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Thread: Speed............ slow it down?

  1. #1
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    Speed............ slow it down?

    OK, I have a Delta Bench grinder, from the US, a buddy left it with me when he moved away from Japan.

    It is a US spec unit, but it seems to run fine on the 100V 50 Hz we have hear.

    I really need a slower speed grinder for my lathe tools, these high speed grinders are not so good. I got a chance to use a real slow speed grinder the other day, and it was so nice.

    Anyway, can the speed of these grinders be slowed down using one of them router speed controllers...........?


    Says.....
    Use on brush-type motor routers up to 3 HP, 20 amp.
    I'm thinking that the Delta bench grinders are induction motors, so this is not going to work.........................?

    There are "Two Speed" grinders, what is the difference, some unit that can be wired in to the grinder, or is it more of a "It's built that way" kind of thing?

    Cheers!
    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
    William Arthur Ward

  2. #2
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    i say plug it in and see if it works? if it makes funny noises or smokes don`t use it ......the wheels usually cost more than bench grinders, unless you pop for a good ol` baldor or the like......
    [SIZE="1"] associated with several importers and manufacturers.[/SIZE]

  3. #3
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    Quote Originally Posted by tod evans View Post
    i say plug it in and see if it works? if it makes funny noises or smokes don`t use it ......the wheels usually cost more than bench grinders, unless you pop for a good ol` baldor or the like......
    Well, them speed controlers cost $70 here and the slow speed grinders cost over $200 for a 6" unit......

    Cheers!
    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
    William Arthur Ward

  4. #4
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    never-mind



    the 6" china grinders are pretty easy to find here for 30-40 bucks, less than a set of good wheels....
    [SIZE="1"] associated with several importers and manufacturers.[/SIZE]

  5. #5
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    My understanding is that this type of speed control is for use with 'Universal motors" and not standard capacitor start motors. I looked long and hard from a way to add variable speed (thats basically what you want to do) to a standard single phase motor and I finally came to the conclusion it wasn't possible. Thats how I go intersted in 3 phase and VFD's.

    I think, but I am not that familiar with motors! That two speed motors have extra winding in them. I have a blower I pulled out of a furnace and it has 4 or 5 speeds. But each speed has it's own lead. It's not a true variable speed.
    Last edited by Jeff Horton; 01-27-2007 at 12:54 PM.
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  6. #6
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    Quote Originally Posted by tod evans View Post
    never-mind



    the 6" china grinders are pretty easy to find here for 30-40 bucks, less than a set of good wheels....
    $20.00 at Grizzly.
    (sometimes I can't help myself )

  7. #7
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    Stu,
    That won't work on an induction motor. The reason why the grinder is happy on 100V50 Hz is because it is seeing the same number (or close to it) of Volt/cycle as it would were it running on 120V/60 hz. That is just a voltage changer and will not change the frequency. Further more single phase motors have a start Capacitor and or starting windings along with a centrifugal switch that cuts the stating capacitor out when the motor reaches 2/3 speed. Years ago a few VFD manufacturers did make Vfds for single phase motors and they limited the low freq to 45 HZ to prevent having the start Cap or starting winding from being run continuously and burning out.

    sorry,
    "Thereís a lot of work being done today that doesnít have any soul in it. The technique may be the utmost perfection, yet it is lifeless. It doesnít have a soul. I hope my furniture has a soul to it." - Sam Maloof
    The Pessimist complains about the wind; The Optimist expects it to change;The Realist adjusts the sails.~ William Arthur Ward

  8. #8
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    Yeah, the start capacitor and its centrifugal cutoff seem to be the fly in the ointment. I did a little reading on VFD's in wikipedia (which makes me a leading expert ). They can be used with universal or induction motors, 3 phase or 1 phase.

    They also say that the VFD delivers more torque per amp at startup. They use the soft start principle seen in var speed routers to slowly ramp up the juice. This creates the same torque with half the current at startup.

    I'm wondering if an induction motor with the capacitor and centrifugal switch removed would start under those conditions. If nothing else, in a belt drive system (not much help for the bench grinder) using an idler to remove the load at startup, it would likely work.

    I have an arbor and pulleys that I used to spin my 8" stone and buffer on, but I don't have a spare motor to play with. And I don't have a VFD. Before anyone says the obvious - yes, I know it's easier to reduce the rpm's here using pulleys

    Now, if anyone wants to send me a free Baldor grinder (postage paid, of course) and a suitable VFD - I'd be happy to perform the necessary experiments. Don't thank me, guys - my offer is made in the name of science !!
    All the best,
    Ian G

    **Now holding auditions for a catchy new signature**

  9. #9
    Steve Clardy Guest
    I've got one of those 6" Delta variable speed grinders.
    Its advertised as two- speed, but it has a variable speed switch, works like a light dimmer switch.
    Have no idea what motor is in it.
    Maybe a little goggling on the grinder specs from Delta would tell you what kind of motor it is. If your motor is the same type--------------

    Delta GR250 ShopMaster [Shopmaster ]

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