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Best wheel for re-surfacing magnetic chuck?

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  • Best wheel for re-surfacing magnetic chuck?

    Sorry for the on-topic post....

    What type of wheel do you guys recommend for re-surfacing a magnetic chuck? I plan to use coolant to help keep thermal expansion to a minimum when resurfacing but I'm not sure what the best type of wheel is for magnetic chuck re-grinding. I did read somewhere that you should have the magnetic chuck engaged while resurfacing, but wouldn't that tend to cause some of the ground off material to stay on the chuck and possibly cause excessive spark-outs, ect? Maybe it's a non issue but seems strange that they suggest grinding the chuck only when it's engaged..

  • #2
    Engage the magnetic? sounds wacky to me. One day I will get my surface grinder back together and will need to do the same. If the chuck is like mine you will need a wheel good for both soft (like aluminum) and hard(er) materials, or swap out wheels for the finish pass(es)
    Last edited by lakeside53; 02-10-2019, 12:45 PM.

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    • #3
      Chucks are soft, so you need a medium/hard wheel. A 46K or L with a nice open grit would be perfect. Plain WA or a 3SG/5SG are fine.
      Eclipse Magnetics in the UK, who've supplied just about every UK toolroom in history with their Mag chucks, recommend that the magnet is OFF for re-grinding.
      This is on permanent magnet chucks btw, don't know what an electro-mag chuck would be.

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      • #4
        Good instruction here:

        https://www.moldmakingresource.com/g...agnetic-chuck/

        The reason you turn the chuck on is because you're going to be doing grinding with the chuck on. Grinding is a game of tenths (or millionths if you're a lot better than I am) and the field of the mag chuck moves things around in that regime. You want things to move to the points that they're going to be when you're grinding work before you grind in the chuck.

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        • #5
          Mechanical magnetic chucks have permanent magnets mounted on a rack beneath the sandwich matrix of the chuck surface. When you move the lever towards the “on” position, a cam system lifts up the rack and brings the magnets into contact and alignment. No matter how tight that sandwich is, things are gonna tweak as the transition to full magnetism takes place.
          That’s why every one of the 15+ shops I worked in always ground them with the magnet on.

          Full diameter, 1/2 wide 46J or K pink wheel was my choice then and what I use here at home. There are wax sticks for grinding wheels and I used to rub wax on the magnet too.

          When I dress the wheel I would relieve a little groove into the wheel center before taking the final dressing pass so it was kind of like having 2 wheels. It seemed to load up less during the early heavier passes. When you’re finishing, you want the lightest most uniform passes your tired arms can provide.

          When you’re done you’ll also have a pretty good idea how good your spindle health is too.

          Electric chucks with variable current power supplies are a whole different animal, but we turned them “full on” and ground them in the condition they would most often see use.

          Don’t get a left arm flu shot the morning you’re gonna grind a chuck. Been there done that and it wasn’t good.

          Good Luck.👍
          Illigitimi non Carborundum 😎
          9X49 Birmingham Mill, Reid Model 2C Grinder, 13x40 ENCO GH Lathe, 6X18 Craftsman lathe, Sherline CNC mill, Eastwood TIG200 AC/DC and lots of stuff from 30+ years in the trade and 15.5 in refinery unit operations. Now retired. El Paso, TX

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          • #6
            Originally posted by 3 Phase Lightbulb View Post
            Sorry for the on-topic post....

            What type of wheel do you guys recommend for re-surfacing a magnetic chuck? I plan to use coolant to help keep thermal expansion to a minimum when resurfacing but I'm not sure what the best type of wheel is for magnetic chuck re-grinding. I did read somewhere that you should have the magnetic chuck engaged while resurfacing, but wouldn't that tend to cause some of the ground off material to stay on the chuck and possibly cause excessive spark-outs, ect? Maybe it's a non issue but seems strange that they suggest grinding the chuck only when it's engaged..
            I was always told to use the same type of wheel that you plan on using most often on the machine. Teh magnetic fields cause all kinds of distortions at microscopic levels, so it is beneficial to have it on when surfacing, and they cancel out when in actual use.

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            • #7
              Wheel type isn't as important as method.
              Do a clean dress of the wheel first of course.
              Use a dial indicator to map the error in the surface.
              Spark off at the highest point and then make a full pass.
              Limit your passes to .0005"or less.
              Use 90+%of your wheel width per pass.

              I don't like to waste chuck face by grinding 100% clean,once the wheel is sparking off over the whole surface that's good enough.Scratches and small dings don't matter as long as the chuck shows contact over the whole face.Those defects if present will correct themselves over the course of subsequent grindings.

              I also use a heavy coat of WD-40 between passes instead of flood coolant.It does a better job of preventing wheel loading than coolant and making light passes with a fresh wheel on cast iron isn't going to generate measurable heat.
              I just need one more tool,just one!

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              • #8
                Thanks for the info.

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                • #9
                  This is from KO Lee's web site.

                  https://leblondusa.com/wp-content/up...esurfacing.pdf

                  JL...

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                  • #10
                    I know very little about grinding, here's some useful info: https://www.model-engineer.co.uk/sit...ckhandbook.pdf

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