"john" wrote in message
...
snip-




That won't work-----not even close. The helix angle is wrong, so you
won't
achieve the lead you require,

The lead and the helix angle are two separate items. The lead is .25 on
a four start 1/4 20 screw. The lead is determined by what you set your
lathe to cut at.

and even if you could, the teeth wouldn't have
proper clearance.

If you have any skill in tool grinding you can increase the relief
without touching the front profile of the four teeth to accomodate the
increased helix angle caused by the larger lead. The front profile of
the four teeth doesnt change for a four start thread.

I'd have to see that to believe it, and I've ground one hell of a lot of
tools by hand, including complex form tools for gear teeth and other
critical applications. I've been hand grinding toolbits since the early
50's, many of those year in commercial shops, including running my own for
16 years. As you might surmise, I'm no stranger to the cutter grinder nor
to threads, which I mastered long ago, and to mil specs.

Yes, I agree----in principle, the helix angle could be altered, but doing it
without a cutter grinder, or even better, a thread grinder, your chance of
success is small. Backing off each tooth exactly to the cutting line
without altering it is a tall order. I'm calling BS on your concept
unless you include specific grinding equipment.

Harold