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  1. #1
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    Default Lathe motor upgrade questions

    Hey guys
    I'm currently upgrading my lathe motor to a 3 phase with a VFD, and I had some questions around the pulleys / belts.

    I will be buying a pulley to fit the new motor shaft size which is 28mm, but I'm unsure as to what the diameter of this pulley should be, or if it matters. My questions

    - Does the size of the pulley matter ?
    - I will obviously need to change the pulley that runs up to the spindle, should I keep the pulley size the same also ?
    - I will need a new belt also, should I be checking the available belt sizes and buy a pulley to suit, or can belts be bought in almost any size ?


    Cheers

  2. #2
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    use the same size PCD pulley as on the old motor...eg same od diameter and belt size is what I would do. only cost one pulley then
    short arms deep pockets...lol

  3. #3
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    Hi there,

    Is the new motor the same (50Hz) speed as the original? If so then in order to keep roughly the same speed range then I would keep the same pulley sizes. While a VFD will give you good variable speed, it will only be useful from maybe 20Hz - 120Hz give or take.

    Can you not bore out the original pulley for the new motor? I assume you will not be running the spindle directly from the motor and hoping to only use VFD for speed control? If you do plan on this then you will be disappointed as the speed variations derived from a VFD will not be sufficient to allow this. You will still need to use some gear reductions from time to time if you want to use full speed range which means you will still need to transmitt the power through the original gearbox.

    I plan on converting my lathe to VFD (one day) and I plan on using the same pulleys and same belts. It will be purely a motor change. It will still drive through the gearbox to achieve the required rpm range.

    A cheapie non vector VFD will provide approx. a 6:1 speed variation (and still provide useful HP and torque). This means that a 4 pole motor running at (say) 1500 rpm will provide useful speeds from about 600 rpm @ 20Hz to about 3600 rpm @ 120 Hz. Now you may get a little more or a little less depending on the motor size etc. but this has been my experience with my mill running a 3 HP motor.

    If you want larger speed ranges without loss of torque or HP then a DC motor and speed controller is the go.

    Cheers,

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  4. #4
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    Simon has given some good info
    However a Vector Drive VSD will give good control and torque considering you are ...err... should be using the existing pulley and gear change negating having to go with dc...but that is it the way transmission is going..like it or not. DC control for motor drives is the way forward.

  5. #5
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    How do you get the VFD to go to 120hz.
    What brand VFD are you running.
    I don't think I've been able to get my danfos one that fast.

  6. #6
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    Programming
    Some that i am aware of start at minimum 200hz with the majority getting to 400hz.

  7. #7
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by eskimo View Post
    Programming
    Some that i am aware of start at minimum 200hz with the majority getting to 400hz.
    Some won't go more than 60Hz

  8. #8
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    Thanks for the detailed responses so far.
    Simon good stuff there, the reason I was going for a VFD and not a DC controller is because I am wanting to get a 4 pole 3 phase motor, simply for the torque benefits.
    In order to do this, as I only have single phase power at home, the VFD provided me with the ability to go 1 phase in, 3 phase out.
    I understand that I'll only be able to go as low as about 600rpm on the lathe with this setup which is fine for me I think.

    In relation to changing the pulleys, it is simpler to just keep the existing pulleys and swap out the motor - I would still use the gear box i think, as eskimo mentioned, which would sort of negate it, but I should be able to wind up the speed quickly without having to mess aroudn too much....

    Unless I am totally confused - it makes sense in my head..i think.

    This is what im looking at anyway, to provide some clarity

    1 5KW 2HP Single TO 3 Phase VFD Freq Upto 400Hz Motor Speed | eBay

    3 PH Three Phase Electric Motor 415V 1 5KW 2HP 1400rpm 4 Pole | eBay

  9. #9
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    Quote Originally Posted by BobL View Post
    Some won't go more than 60Hz
    yeah I know Bob, wasnt thinking of them tho, as whats the point if its restricted to 60hz or even 100. If one wants a VFD get one that will make it go faster.

  10. #10
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by eskimo View Post
    yeah I know Bob, wasnt thinking of them tho, as whats the point if its restricted to 60hz or even 100. If one wants a VFD get one that will make it go faster.
    Many things definitely don't want to go faster, if anything you want them to go slower, e.g. air con pumps, conveyor belts, and even lift doors. The used VFDs we got through Jhovel were 99Hz max lift door controllers.

  11. #11
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    Quote Originally Posted by BobL View Post
    if anything you want them to go slower, e.g. air con pumps, conveyor belts, and even lift doors
    I know what you mean Bob...but as I said....why go slower with a vsd....some things just want to go fast... ie a chiller I put in last Oct gets up to 27K to meet capacity. Lowest speed is 16K or thereabouts ..but can be programmed to get up to 36K to meet capacity at designed parameters so I understand. Oil less too...magnetic bearings. Pumps have own VSD both controlled from Chiller to be driven for best COP for energy efficiency. Pumps do need to be able to get up 70hz to meet flow requirements during peak demand..normally run somewhere between 40-55hz tho.

    oh and I am putting one on a 3ph grinder ...only to make it go slower when needed.

  12. #12
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    Ok, So should I be looking at getting a DC motor and a DC controller, using the same pulley sizes that I currently have or the 3phase with a vfd.

    Because now, I think I am even more confused than i was before !

  13. #13
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    Quote Originally Posted by oohsam View Post
    Ok, So should I be looking at getting a DC motor and a DC controller, using the same pulley sizes that I currently have or the 3phase with a vfd.

    Because now, I think I am even more confused than i was before !
    what ever is easiest and most cost effective for you.

    what you posted above in those links seems fine.

  14. #14
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    Go with a cheapie VFD like a HY. They will go to 400Hz but your motor won't. You can program the max and min Hz in the parrameters of the VFD. For speed control, a 3 Ph motor and VFD are the most cost effective. You will not look back but you just need to realise the limitations of the system and design around those.

    Also, bare in mind that your lathe headstock and spindle bearings will most likely be splash lubricated if it is filled with oil. You really want to make sure that if you are running the motor very slow that the oil is still getting splashed around and the bearings are still getting adequate lubrication. 600 rpm @ 20Hz should still be fine but for slower speeds I would be achieving with the gearbox even if you find your motor works down to say 10Hz. Also your motor may run warmer too since it relies on it's fan for cooling. Slower speeds means less cooling for the motor. The motor on my mill hardly gets warm even at 20Hz but it's only rotating the cutter, not a heavy chuck and workpiece. No big deal but just things to be aware of. Some initial testing once it's all installed will most likely put your mind at ease...

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  15. #15
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by simonl View Post
    No big deal but just things to be aware of. Some initial testing once it's all installed will most likely put your mind at ease...
    Just a reminder that alow speed tests must be done under load otherwise the motor is not rating enough current to heat it up.

    If you want to make sure, it's easy enough to add a small fan to cool the motor.

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