Thread cutting, making your own sizes?

[Pete.]

Can't

Wouldn't want the bill for it if you could! I read someplace that early DSG's had no interlock.

 

[graffian]

As others have said, you're probably working somewhere between the two. Full profile tools give exactly the right radius at the root (and the crest, but that's irrelevant for the table on my website) of the thread. Sharp tipped tools are really only for very fine pitch thread: for example I've never had confidence in grinding the right radius on a tool for cutting 0.4 mm pitch threads, so I just use a sharp tip there.

If you're using a partial profile insert tool or a home-ground tool with some arbitrary radius, then the in-feed distance will depend on that radius. Having said that, it'll be somewhere between the two values (full profile and sharp tip) shown in the tables on my website.

I've added an explanatory note on the page to help future visitors.

I always put some radius on tools. I don't grind them as there is so little metal to remnove, I use a stone or a diamond lap.
You need a radius, with a pointed tool the tip will either chip or wear away.
It's doesn't have to be the right radius but the flanks of the tool need to touch the sides of the V, so you want the nose to touch if you poke the tool into a thread or gauge.