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  • Advice building a tool post grinder

    I have a Dremel Advantage rotary tool that might serve as a suitable motor, consumes 4.5 amps and runs at 27000 and 34000 rpm no load. I think this is more powerful than a sewing machine motor which Rudy Kouhoupt seemed to be able to use satisfactorily but correct me if I am wrong. The 3" abrasive wheels have a max 10000 rating so a >3:1 reduction is required. I propose making a spindle as outlined in Workshop Practice Series 27 Spindles. What is the best means of having the Dremel drive the spindle? I don't want a spindle pulley greater than 2" dia. What are the pros and cons of timing and V belts. Small timing belt systems seem to be hard to source.

    The grinder will hopefully be mounted on an AXA tool post and on an MT3 mill taper.

    Perhaps there is a better way to tackle this, any helpful suggestions or criticism welcomed.

    John.

  • #2
    Well, read this first... some down-to-earth advice in answer to "what is a tool post grinder for?".

    http://www.practicalmachinist.com/vb...rinder-266189/

    If you really still want to spend the time to make one after reading that, you might recall that a dremel can be speed-reduced, even by as simple a means as putting a suitable rectifier in series with it to reduce the average voltage. You don't have to do it all with pulleys, although they are a good and reasonably foolproof method.

    I have had two TPGs. One I gave away to my Father-in law. the otehr got moved to an old Tool and cutter grinder base, where it is happily grinding cutters. I can also do between centers grinding on that setup, to around 18" or so long.
    1601

    Keep eye on ball.
    Hashim Khan

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    • #3
      If you're going to build it, I would look at microV belts for the drive. They are quite efficient, which could be important with your motor, and will work well around smaller pulleys. Some setups use an O-ring for a belt (one of mine does) but there are issues with that. I don't think you need a toothed belt since there's no need to maintain some exact timing relationship, and they can be noisy (but are usually pretty good) I think the smoother the drive, the better the results could be. You would probably get all the power you need through a 3 rib microV belt, and you could use a drive pulley as small as about .8 inch in diameter. I wouldn't worry about not getting the full 3-1 step down ratio- as suggested you can use an electronic means of slowing the motor some. It's not likely you would need to reduce the motor speed by as much as half, so I think you'd be fine with a 2 inch driven pulley and the 2.5-1 ratio you would get with the .8 inch drive pulley.

      Assuming the Dremel Advantage has a brush motor, you should be able to run it from a router speed control. Some of those are fairly inexpensive. You will find that it's handy to be able to control the rpm smoothly, since there are certain rpm ranges that will tend to vibrate more. Nice to be able to dial in the smooth spots, or more to the point- dial away from the rough spots. Resonances are usually to be avoided.

      When it comes to the spindle you'll want to fit a high class of bearing, and do a good job of making close fits. Any anomalies in the bearings will transmit directly to what you're grinding on, and you'll find that there's a limit to how smooth of a job you can do, regardless of the care you take.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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      • #4
        For the drive belt, a circular profile 5mm urethane belt is all you need - cut to length and melt the ends together with a hot blade - and turn pulleys to match. There should be very little power being transmitted here.

        I made a TPG-like drilling machine for drilling off centre and radial holes years back. When I came to use it occasionally as a TPG it was worth its weight in... well, in hardened O1. I built my T&C grinder later, but I'd still use the TPG for larger stuff.

        Cleanliness bordering on the obsessive required after a grinding session, though. And watch out for the main danger - overspeeding a wheel.
        Richard - SW London, UK, EU.

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        • #5
          You need properly designed bearings for a toolpost grinder.
          The Dremel does NOT have properly designed bearings for this use.
          The Dremels I have taken apart have even had the bearings mounted in rubber!?!!

          -Doozer
          DZER

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          • #6
            Originally posted by Doozer View Post
            You need properly designed bearings for a toolpost grinder.
            The Dremel does NOT have properly designed bearings for this use.
            The Dremels I have taken apart have even had the bearings mounted in rubber!?!!

            -Doozer
            But, the Dremel is not proposed by the OP as the spindle, "just" the drive. As such it will contribute vibration, but likely not actual off-center rotation.

            My own belief is that after all that work, it will get used relatively infrequently. I think I used mine (both of which I bought used for very low $$) maybe 6 times, ever, on the lathe, largely because setting it up with all the covering of ways etc was a pain.
            1601

            Keep eye on ball.
            Hashim Khan

            Comment


            • #7
              Doozer is certainly correct about the need for good bearings though. The Dremel bearings are terrible. Since a Dremel is typically hand-held it doesn't usually matter, but when I tried to use mine as a toolpost grinder it left chatter marks like the waves of the ocean.
              The vibration may be an issue if the Dremel is used as the motor to drive a separate spindle. Try to isolate the two from each other as much as possible. Dumore balances its motors and spindles and their grinders have virtually zero vibration. It's also why they cost so much.
              Last edited by SGW; 05-24-2013, 09:51 AM.
              ----------
              Try to make a living, not a killing. -- Utah Phillips
              Don't believe everything you know. -- Bumper sticker
              Everybody is ignorant, only on different subjects. -- Will Rogers
              There are lots of people who mistake their imagination for their memory. - Josh Billings
              Law of Logical Argument - Anything is possible if you don't know what you are talking about.
              Don't own anything you have to feed or paint. - Hood River Blackie

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              • #8
                Originally posted by Doozer View Post
                You need properly designed bearings for a toolpost grinder.
                The Dremel does NOT have properly designed bearings for this use.
                The Dremels I have taken apart have even had the bearings mounted in rubber!?!!

                -Doozer

                Just a small note:- resiliently mounted bearings are perfectly acceptable engineering design for high speed spindles. they're also used for the 100+ krpm bearings in precision dentist drills. With them, the rotor rotates about its centre of mass and does not try to drag the casing with it. Thus giving lower vibration.

                This obviously conflicts with a grinding spindle where you want a rigid mount to avoid chatter. In that case rotor balance gets more important.
                Last edited by Mark Rand; 05-24-2013, 06:06 PM. Reason: Poor engrish
                Location- Rugby, Warwickshire. UK

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                • #9
                  Thanks for all the replies. I had not thought of reducing the Dremel's speed (thanks to darryl), it is a universal motor, so simple enough. I will heed the advice about quality bearings. The micro V belt sounds good but a search has not shown up much. Gates PJ series seems to be the only one I can find. Does any one know of a source for a 2 or 3 ribbed belt in North America of suitable length? I am in Ottawa, Ontario, Canada.

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                  • #10
                    I had a Makita belt sander apart a few days ago- it uses a v-rib or microV belt (same thing- there's a couple other names for them as well). The length is probably about right- I don't recall the number of ribs, but if it was 4, then you could slit it in half and get two 2-rib belts. The slitting is how they are cut into distinct widths in the first place, so it's not a compromise to the integrity of the belt. We put a lot of use on these belt sanders, and the drive belts last- I can't recall ever needing to change one.

                    There are likely other power tools which use the same type of belt, so you could ask at a tool seller or repair depot. We also use a Bosch belt sander, which is a bit smaller than the Makita. I haven't had it apart, but it looks like the same type of drive system and probably uses a microV belt as well.

                    Gates makes these belts, so does Goodyear. I'm not sure if Bando is a maker or just a supplier, but they list the full range of these belts, plus a lot of other types.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                    • #11
                      Good idea darryl, there are several service centers in Ottawa, I'll check them out. Thanks, John.

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