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Thread: Benchtop grinder speed control

  1. #1
    Join Date
    Jun 2008
    Location
    Huntsville, AL
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    326

    Benchtop grinder speed control

    I have some sharpening to do. I don't think I will be utilizing the grinder for this as I just have the stock grey wheel on mine. However I had a random thought pop up. Yes, I know dangerous

    I have an independent speed control for a router. It should be able to slow down a grinder. Anyone ever use a speed control on their grinder? I was hypothesizing that with a white oxide wheel and slower speed the grinder could come in handy on the chisels. Any comments?

  2. #2
    wow - I never noticed this until now, but there some links at the bottom of each page that show "Similar" threads... well one of them addresses your issue directly:

    http://www.sawmillcreek.org/showthread.php?t=10136

    How about that!?

    I was also interested in this and will be reading over there.

  3. #3
    Oops - your want to know about your grinder - sorry - stupid my for hasty posting!!!

    I'm still interested in this because I will also want to reduce spin speed for my grinders...

  4. #4
    Join Date
    Apr 2008
    Location
    Richmond, VA
    Posts
    664
    Douglas,

    Most bench grinders use an induction motor, not the universal motor found on routers. You can purchase speed controllers for induction motors, however, they are expensive.

    After the recent FWW articles on grinders/sharpening, I started "practicing" with some old tools and such with the idea of moving on to chisels and irons. Haven't quite gotten there yet, but I have begun to develop some bench grinder technique. At this point I have a new set of screwdrivers and some knives. Fun to learn new stuff!

    Best!

    -Jerry

  5. #5
    yup - good idea - practice

    just wait for the HarbFrt ones to go on sale - I won't car about grinding those down to the nubb!

  6. #6
    Be ever watchful what other people are throwing out! My dear old mother just threw out (almost) two foot controls for old sewing machines. One of them is a two outlet , one on full time, labeled light. They went right to the shop for various tools. If your wife or other has one, maybe you could borrow it to experiment with your grinder.
    Creation is a transfer of ideas to matter.

  7. #7
    Quote Originally Posted by Reed Wells View Post
    Be ever watchful what other people are throwing out! My dear old mother just threw out (almost) two foot controls for old sewing machines. One of them is a two outlet , one on full time, labeled light. They went right to the shop for various tools. If your wife or other has one, maybe you could borrow it to experiment with your grinder.
    Won't work. Speed controls mainly work by varying the voltage, which is fine for motors that have brushed (AKA universal motors). You could take a standard (3450 RPM) bench grinder and put a pulley where one of the wheels are and use a belt to drive a mandrel When equipted with a friable wheel, a standard grinder does just fine. Just requires a lighter touch.

  8. #8
    Old thread, but since it's one of the first results when searching google for "bench grinder speed control", I will post anyway.
    These days, there are (relatively) affordable single phase input, single phase output variable frequency drives (VFDs). No-name Chinese units are available on eBay for 60-70 USD including shipping.
    Whether or not it's worth it, is up to you.

  9. #9

    freq speed control for a Metabo BS 175 grinder.

    Quote Originally Posted by Gene Pavlovsky View Post
    Old thread, but since it's one of the first results when searching google for "bench grinder speed control", I will post anyway.
    These days, there are (relatively) affordable single phase input, single phase output variable frequency drives (VFDs). No-name Chinese units are available on eBay for 60-70 USD including shipping.
    Whether or not it's worth it, is up to you.

    I keep running into sawmillcreek when looking for a speed controlled grinder and i read your post about frequency control. Googing that i found a german forum where somebody converted a rageingly popular european Metabo BS 175 grinder to control speed. I'm guessing many people looking for a speed controlled grinder ending up on sawmill creek, to help them out im going to post the translated german post below.

    Copied from the german forum (link below the post)

    "
    Since the processing of my tools (which are mainly made of titanium knifes) depends on the correct belt speed, we had to find a way to control the speed of the grinder (RPM).

    Metabo BS 175 -1.jpg
    There are a few possibilities there


    1.) With a potentiometer (not discussed, not feasible)
    2.) With a power regulator (not discussed, not feasible)

    3.) Frequency converter (FU)


    If the speed (frequency) is reduced, the frequency converter will supply the motor with current up to the programmed value and the torque will be retained as long as the motor can.
    You can of course turn the parameters a little and, for example, allow him to exceed this value for time X, or specify a higher rated motor current from the start, or or or.
    As I said, until the motor goes up in smoke
    A problem with the capacitor motor is that the auxiliary winding has a smaller cross-section than the main winding, not like a three-phase motor, where all have the same cross-section.


    What do you have to consider with such a frequency converter?


    1.) The frequency converter should be able to have more KW than the motor has.


    2.) Programming is child's play, because the basic parameters only have to be read off the data from the motor nameplate (nominal motor voltage, nominal motor current and nominal motor frequency) and entered into the frequency converter. If there are problems at start-up, there are certainly some boost functions that ensure that it overcomes its start-up difficulties


    3.) When it comes to a frequency converter, you always hear something about a line filter. There are a few things to keep in mind about this.


    3a.) A line filter can also cause problems.
    When interference suppression capacitors come into play, the situation becomes more complicated.
    If you have installed a type A Fi (the standard in a private house), it cannot cope with the direct current component, for example.
    You could also drive the monitoring electronics of the FI into saturation and your FI no longer has any function and and and.
    The solution could be a separate supply line that does not go through the FI and is hard-wired.
    Install a type B FI and ensure that the FI is disconnected from the mains in less than 30ms (e.g. relay / contactor, or press the on / off switch quickly)


    Please, if you should plan something like this, get a specialist in the house!


    4.) What do I need a braking resistor for?
    This is for the impatient. With an additional braking resistor, the motor comes to a standstill much faster, so that you can change your sanding belt.


    5.) Do I regulate or control the speed?
    I'm talking about a control system; it would be a closed-loop control if a speed feedback were to take place.


    6.) FU's don't like dusty air (if they have an internal fan), so it is better to build it in a case, but this should be generously dimensioned so that it still has enough air to circulate.


    I decided on the PETER electronic VD i 075 / E, but you cannot add a braking resistor here, this is only possible with the larger version, but the line filter is already integrated. You even get the speed displayed, but this is only a calculated value. Current and frequency are displayed for all.


    7.) What about the cooling?
    I haven't screwed it on so far and I can't say whether a fan is mounted on the armature, but even if there is, these fans are usually designed for the nominal speed and if you reduce the speed, you also reduce the cooling of the motor


    FUPETER electronic VD i 075-E_.jpg


    8.) When using shielded cables between the converter and the motor, the shield should be connected to earth on both sides


    If you want torque and speed control / regulation, You should use a three-phase converter and a three-phase motor instead.
    "


    Source: https://www.bladecommunity.de/thread...674#post142674

  10. #10
    Join Date
    Dec 2006
    Location
    Toronto Ontario
    Posts
    10,901
    Any single phase induction motor with a start winding controlled by a centrifugal switch cannot run at reduced speed because the start winding will engage.

    A split phase motor can be run at reduced voltage/frequency to reduce the speed, however power will be reduced as well. In addition cooling will be impaired however for a grinder that shouldn't be a problem as the grinder isn't in operation continuously......Regards, Rod.

  11. #11
    Join Date
    Sep 2016
    Location
    Modesto, CA, USA
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    7,575
    Original post is unclear. A speed contriol will work fine on a grinder with a ac/dc motor as most handheld grinders have. If he means bench grinder then either belt drive or buy a 3phase bench grinder and run it with a vfd.
    Bill D.

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