Bob, I bought an Alexander so years ago now, and after consideration went for the replacement motor route plus a VFD. Installing the new motor was not much work to be honest, the motor is smaller, so just make a new base plate for it, and you will need a new pulley and belt. The coolant runs from a gear pump, so you should be OK.

Chris Gunn

It is possible to buy VFDs that take 230v single phase as input and give 415v three phase as output. In the UK, Drives Direct sell them.

Overseas sellers, available via Amazon, eBay and other sites also sell this device at a more reasonable price. Look for AT4 in the description.

There is discussion of one here:

https://www.model-engineer.co.uk/forums/postings.asp?th=163844

Doing the above is equivalent to option 1a in your list.

You would have to do a little work on the electrical side of the machine: reconfigure switching on the machine to be part of the low voltage control circuit of the VFD and put some sort of interlock in place so that you cannot change the motor speed when the VFD's output is active.

The original motor is probably a Dahlander connected motor (Google it) and will be very difficult to connect to a 220 volt output VFD as you can't simply connect it in delta as you would with a single speed motor. If you need the two speeds the easiest way would be to do this with pulleys.

This then gives you a choice of using a single phase motor or a suitable 3 phase motor and a VFD (if you want the luxury of variable speed) .

Bob, I cannot remember, but I will have a look in the morning. The whole package came from Newton Tesla, and no issues at all. I was told at the time the 2 speed motor would not run with a phase converter, and being 440 v not a VFD available then either. I took the next best option for me, I failed Principles of Electricity back in the day, so faffing about with the existing motor was not an option for me.

Chris Gunn

Bob, I had a look for my motor plate, but sods law it was on the wrong side for me to get at, or even take a pic. However the inverter in the panel is a Mitsubishi E500, with a max motor size of 1.5KW. I hope this helps a bit.

There is no reason why you could not fit a single speed motor and stepped pulleys to give some extra speeds, but bear in mind the original has a 2 speed motor which doubles the motor speed, you would need the high speed if you have the low speed head driven from the main motor. I do not think you could easily double motor speed using double pulleys. You will need to release the belt tension and reapply it when changing speed, so you will need access to do that. You will still have the gearbox as well. It depends what you will be doing as well, using small end mills will need higher speeds than horizontal milling for example. You could work out the various speeds using the motor of your choice and the various gears and how this would compare with what you want to do, and go from there.

Chris Gunn