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Which Milling machine motor?

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Arthur C21/02/2019 17:37:15
4 forum posts

Hi, I am new to this forum and not really into model engineering as such but find a great deal of useful information here. I have an old myford ML7 and a Harrison mill (vertical) which I have had for some years, and am into old motorcycles.
Recently the motor on the mill stopped with a burst of smoke. I have not touched the electrics since I bought it, and was originally changed to single phase by a previous owner many years ago. I have taken the motor out out and it is an old Ferguson and Sons induction motor, rated single phase and 0.75hp. The wiring on the motor was actually very suspect with crumbling insulation, not helped with it being suspended over the coolant reservoir ( not used) I guess,so will have to replace everything and rewire at the same time.
The motor should be 2hp - so do I replace with a single phase motor or 3 phase through a VFD which could give variable speed control. The table drive is 3 phase and converted through a nest of capacitors so the latter might be better?

I would welcome any thoughts as VFD's seem quite cheap now, but a single phase motor would be a straight swap and a VFD for the table drive?

Phil Whitley21/02/2019 18:48:40
814 forum posts
105 photos

Going three phase is the way, if you have the cash! you would need two VFD's one for the main motor, and a smaller one for the feed motor, I would certainly go back to 2hp, 3/4 hp motor has done well to last this long! I have a harrison horizontal mill with the optional vertical head, superb machines, Single phase swap would be ok, but go for at least a 2hp motor. 3ph would be smoother, and also you get infinitely variable speeds and soft start. You could of course just get a three phase main and vfd and leave the feed motor as is!

Good luck with it all

Phil.

Edited By Phil Whitley on 21/02/2019 18:49:29

not done it yet21/02/2019 18:55:16
2811 forum posts
11 photos

Personally, I would not countenance fitting a single phase motor, if there is an opportunity/necessity to fit a new drive. That applies to most of my machines currently running with induction motors. Perhaps not worded ideally, but you should get my drift.

Arthur C21/02/2019 20:27:35
4 forum posts

Thanks for the advice - 3 phase main is definitely not an option! I like the idea of a 3 phase motor. Price wise 3 phase and 2 phase look comparable to be honest. I might leave the table drive for another time. It actually blew in the middle of a job and so needs to be done. I really like the machine to be honest it does all that I need it to / am capable of so feel a little investment will be worth it.

Mike Poole21/02/2019 20:44:49
avatar
1866 forum posts
45 photos

As I was in the fortunate position of having a 2hp inverter laying around I decided to convert my VMC mill, I got a TEC motor from bearing boys and it was good service and very well packed. Although the motor is made in China it is very well made and runs sweetly. The late John Stevenson endorsed these motors on this forum and they are a fair bit cheaper than Brook Crompton.

Mike

Arthur C22/02/2019 11:41:06
4 forum posts

Just had a look at the website and there is a sale on! Thanks for the tip.

Vic22/02/2019 12:37:11
2016 forum posts
10 photos

My lathe and mill came with single phase motors and they both work fine. If one of them let the smoke out I’d replace it with another motor of the same type.

Arthur C22/02/2019 18:47:57
4 forum posts

Just been looking at the rear driver pulley which is much smaller than the driven pulley at the top of the belt. This will reduce the RPM of the spindle.

The driver pulley on the motor was 80mm diameter which seems small. 1 turn of the top pulley in the highest ratio gives 1.75 turns of the vertical spindle. Has anyone got measurements for the driver pulley on their machine as I think it should be slightly larger than the top one to get the right spindle speed with a 1400 rpm motor or am I completely off track?

Phil Whitley22/02/2019 20:36:21
814 forum posts
105 photos

Some one will have, but if no one does, I am back at my workshop on monday and will measure mine for you, Mine is three phase.

Phil

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