Full disclosure - away from home and with the wife, so (a) bored not being able to tinker and (b) unable to check the machine to see what I have...

Anyway.

I'm converting a Myford ML7 to CNC operation, and got as far as glaring at the original single phase AC motor with the pulley reduction and 3-position cone pulley gear reduction system and wondering, in the case of automated speed control that I must be able to do something better. "Better" starts with removing the single-phase AC motor and buying something else to go in its place.

Basic numbers, original motor somewhere around 1/2 HP, 1450 rpm. The existing belt gearing taking this to around 200-700rpm, depending on belt position on the cone assy. Ideally I'd like to up the rpm a tadge to around 1000rpm max (it's a build option with a different spindle motor pulley choice).

Also, I'd like options where I don't have to fiddle (and crush fingers) with belt changing on the cone assy. LinuxCNC/Mesa look to support both 0-10V and step/dir options for spindle control. Of course in an ideal world I'd like to have the option of managing constant surface speed through the control software. Somewhere in the mix is a spindle encoder.

So, it feels like I probably want something capable of driving 0-3000rpm, with constant power (more torque at lower speed) - to a sensible limit of course (I do have the back gear option for heavy cutting/threading).

In the past my experience is largely around the Chinese water cooled spindles, but these are far too high revving with poor performance below 1/3rd rated speed. A general eBay trawl shows a form/fit/function replacement of 4 pole 3-phase motors with VFDs, but I'm a little concerned that these will have similar poor performance at 1/3 rated speeds - necessitating the use of the cone pulleys.

Is there something better that I should be looking at? I know I can get a stepper with a similar electrical power rating but conventional wisdom seems to be that these are poor choices for a lathe spindle drive (even though I'd be going through several feet of rubber drive belts). Are servos better? (and the whole murky world of servos is something that I've never delved into).

Cost is a (not major) consideration - though not a Yorkshireman I like to think growing up in Lancashire that I share some of our cousin's frugal nature. Shiny is not a consideration (I don't need to buy new if it works). I get a bit sweaty thinking beyond around £300 for a replacement.