.5° (Slightly less than half the thread angle)?

 

[kd4gij]

First are you using taping fluid? Second I start at .030 dia. .015 rad. in steal, and .040 dia. in softer metals.

 

[Paul in OKC]

I am also a cross slide only threader for 90% of my threading. Deep threads, like 8tpi, Sometimes I will use the compound. One thing I haven’t seen asked is diameter of bar and how much is it sticking out of the tool post?

 

[tertiaryjim]

I don't see that you mentioned what lathe you have. Most of the china and many of the taiwan machines were poorly fit.
This allow'es Flex of the cross slide and compound and can cause your problem even with everything locked down tight.

 

[MSD0]

I was doing some M6-1.0 threads last week and decided to try running the lathe in reverse with the tool inverted (so I could tread away from a shoulder) and the threads came out much nicer than normal.

 

[MarkM]

I ll throw a few things out there. Set your compound less than thirty degrees and more than twenty nine. Somewhere in between is fine to keep just your leading edge only cutting. Try high speed steel with some rake added. Your speed in my opinion is too low for inserted carbide. If you want to use them run it three times your speed in reverse with the tool upside down heading toward the tailstock. I ve seen similar looking threads from single phase lathes at low rpm. Not all but have seen some solved by rubber mounting the motor or going three phase. It very well may be harmonics.

 

[BaronJ]

Hi Guys,

This is a 4-48 thread that I did a little while ago !

Here I'm just setting the threading tool to clear the work.


The finished article after parting off.

 

[mickri]

I am having this same problem. Ugly threads. I use a HSS cutter. I run the lathe at the slowest speed, 28 rpm, and take light cuts. The compound is at 29.5 as best as I can eyeball it. I use a craftsman threading tool for external threads.



and this boring bar for internal threads which I also believe is craftsman.

 

[NortonDommi]

Do you get the problem regardless of what material you are turning? I get some truly horrible looking threads in low Carbon steel,(the sticky stuff), but find a couple of runs over at the final setting has them looking almost polished. Time consuming but worth it. No problems with medium of high Carbon.