Should I buy this grinder? Advice please
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    Default Should I buy this grinder? Advice please

    I have found a cylindrical grinder that has been sitting on a factory floor for about 10 years unused. I can pick this machine up relatively cheaply. I would only be for hobby use. It is a Jack Mill GU 750 FA.

    I have no data on this machine other than what is on the name plate and the motor data plates. I know that it is a hydraulic machine because it comes with a pump. The table moves left and right freely. The control that moves the main spindle back and forth just spins but doesn't move the spindle at all. I assume this control is hydraulic.

    The machine is covered in old grindings and coolant gunk. There is a lot of brown/orange corrosion but a good wipe with a rag reveals good flat looking machine surfaces without pitting.

    The OD spindle turns freely. It ID was a bit seized up but came loose when I turned it with my hand. It still doesn't spin freely and feels like there is some kind of gunk in there? Could be crusted up grease or corrosion or something I don't know. Hopefully not grindings that have somehow found their way in.

    The main spindle is 5hp 3 phase. Unfortunately I only have single phase in my shed. I would need to use some kind of VFD to power it. This may be a problem that prohibits me from buying this machine.

    I would appreciate anyone's input.

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    Quote Originally Posted by gtrdude View Post
    The main spindle is 5hp 3 phase. Unfortunately I only have single phase in my shed. I would need to use some kind of VFD to power it. This may be a problem that prohibits me from buying this machine.
    Why is that a problem for you? These days VFD or RPC are relatively cheap. I like RPC's because you can make one yourself easily, less than 500.00 here in the states and can run more machines as you grow. A VFD is also fine.

    The only two problems, I can see, is if you don't have enough electricity coming to your shed or don't have the money to swing the power converting device right now...

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    Quote Originally Posted by swatkins View Post
    Why is that a problem for you? These days VFD or RPC are relatively cheap. I like RPC's because you can make one yourself easily, less than 500.00 here in the states and can run more machines as you grow. A VFD is also fine.

    The only two problems, I can see, is if you don't have enough electricity coming to your shed or don't have the money to swing the power converting device right now...
    Hi, thanks for the reply. The machine has a grand total of 4 motors which are all 3 phase. I may be able to make do with running only 3 of these at a time. I'm guessing that the total power requirement to run these together (through the machine's control panel) would be prohibitive. I was thinking that I may be able to run 3 separate VFD's for each motor but I'm not sure if I would lose the back-and-forth automation or even if it could be done at all. Does that make sense?

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    Quote Originally Posted by gtrdude View Post
    Hi, thanks for the reply. The machine has a grand total of 4 motors which are all 3 phase. I may be able to make do with running only 3 of these at a time. I'm guessing that the total power requirement to run these together (through the machine's control panel) would be prohibitive. I was thinking that I may be able to run 3 separate VFD's for each motor but I'm not sure if I would lose the back-and-forth automation or even if it could be done at all. Does that make sense?
    One 10 HP RPC will run the machine with ease. And cost a lot less..

    I'm not familiar with your country's electrical supply or availability or parts so I'm of very little help.. I can tell you what I do to power my shop.

    I am far away from 3 phase power and RPC is the best solution for me. I do have one VFD running the spindle of a Bridgeport Boss CNC machine with a 3 HP motor but that is the only machine I have found practical for me to install a VFD and that is only because I'm using it to control spindle speeds.

    I can easily build a control box for a RPC, you can too with the help available here, but it is just cheaper, time to source the materials mainly, for me to call Jim at Phase Craft and order a ready made box. I can buy a 10 HP control box for 250.00 and source a used 10 HP three phase motor for about 150.00. Less than 500.00 has me set up with everything but wire. My first 10 HP RPC powers about 8 different machines, most with multiple motors. I needed a 240 volt, 50 amp single phase circuit to power that RPC.

    My second RPC is a 20 HP unit and the motor and control box for it was under 1000.00 It powers a 20 HP hydraulic planer, very well I might add, and uses a 70 amp, 240 volt single phase power circuit.

    You have many options, If you need the machine I would not let making three phase deter me

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    Quote Originally Posted by swatkins View Post
    One 10 HP RPC will run the machine with ease. And cost a lot less..

    I'm not familiar with your country's electrical supply or availability or parts so I'm of very little help.. I can tell you what I do to power my shop.

    I am far away from 3 phase power and RPC is the best solution for me. I do have one VFD running the spindle of a Bridgeport Boss CNC machine with a 3 HP motor but that is the only machine I have found practical for me to install a VFD and that is only because I'm using it to control spindle speeds.

    I can easily build a control box for a RPC, you can too with the help available here, but it is just cheaper, time to source the materials mainly, for me to call Jim at Phase Craft and order a ready made box. I can buy a 10 HP control box for 250.00 and source a used 10 HP three phase motor for about 150.00. Less than 500.00 has me set up with everything but wire. My first 10 HP RPC powers about 8 different machines, most with multiple motors. I needed a 240 volt, 50 amp single phase circuit to power that RPC.

    My second RPC is a 20 HP unit and the motor and control box for it was under 1000.00 It powers a 20 HP hydraulic planer, very well I might add, and uses a 70 amp, 240 volt single phase power circuit.

    You have many options, If you need the machine I would not let making three phase deter me
    I'm not sure if the power sockets in my shed are capable of 15amps @ 240v. Most likely they are 10amp. So the max I could put from a single socket is 3hp correct? Otherwise if it was 15amps I could get roughly 5hp?

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    Also, any suggestions on getting the ID spindle to turn freely?

    What about the hydraulics? What is the likelihood that the hydraulic lines be blocked up with gunk? Or should I just fill up the tank with oil, connect up the lines and go for it?

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    Quote Originally Posted by swatkins View Post
    One 10 HP RPC will run the machine with ease. And cost a lot less..

    I'm not familiar with your country's electrical supply or availability or parts so I'm of very little help.. I can tell you what I do to power my shop.

    I am far away from 3 phase power and RPC is the best solution for me. I do have one VFD running the spindle of a Bridgeport Boss CNC machine with a 3 HP motor but that is the only machine I have found practical for me to install a VFD and that is only because I'm using it to control spindle speeds.

    I can easily build a control box for a RPC, you can too with the help available here, but it is just cheaper, time to source the materials mainly, for me to call Jim at Phase Craft and order a ready made box. I can buy a 10 HP control box for 250.00 and source a used 10 HP three phase motor for about 150.00. Less than 500.00 has me set up with everything but wire. My first 10 HP RPC powers about 8 different machines, most with multiple motors. I needed a 240 volt, 50 amp single phase circuit to power that RPC.

    My second RPC is a 20 HP unit and the motor and control box for it was under 1000.00 It powers a 20 HP hydraulic planer, very well I might add, and uses a 70 amp, 240 volt single phase power circuit.

    You have many options, If you need the machine I would not let making three phase deter me
    I take it the RPC needs to be wired directly from the switch board itself (not wall socket)? I will have to do some more research on that one.

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    Quote Originally Posted by gtrdude View Post
    I have found a cylindrical grinder that has been sitting on a factory floor for about 10 years unused. I can pick this machine up relatively cheaply. I would only be for hobby use. It is a Jack Mill GU 750 FA.

    I have no data on this machine other than what is on the name plate and the motor data plates. I know that it is a hydraulic machine because it comes with a pump. The table moves left and right freely. The control that moves the main spindle back and forth just spins but doesn't move the spindle at all. I assume this control is hydraulic.

    The machine is covered in old grindings and coolant gunk. There is a lot of brown/orange corrosion but a good wipe with a rag reveals good flat looking machine surfaces without pitting.

    The OD spindle turns freely. It ID was a bit seized up but came loose when I turned it with my hand. It still doesn't spin freely and feels like there is some kind of gunk in there? Could be crusted up grease or corrosion or something I don't know. Hopefully not grindings that have somehow found their way in.

    The main spindle is 5hp 3 phase. Unfortunately I only have single phase in my shed. I would need to use some kind of VFD to power it. This may be a problem that prohibits me from buying this machine.

    I would appreciate anyone's input.
    I have an identical machine. The spindle infeed handle is a two speed, the middle of the handle there is a pull in/out knob. One position for fine feed, the other position for normal. It is not hydraulic, the hydraulic system only does two things on these simple machines. It moves the table left and right thanks to a hydraulic motor operating a spur gear that moves a rack on the table. And there is the spindle rapid retract which is a hydraulic ram at the rear. The spindle is a plain bearing affair. It should not start until oil pressure reaches a determined level. Stiff is normal. They are a very basic machine, certainly not the best out there, but if the price is right. Although you will need to run coolant.

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    Quote Originally Posted by RC99 View Post
    I have an identical machine. The spindle infeed handle is a two speed, the middle of the handle there is a pull in/out knob. One position for fine feed, the other position for normal. It is not hydraulic, the hydraulic system only does two things on these simple machines. It moves the table left and right thanks to a hydraulic motor operating a spur gear that moves a rack on the table. And there is the spindle rapid retract which is a hydraulic ram at the rear. The spindle is a plain bearing affair. It should not start until oil pressure reaches a determined level. Stiff is normal. They are a very basic machine, certainly not the best out there, but if the price is right. Although you will need to run coolant.
    Thanks for the info! So am I correct in thinking that you can operate this machine without the hydraulic pump ON?

    So there is an oil pump that send oil to the spindle?

    Basic is fine but when you say "not the best" what do you mean by that?

    BTW, do you know if/where I could find an operating manual or further info on these machines?

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    Quote Originally Posted by gtrdude View Post
    Thanks for the info! So am I correct in thinking that you can operate this machine without the hydraulic pump ON?

    So there is an oil pump that send oil to the spindle?

    Basic is fine but when you say "not the best" what do you mean by that?

    BTW, do you know if/where I could find an operating manual or further info on these machines?
    Yes you can operate it without the hydraulic pump, although it would be slow.

    Yes there is an oil "pump" that sends oil to the spindle. There is a separate oil reservoir for the spindle with what is normally a coolant pump on it. I used ISO15 oil for the spindle in mine, which was a stab in the dark guess as to what oil is supposed to be used.

    I went and had another look at mine, it has been awhile since I used it, and the spindle in feed wheel has no high/low, but rather the centre knob pushed in is neutral and the wheel free spins, pull it out and it engages the spindle feed screw.

    What I mean by not the best is it does not have dwell or automatic infeed. I am a complete amateur and self taught when it comes to grinding. About the only way you will get a manual will be invent a time machine and go back in time when they were selling these models. I did email Jackmill when I got mine, but never got a response.

    20131110_175534.jpg 20131117_142718.jpg

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    I think the larger question is this:

    if your just a Hobbyist, what are you going to use it for ?

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    Quote Originally Posted by digger doug View Post
    I think the larger question is this:

    if your just a Hobbyist, what are you going to use it for ?
    Looks like a very nice grinder...Od ,Id, perhaps other jobs..but yes you need to have a need..

    Stuck bearings are often noisey or short life.. likely tear down wold be good..If plane bearing likely easy to save..

    QT: [some kind of gunk ] may just be dry needing a cleaning and lube..run fast dry and it may be shot from doing that..

    Saw a grinder spindle filled with oil to run out and so perg the bearings ..that seemed to work last time I saw the grinder...

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    Quote Originally Posted by digger doug View Post
    I think the larger question is this:

    if your just a Hobbyist, what are you going to use it for ?
    What can I say? I watch too many YouTube videos 😂😂😂

    I don't have any specific application for it as such but I like the idea of being able to grind my own tool holders and things like that. Hours of fun for the whole family. I'm a single guy who lives for his hobbies, I have plenty of room and is within my budget to aquire the machine.

    So why not?

    Sent from my SM-J105Y using Tapatalk

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    Here are a few pictures of my 20 HP RPC install. The box in the middle is a RPC control panel from Phase Craft. On the right is a single phase sub panel with a 70 amp, 240 volt breaker that feeds the control panel. The switch box above that has fuses that protect the idler motor. On the left is a three phase panel that accepts the output from the control box and distributes it to the individual machines.

    e1.jpg efinish.jpg

    To keep things quiet in the shop I installed the 20 HP idler outside in a dog house

    20170202_172640.jpg 20170202_172817.jpg

    You can also just run the output from the control panel as a common feed around the shop and splice in a fused disconnect with the correct sized fuses for each machine... That is what I did for my 10 HP RPC. By the time I bought all the fuses and boxes it would have been cheaper to build it as I did my 20 HP RPC with a three phase breaker box.

    Steve

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    Quote Originally Posted by swatkins View Post
    Here are a few pictures of my 20 HP RPC install...
    Your setup looks awesome Steve. The dog wont be happy about his kennel though Here in Australia it's kind of frowned upon to fiddle with your own electrical circuit. They tend to like a qualified electrician to do all of the voodoo so us mere mortals can stay safe. I might have to talk to a sparky about what I can and can't do myself.

    I found a company that's based here in Melbourne who manufacture RPCs. They don't have any pricing on their website though (no surprise). I will call them tomorrow and see how many pesos they want for one of these wiz bang boxes.

    Home Page | Phase Change Converters

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    Be sitting down when they tell you. They do work OK. I have had one for eight years. It has blown up three controller boards in that time although to be fair I originally bought one that had an obsolete controller. It has now been updated and the new board is massively more sturdy.

    Home made phase converters in Australia have the problem of voltage. Run it off the mains and you will have 240V three phase. But most three phase machines here are 415V.

    The Jackmill grinder, at least on mine all the motors are dual voltage so you could buy two VFD's and run it off single phase. One VFD to run the hydraulic motor and the spindle lube pump. And another to run the main spindle.

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    Quote Originally Posted by gtrdude View Post
    What can I say? I watch too many YouTube videos ������

    I don't have any specific application for it as such but I like the idea of being able to grind my own tool holders and things like that. Hours of fun for the whole family. I'm a single guy who lives for his hobbies, I have plenty of room and is within my budget to aquire the machine.

    So why not?

    Sent from my SM-J105Y using Tapatalk
    "Grind your own toolholders" ? Yup, just needed to do 3 last night....not.

    I am in the same boat as you, however I have some restraint (not much)
    and this grinder don't sound like much of a "Deal" with all the rust
    you describe.

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    Quote Originally Posted by digger doug View Post
    "Grind your own toolholders" ? Yup, just needed to do 3 last night....not.

    I am in the same boat as you, however I have some restraint (not much)
    and this grinder don't sound like much of a "Deal" with all the rust
    you describe.
    What? You don't even grind your own toolholders?

    Restraint is for blokes with "significant others" LOL. I do what I want

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    Quote Originally Posted by gtrdude View Post
    What? You don't even grind your own toolholders?

    Restraint is for blokes with "significant others" LOL. I do what I want
    This forum is called "Practical" machinist for a reason.

    Not "Theorectical Tenured Prefesser's hobbyies"

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    Quote Originally Posted by gtrdude View Post
    What? You don't even grind your own toolholders?

    Restraint is for blokes with "significant others" LOL. I do what I want
    No significant other? No restraint? Get out of your basement and buy a boat/motorcycle/airplane.


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