# Ian's Bridgeport mill



## Canadium (Apr 8, 2022)

A continuation of https://canadianhobbymetalworkers.com/threads/bridgeport-1200-00.5001/

I'm dedicating this thread with thanks to the two wonderful guys @trlvn  and @Rauce who came out and busted their butts to help me bring my Bridgeport home as well as to this general forum which has enabled me to meet so many wonderful people! I just finished my radiation treatments and was far from 100%. At the end of the moving day yesterday I was totally exhausted even though the other guys did most of the work. They say good help is priceless. I can vouch for that!!! I've always marvelled at how guys on this forum and elsewhere seemed to be able to bring home full sized vertical mills as though they were just bringing home the groceries! Now I can brag that I have actually participated in the moving of a mill!

It's my first ever milling machine, the beginning of an exciting journey for me, and I hope you won't mind the many questions I will have to follow in the coming days!


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## trlvn (Apr 8, 2022)

Glad to help.  This was the most 'hands-on' time I'v ever spent with a Bridgeport.  It really is astounding how the head can be contorted!  

I think you've got a solid addition to your little menagerie there!  Everything went pretty smoothly even with that pesky rain shower!

Craig


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## 140mower (Apr 8, 2022)

Congratulations on your new toy. Hopefully you are feeling better sooner than later and the projects start rolling off the table. I'll leave most of  the question answering to those that know more than l, and hopefully I can learn something at the same time.


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## Brent H (Apr 8, 2022)

Awesome Ian!!  If you have any issues let me know!


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## Hruul (Apr 8, 2022)

Congrats on the mill!!  Hope you feel better soon and good luck with the rest of the recovery.


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## kevin.decelles (Apr 8, 2022)

Nice grab!  Wish I had one myself.  A day manipulating metal with the forum members is a good day indeed.


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## Dabbler (Apr 8, 2022)

very nice piece of kit - congrats

I hope your recovery goes as smoothly.  get fully well soon


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## David_R8 (Apr 8, 2022)

New mill day! Well done everyone 
And here's to a speedy recovery @Canadium!


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## Susquatch (Apr 8, 2022)

Nice post! Nice machine! Must be something about the guy! 

Congrats!


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## architect (Apr 8, 2022)

Congrats!!!


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## 6.5 Fan (Apr 9, 2022)

Congrats on the mill.


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## Canadium (May 4, 2022)

Because of health issues progress on the mill has been going at a snails pace. Initially I was thinking I would just do a minimum of work to get it running and making chips. After all the work I did on my lathe last year I wasn't eager to go through such a lengthy process again. However the more I look at the project the more I see things have to be disassembled, cleaned and repaired anyway so might just as well go the whole way.  I've determined slop on the x-axis is about 62 thou, y axis about 72 thou. Very worn but to be expected. The table looks to be in fairly decent shape considering the age. The quill feed handwheel is missing and feed reverse knob is broken off and also missing. The power feed for x axis was not connected so couldn't tell how/if it works. In fact the entire power in cable for the power feed was removed so it was not even clear what the power requirements were and how the power was supposed to be connected. Eventually I decided to look inside the electrical box in case any clues about hookup resided there. As the door fell open out dropped 3 pages of notes with wiring diagrams! After studying the diagrams and the circuit boards I hooked up 120V of power to a board and flipped the switch. I was fully expecting a pop as the thing blew up or at the very least some magic smoke. But instead nothing! The on switch made the power light go on as it should but the motor still didn't run. Have to study those diagrams some more and order some parts!


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## Brent H (May 4, 2022)

Hey Ian, 

Attached are pages from the manual I sent you - See what applies to your situation - some of the electronical folks on here may be able to assist you out with the drawings.


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## Susquatch (May 4, 2022)

Canadium said:


> Because of health issues progress on the mill has been going at a snails pace. Initially I was thinking I would just do a minimum of work to get it running and making chips. After all the work I did on my lathe last year I wasn't eager to go through such a lengthy process again. However the more I look at the project the more I see things have to be disassembled, cleaned and repaired anyway so might just as well go the whole way.  I've determined slop on the x-axis is about 62 thou, y axis about 72 thou. Very worn but to be expected. The table looks to be in fairly decent shape considering the age. The quill feed handwheel is missing and feed reverse knob is broken off and also missing. The power feed for x axis was not connected so couldn't tell how/if it works. In fact the entire power in cable for the power feed was removed so it was not even clear what the power requirements were and how the power was supposed to be connected. Eventually I decided to look inside the electrical box in case any clues about hookup resided there. As the door fell open out dropped 3 pages of notes with wiring diagrams! After studying the diagrams and the circuit boards I hooked up 120V of power to a board and flipped the switch. I was fully expecting a pop as the thing blew up or at the very least some magic smoke. But instead nothing! The on switch made the power light go on as it should but the motor still didn't run. Have to study those diagrams some more and order some parts!




Happy to help if I can. 

Does that mill have a barrel switch up on the motor? If so, you can temporarily bypass the entire control system by  disconnecting the power cable from the center poles of the switch and then connect 220 3ph to those center poles. Then you can literally use the drum switch to turn on the power for forward or backward. 

That will tell you if the motor works. It's a good place to start.


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## Rauce (May 4, 2022)

I think the machine is currently set up for 575v 3 phase right?

A VFD and a new motor or a rewind of the current motor will bypass everything in that electrical cabinet.

Most motor shops won’t bother rewinding small motors anymore but there’s a place I’ve used in the Toronto area that’s happy to do it at a reasonable price. I don’t know if the Bridgeport motor is a custom mount but my excello is, which is why I went for a rewind over a new motor.

Also, is the slop you measured backlash or in the ways themselves? I know with my Excello a gib adjustment was all that needed on the X axis, the topside of the saddle was worn evenly and holds good tolerances. The Y axis not so much but your mill looked better than mine since flaking was still visible across the top of the knee.


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## Brent H (May 4, 2022)

Ian's mill may have a 575 3 phase head - not sure, but the auxiliary power is only 120 volt single phase.  The feed motor typically plugged into the side of the power box that Ian has open and that box I believe provides all the speed control.

This diagram is of the connections at the motor area.  You can see the 120 Volt supply and the ambilicle for the motor control would have been a


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## Brent H (May 4, 2022)

You can see the motor is DC so Ian is poking around the rectification circuitry


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## Rauce (May 4, 2022)

Brent H said:


> Ian's mill may have a 575 3 phase head - not sure, but the auxiliary power is only 120 volt single phase.  The feed motor typically plugged into the side of the power box that Ian has open and that box I believe provides all the speed control.
> 
> This diagram is of the connections at the motor area.  You can see the 120 Volt supply and the ambilicle for the motor control would have been a
> View attachment 23678


Ah, I thought we were also talking the head.


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## Susquatch (May 4, 2022)

Rauce said:


> Ah, I thought we were also talking the head.


So did I.


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## Rauce (May 4, 2022)

For what it’s worth regarding the motor in the head, LN Electric is where I have had motors rewound. They did the motor on my old Williams horizontal mill and my excello. Both times a rewind and new bearings was around $400. The only place in Hamilton that would even give me a quote rather than try to sell me a new motor wanted $800. 






						Electric Motors Toronto | Swimming Pool Pumps Toronto & Vaughan| LN Electric Motors
					

LN Electric Motors sells and services electric motors and swimming pool pumps in Vaughan, North York and Toronto. Give us a call at (416) 661-5667.




					www.lnelectric.com


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## Canadium (May 4, 2022)

Brent H said:


> You can see the motor is DC so Ian is poking around the rectification circuitry



Exactly correct! I did notice there was one loose wire inside. I suspect it got inadvertantly disconnected when the power cable was being removed. I will have to trace it and figure out where its supposed to be connected.


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## Canadium (May 4, 2022)

Rauce said:


> For what it’s worth regarding the motor in the head, LN Electric is where I have had motors rewound. They did the motor on my old Williams horizontal mill and my excello. Both times a rewind and new bearings was around $400. The only place in Hamilton that would even give me a quote rather than try to sell me a new motor wanted $800.
> 
> 
> 
> ...



 Thanks @Rauce for the info!


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## Canadium (May 5, 2022)

Just had another look at the wiring for the x-axis power feed. Studied the wiring very carefully, decided where the aforementioned loose wire should go and did the test. Voila the power feed now works!!! And I am a very happy camper!


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## Susquatch (Jul 27, 2022)

It's been a little while. But I see your posts here and there so I hope you are doing better. 

After reading this thread over again, I'd suggest the following approach:  first and foremost, separate the power feed, DRO functions, and mill functions. That way you can debug them one at a time. After you have each of them working, you can reconnect them as appropriate having full knowledge of how each works. 

I think your first task should be getting the mill portion wired up and working. The good news is that motor changes on the pulley version of the Bridgeport are MUCH simpler than they are on the VariDrive model. 

For your mill, I believe you have 3 choices to make. 

1. Have the motor rewound to 3 phase 220V and get a VFD to convert 2 phase to 3 phase. 

2. Get a rotary converter or similar device to generate the existing power requirements. 

3. Replace the existing motor with a new or old 220 3Phase motor and get a VFD to convert 2 phase to 3 phase. 

I favour number 3 and that's what I did with mine. Mine is a pulley drive like yours but was 440V instead of 575.

The reasons I chose #3 is detailed in my thread on my new to me Hartford. But it can be summarized very simply. I wanted to get a VFD ready motor and a good VFD so I could get much wider and better speed control. This also leaves me with the original motor should I ever want to go back, and it makes my mill much more sellable if I have a stroke or similar life changing event. I am mid 70s so I have to be realistic about my future expectations. 

In hindsight, I am glad I chose that direction. A good VFD and VFD ready motor are an amazing combination and a pure joy to use.


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## Canadium (Jul 27, 2022)

Thankyou @Susquatch  for the reply!



Susquatch said:


> After reading this thread over again, I'd suggest the following approach:  first and foremost, separate the power feed, DRO functions, and mill functions. That way you can debug them one at a time. After you have each of them working, you can reconnect them as appropriate having full knowledge of how each works.


The power feed has already been wired separately and found to be in working condition. The DRO was removed before I got it, only the scales remain and I was told will be useless so should be removed. It's the mill functions that have me stumped.


Susquatch said:


> I think your first task should be getting the mill portion wired up and working. The good news is that motor changes on the pulley version of the Bridgeport are MUCH simpler than they are on the VariDrive model.
> 
> For your mill, I believe you have 3 choices to make.
> 
> 1. Have the motor rewound to 3 phase 220V and get a VFD to convert 2 phase to 3 phase.


I'm told could cost about $400. Would require taking it to a distant shop.


Susquatch said:


> 2. Get a rotary converter or similar device to generate the existing power requirements.


By coincidence there is a transformer attached to the back of the mill that reduces 575V 3 phase to 120V or 240V single phase. If I'm not mistaken this could be wired backwards to take 220V 3 phase from an RPC to deliver 575V 3 phase. Just some capacitors and a pony 220V 3phase motor and I could have 575V 3 phase in my shop? Or is that mistaken? Since a lot of old industrial machinery around here seems to require 575V 3 phase including my mill this option appeals a lot. Of course the devil is in the detail.



Susquatch said:


> 3. Replace the existing motor with a new or old 220 3Phase motor and get a VFD to convert 2 phase to 3 phase.


I already have an old 220V 3 phase motor from a different model of Bridgeport ie it doesn't fit mine and would require an adapter plate. I am uncertain if this option would require completely altering the look of the machine since the motor might not fit the housing the same. I appreciate the advantages of using a vfd but don't don't want to change the original appearance of the machine by way of using a different motor. Also the motor I have is not VFD ready.



Susquatch said:


> I favour number 3 and that's what I did with mine. Mine is a pulley drive like yours but was 440V instead of 575.
> 
> The reasons I chose #3 is detailed in my thread on my new to me Hartford. But it can be summarized very simply. I wanted to get a VFD ready motor and a good VFD so I could get much wider and better speed control. This also leaves me with the original motor should I ever want to go back, and it makes my mill much more sellable if I have a stroke or similar life changing event. I am mid 70s so I have to be realistic about my future expectations.
> 
> In hindsight, I am glad I chose that direction. A good VFD and VFD ready motor are an amazing combination and a pure joy to use.



So in summary I like all 3 options equally and can't make up my mind which way to go. I'm wondering if any one would know where I could get a suitable VFD ready 220V motor at an affordable price.


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## Dabbler (Jul 27, 2022)

Canadium said:


> If I'm not mistaken this could be wired backwards to take 220V 3 phase


You don't quite have the right of it.  When wired as it was installed, it converts the 575 3PH to 120 or 240 3PH - If you only use on leg of it, it is single phase.

When wired backwards, it doesn't do the thing you hope for.  If you only power one of the 3 phases, it will heat up and not magically convert the output to 3 phase in any meaningful way (there will be potential on all 3 phases, but not *power* to those phases.  The majority of the power input will be converted to heat by parasitic inductance on the *240V side*.


Canadium said:


> Also the motor I have is not VFD ready.


All of my motors on VFDs are conventional non-VFD motors.  In milling and lathe work, we only use a portion of the horseopwer in continuous mode, and they work find in lathes and mills without the extra expense. I have a RPC and rarely use it.


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## Canadium (Jul 27, 2022)

Dabbler said:


> You don't quite have the right of it.  When wired as it was installed, it converts the 575 3PH to 120 or 240 3PH - If you only use on leg of it, it is single phase.
> 
> When wired backwards, it doesn't do the thing you hope for.  If you only power one of the 3 phases, it will heat up and not magically convert the output to 3 phase in any meaningful way (there will be potential on all 3 phases, but not *power* to those phases.  The majority of the power input will be converted to heat by parasitic inductance on the *240V side*.



Perhaps I wasn't clear in my meaning. I meant if an RPC converting 220 single to 220 3 were connected to the transformer then you would get 575 3 phase out.


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## Susquatch (Jul 27, 2022)

Canadium said:


> I'm wondering if any one would know where I could get a suitable VFD ready 220V motor at an affordable price.



If you want to use the existing motor as is you must go RPC. I don't think the transformer you have will work. As I understand it (keeping in mind that I am NOT a high power expert) single-phase power can be derived from a three-phase power source using a transformer, but *a transformer cannot convert single-phase power to three-phase power*. Converting single-phase power to three-phase power requires either a rotary phase converter (RPC) or a variable frequency drive (VFD). As of right now, I don't know of any VFDs that will convert 220 to 550.  This is my understanding.

With the wonder of electronics, there may be other solutions here now or around the corner, but I am not aware of them.

Therefore, to use your existing motor, you only have two options - RPC or a rewind.

I bet you can find a better price on a rewind but don't have any recommendations.

A rewind will not achieve VFD ready. You will be limited to about 45Hz to 100Hz. Safe would be 50 to 75.  Not really enough to make chasing it a no-brainer.

If you want good variable speed control 5Hz to 120Hz, you need a VFD ready motor. It will NOT LOOK THE SAME and YOU WILL NEED an adapter plate. In my mind a VFD ready motor is a highly desirable solution.












E-Motors has great delivery and good support. I was lucky and got a seconds motor (prolly a return but they guaranteed it), but I gotta tell you that knowing what I know now, I would buy a new one at full pop without batting an eye.

You will also need to make an adapter plate. It was way easier than I imagined. If I had to do it over I would use a rotary table to make it. But that assumes you have a working mill and a rotary table. So I did what I had to do. I used a cutting torch and a side grinder. It's not gorgeous but I don't even notice it anymore.

The mounting plate on the motor will take a box of some kind in the future for controls and master switch etc. Today it sits there looking ugly and..... I don't even notice it now.

Edit - I didn't see @Dabbler s post till I pressed submit. What he says complements what I said.


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## Susquatch (Jul 27, 2022)

Canadium said:


> Perhaps I wasn't clear in my meaning. I meant if an RPC converting 220 single to 220 3 were connected to the transformer then you would get 575 3 phase out.



Assuming the transformer has 3 phase in and out then Yes. But not anywhere near the power level you need. That transformer was just used to create lower power for the other devices on the mill. Not to run the mill.

But I bet the transformer only has 220 single phase out not 3 phase. In fact it might only be 120 single out.


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## Canadium (Jul 27, 2022)

Susquatch said:


> If you want to use the existing motor as is you must go RPC. I don't think the transformer you have will work. As I understand it (keeping in mind that I am NOT a high power expert) single-phase power can be derived from a three-phase power source using a transformer, but *a transformer cannot convert single-phase power to three-phase power*.


I wasn't considering trying to change single phase to 3 phase through a transformer. I wanted to make an RPC that took the 220 single to 220 3 phase then transform to 575 3 phase. My "magic" is in the RPC.


Susquatch said:


> Converting single-phase power to three-phase power requires either a rotary phase converter (RPC) or a variable frequency drive (VFD). As of right now, I don't know of any VFDs that will convert 220 to 550.  This is my understanding.
> 
> With the wonder of electronics, there may be other solutions here now or around the corner, but I am not aware of them.
> 
> Therefore, to use your existing motor, you only have two options - RPC or a rewind.





Susquatch said:


> I bet you can find a better price on a rewind but don't have any recommendations.
> 
> A rewind will not achieve VFD ready. You will be limited to about 45Hz to 100Hz. Safe would be 50 to 75.  Not really enough to make chasing it a no-brainer.


Great point! I wasn't thinking about that.



Susquatch said:


> If you want good variable speed control 5Hz to 120Hz, you need a VFD ready motor. It will NOT LOOK THE SAME and YOU WILL NEED an adapter plate. In my mind a VFD ready motor is a highly desirable solution.


The aesthetics are precisely what is holding me back. I would prefer to keep the original look of the machine and that is a big reason I'm leaning towards RPC. I guess its a matter of performance over aesthetics and which matters most.



Susquatch said:


> E-Motors has great delivery and good support. I was lucky and got a seconds motor (prolly a return but they guaranteed it), but I gotta tell you that knowing what I know now, I would buy a new one at full pop without batting an eye.
> 
> You will also need to make an adapter plate. It was way easier than I imagined. If I had to do it over I would use a rotary table to make it. But that assumes you have a working mill and a rotary table. So I did what I had to do. I used a cutting torch and a side grinder. It's not gorgeous but I don't even notice it anymore.



Where did you get the steel for the adapter plate and how big a piece did you need?


Susquatch said:


> The mounting plate on the motor will take a box of some kind in the future for controls and master switch etc. Today it sits there looking ugly and..... I don't even notice it now.
> 
> Edit - I didn't see @Dabbler s post till I pressed submit. What he says complements what I said.


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## Susquatch (Jul 27, 2022)

Canadium said:


> So in summary I like all 3 options equally and can't make up my mind which way to go. I'm wondering if any one would know where I could get a suitable VFD ready 220V motor at an affordable price.



I think you need to jump in your car/truck and come pay me a visit. Nothing beats hands on to see what you might want to do, or not do. My shop is messy but its a barn first and a shop second and I personally prefer organized chaos over so clean you are afraid to get it dirty. 

Maybe find someone running an RPC and go visit them too. 

Just keep in mind that variable speed is much harder to do with an RPC. That said, the pulley choices built into your mill will do everything you want it to do. 

My decision to go VFD instead of RPC was based on my desire to have variable speed tools and to stay away from high voltage. My future plans are to stick with 220V 3Phase and 1phase power throughout my shop.


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## Canadium (Jul 27, 2022)

Susquatch said:


> Assuming the transformer has 3 phase in and out then Yes. But not anywhere near the power level you need. That transformer was just used to create lower power for the other devices on the mill. Not to run the mill.
> 
> But I bet the transformer only has 220 single phase out not 3 phase. In fact it might only be 120 single out.



Transformer plate says 5kVA. Dunno if thats enough or not? I thought I read somewhere that 3 phase can easily be converted to single phase by just drawing on one of the 3 lines?


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## Canadium (Jul 27, 2022)

Susquatch said:


> I think you need to jump in your car/truck and come pay me a visit. Nothing beats hands on to see what you might want to do, or not do. My shop is messy but its a barn first and a shop second and I personally prefer organized chaos over so clean you are afraid to get it dirty.


If your shop is messy I bet mine is messier! I would love to drop by sometime to see what you have. Will PM about a mutually convenient time.



Susquatch said:


> Maybe find someone running an RPC and go visit them too.
> 
> Just keep in mind that variable speed is much harder to do with an RPC. That said, the pulley choices built into your mill will do everything you want it to do.






Susquatch said:


> My decision to go VFD instead of RPC was based on my desire to have variable speed tools and to stay away from high voltage. My future plans are to stick with 220V 3Phase and 1phase power throughout my shop.


That somehow sounds like very sage planning to me! Thanks!


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## Susquatch (Jul 27, 2022)

Canadium said:


> I wasn't considering trying to change single phase to 3 phase through a transformer. I wanted to make an RPC that took the 220 single to 220 3 phase then transform to 575 3 phase. My "magic" is in the RPC.



Yes, I saw that in your reply to @Dabbler. And replied that your transformer won't work because it's too small. 

Yes, an RPC will work but you will lose variable speed. 



Canadium said:


> Great point! I wasn't thinking about that.
> 
> 
> The aesthetics are precisely what is holding me back. I would prefer to keep the original look of the machine and that is a big reason I'm leaning towards RPC. I guess its a matter of performance over aesthetics and which matters most.



Ya, I get that. Get a nice paper bag to put over the motor...... Well, maybe not paper..... 

Seriously, keep your original motor like I did and remember that you want to make nice things with your mill not sit there and look at it. 

Besides, I bet my mill will be beautiful after I put a nice control box on the motor mounting plate. If not, maybe I'll make a red velvet bag to slip over the motor...... LOL! 



Canadium said:


> Where did you get the steel for the adapter plate and how big a piece did you need?



10x10x0.5 at Metal Supermarkets (I think). 

I cut it with an OA torch, cleaned it up a little bit with a side grinder, then put it on my lathe to recess it by 3/8 inch for the motor and cut the nose out for the motor. Then I drilled all the mounting holes on my old mill/drill.


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## Susquatch (Jul 27, 2022)

Canadium said:


> I thought I read somewhere that 3 phase can easily be converted to single phase by just drawing on one of the 3 lines?



Yes, but not the other way around. In fact, you don't even need a transformer to do that. But the result will be an unbalanced load.

If you go out into the country and look at the overhead power lines, you will find that it's common to just split off one of the 3 phases to run a line to someplace with just one of the three phases. There won't even necessarily be a transformer there. Generally they do that so that one wire (one phase) serves one group of customers and the other wires serve other customers.

If you come and visit I'll show you an example right close by.


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## trlvn (Jul 27, 2022)

@Canadium You might consider giving a call to PhaseQuest in Mississauga:






						Phase Quest - Canadas #1 Transformers, Phase Converters, AC DC Motors
					

Phase Quest - Canadas #1 Transformers, Phase Converters, AC DC Motors




					www.phase-quest.com
				




They sell both rotary phase converters and VFD systems.  They're local so hopefully you could get some good information.  I expect they're familiar with the issue of 575V requirements whereas a US-based outfit might not be.   If you describe your situation and have the motor and transformer tags handy, hopefully they can lay out the options.  

OTOH, they seem pretty expensive from a gander at the web site.  YMMV...

Craig


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## David_R8 (Jul 27, 2022)

The other place I'd try is e-Motors Direct. I've bought two VFDs and the three-phase motor for my mill from them and am very pleased with their pricing and service.








						eMotors Direct - Canada's Online Source for Electric Motors, Gearing, and Controls
					

Delivering anywhere in Canada, eMotors Direct provides the best selection and knowledge of electric motors, parts, and accessories to get them what they need fast so that they can get back to business.




					www.emotorsdirect.ca


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## Rauce (Jul 27, 2022)

David_R8 said:


> The other place I'd try is e-Motors Direct. I've bought two VFDs and the three-phase motor for my mill from them and am very pleased with their pricing and service.
> 
> 
> 
> ...


I can second that, I had great service there and picked up my order in person at the Oakville warehouse.


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## Susquatch (Jul 27, 2022)

Rauce said:


> I can second that, I had great service there and picked up my order in person at the Oakville warehouse.



If you guys didn't catch it, that's where I got my VFD Ready Motor too. I was lucky to get a returned motor though. Regardless, I would have paid full pop. They were great to work with.


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## Canadium (Jul 30, 2022)

Susquatch said:


> Assuming the transformer has 3 phase in and out then Yes. But not anywhere near the power level you need. That transformer was just used to create lower power for the other devices on the mill. Not to run the mill.



According to https://www.inchcalculator.com/horsepower-to-kva-calculator/ the 5kVA transformer should easily handle the 1HP 3 phase motor on my mill?


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## Susquatch (Jul 30, 2022)

Canadium said:


> According to https://www.inchcalculator.com/horsepower-to-kva-calculator/ the 5kVA transformer should easily handle the 1HP 3 phase motor on my mill?



I think perhaps you missed the nuances of my comment. Although the transformer might be sized and rated for this task. The wiring may not be. To be more clear, the amperage on the low voltage side will be inversely proportional the voltage ratio. If the wires and terminals on the low voltage side are not sized for the current required on the low voltage side to generate the output power for the mill on the high voltage side, they will be seriously compromised. 

It seems very odd to me to think that the transformer was sized that big though. I can't appreciate that there was any need for that. It seems more like an over designed system assembled by someone who didn't really know what they were doing and chose to err on the safe side or perhaps even more likely by someone who did know what they were doing but chose to use what was available rather than to buy and use ideal components. We might never know. 

In any event, I can't really see any advantage to using the transformer to step up the voltage from 120 or 220 to 575. To do so will require 120 or 220 3 pH and careful analysis of the wiring limits as described earlier. Also, to be very clear, the 3phase output of a VFD is not a suitable input for any transformer. At a minimum, transformer influenced feedback to the VFD will be misinterpreted to the detriment of VFD output voltage control and at worst could result in serious damage to the VFD circuits. 

On the other hand, using the transformer to generate single phase low voltage output to power other devices such as DROs and power feeds would work quite well and given that they exist on the subject machine I am reasonably confident that this is how the transformer was used - albeit overdesigned. 

Without detailed knowledge of the previous usage of the system all of the above is just educated speculation on my part.


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## Degen (Jul 30, 2022)

It comes down to power consumption basically forget losses for the moment, consider watts required.  This is basically V x A = Watts used.  So as the voltage goes lower the amps increase.  This is where you tun into trouble increased amperage requires increased conductor size.

Now as to VFD conversions here is done through a little electronic switching magic transformation (same power Watts).

Now using a transformer in the system with a VFD adds another complexity of induction that must be neutralized to keep the electronics happy.

It is likely less costly to get the motor rewound or replaced with something to match (or closely match) your existing supply.


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## Canadium (Jul 31, 2022)

Susquatch said:


> I think perhaps you missed the nuances of my comment. Although the transformer might be sized and rated for this task. The wiring may not be. To be more clear, the amperage on the low voltage side will be inversely proportional the voltage ratio. If the wires and terminals on the low voltage side are not sized for the current required on the low voltage side to generate the output power for the mill on the high voltage side, they will be seriously compromised.
> 
> It seems very odd to me to think that the transformer was sized that big though. I can't appreciate that there was any need for that. It seems more like an over designed system assembled by someone who didn't really know what they were doing and chose to err on the safe side or perhaps even more likely by someone who did know what they were doing but chose to use what was available rather than to buy and use ideal components. We might never know.
> 
> ...



My intended point was that if I went the RPC route the transformer was already here making that option more attractive. I wasn't planning on using the transformer for anything else, at least not yet. Presumably modding former output wires to appropriate capacity as input wires would not be a big problem. I suppose a 5kVA transformer might be as small as they get in an industrial shop but in my shop there's only myself at work and I've never used two machines at once. The mill I think is a relatively small Bridgeport and not a big juice consumer. Probably perfect for my small shop though.


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