Configuration for G0709 in ASW8 with iSV57T-180 servo

[johnsonm]

⚠️ Not intended for merge! ⚠️

⚠️ This PR is just to make my configuration available for others with the same lathe ⚠️

I have mounted my iSV57T-180 servo on the existing banjo, with an 11-tooth 1.5 module gear printed in PETG driving the 66-tooth change gear, and the lathe transmission in ASW8 mode. This mode drives both the feed bar and lead screw.

I have characterized the gearbox of the G0709 lathe and used that to create a working configuration.

It is probably a bad idea to drive this lathe with a servo, because with any transmission selection that drives both the feed bar and lead screw, it will be unlikely that you will end up with an integer number of steps per lead screw revolution. Using a servo with a configurable number of steps per rotation, like the iSV57T-180, will let you be precise.

Because the G0709 has separate X and Z feed rates, this configuration has true Z feed; X feed is approximately 1/4 of the Z feed. See #253

This branch includes:

• Thread to shoulder, custom thread, multi-start threads (and menu to use). #232 @kwackers marvelous thread-to-shoulder, position, and thread table
• Add optional config for more thread specs, default thread/feed on start #255 which enables all the threads that the G0709 comes with "out of the box" except for Modules and diametral pitches #267 diametrical and module pitches for worms (use custom threads and multiply by pi instead?)
• Configuration including comments describing how to select different transmission settings. Note that if you use more aggressive transmission settings, you will need a more powerful servo.

⚠️ Not intended for merge! ⚠️