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  • Grinder speed control

    I have a bench grinder that runs at 3400 RPM. I would like to be able to reduce the speed on it to about 1700 RPM. Is it possible to use a rheostat (dimmer switch) to reduce the speed or will that just cause the motor to overheat? Any suggestions?
    Ken K in White Rock

  • #2

    Re: Grinder speed control

    Re: Grinder speed control

    You can't slow it down. Maybe a better grinding wheel would do the trick. What are you trying to sharpen?
    sigpic
    hobby woodworking since 1972

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    • #3

      Re: Grinder speed control

      Re: Grinder speed control

      Originally posted by Ken Kimberley View Post
      I have a bench grinder that runs at 3400 RPM. I would like to be able to reduce the speed on it to about 1700 RPM. Is it possible to use a rheostat (dimmer switch) to reduce the speed or will that just cause the motor to overheat? Any suggestions?
      Interestingly enough, I was just about to try this, myself. I have an old purpose-made rheostat for slowing motors. It's not just a dimmer switch, it's a 3-pound box with some 'stuff' in it. For a while there you could buy boxes made for adding a variable-speed ability to the first generations of hand-held routers. These might work as well. I'm going to grab my rheostat from my old shop this weekend and try it out. I'll let you know how it goes. I'm not sure how well it will work because most of the variable-speed stuff out there is based on a 'universal' motor which is almost a re-badged DC motor... it's got brushes and whatnot. Lots of hand-tools have universal motors, but standard bench grinders don't. So it might not work, and it might burn out the motor by running it so slowly that the starting coil never de-energizes... but as I said I'll let you know.
      Mike in Orangeville, ON
      http://ifonlyyouwood.blogspot.com/

      SPCHT

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      • #4

        Re: Grinder speed control

        Re: Grinder speed control

        What about a foot actuated switch? Turn the grinder on and off to maintain the speed you want. Probably no worse then a rheostat?

        Probably a whole host of things wrong with the idea that I can't think of. (read: disclaimer )

        Cheers,
        Erron.
        ---
        The grain has more direction then me sometimes.

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        • #5

          Re: Grinder speed control

          Re: Grinder speed control

          A dimmer switch is NOT the item to use. What you need is a speed control like what is used for a router. This is one that is sold from Rockler but i am sure there are lots of different ones around.
          If you want me to make it i need this new tool first

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          • #6

            Re: Grinder speed control

            Re: Grinder speed control

            Originally posted by Todd View Post
            A dimmer switch is NOT the item to use. What you need is a speed control like what is used for a router. This is one that is sold from Rockler but i am sure there are lots of different ones around.
            I see they still make those things. Cool. If you look at the label on the front of it in that picture you posted you'll see that it specifies that it's for universal motors. Bench grinders don't have universal motors, so I'm not positive yet that it's going to work, but I'll try it out. My grinder is cheap enough that I'm not overly worried about burning it out.
            Mike in Orangeville, ON
            http://ifonlyyouwood.blogspot.com/

            SPCHT

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            • #7

              Re: Grinder speed control

              Re: Grinder speed control

              The other thing to do is to check with an electrical wholesaler like Westburne, Nedco, Guillevin Int. or some place like that and see what they have available to suit your needs.
              If you want me to make it i need this new tool first

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              • #8

                Re: Grinder speed control

                Re: Grinder speed control

                I think it can be done but you need a speed controller designed specifically for induction motors. It would likely be cheaper to buy a new grinder. Also, it's not good for the motor and could over heat it.
                There are speed controllers for ceiling fans which have induction motors but it's a different type of wiring then a grinder motor and it's built for that propose.
                Is it viable to put a smaller wheel on the grinder to bring the rim speed down to equal that of a slower grinder? On an 8" grinder that would mean a 4" wheel but 6" would at least get you closer.
                At 3450 RPM, The rim speed of an 8" wheel would be around 7200FPM. The rim speed of a 6" wheel on the same grinder would be around 5400 FPM.
                The rim speed of an 8" wheel at 1725 RPM would be around 3600 FPM.

                FWIW
                J.P. Rap Mount Hope Ont.
                Carpe Ductum (Seize The Tape)


                "In this world, you must be oh so smart, or oh so pleasant." Well, for years I was smart. I recommend pleasant. Elwood P. Dowd

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                • #9

                  Re: Grinder speed control

                  Re: Grinder speed control

                  Instead of destroying a good grinder, why not get something that grinds easier. Use a belt sander if you have one. My favourite sharpening machine before I got a worksharp is a 1" wide belt sander. I only use the 8" grinder for very heavy sharpening , like lawn mower blades. Using a reheosat on your grinder won't work, wrong type of motor, and once you let the smoke out , it's done
                  sigpic
                  hobby woodworking since 1972

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                  • #10

                    Re: Grinder speed control

                    Re: Grinder speed control

                    Thanks for all the input. Most of it is what I expected - don't do it! I'm finding it far too fast for sharpening chisels for turning. It's an 8" and I'm using a white Norton stone (I can't remember what the exact grit is). I'll probably look at the Delta variable speed or the work sharp.

                    Thanks again.
                    Ken
                    Ken K in White Rock

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                    • #11

                      Re: Grinder speed control

                      Re: Grinder speed control

                      I would search the turning forum or ask again on the turning section about sharpening lathe chisels. I think you would be disappointed in trying to use a Worksharp for the different types of lathe chisels. I find mine is more suited to bench chisels and plane irons. Lathe chisels seem to need touch up every 10 minutes. I still use my 1" belt sander , though not ideal for lathe chisels it does what I need and doesn't burn. I don't turn enough to have have a proper set-up. J.P. would be the one to ask. He has a tutorial in tutorial section, but seems the pictures are missing. I think you have the right tool, just need to refine the method.
                      sigpic
                      hobby woodworking since 1972

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                      • #12

                        Re: Grinder speed control

                        Re: Grinder speed control

                        Ken, I use both a 3450 RPM 6" grinder and a 1750 RPM 8" grinder both of which are fitted with white 120x Norton wheels for sharpening my HS Steel turning tools. Neither is a problem for overheating unless I get too aggressive. I use the Wolverine jig for my gouges with a very light touch and bluing the edge is never a problem. I do make a point of keeping a can of water close by to cool the tool regularly if I'm grinding a new profile or modifying an existing one.



                        Steve
                        Richmond, BC

                        Anything worth doing is worth overdoing.

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                        • #13

                          Re: Grinder speed control

                          Re: Grinder speed control

                          Originally posted by Ken Kimberley View Post
                          It's an 8" and I'm using a white Norton stone (I can't remember what the exact grit is). I'll probably look at the Delta variable speed or the work sharp.
                          Ken
                          An 8" at 3450 RPM is way to fast for turning tools. I use a 6" 3450 RPM grinder and it works very well but it took a considerable amount of practice to get the a point where I wasn't burning the chisels. That said I use gray stones and they aren't nearly as friable as the white stones.
                          Try just putting a 6" wheel on you 8" grinder. Lowering the rim speed a bit might be just what you need.

                          Originally posted by Bryan @ Woodstock View Post
                          J.P. would be the one to ask. He has a tutorial in tutorial section, but seems the pictures are missing.
                          Yes. I've been meaning to fix that for some time now. The hosting site I was using at the time closed down and I have to find the pictures in this pile of discs.

                          Edit...I did a search for past threads as I knew there were a bunch of them.
                          Have a look here. Scroll down a bit to "grinders and wolverine". You'll find that one full of info as well as a few other interesting threads.
                          Last edited by J.P. Rap; 08-30-2008, 11:49 PM.
                          J.P. Rap Mount Hope Ont.
                          Carpe Ductum (Seize The Tape)


                          "In this world, you must be oh so smart, or oh so pleasant." Well, for years I was smart. I recommend pleasant. Elwood P. Dowd

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