whats wrong with my thread/screwcutting

I'm confused by the reference to it being a metric thread. If the manufacturer say it is 3/8"x24 that is a standard imperial size, known as 3/8" UNF.

If you are converting it to metric because your lathe can only cut metric pitches, then its a different problem and easies would be to cut thread with a die.

Ian

Hi
It could be 10 x 1mm pitch witch is close to 1/8 bsp We used 1/8 bsp for water plugs on plastic moulds Until metric Now 10 x 1 mm fine not to be confused with M10 .
Nobby

And if it is a UNF thread or you opt for metric then you want a 60degree tool not 55degree and offset the topslide accordingly.

J

My late father taught me when screw cutting a standard thread to stop when nearly to the correct depth of thread and to finish it with a die or a dienut. This technique gives a finished thread to size and the correct thread form. Obviosly this cannot be done with a non-standard thread.

My screw cutting tips are; to make sure the tool has the correct clearance angles to take account of the thread helix, set it dead on centre height and square to the job when using the straight-in method. Use a screw cutting template to get this right.

Always cut a run-out groove to the correct thread depth using a parting tool. If possible on small diameter work use tailstock support.

To get screw cutting down to a fine art practice, practice and practice!

You would be best to find a 3/8" UNF bolt and try that in the hole, either regrind, or get a 60* tool, and go straight in, You don't need to go in side ways with 3/8", I'v done dozens of them, your last two or three cuts should be done at the same depth , just skimming the last few tenths of a thou off. Ian S C