Re: Electronic Lead Screw Drive Article ? | Threading Ratios ?

This PLL circuit fixes the speed of the lead screw to some ratio of
the the spindle speed. The circuit as it stands has a fixed "table"
of ratios, but it seems to me - with microprocessor control - any
ratio between spindle and leadscrew speeds is possible, so this
circuit could cut any metric or English threads - even non-standard
threads.

The problem of releasing the half nuts and traversing back manually to
pick up the thread would still remain, but the half-nuts need not be
released - the traverse direction can simply be reversed...

Am I missing something ?

> >I have an old SB lathe with manual change gears.
> >
> >I was thinking something like this would be a way to just add variable
> >speed to the spindle and also add electronic thread cutting.
> >
> I don;t think this device, as it stands, would be useful for Imperial
> threading.
> It was aimed at standard metric threads, where a very limited number
> of ratios will suffice. It could probably be expanded on to give most
> of the standard imperial threads. But, 11, 13 and 27 would be a
> problem, for sure. I'm not sure it actually has a limitation to
> even ratios, but I thought it might.
>
> Also, I'm not sure what happens if you stop the spindle, or open the
> halfnuts and have to move the carriage. I guess that would be the same
> problem as with standard threading gear systems, you have to sync the
> carriage to the leadscrew with the threading dial, and the thread pitch
> determines which marks you can use.
>
> Jon