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Bridgeport Mill - Convert to 240v Single Phase

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mtrehy mtrehy26/04/2018 19:33:06
22 forum posts
10 photos

img-20180426-wa0000.jpgHi All,

I've just become the owner of a Bridgeport Mill. Even better it was free (except £150 delivery).

On the motor plate it says 380/420, 3.2/2.1, 2700,1420, CONT INS E, SC, Frame 7, HP 2.0/1.0

I want to run it off 240v single with a VFD. I have already setup a lathe like this. I assume that this motor would not be compatible as it's not 240/415 - could someone with more knowledge than me please confirm this please.

I've attached a few pics.

Any help much appreciated.


Brian H26/04/2018 19:44:40
1393 forum posts
100 photos

I'm currently (no pun intended) trying to set up a miller/engraver that is dual voltage, to run on a Yaskawa AC Drive J1000 from:

A 'phone call or email to them may get you under way.


Oldiron26/04/2018 20:02:13
355 forum posts
22 photos

Might be an idea to contact Transwave who advertise on this site. One of their phase converters or similar might be a better option.


Andrew Johnston26/04/2018 21:46:24
5112 forum posts
594 photos

The motor is definitely not dual voltage, although it is two speed. Presumably there's a switch in the control box somewhere that looks after the pole switching. Since the hp values are in a 2:1 ratio the pole switching is not accompanied by star to delta switching.

The motor appears to be a "pancake" style which is integrated into the drive so will be tricky to change to asingle phase or dual voltage motor.

Best bet is to find a way of generating some sort of approximation to 415V 3-phase. A good place to start would be to take Oldiron's advice.


David George 126/04/2018 22:36:18
1056 forum posts
333 photos

You will struggle to change the motor to vfd and if it was me I would go for a phase converter as other motors coolant pump, traverse motor and relays will also work no problem.


Trevor Drabble26/04/2018 23:48:57
205 forum posts
5 photos

I would suggest you also talk with Direct Drives on 01623 720710 . They also have a useful web page . I have no connection with the company .

Trevor .

Michael Gilligan27/04/2018 00:09:02
14774 forum posts
635 photos

I've just found an old thread on 'rcgroups' discussing the same issue.

... Includes wise input from John Stevenson: **LINK**


Chris Evans 627/04/2018 07:23:41
1565 forum posts

If you go the phase converter route look for a rotary converter. I tried to run my Bridgeport from a static converter and whilst it would run it stopped every few minutes throwing a trip out in it's electrics box. Transwave were more than helpful in trying to solve the issue but the static converter was not compatable, it has however run my lathe for years.

Neil Lickfold27/04/2018 08:11:40
584 forum posts
102 photos

I think your best option, is to replace the current motor with a suitable 220V 3phase, and then make a new control panel that has a variable speed pot, and a forward reverse switch. It is essentially what I have done on my Myford lathe. I am going to make a similar setup for my new to me ZX45 mill. It is a clone of the RF45. Like the lathe, I will set up a micro switch that I can use when tapping holes. So when it gets to the desired depth, it stops. How quick depends on the deceleration settings on the VFD box. So if I ever wnat to put it back to it's standard configuration, I can just put the original motor back on, and reconnect all the wires etc.


Andrew Johnston27/04/2018 08:23:57
5112 forum posts
594 photos
Posted by Neil Lickfold on 27/04/2018 08:11:40:

I think your best option, is to replace the current motor with a suitable 220V 3phase......

Easy to say but difficult to do. Sure it's easy on something like a Myford, but on the Bridgeport the motor is non-standard in it's fittings and drive arrangement. No doubt it could be done, but you'd end up rebuilding the head.


norm norton27/04/2018 10:14:07
111 forum posts
6 photos

I have a Bridgeport and have converted it to to a VFD driven 220v 3 phase motor - BUT... it is not a simple job.

You have what is called a 'pancake' motor and these CANNOT be converted to 220v. Your quickest way of getting it working from a domestic supply is to use a rotary converter (Transwave) but these are not cheap. I did use a static converter for a couple of years and it worked, but it was fussy about the higher speed if selected.

To fit a conventional flange 220v motor in place of the 'pancake' you need a simple, thick steel adapter plate. There is no head rebuilding, just an 8mm plate that slides in place of the 'pancake' flange and holds the motor in the middle.

The problem then is that no readily available motors have long enough shafts to hold the pulley in the right place. I was fortunate in getting help from John Stevenson and he modified a new motor. I have heard of others who fitted extension stubs, but then suffered vibration. Personally, I think an extension stub, locked onto the shaft, and then turned true by spinning the motor clamped to a lathe bed, would give an acceptable result.

Once you have lengthened a motor shaft, and made an adapter plate, you then need to do quite a bit of re-wiring in the cabinet. It is best to set that all to single phase so that the front switch box still operates the contactors and nicely switches on the VFD. If you have a Bridgeport table axis drive then that will still happily operate on its 110V single phase once you have re-tapped the transformer.


SillyOldDuffer27/04/2018 11:07:57
5134 forum posts
1074 photos

A little out of the ordinary but VFDs for 240 to 415V do exist. As might be expected they are more expensive than their low voltage relatives, but then you got the Bridgeport for free! This cheaper example is from Drives Direct - worth a call I think unless the asking prices are too much.

Like the chap in the photo: he's wearing a high-vis jacket and slippers. That's exactly what I want for xmas - carpet-slippers fitted with steel toe-caps!smiley

Neil Lickfold27/04/2018 11:25:37
584 forum posts
102 photos

This is what I did for my lathe. I am making another box with a bigger drive, 2.2kw for my FR45 clone. Not the same as a Bridgeport. But the concept is similar. Where the motor controls are not connected to the original switch or carbonate. Some place are bringing in motors with longer shafts, maybe that is an option for the Bridgeport.


Nealeb27/04/2018 11:30:16
45 forum posts

I've seen recommendations for inverters like this one. I've been considering one of these - 240V single phase in, 380V 3-phase out - for my lathe. The inverter I currently use with that struggles with the load when I wind the speed up because of the way it does the 240V-380V conversion. Might do for the Bridgeport, as you could buy an over-specced version to easily handle the load at quite a good price. There are a number of reviews of the Ecogoo inverters available via a Google search.

mtrehy mtrehy27/04/2018 20:03:25
22 forum posts
10 photos

Thanks for the replies.

I'm not too keen on a static converter - read lots about them not working well with milling machines so feels a bit hit and miss..?

Rotary phase converter seems very expensive and I would think I could get a 2nd hand 230V 3-Phase motor and make it fit and then add VFD considerably cheaper.

That chinese Ecogoo option sounds perfect though - almost too perfect. Is it too good to be true?

duncan webster27/04/2018 20:25:19
2338 forum posts
34 photos

If you have a motor rewinder near you it might be worth finding out what it would cost to bring out the star point and convert it to delta. I've actually done it on a bench grinder, but it didn't matter if that dies. Replacing a Bridgeport motor would be a bit more expensive to put it mildly, so consult an expert.

davidk27/04/2018 21:57:18
46 forum posts

I took my 3-phase Bridgeport 2-speed 380/440V pancake motor to a motor rewinder in Southampton. He rewound it for me, so it's now a 3-phase 2-speed 230V motor. It now runs just fine on an IMO Jaguar VXR inverter which is 230V single phase in, 230V 3-phase out. The rewinding cost me about £300 three years ago. I only power this motor with the inverter, not the rest of the (Denford) milling machine that the head is fitted to.


mtrehy mtrehy27/04/2018 22:03:06
22 forum posts
10 photos
Hi David, that sounds promising. Do you have the contact details for the people who did it? I'm close to Southampton myself. Cheers
davidk28/04/2018 07:53:42
46 forum posts

The company is C&C Rewinds Ltd, 7 Test Valley Business Centre, Test Lane, Southampton SO16 9JW. No connection, just a very satisfied customer.


larry phelan 128/04/2018 19:25:59
577 forum posts
11 photos

If you got the machine for nothing,I would not bother arsing around changing motors ect. Talk to Transwave,buy a rotary converter and forget about messing about,that,s what I did,and never looked back Over time,the cost will be buttons and at least you will be up and running

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