Spindle feedback - how did encoder attach?

I'm looking towards the future and thinking seriously about getting myself a VFD so I can have a closed loop to my spindle for tapping and precise speed control.

My mill is a Lagun FTV-3 with a varispeed head, 3 HP. It has a backgear with a manual shift lever and when shifted into backgear, the spindle runs the opposite direction as when its in high gear.

I'm curious how those of you with a varispeed head have coupled your encoder to the spindle, firstly, and secondly how you set up the HAL so computer knows when to run the motor forward and reverse in order to do different operations. A lot of what I've been doing lately has involved drilling some bigger holes and speed is way too fast, even when the varispeed head is cranked all the way down. I know a VFD can drop that speed by 50% or more but I'm also under the impression that torque drops off quickly past a certain point and the varispeed belt robs a fair bit of power getting it to the spindle.

On the opposite side, if you need the spindle to go fast enough can LinuxCNC be set up to warn you that you are brushing up against the max you've specified in the VFD and its a good idea to run up the ratio in the varispeed to acheive your desired RPM, or how does that work?

greenbuggy wrote:

I

I'm curious how those of you with a varispeed head have coupled your encoder to the spindle

There's no easy way to put an encoder in a Bridgeport head without blocking the drawbar.
So, I made the bull gear into an encoder wheel. See
pico-systems.com/bridge_spindle.html

This is on a Bridgeport 1J head, where the bull gear stays put, axially. On the 2J
head, the bull gear goes up and down to select direct drive or back gear. That
is a slight complication in getting the sensors in the right place. Hopefully
your Lagun is not made that way.

Jon

Big John - What are the specs on that encoder?