Alexander Milling Machine

I am in the very early stages of thinking about refurbishing an Alexander Milling machine which has been virtually unused for about 30 years. I don't think there is very much wrong with it apart from needing a good strip down and clean. Before I do though I want to be sure that I will be able to run it. I only have a single phase supply but the machine has its original 2hp two speed three phase motor which is physically enormous.

I think I have three options

1) Get a rotary 3 phase convertor. These are very expensive and would it be sensible to get one when I am not even certain the original motor is OK.

2) Replace the motor with a new 3 phase motor and a VFD. This would be much cheaper but installing the new motor would require a bit of work.

3) Replace the motor with a single phase motor. This is the cheapest option but I would lose the 2 speed facility and I would still have to do work to fit it.

I would love to hear people views.

Bob

I would try using the existing motor with s VFD, you might be pleasantly surprised.

There are tales of old motors not being amenable to VFD's but as long as it can be connected for 240V operation you have little to lose.

Ian P

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

Hi Ian & Chris,

Thanks for your thoughts. From what I have read it is very hard and probably beyond my skills to convert the existing motor to 240v.

Chris - can you remember what power of replacement motor you used? I was wondering if I should go for a bit more than 2hp.

Bob

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.

I have actually done what you are contemplating on my FN22 milling machine (a clone of the Deckel just like your Alexander is). It's rather a forbidding prospect and since I'm still in the rebuild process I cannot tell you how successful it has been except to say that the motor does actually run.

**link**

I am fully expecting sooner or later to have to exchange the motor for a modern one but the challenge of re-configuring the original was too great to pass up.

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) .

My Alexander is fitted with a 1HP single phase motor in place of the massive original 2 speed one.

I have never had any problems with it being under powered for the model engineering work that I use it for.
My machine also has the original 3 phase High Speed Head with it, so I run that on an inverter. The main motor more often than not is just running to provide the table feeds, whilst milling with the high speed head.
I do use the geared vertical head from time to time when I need the slower speeds for heavier cuts.

The Alexander is a fantastic machine for its size, with a bit of ingenuity there is not much you cannot do with it.

Phil

Edited By Phil P on 03/01/2023 21:53:02

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

Until I saw the post from Phil, I hadn't really thought that fitting a single speed motor was a viable option, although I only have the geared vertical head.

I wonder if it would be possible to fit a a pair of stepped pulleys so I could change the speed by moving the belt.

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

Bob

I forgot to mention that mine does indeed have a pair of stepped pulleys, however I cannot remember ever changing over to the faster ratio, it lives in low gear all the time.

You can just about make out the pulleys in this shot of it set up for gear shaping.

Hi All,

I only joined this forum a couple of days ago and I am really pleased about the interest and advice I have received already. I think I have concluded that I shall go down the new motor/VFD route as it will give me the most flexibility.

Now that you have given me confidence that I will be able to successfully re-power the machine. I am going to very slowly strip it down and clean it up. If I end up with a machine looking like Phil's above I will be very pleased.

Firstly though I need to buy lots of cake so that I can bribe some friends to help me move the machine into the middle of my garage/workshop. I am sure that my wife will not mind squeezing past it to get to the freezer!

Bob

I would try and rig up some lifting device to help with dismantling, the parts are very heavy.

I have a lifting frame over the machine all the time for removing heads and tables etc.

Phil

Phil

That is a good suggestion. Is the blue strut in the corner of your photo part of your lifting frame?

Bob

The easy way to do this would be to ask for the following when specifying the new motor and controller package:

• "I would like a [Number of poles in "slow" motor] Pole, 20-400hz rated, 3-phase motor with a [old motor frame size number] mount and a compatible inverter to be power it from a single phase 240v supply. The whole package should be rated to deliver [power output of the existing motor] kW when running at 100Hz".

It's now usually an inexpensive optional extra for motors to come rated for running at frequencies other than the normal line frequency of 50Hz, and this is generally how one would achieve dual (or multiple) set speeds from a motor in a modern industrial design.

​

I'm not a big fan of removing working motors from machines just to add a VFDs... However replacing dual-speed motors is one of the scenarios where it's often undeniably the best option, as long as you specify the package appropriately to ensure that the low end torque and high end power are preserved.

Edited By Jelly on 05/01/2023 14:06:47