Radial Screwcutting

[ovenpaa]

A question for those that use lathes here.

I do a fair amount of screw cutting, it goes with the job and for the most I am cutting 60 degree threads (Metric SAE etc) so I have my compound slide set at around 29,5 degrees, this means as I increment the slide the cut is made on the forward face so reducing the load on the tool and also reducing the chance of chatter plus it allows the chips to clear however I am usually taking relatively small cuts with quite hefty tool holders and tools so chatter is not going to happen plus I use a flood coolant so chips are washed away. This is the way I was taught so this is the way it is.

Just recently a couple of gunsmiths have mentioned they screw cut radially that is the compound slide is set to 90 degrees and the cut is made uniformly across the thread instead of the leading edge. OK I thought, well at least it saves returning the cross slide to zero and then taking the cut, then I promptly disregarded it. That is until tonight when I read an article on radial screw cutting which has set me thinking about it again.

I have some lumps of barrel so it is easily tested however I did wonder if anyone else has tried it?

[Jame5m]

There's really no need for all that angled cross slide stuff with today's modern inserts,

I haven't used that technique since the 2nd year of my apprenticeship! For example...

1/2 unf, turn the bar to 12.8 keep feed in witht eh correct insert till the bar measures 12.7 /.75 and test, the modern inserts create nice formed thread geometry, superb finishes and it's very hard to get it wrong!

[ovenpaa]

Thanks James, guess I am a little behind the times in that respect. I will run a couple of test pieces before the next job. I must admit the finish with the new inserts is absolutely spot on and I would never consider using anything else these days.

[Jame5m]

Most I've ever had to do was push a chunk of wood on the thread while its in the lathe to knock off a galling on some really low quality Latvian steel!

[Tony-c]

main threads I cut are 20 28 and 36 tpi

all done at 90 degree, rocol flooding it, but like you I take light cuts, the lathe is a big unit with large tool holder and post etc, so no chance of chatter

[ovenpaa]

Hmm... Many thanks all, I am warming to the idea and will give it a try this afternoon. So an old dog can learn new tricks