Single to 3 phase conversion problem

Shawn_Laughlin

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I’ve Been thinking about doing a 1 to 3 phase conversion on my grizzly g0791 lathe/mill combo,the biggest combo that’s made.

Here’s where im going to run into a problem. Since the lathe and mill are two seperate motors and all wired together in line through switches so you can’t run both at the same time,how would I wire a vfd but still use the single phase for the mill? I’m lost as lost can be.
Side note: Honestly I would like to be able to use both at the same time so I could take advantage of power feed, and in that case I know I would have to have two vfd’s.

Or if I can find a 3 phase motor that will fit my mill,can two motors be wired through one vfd or would I need to buy two?

Whichever way I go, the only way I will be able to do this, is with help from someone that is familiar with this. I’m not an idiot and I catch on extremely fast and I’ve wired single phase and 4 and 3 wire 3 phase but I’ve never had to do a fresh build. I can do iso drawing for pipe but you show me an electrical schematic and it’s alien language.

I’d appreciate the help,thanks

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matthewsx

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I'm assuming you want 3 phase for the lathe spindle but it's wired in series with the mill spindle with a switch between so you can't use both at the same time.

Unfortunately if you want to accomplish this you will need to get familiar with the schematic for your machine since it will involve bypassing and/or re-purposing the existing switches and safety interlocks. If someone has done this exact conversion they might be able to provide schematics for what they did but you will still need to read and understand that.

If you can do plumbing you should be able to do electrical, just requires a little study.

Cheers,

John
 

Shawn_Laughlin

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Thank John. I can follow a schematic it’s just the symbols I will have to go back and forth. I need to write them all down on a piece of paper so they are right in front of me. I think I might just do a conversion on both motors as it will be the least trouble I believe and should be pretty generic.
 

Jackle1312

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You may be able to wire the vfd to the output side of the lathe motor relay so that it only has power when the lathe is selected. Depending on the vfd and the switches on the machine, it may be possible to tie them in to the vfd and keep the original controls.
 

Shawn_Laughlin

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The more I think about jackle since the only way the power carriage and cross slide can be used is when the lathe is running I thought about have it wired so both can be on at the same time “with the chuck removed from lathe obviously” so I will have power feed when using the mill. I haven’t completely decided on that yet though
 

MikeInOr

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I appreciate having a VFD and variable speed on my mill and lathe... but in your case I don't think I would convert your mill/lathe to 3 phase.

The proper way to convert your machine would be to buy 2 VFD's... one for each new 3ph motor.

My number 1 rule for installing VFD's is there should never be any switches or contactors/relays between the VFD and the motor it is powering. Cutting the power between your VFD and motor while the motor is running will likely cause irreparable damage to your VFD.

I do NOT believe running 2 motors off the same VFD at one time is a good idea. If you have one motor running and power on the second motor you will probably draw more inrush current than the VFD can handle and throw an error on the VFD or damage the VFD. I am not saying it can't be done... I am just saying I would not do it. VFD's are designed to limit the inrush current of a motor starting by soft starting (ramping up the speed) the motor... hence I believe most VFD's are designed to operate and MUCH lower current levels than the inrush current from starting a motor from a dead stop to full speed without the ramp up.

If you only want variable speed for your lathe you should completely isolate the lathe controls from the mill controls then use the VFD to control start/stop/reverse functions of the lathe motor. Wire the 1ph mill controls completely separate from the lathe and the VFD controlling the lathe.

Due the expense and trouble of converting your mill/lathe to 3ph and having to buy 2 new 3ph motors and 2 new VFD's... I would consider selling the mill/lathe and look for used replacements that are already 3ph machines. You will most likely get more for your mill/lathe as it sits (single phase) than you could sell it for after replacing the motors and adding the VFD's.
 
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markba633csi

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Shawn question: why do you want to do this, or in other words, what is the perceived benefit? Disregarding the labor and cost for the sake of discussion
Mark
 

Bi11Hudson

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Thought I would weigh in on this one, even though I'm not really qualified to discuss VFDs. I lay claim to speaking three languages, albeit somewhat archaic these days. The three being: English, Electricity, and Computers. I do not speak WinDoze, I speak Computers. At the core level. Same with Electricity, not Electronics. They both have their own language, entirely seperate.

As I understand it, the machine is single phase and you want to use a three phase motor on the lathe while retaining the single phase motor on the milling head. If that is indeed the case, the answer is relatively simple. On the other hand, if it is not the case, I can be dismissed (ignored) with no hard feelings or misunderstandings.

To keep things simple, let's start with the power supply. It must be for 240 volts, single phase. Get that done and out of the way before proceeding. Two motor conversions, and whatever relays or starters are involved. Anything rated at 120 volts must be converted to 240 volts.

You could reference 120 volts by using the neutral, but that involves a four wire plug and considerable complexity. Which I recommend against for a rank (as self described) amateur. You must not use the equipment ground as a neutral. It can be done, but is dangerous on a good day. And a disaster on a bad day. When, and only when, that is out of the way, we concentrate on the spindle motor, the three phase portion of the desired circuit.

Assuming there to be a reversing switch, that must be disabled. Probably set for forward and left alone. The idea is to have two wires to the motor for run. Disconnecting them stops the motor. Connecting them causes the motor to run. That is where you would insert the VFD, in place of the motor. Overload devices such as fuses and the like will need to be a higher rating. Refer to the VFD manual for details on how much larger. Motor overloads(heaters), if they exist, will be hardwired around. The VFD will handle any overload condition.

Next step is to hook up the VFD and the motor. Any reversing will involve swapping any two of the three wires to the motor. Usually handled by the VFD internals. Do not use an external reversing switch, it will cause gastric upset for the VFD. Adjustment of the VFD (tweaks) will be per the manual for the VFD. The ON/OFF function of the lathe spindle will kill power to the VFD electronics.

To run the mill motor will be as usual. If you want to run both at the same time, take up the matter with the Grizzly schematics and/or the dealer. That is a completely different issue to running a three phase motor off of single phase.

In many (most) cases, electrical schematics are developed by engineers in their native language. And then translated to English and (almost) ANSI symbology sufficient to claim documentation for a machine. They will be reasonably accurate, in their native language. One must build a cross reference to standard ANSI symbols on their own. I've been an industrial electrician for almost 50 years and still must make this translation effort. Then, you must be able to see in your mind how the machine works.

I have hopes that this clarifys your situation, at least to the point you know where you're headed.

Bill Hudson​
 

matthewsx

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Shawn question: why do you want to do this, or in other words, what is the perceived benefit? Disregarding the labor and cost for the sake of discussion
Mark
This is actually the first question that must be answered.

Assuming the machine is setup and operating properly it should be able to do work within the specified envelope and tool sizes. If you're having trouble with making smooth consistent cuts in normal materials with normal feeds and speeds then there might be something else wrong. The lathe has a 2hp motor and 9 speeds which should be enough to work most materials, if not why not?

From the specs it looks to be a very capable machine, it would be a shame to go through a conversion only to find out that there was some other issue.

John
 

Shawn_Laughlin

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The reason I’m eating to do this is bc of the finish I’m getting using the lathe. The 1 phase 220 motor is causing hormonics that are showing up in my turnings no matter what metal I’m turning down.

I’ve isolated the motor and lathe with thick rubber.1/4 thick Red rubber used like on pipe work flanges. It’s very secure to the concrete floor and I’ve even went and spent 70 dollars on two link belts which helped but not cured the problem. The vibrations come and go with the harmonics the motor is making so I figured 3 phase would cure it. As far as buying motors I have two Baldor ,one 1.5 hp and one 2 hp, motors that are in great shape. Both are explosion proof motors even though I don’t need it. One was used for a tube axial fan for a paint booth and the other I can’t actually remember what I took it off of M.B. but I do know they were working when I removed them. So all I would have to do is buy the vfd and I’ve seen new 2hp vfd for about 100 bucks. That’s not an American made but I can’t afford that anyways.
 

MikeInOr

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The reason I’m eating to do this is bc of the finish I’m getting using the lathe. The 1 phase 220 motor is causing hormonics that are showing up in my turnings no matter what metal I’m turning down.

I’ve isolated the motor and lathe with thick rubber.1/4 thick Red rubber used like on pipe work flanges. It’s very secure to the concrete floor and I’ve even went and spent 70 dollars on two link belts which helped but not cured the problem. The vibrations come and go with the harmonics the motor is making so I figured 3 phase would cure it. As far as buying motors I have two Baldor ,one 1.5 hp and one 2 hp, motors that are in great shape. Both are explosion proof motors even though I don’t need it. One was used for a tube axial fan for a paint booth and the other I can’t actually remember what I took it off of M.B. but I do know they were working when I removed them. So all I would have to do is buy the vfd and I’ve seen new 2hp vfd for about 100 bucks. That’s not an American made but I can’t afford that anyways.
I have a variety of VFD's including Hitachi's, Allen Bradley's, Teco's and generics. The pricey ones generaly have more features but as far as actually running the motors I can't tell a difference between any of them. There are a couple of specific function integrated VFD control chips that I believe most manufactures and all the generic VFD's use... which is what has made VFD's so affordable.

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.nxp.com/docs/en/white-paper/MC3PHACWP.pdf&ved=2ahUKEwiK6K_bv-_iAhXbHzQIHfejBucQFjABegQIBBAB&usg=AOvVaw1osb3GeNB-aqEUBWxP0w-0

At first I questioned whether a 3ph motor would make much difference in the finish of your parts... I doubt just changing to a 3ph motor will make any difference but being able to tweak the speed a bit with a VFD should definitely change any harmonics issues you are having.

If you are set on trying a VFD and 3ph motor I would reccomend isolating the lathe spindle motor control from the rest of the machine controls and ONLY running the 3ph lathe spindle motor on the VFD with no switches or relays between the VFD and the motor. If it works well and you love it so much that you want to change the mill spindle to 3ph and a VFD I would HIGHLY reccomend you purchase a second VFD and dedicate it to the mill spindle without any switches or relays between the VFD and the mill 3ph motor.

If it were me I would try to leave the original single phase control wiring intact to allow you or a future owner to easily convert the machine back to 1 ph if it is ever desired.
 
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BROCKWOOD

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Was just taking a quick overview of the schematic for your combo. Gotta love that Grizzly makes their manuals so readily available! Separating out the lathe & mill power is indeed beneficial in just the way you mentioned. Power feed on milling operations! It was easy on my G0773 (discontinued). Just plug the mill into a separate outlet on a separate circuit breaker - all 120V. Yours is much more complicated with many nice features. Since the guys with VFD experience are saying direct drive between VFD & motor, it appears that you would be abandoning those features - if they are not available functions of the VFD itself. If I recall, your reasoning for wanting a 3ph VFD on the lathe portion is your disappointment in surface finishes? I struggle with that as well - but, in my case, it is a lack of experience that I struggle with. Best wishes.
 

Shawn_Laughlin

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I have been out of town working a shutdown since July and have been so tired when getting off work I just wanted to sleep when I got off so that’s why it’s taken me so long to reply to all of you guys’ very helpful comments. I’ve actually learned quite a bit since then and have decided like suggested above to wire both motors separately and leave the original wiring for future if need to revert. I bought two Vfds for 110 a piece and have every bit the benefits of a unit 3 tines the price. Braking without an external resister is the feature that made my mind up. The only thing I can’t use is a wireless control pad but that obviously wasn’t a kill all bc I bought 2. They work flawlessly and the instruction manual was surprised easy to ready like the Chinese company paid a fluent English speaking person to write it which I didn’t think was going to be the case by reading the description on Amazon. And both are overrated at 3 hp so I shouldn’t see any overheating of the vfd. I have decided to find a lower hp motor than the 1.5 I originally was going to use. I think 1hp will be perfect. And I didn’t really explain what the main reason for the mill motor. The gears in the head have so much slop it’s ridiculous and they are extremely loud so I decided to make a single speed pulley and belt system and with the 3 phase motor controlled by the vfd I will then have control of the rpms and be able to have much faster rotator for small end mills. I just don’t see the benefit of small end mills and 2200 rpms, it just doesn’t work so well as y’all know and my machine isn’t rigid enough,even though I’ve fixed a lot of that too, to mill will larger end mills. Thank y’all for the help
 
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