Bridgeport Power power supply + power feed

[adamcowmanParticipant @adamcowman]

Hi there.

I recently bought a Bridgeport milling machine for my workshop to accompany my lathe. I’m a plant mechanic by trade and I’m only 23, so machining and the workings of these machines is relatively new to me. Anyways there is a dilemma I need helped with and I’d hoped I’d find it here.

The mill I bought runs perfectly as I seen it in operation where I bought it. Only thing that doesn’t work is the power feed for the table. I’ve not got 3PH power to the mill yet to test anything, but after a bit of rooting and research I would imagine that the Erskine controller could be kaput, as there’s no wires going into it or out of it to the power feed motor, and the potentiometer and fast traverse buttons were taken out of the motor. If I was a betting man I’d say the controller jacked up and then somebody robbed the other bits to mend another machine.

I have wiring diagrams for the power feed and the mill so rewiring this is not an issue, nor is buying a reconned Erskine controller. My issue is I don’t know how I should power the mill on the head of this.

In my mind I’ve got 2 options, a VFD or a Static phase converter, each with pros and cons, but someone on here may advise me otherwise.

Option 1 is I use a VFD that I already have to provide the mill with 3 phase and incorporate the existing Fwd./Rev. switch on the mill and setup the VFD up that its only providing 3PH and I can control the spindle speed using the Variable belt drive on the machine still.

My fear with this is the VFD wont be able to supply 110v for the power feed, as I’m led to believe it works on single phase 110. I’m also worried how the VFD would power the DRO, as I definitely don’t want to loose that.

I can imagine there are ways around this, but as I say this ain’t my area of expertise and doing so could get complicated very quickly and I was hoping for an easier option.

Option 2 is a get a 3Hp static phase converter to just ‘plug and play’ the mill. Yes, a static phase convertor is more expensive, but If everything on the mill works 100% without any messing about, that’s money well spent.

I’m kind of leaning more towards option 2, as in my mind, if the mill if wired as it was from factory (provided I get a new Erskine controller if necessary) then it should work straight away when plugged in.

Now this is where I’m second guessing myself and not sure if this is in fact the case. Logic would tell me yes but sometimes logic goes out the window.

If anybody can help me out in anyway please do. If the answer is ‘Yes the machine will work straight away when plugged into a static phase converter’ then that’s what ill be getting.

But If its not that simple and a VFD is needed then I would appreciate any help or advice on wiring it up, as this is like rocket science to me.

Thanks A million

Adam.

 

[FulmenParticipant @fulmen]

I have the same machine (A&S with a 2J head) that I rewired from 3ph to 1ph with a VFD. Couldn’t be more happy with the result.

I ended up wiring the VFD directly to the motor. The only thing wired to the third phase was the main motor and the coolant pump and that works fine with a steinmetz setup. Besides, as you yourself point out electronics and VFDs are a baaaaad idea.

This way you can utilize the VFDs functions more fully, like soft start and current limiting. However I don’t change speed with the VFD, I worry over the gear box wearing unevenly.

[Clive FosterParticipant @clivefoster55965]

The Erskine unit gets its power from the big transformer in the electronics box. You have a choice of input voltages so its perfectly practical to run 220 volts to that and drive all the control gear, Erskine unit and any other bits and bobs off that.

Common practice is to use the VFD to drive the head motor directly either completely independent of the rest of the machine or via a bit of relay jiggery pokery to replicate the interlock functions of the contactors. I’d probably look into putting some interlocking in and retain the forward-off-reverse switch up on the head but many folk dispense with all that and just use the VFD controls. I like the standard set up with the motor direction selector switch high up and visible and the stop button low down in knee reach.

Sounds like you have the Bridgeport manual and wiring diagrams but what about the Erskine unit. I have a data pack in pdf format on the beast with a typical circuit along various installations and testing data. PM me if you’d like a copy.

If planning to keep the machine I’d replace the contactors and control gear with modern DIN rail components for easier access. The overload auto reset devices on the original gear are known to get crotchety in old age. Mine is on its final warning after two incidents in the last 10 years.

Clive

[adamcowmanParticipant @adamcowman]

<p style=”text-align: left;”>Thanks for the replys lads.</p>
Very greatful for the help. Most of my issue is that im from Ireland and there is NO places to get parts or service for machines. Luckily folks from Sorted machine spares helped me out for a few spares, and ofc people on here giving opinions.

I have an electrician friend whos going to help me out with wiring this up so I wont be on my own if i need help with a VFD or any circuitry.

Regardless of wether i go with the Vfd or Static phase converter i need help getting them setup.

Thanks again.

[John McCullaParticipant @johnmcculla]

Ah, where abouts in Ireland are you from?

I’m from Northern Ireland, there seems to be a real lack of machinery for sale over here, doesn’t there. I look with envy at all the shapers and mills and lathes for sale on FB marketplace/gumtree/eBay over in the UK. It’s a real shame because you need to be fairly sure you’re going to buy something if you want to go and see it. Don’t want to pay a couple of hundred pounds, get the ferry over, and come back with nothing!

[adamcowmanParticipant @adamcowman]

Aye John im from Wicklow in the Republic and there is a serious lack of knowledge on machinery if nothing else. Ive a colchester lathe that I had a woeful time getting parts for. And now with customs ordering parts from UK is double the price.
<p style=”text-align: left;”>Anytime ya google anything for machines the results usually revolve around the UK or US which 60% of the time is of feck all use!</p>
Still forums like these are great ways to talk to likeminded folks and get ideas.

[larry phelan 1Participant @larryphelan1]

Might not be much use to you, but I drive my  Lux mill from a rotary converter and the table feed from a 110v site transformer. Just an idea. You want a look ?, feel free, I,m  not too far away from you, in the “Sunny South East”,

As you say, you can get little or nothing here, not even material.

[FulmenParticipant @fulmen]

I didn’t notice the 110V issue at first. So the Erskine unit will be (US) 110V while the rest of the mill is 220?

[Fulmen]

On Fulmen Said:

I didn’t notice the 110V issue at first. So the Erskine unit will be (US) 110V while the rest of the mill is 220?

Erskine is 110 volts because it is designed to drive a (nominal) 100 volt DC servo motor.  From the specification:-

—————-

The E.S.L. controller is designed to drive a 0.5HP Fracmo D.C.motor,

Armature :- 90V, Field :- 100V. Full load current :- 4.6 Amps at 4500 r.p.m. Supply :- 110 V ± 10% at 50 / 60 H from Bridgeport transformer.
Operating ambient temperature :- +10 degrees C to +35 degrees C.

Feed rate adjustment by external 50 Kohm linear potentiometer.

Motor drives a 5 mm (5 t.p. i.) lead-screw through a 28: 1 gearbox.

Minimum feed rate :- 20 mm (0.75 ins) per minute.
Maximum feed rate :- 875 mm ( 35 ins) per minute.
Maximum torque :- 36 Nm (320 lbs/ins.) for all feed rate settings.

————–

Nominal 100 volt servos are a standard and very common. Easy enough to swop in modern drive board if you so desire at pretty similar cost to a repair. But you loose the lovely connector strip that makes it almost impossible to wire it up wrong.

Nothing to do with USA voltages. Our colonial cousins had to put up with significantly inferior devices to drive their power feeds.

Clive

[FulmenParticipant @fulmen]

Ah, that makes more sense. Thank you.

 

[Martin CargillParticipant @martincargill50290]

Using a 110 volt tool transformer is a good idea. Just beware that some 110 volt supplies on machines have one end of the supply earthed (to stop the 110 volts from “floating”). Tool transformers are centre tap earthed so you have to disconnect the original 110 volt earth on the machine to avoid a short circuit.

 

Martin

[adamcowmanParticipant @adamcowman]

One thing I dont understand is why the VFD cant just supply the entire machine with 3 phase.

As in why cant I just wire the mills orginal power cord to the 3 phase terminals of the VFD, and then still have use of the machines fwd/rev switch and let the mills transformer handle the DRO, powerfeed etc.

Maybe theres an obvious reason why this cant be done, but again, im a novice at this.

[adamcowman]

On adamcowman Said:

One thing I dont understand is why the VFD cant just supply the entire machine with 3 phase.

Several reasons, some of the main ones are as follows:

One, the VFD does not output sine waves. Instead the outputs are cycle by cycle PWM signals that are effectively smoothed to approximate sinusoidal currents by the motor winding inductances.

Two, the VFD is controlling output current, the voltage is simply adjusted to ensure the desired current flows in the motor windings.

Three, the output of most simple VFDs running from a 240VAC single supply is 240VAC between phases, not the usual 415VAC.

Andrew

[adamcowman]

On adamcowman Said:

One thing I dont understand is why the VFD cant just supply the entire machine with 3 phase.

As in why cant I just wire the mills orginal power cord to the 3 phase terminals of the VFD, and then still have use of the machines fwd/rev switch and let the mills transformer handle the DRO, powerfeed etc.

Maybe theres an obvious reason why this cant be done, but again, im a novice at this.

This can be done but it needs a significantly over-rated VFD set to 50 Hz and already running before the machine is turned on. The over-rating is needed to provide the overload capacity to supply the high current drawn by the motor on start up and running up to speed.

I run my workshop from a “plug and play” VFD unit permanently set to 50Hz from Drives Direct that works in this manner. I just switch it on and pretend it’s a normal 3 phase utility supply. But its a 10 hp nominal rated VFD, Drives Direct advise the maximum size motor it can safely start is 5 hp, ie 50% or rating. I reckon around 1/3 of the VFD rating is more appropriate. Especially as my Smart & Brown 1024 lathe has no clutch and must start up under load. I also run a Hydrovane compressor off it which also has a loaded, albeit light, start up. My box feeds through a set of smoothing chokes and inductors which cleans up the supply so it is safe to use with electronic devices. They also, for all practical purposes, eliminate the potential radiated interference problem if long cables are used between VFD box and machine. For various arcane reasons I personally would not use such a device without the inline smoothing.

Very much not cheap but at the time well worth it to run 10 machines when compared to individual VFD boxes for each machine. These days I’d probably go for individual VFD boxes and accept having to replace the motor on my P&W lathe with is irredeemably 440 volts due to being a two speed one.

Summarising:-

VFD boxes are fundamentally designed to run one motor and bring it up to speed by adjusting the frequency so the current draw is well controlled and generally close to that drawn at maximum power. Dumping 50 hz directly not a stationary motor creates a very large start up current draw and much greater than normal running current demand as the motor accelerates up to speed. So a conventional VFD can be much smaller and cheaper than one designed to mimic utility 50 hz. It also gives you easy speed change. How cool is that.

Clive

[Robert Atkinson 2Participant @robertatkinson2]

Using a VFD as a fixed frequency static converter to power the whole mill is a waste of it’s capabilites. you loose variable speed, soft start, overload protection controlled braking to name a few.
To add to Andrews list, most VFDs are not designed to run with no load or have the load switched on or off with the VFD running.
The ideal setup is to connect the VFD output directly to the motor (connected as delta) with it supplied from single phase 240V and the existing stop /start & E-stop connected to the VFD control inputs. To use variable speed add a pot to the existing control panel. The little control panel on the front of the VFD is NOT meant for normal operation, just commissioning and testing. The power feed can be run from the existing 110V ouput transformer if the primary has a 240V tap (most do)  or an new 240V to 110V transformer.
If you have a suds (coolant) pump it can be run with a capacitor in steinmetz configuration.

Robert.

[Clive Foster]

On Clive Foster Said:

On adamcowman Said:

One thing I dont understand is why the VFD cant just supply the entire machine with 3 phase.

As in why cant I just wire the mills orginal power cord to the 3 phase terminals of the VFD, and then still have use of the machines fwd/rev switch and let the mills transformer handle the DRO, powerfeed etc.

Maybe theres an obvious reason why this cant be done, but again, im a novice at this.

My box feeds through a set of smoothing chokes and inductors which cleans up the supply…

I’m confused; chokes and inductors are the same thing. Series inductors on the output of a VFD are generally used to reduce dv/dt, ie, slow the switching edges. To generate an output sine wave really needs a proper lowpass filter. That consists of a series inductor and a parallel capacitor.

Andrew

[adamcowmanParticipant @adamcowman]

Right OK Thats that answered. Thanks.

Getting my electrician pal to look at the mill during the week.

My aim with the VFD anyway if i use it is to not use it for variable speed, direction change and on/ogf anyway cos Id rather use the mills existing switchs.

So basically if i let the VFD run the spindle motor alone (and wire in the existing Fwd/Rev switch to switch the direction) I then just need to provide a seperate power to the rest of the machine to control the light, DRO and powerfeed (ignoring coolant pump for the minute cos i believe mine needs 3 phase)

Then I should be good to go. The previously mentioned site transformer is a good idea but ideally i want to use as much of the machines orginal compenents as possible, cos i know they work.

Thanks.

 

[norm nortonParticipant @normnorton75434]

Hi

I have a Bridgeport that I have rewired to run from 240v AC. Not too hard to reconfigure the control box to use the existing contactors and switch gear from the front. If I can remember what I did I am sure the table X drive motor runs from a single phase so that is easy to reconnect.

I have a 240V VFD running a replacement motor – the VFD MUST be wired directly to the motor with no switches or breaks possible in the three wires. The contactors now supply power to the VFD. You don’t mention the motor. Most Bridgeport motors can’t be rewired to run from a 240v VFD. Others can comment here but it is well documented on this (older?) forum.

Norm

[adamcowman]

On adamcowman Said:

So basically if i let the VFD run the spindle motor alone (and wire in the existing Fwd/Rev switch to switch the direction) I then just need to provide a seperate power to the rest of the machine to control the light, DRO and powerfeed (ignoring coolant pump for the minute cos i believe mine needs 3 phase)

Then I should be good to go.

Correct, this is exactly how I run mine. The original switch is rewired to control the direction, so it operates like it always has. The coolant pump will probably be 3phase, but this can be fixed with a steinmetz setup (basically a simple run capacitor). It provides about 2/3 the power and 1/3 starting torque, but that shouldn’t be a problem for a coolant pump like this.

[Clive FosterParticipant @clivefoster55965]

All the Bridgeport motors I’ve seen can be re-configured to 220 volts. Although the US Electrics motor on my varispeed head is more than little intimidating with a bunch of American type “twist together and screw a plastic cap on” connectors. I find the much harder to keep straight than the UK style studs on a small board variety.

If it’s a two speed motor you have to decide whether to run on high or low speed. Not an issue with a VFD to provide speed changes.

The transformer in the machine is wired across one phase of the incoming 3 phase so it takes 220 volt single phase just fine. No need for a site transformer.

Wouldn’t worry about the coolant pump. Uber messy when working and somewhen you will need to clean out the sump in the base. A job best delegated to someone you totally hate! I have a Bjur spraymist system on mine that works OK after I lost my temper with the finicky adjustment and re vamped it to give more of a spray than a mist. Various designs for home brew low volume coolant / air mix systems on the internet that seem to be effective. Frankly for folk like us I thing a fine air spray, sans coolant, is as good as is needed for most jobs. Keeping the chips out of the cut being the important thing rather than cooling and lubrication because we rarely drive our machines hard.

Concerning the Steinmetz “capacitor trick” for running a three phase motor off single phase the major loss on a properly done system is in starting torque. Adding an extra start capacitor helps but it’s still relatively low. A Steinmetz set up properly balanced for its load gives over 90% of nominal motor power if need be. But efficiency is very load dependant and falls off badly if the load varies by too much. Which is why commercial static converters, which are Steinmetz devices, have a power setting switch. The 2/3 rds power rule of thumb applies more to our American friends who habitually don’t bother with a balancing capacitor for the third phase so effectively run the motors on two phase. I’ve built a number of Steinmetz static converters with automatic start capacitor connection / disconnection making them pretty foolproof. Once you go past about 1 1/2 hp getting them to run properly and efficiently is a right pain. At today’s prices the component costs of doing it properly come to more than a VFD. Going all crude by just hanging a capacitor between two motor connections will kill the motor eventually. But for something like a coolant pump the question is will you live that long.

Clive

 

[larry phelan 1Participant @larryphelan1]

Hi Martin and Adam,

Point taken Martin re the earth connection ! The only reason I mentioned a site transformer is because my Chester Lux machine does not have a built-in powerfeed and Chris at Chester suggested a 110 site transformer, and that,s what I,ve been using.

Different machines, different set-ups.

PS My mill has 6 speeds, but just looking through a Chester catalogue I picked up around the time I bought the machine, It is listed as having 12 speeds !

How did I miss that ? Dont even ask !

Never even copped it until Adam drew my attention to the subject after so many years.

Just goes to show, Old Age is a curse !

[SlumesParticipant @slumes]

Hi All.

Looking for a 240v motor with variable speed option. Anyone know of any Bridgeport ready kits out there? I have no motor currently and no 3P either. Needed for general hobbying but looking for the easiest install option really. All help appreciated. Cheers.

[Clive FosterParticipant @clivefoster55965]

Changing motors on a Bridgeport is difficult because the output shaft is rather longer than a standard motor. So you either have to extend it or modify the drive arrangements.

Best bet is to find a used Bridgeport motor and use a VFD to convert your single phase to three phase. Need to have the appropriate motor pulley to match your spindle drive.

Alternative is to use a standard face mount 3 phase motor and recess the mounting so it’s actually inside the head. This will bring the motor low enough to get a pulley or two aligned on a step pulley head. VFD drive will give you speed variation. If starting with a varispeed you will need to source all the drive pulleys your self but same in principle.

Frankly finding a standard motor is probably easiest.

Clive

[SlumesParticipant @slumes]

Thanks. Its a J-head. Machine has an old 1/2 hp motor not from machine but fitted afterwards. No markings or details. Has step pulley fitted to it. Was hoping to simply install new motor to get vari speed. Will look some more. Cheers.

[mr fixitParticipant @mr-fixit]

Hi,

I have just been reading all these comments, I don’t know anything about Bridgeport motors, so I don’t know how old they are but I found out that older motors can be damaged by VFDs. if the motor is not Inverter Rated, more modern 3 phase motors can safely be powered by VFD’s if it says VFD rated on the Motor Plate, no one has mentioned anything about this. see this informative video below. -:

Trevor

 

 

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