Yes, I was thinking something like this. Although to be fair a 1:1 ratio with that motor is going to be more than enough for threading most things. I don't like too much the idea of having a slow inductive sensor bypassing a encoder. On the other side, having a sensor on the spindle is safer in case the belt fails. I think the optimal would be to attach the spindle sensor to the index-enable signal with an AND in HAL, and getting it mechanically syncronized with the encoder index. This way, no matter if the ratio is 1:2, 1:1 or 2:1, it will read the encoder signal in the right moment, once per revolution.
I know that a induction motor wiht a VFD will be way cheaper and easier to setup, but is not about money. To be fair, the original BLDC 1.5kW motor is better than a induction one, plus a similar power one will not fit on the space my lathe has. I don't like the drive because it has pre-programmed some really slow acceleration and deceleration ramps. The drive lacks any kind of documentation so I'm stuck with this parameters. I could also replace the drive, I could probably even use a servo drive to run the motor, but I don't have the time to do experiments.
The 3.8kW servo happens to be the biggest motor I can install without any mayor modification. To be fair, the thing that stops me more is the lazyness of having to deal with making the pulleys. If I happen to deal with it, I want to have provisions for further improvements: spindle brake, pneumatic collet closer and maybe even a worm gear.
