What am I doing wrong?

[Mitch Alsup]

29.5º from 90º is 60.5º not 59.5º

 

[matzo]

If you want to use the compound then it should be feeding at the same angle, to the centerline of the work, as one half of the thread angle. Different machine makers put their degree scales with the angle reading either from the centerline or off perpendicular to the centerline (ex; 30 degrees either side of perpendicular. Dave Pane shows a sure fire way to make sure your set up at the correct angle.

I have the compound removed from my lathe and the QCTP mounted direct to the cross slide to increase rigidity this means I must cut threads by feeding the cross slide. With a good sharp tool this presents no issues and I actually find I get better threads with the set up I have. Cross slide seems to be the weak link on a lot of lathes.

I cant see the insert tool you have close enough to tell so forgive me for asking, is that a specific threading insert or a standard 60* insert?

The tool that I took the picture with is a standard 60* tool, I am actually using a Mesa Tools threading tool with a carbide insert. After I reset the compound with the jig that Dave Pane showed it cut a nice 60* thread.
Thanks for the help.

 

[matzo]

The tool that I took the picture with is a standard 60* tool, I am actually using a Mesa Tools threading tool with a carbide insert. After I reset the compound with the jig that Dave Pane showed it cut a nice 60* thread.
Thanks for the help.

Just curious,should you not use a standard 60* insert tool to cut threads?

 

[Asm109]

If you are talking about the equilateral triangle inserts, they will work but you cannot thread close to a shoulder with them.

 

[Dave Paine]

Just curious,should you not use a standard 60* insert tool to cut threads?

I have an HSS threading tool and a couple of carbide inserts, one is partial profile and one is full profile. Both cut 60 deg threads.

For fine threads I may use a plunge cut with the carriage, e.g., 1/4x20 tpi. I also need to cut coarse threads like 1 1/4in x 8pi for wood lathe spindle threads. I use single point so using the compound at 29.5 deg. I prefer a partial profile insert for this cut since some of the full profile inserts are not deep enough for this thread. Check your insert for the maximum TPI it is designed to cut.

 

[matzo]

If you are talking about the equilateral triangle inserts, they will work but you cannot thread close to a shoulder with them.

Is there some secret to getting clean cuts? My lathe recommends 125 RPM and lubricant. They turn out decent but require some clean up with a wire brush and file. I am not taking deep cuts.

 

[Technical Ted]

In my experience, I get the best results using a nice, sharp HSS tool and use a good quality cutting oil. Others may have had different experiences, but when I used carbide to thread I found I needed to run at a high surface speed to get good results.

With HSS I've found you can run things slowly and still get good results, so that really helps when threading up to a shoulder.

YMMV,
Ted

 

[BGHansen]

Not adding anything, but from your first photo it looks like you're at 60 deg. On my G0709 lathe I set the compound to just a shade past 60 degrees to get what is conventionally called 29.5 deg. The gauge idea above is great. Your compound should be advancing on the angle of the right hand side of the cutter (at 30 deg.).

Bruce

 

[mikey]

Is there some secret to getting clean cuts?

Can you grind an accurate 60 degree HSS tool? If so, try a 15 degree relief angle on both sides and stone a 1/64" flat at the nose. Hone both sides and the top accurately. Use sulfur-bearing cutting oil (thread cutting oil from your local hardware store works) as a lube. Thread cutting is a high-pressure operation and sulfur-bearing oils work well for this. As Ted said, it is very difficult to beat the finish produced by a really sharp HSS tool, especially one that is ground with increased relief angles to reduce tangential cutting forces.

 

[TakeDeadAim]

60 degree "Thread cutting" inserts are specific to that purpose. As I said I can't see the photo clear enough to tell if this is a threading insert or a 60 degree turning insert.

Sorry I did not read down to the end, the Mesa thread tool and insert should work fine.