Rheostat for Bench Grinder

Discussion in 'Electrical Engineering' started by buckaroo, Dec 20, 2003.

  1. buckaroo

    buckaroo Guest

    Forgot all the electrical schooling I ever had. Is it feasible or even
    possible to take a standard $40 bench grinder and convert it to variable
    speed by using some sort of rheostat... Possibly a cheap $3 one designed for
    dimming lights..... Or will this burn up the grinder motor or worse yet burn
    my garage down. If this won't work, do they make any gizmo for this
    purpose.

    Thanks for Help
    buckaroo, Dec 20, 2003
    #1
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  2. buckaroo

    John G Guest

    "Repeating Rifle" <> wrote in message
    news:BC0A03AC.2590%...
    > in article

    65d94$3fe4a15e$4503c914$,
    buckaroo
    > at wrote on 12/20/03 11:27 AM:
    >
    > > Forgot all the electrical schooling I ever had. Is it

    feasible or even
    > > possible to take a standard $40 bench grinder and

    convert it to variable
    > > speed by using some sort of rheostat... Possibly a cheap

    $3 one designed for
    > > dimming lights..... Or will this burn up the grinder

    motor or worse yet burn
    > > my garage down. If this won't work, do they make any

    gizmo for this
    > > purpose.
    > >
    > > Thanks for Help
    > >
    > >

    > It may be practical for universal motors that really are

    series wound
    > motors.
    >
    > Bill


    But bench grinders are not generally series wound.
    --
    John G

    Wot's Your Real Problem?
    John G, Dec 20, 2003
    #2
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  3. On Sun, 21 Dec 2003 10:26:46 +1100, the renowned "John G"
    <greentestatoptusnet.com.au> wrote:

    >
    >"Repeating Rifle" <> wrote in message
    >news:BC0A03AC.2590%...
    >> in article

    >65d94$3fe4a15e$4503c914$,
    >buckaroo
    >> at wrote on 12/20/03 11:27 AM:
    >>
    >> > Forgot all the electrical schooling I ever had. Is it

    >feasible or even
    >> > possible to take a standard $40 bench grinder and

    >convert it to variable
    >> > speed by using some sort of rheostat... Possibly a cheap

    >$3 one designed for
    >> > dimming lights..... Or will this burn up the grinder

    >motor or worse yet burn
    >> > my garage down. If this won't work, do they make any

    >gizmo for this
    >> > purpose.
    >> >
    >> > Thanks for Help
    >> >
    >> >

    >> It may be practical for universal motors that really are

    >series wound
    >> motors.
    >>
    >> Bill

    >
    >But bench grinders are not generally series wound.


    Or universal or PM motors..

    Best regards,
    Spehro Pefhany
    --
    "it's the network..." "The Journey is the reward"
    Info for manufacturers: http://www.trexon.com
    Embedded software/hardware/analog Info for designers: http://www.speff.com
    Spehro Pefhany, Dec 20, 2003
    #3
  4. buckaroo

    repatch Guest

    Not possible. Only way to properly speed it down is to change the frequency
    fed to it.

    "buckaroo" <> wrote in message
    news:65d94$3fe4a15e$4503c914$...
    > Forgot all the electrical schooling I ever had. Is it feasible or even
    > possible to take a standard $40 bench grinder and convert it to variable
    > speed by using some sort of rheostat... Possibly a cheap $3 one designed

    for
    > dimming lights..... Or will this burn up the grinder motor or worse yet

    burn
    > my garage down. If this won't work, do they make any gizmo for this
    > purpose.
    >
    > Thanks for Help
    >
    >
    repatch, Dec 21, 2003
    #4
  5. buckaroo

    repatch Guest

    "Repeating Rifle" <> wrote in message
    news:BC0A03AC.2590%...
    > in article 65d94$3fe4a15e$4503c914$,

    buckaroo
    > at wrote on 12/20/03 11:27 AM:
    >
    > > Forgot all the electrical schooling I ever had. Is it feasible or even
    > > possible to take a standard $40 bench grinder and convert it to variable
    > > speed by using some sort of rheostat... Possibly a cheap $3 one designed

    for
    > > dimming lights..... Or will this burn up the grinder motor or worse yet

    burn
    > > my garage down. If this won't work, do they make any gizmo for this
    > > purpose.
    > >
    > > Thanks for Help
    > >
    > >

    > It may be practical for universal motors that really are series wound
    > motors.


    Pretty much every bench grinder I've seen uses an induction motor. At
    least all the ones designed to run off the mains.
    repatch, Dec 21, 2003
    #5
  6. buckaroo

    buckaroo Guest

    Harry-
    Ryobi 6" wheels......Model BGH615............ $39/Home Depot......... 2.1
    Amp.....Induction Motor......3600 RPM.......Looking for RPM around 2100-2400
    Based on what you already said probably won't work

    Thanks for helping




    "Harry Conover" <> wrote in message
    news:...
    > "buckaroo" <> wrote in message

    news:<65d94$3fe4a15e$4503c914$>...
    > > Forgot all the electrical schooling I ever had. Is it feasible or even
    > > possible to take a standard $40 bench grinder and convert it to variable
    > > speed by using some sort of rheostat... Possibly a cheap $3 one designed

    for
    > > dimming lights..... Or will this burn up the grinder motor or worse yet

    burn
    > > my garage down. If this won't work, do they make any gizmo for this
    > > purpose.
    > >
    > > Thanks for Help

    >
    > Out of curiousity, where does one find a bench grinder for $40?
    >
    > In response to your question, if the grinder has a conventional 1750
    > or 3600 rpm synchronous induction motor, it really doesn't lend itself
    > to variable speed use. Motors like this are common in 1/4 through 1/2
    > HP grinders.
    >
    > On the other hand, a $40 grinder may have some sort of brush type or
    > ac/dc motor which lends itself to variable speed operator that may or
    > may not be controllable through use of something akin to an ordinary
    > lamp dimmer. The problem here is that the dimmer may not respond well
    > to an inductive motor load and the voltage spikes it produces.
    >
    > It all depends on the HP of the motor and its type of design, plus
    > what sort of a speed reduction you are searching for.
    >
    > Harry C.
    buckaroo, Dec 21, 2003
    #6
  7. On 20 Dec 2003 16:04:49 -0800, the renowned (Harry
    Conover) wrote:

    >"buckaroo" <> wrote in message news:<65d94$3fe4a15e$4503c914$>...
    >> Forgot all the electrical schooling I ever had. Is it feasible or even
    >> possible to take a standard $40 bench grinder and convert it to variable
    >> speed by using some sort of rheostat... Possibly a cheap $3 one designed for
    >> dimming lights..... Or will this burn up the grinder motor or worse yet burn
    >> my garage down. If this won't work, do they make any gizmo for this
    >> purpose.
    >>
    >> Thanks for Help

    >
    >Out of curiousity, where does one find a bench grinder for $40?


    Just about anywhere these days. I bought a scary-large** 8" Ryobi for
    about US$70 including a wheel dressing tool, the 6" ones are cheaper,
    the no-name China-made ones cheaper again. It won't get you a Baldor,
    of course. Harbor Fright has 6" no-name China ones (with lamp) for US
    $35.99 at the moment.

    >In response to your question, if the grinder has a conventional 1750
    >or 3600 rpm synchronous induction motor, it really doesn't lend itself
    >to variable speed use. Motors like this are common in 1/4 through 1/2
    >HP grinders.
    >
    >On the other hand, a $40 grinder may have some sort of brush type or
    >ac/dc motor which lends itself to variable speed operator that may or
    >may not be controllable through use of something akin to an ordinary
    >lamp dimmer. The problem here is that the dimmer may not respond well
    >to an inductive motor load and the voltage spikes it produces.
    >
    >It all depends on the HP of the motor and its type of design, plus
    >what sort of a speed reduction you are searching for.
    >
    > Harry C.


    ** If you don't think an 8" 3500 RPM bench grinder is scary, you need
    to think about what happens when one of the wheels shatters (and it
    does happen). There is a LOT of energy in those stones.

    Best regards,
    Spehro Pefhany
    --
    "it's the network..." "The Journey is the reward"
    Info for manufacturers: http://www.trexon.com
    Embedded software/hardware/analog Info for designers: http://www.speff.com
    Spehro Pefhany, Dec 21, 2003
    #7
  8. buckaroo

    buckaroo Guest

    Thanks to All..... I am convinced that this is not possible.... I do know
    that they make some grinders with variable speeds but I assume that they are
    wired differently. I knew it sounded too easy...


    "buckaroo" <> wrote in message
    news:65d94$3fe4a15e$4503c914$...
    > Forgot all the electrical schooling I ever had. Is it feasible or even
    > possible to take a standard $40 bench grinder and convert it to variable
    > speed by using some sort of rheostat... Possibly a cheap $3 one designed

    for
    > dimming lights..... Or will this burn up the grinder motor or worse yet

    burn
    > my garage down. If this won't work, do they make any gizmo for this
    > purpose.
    >
    > Thanks for Help
    >
    >
    buckaroo, Dec 21, 2003
    #8
  9. buckaroo

    repatch Guest

    Actually it isn't a matter of how they are wired, it's a matter of the motor
    used. Those might very well be universal motors. Easy way to tell, many
    universal motors have ports to replace their shoes. TTYL

    "buckaroo" <> wrote in message
    news:17348$3fe50db4$4503c8fe$...
    > Thanks to All..... I am convinced that this is not possible.... I do know
    > that they make some grinders with variable speeds but I assume that they

    are
    > wired differently. I knew it sounded too easy...
    >
    >
    > "buckaroo" <> wrote in message
    > news:65d94$3fe4a15e$4503c914$...
    > > Forgot all the electrical schooling I ever had. Is it feasible or even
    > > possible to take a standard $40 bench grinder and convert it to variable
    > > speed by using some sort of rheostat... Possibly a cheap $3 one designed

    > for
    > > dimming lights..... Or will this burn up the grinder motor or worse yet

    > burn
    > > my garage down. If this won't work, do they make any gizmo for this
    > > purpose.
    > >
    > > Thanks for Help
    > >
    > >

    >
    >
    repatch, Dec 21, 2003
    #9
  10. buckaroo

    Guest

    buckaroo wrote:
    >
    > Forgot all the electrical schooling I ever had. Is it feasible or even
    > possible to take a standard $40 bench grinder and convert it to variable
    > speed by using some sort of rheostat... Possibly a cheap $3 one designed for
    > dimming lights..... Or will this burn up the grinder motor or worse yet burn
    > my garage down. If this won't work, do they make any gizmo for this
    > purpose.
    >
    > Thanks for Help


    Why would you want to slow down a grinder?
    (Asking as someone with no expertise at all with them.
    You can have my Black and Decker grinder which slows down
    if you look at it cross-eyed - or if you use it to grind
    something - in return for one that doesn't slow down!)
    , Dec 21, 2003
    #10
  11. buckaroo

    buckaroo Guest

    Why slow down a grinder?... When sharpening chisels and lathe tools on a
    bench grinder a slower speed is much better since it will not burn (blue)
    the steel. They make bench grinders that run at a slower speed as well as
    variable speed ones. I just happen to have bought a "normal speed" one and
    was just thinking that maybe a rheostat may work also but I have found out
    that it is not true..... at least for this induction motor. I use to know
    some about electricity, etc but as I get older my mind destroys all of my
    old data....

    <> wrote in message
    news:...
    >
    >
    > buckaroo wrote:
    > >
    > > Forgot all the electrical schooling I ever had. Is it feasible or even
    > > possible to take a standard $40 bench grinder and convert it to variable
    > > speed by using some sort of rheostat... Possibly a cheap $3 one designed

    for
    > > dimming lights..... Or will this burn up the grinder motor or worse yet

    burn
    > > my garage down. If this won't work, do they make any gizmo for this
    > > purpose.
    > >
    > > Thanks for Help

    >
    > Why would you want to slow down a grinder?
    > (Asking as someone with no expertise at all with them.
    > You can have my Black and Decker grinder which slows down
    > if you look at it cross-eyed - or if you use it to grind
    > something - in return for one that doesn't slow down!)
    buckaroo, Dec 21, 2003
    #11
  12. They are generally asynchronous motors, so forget the rheostat or dimmer,
    you will burn the motor down.Speed adjustment to an asynchronous motor
    (i.e.brushless motor)is possible only by changing the frequency of the AC.In
    the lab, when I was still studying, we burnt a motor down (it was
    smoking!)by applying on it 150 volts instead of 220.
    Visit our website www.patriko-kreta.com

    --
    Dimitris Tzortzakakis,Greece


    Ï John G <greentestatoptusnet.com.au> Ýãñáøå óôï ìÞíõìá óõæÞôçóçò:
    3fe4dab6$0$18688$...
    >
    > "Repeating Rifle" <> wrote in message
    > news:BC0A03AC.2590%...
    > > in article

    > 65d94$3fe4a15e$4503c914$,
    > buckaroo
    > > at wrote on 12/20/03 11:27 AM:
    > >
    > > > Forgot all the electrical schooling I ever had. Is it

    > feasible or even
    > > > possible to take a standard $40 bench grinder and

    > convert it to variable
    > > > speed by using some sort of rheostat... Possibly a cheap

    > $3 one designed for
    > > > dimming lights..... Or will this burn up the grinder

    > motor or worse yet burn
    > > > my garage down. If this won't work, do they make any

    > gizmo for this
    > > > purpose.
    > > >
    > > > Thanks for Help
    > > >
    > > >

    > > It may be practical for universal motors that really are

    > series wound
    > > motors.
    > >
    > > Bill

    >
    > But bench grinders are not generally series wound.
    > --
    > John G
    >
    > Wot's Your Real Problem?
    >
    >
    Tzortzakakis Dimitrios, Dec 21, 2003
    #12
  13. buckaroo

    Ross Mac Guest

    "buckaroo" <> wrote in message
    news:65d94$3fe4a15e$4503c914$...
    > Forgot all the electrical schooling I ever had. Is it feasible or even
    > possible to take a standard $40 bench grinder and convert it to variable
    > speed by using some sort of rheostat... Possibly a cheap $3 one designed

    for
    > dimming lights..... Or will this burn up the grinder motor or worse yet

    burn
    > my garage down. If this won't work, do they make any gizmo for this
    > purpose.
    >
    > Thanks for Help
    >
    >

    No cheap way here....but, you could use a dc motor/tach feedback and apply
    power to it with a pwm amplifier that supports tach feedback. Your drive
    signal could be a very small 0 to 10 volts DC signal...in the milliamp
    range. This would give you precision throughout the range. Of course you
    would probably have the most expensive bench grinder in the
    state!.........Ross
    Ross Mac, Dec 21, 2003
    #13
  14. buckaroo

    Guest

    buckaroo wrote:
    >
    > Why slow down a grinder?... When sharpening chisels and lathe tools on a
    > bench grinder a slower speed is much better since it will not burn (blue)
    > the steel.


    Thanks! That makes sense. I'm not brave enough to sharpen
    my chisels on a grinder - I'm afraid of ruining them. I
    do it by hand.

    > They make bench grinders that run at a slower speed as well as
    > variable speed ones. I just happen to have bought a "normal speed" one and
    > was just thinking that maybe a rheostat may work also but I have found out
    > that it is not true..... at least for this induction motor. I use to know
    > some about electricity, etc but as I get older my mind destroys all of my
    > old data....


    I can relate to that!

    >
    > <> wrote in message
    > news:...
    > >
    > >
    > > buckaroo wrote:
    > > >
    > > > Forgot all the electrical schooling I ever had. Is it feasible or even
    > > > possible to take a standard $40 bench grinder and convert it to variable
    > > > speed by using some sort of rheostat... Possibly a cheap $3 one designed

    > for
    > > > dimming lights..... Or will this burn up the grinder motor or worse yet

    > burn
    > > > my garage down. If this won't work, do they make any gizmo for this
    > > > purpose.
    > > >
    > > > Thanks for Help

    > >
    > > Why would you want to slow down a grinder?
    > > (Asking as someone with no expertise at all with them.
    > > You can have my Black and Decker grinder which slows down
    > > if you look at it cross-eyed - or if you use it to grind
    > > something - in return for one that doesn't slow down!)
    , Dec 22, 2003
    #14
  15. buckaroo

    buckaroo Guest

    Ross- You sound like McGiver....LOL
    I knew it was a long shot, but I wasn't sure.... Now I am!
    Thanks to everyone


    "Ross Mac" <> wrote in message
    news:CVlFb.506925$...
    >
    > "buckaroo" <> wrote in message
    > news:65d94$3fe4a15e$4503c914$...
    > > Forgot all the electrical schooling I ever had. Is it feasible or even
    > > possible to take a standard $40 bench grinder and convert it to variable
    > > speed by using some sort of rheostat... Possibly a cheap $3 one designed

    > for
    > > dimming lights..... Or will this burn up the grinder motor or worse yet

    > burn
    > > my garage down. If this won't work, do they make any gizmo for this
    > > purpose.
    > >
    > > Thanks for Help
    > >
    > >

    > No cheap way here....but, you could use a dc motor/tach feedback and apply
    > power to it with a pwm amplifier that supports tach feedback. Your drive
    > signal could be a very small 0 to 10 volts DC signal...in the milliamp
    > range. This would give you precision throughout the range. Of course you
    > would probably have the most expensive bench grinder in the
    > state!.........Ross
    >
    >
    buckaroo, Dec 23, 2003
    #15
  16. buckaroo

    Ross Mac Guest

    "buckaroo" <> wrote in message
    news:8e19e$3fe87cdd$4503c8ab$...
    > Ross- You sound like McGiver....LOL
    > I knew it was a long shot, but I wasn't sure.... Now I am!
    > Thanks to everyone
    >
    >
    > "Ross Mac" <> wrote in message
    > news:CVlFb.506925$...
    > >
    > > "buckaroo" <> wrote in message
    > > news:65d94$3fe4a15e$4503c914$...
    > > > Forgot all the electrical schooling I ever had. Is it feasible or

    even
    > > > possible to take a standard $40 bench grinder and convert it to

    variable
    > > > speed by using some sort of rheostat... Possibly a cheap $3 one

    designed
    > > for
    > > > dimming lights..... Or will this burn up the grinder motor or worse

    yet
    > > burn
    > > > my garage down. If this won't work, do they make any gizmo for this
    > > > purpose.
    > > >
    > > > Thanks for Help
    > > >
    > > >

    > > No cheap way here....but, you could use a dc motor/tach feedback and

    apply
    > > power to it with a pwm amplifier that supports tach feedback. Your drive
    > > signal could be a very small 0 to 10 volts DC signal...in the milliamp
    > > range. This would give you precision throughout the range. Of course you
    > > would probably have the most expensive bench grinder in the
    > > state!.........Ross
    > >
    > >

    >
    >

    Enjoyed your reply....have a great holiday season...Ross
    Ross Mac, Dec 23, 2003
    #16
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