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Slow speed finish on my DVR

Discussion in 'Tutorials and Tips' started by Gary Beasley, Aug 1, 2019.

  1. Gary Beasley

    Gary Beasley

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    I was at a meeting of the Etowah River Woodturners and was admiring the finish on another members project. On asking about it I got an invite to come see the process. Turns out Ron Comtois had added a small dc motor to an old Delta lathe so he could mount a piece on it and leave it rotating at 16 rpm while applying and drying the poly finish resulting in a dead smooth surface.
    I figured I could cobble something together for myself and only having the one lathe I would build an accessory drive that can be mounted and dismounted easily.
    I got a used reduction motor off ebay for a few bucks that had a speed control board with it. Only big hurdle was how to transfer the power to my chuck. Fortunately I was looking online at Northern tool at their reasonably priced pulleys and belt and found what I needed. First was a two inch pulley with a half inch hole to fit the gearmotor, then there was a six inch pulley I planned to cut the hub out of and machine the hole to fit the lathe and a 37” v belt to hook it up.
    After I got it home I had the extreme good fortune to find the big pulley had a core welded into a 1 1/4” hole, exactly the size needed so all it took was cutting the weld off and tapping the piece out.
    So far I dont have a permanent mount yet. I took a board and clamped it to the bed and clamped the motor to it. The pulley went on the head behind the chuck and tightened up a bit. Slipped the belt on, snugged it and applied power. I was able to set the speed right on the money.
    All I need now it to build the mounting of the platform for the motor and put the control board into a box with the control knob mounted on it.

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  2. hockenbery

    hockenbery AAW Advisor Staff Member

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    Thank for sharing this idea.

    Many of our club members use BBQ spit motors to turn a shaft.
    I think one uses a microwave turn table motor.

    This works for leveling lacquer and epoxy finishes too.

    One of the higher production designs turns multiple shafts at once. (6 I think)
    Says by the time he applies finish to the piece on the last shaft he can do a second coat on the piece rotating on the first shaft.
     
  3. Gary Beasley

    Gary Beasley

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    The seller of the motor said it came out of a treadmill, there probably quite a few of those floating around that could be salvaged.
     
  4. Gary Beasley

    Gary Beasley

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    AF6B8055-7A0B-4C21-8AE0-8576CFF3505A.jpeg I finished the mount and boxed the control board. I timed the rotation to 47 rpm at max and 0 min with marks in between timed. I mounted my flat vacuum chuck as it was the biggest thing I would mount and I do plan to be able to throw a bowl on the vacuum chuck and put finish on the bottom.
     
    hockenbery likes this.
  5. John Torchick

    John Torchick

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    Great idea! Custom fishing rod builders will fight over a microwave oven at the curb. The motors are used to allow the epoxy on the rod to cure without running or dripping. Most go 3-6 rpm and will take a bit of weight. Consider what they turn in the MWO.
    Edit- Good to see shaving on the lathe and floor. Always a good sign of a serious turner.
     
  6. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I would suggest not doing that ... at least not with a vacuum applied. :eek:

    You could use tailstock pressure to hold the bowl.
     
    hockenbery likes this.
  7. Gary Beasley

    Gary Beasley

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    You think it would fail to hold? The pump I have puts a good vacuum on even with a leaky hole or two at 10cfm. After a first coat there shouldnt be a problem with it pulling finish to the inside.
     
  8. Gary Beasley

    Gary Beasley

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    At least at this size bowl, if the vacuum gauge is correct at 20”, theres about a thousand pound of pressure holding it in place. For simply applying finish its more than enough. B48C068F-39BB-4D1D-BE43-413D65EE2ABC.jpeg
     
    Gerald Lawrence likes this.
  9. Gerald Lawrence

    Gerald Lawrence

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    Now is this just wipe on or brush on Polyurethane?
     
  10. Gary Beasley

    Gary Beasley

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    I think its brush on. Minwax fast dry is on the label.
     
  11. Bill Boehme

    Bill Boehme Administrator Staff Member

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    No, not that at all. Don't be surprised that the vacuum can pull a finish right through the wood and into the vacuum chuck line ... potentially gumming up the dust filter ot the pump itself. If you see the finish pulled to the inside, there is no reason to assume that it stopped there.
     
    Tim Tucker likes this.
  12. Mark Jundanian

    Mark Jundanian

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    Well since you don't need half a ton of force to hold the bowl on, you could reduce the vacuum. Based on your calc's even 5 inches of vac would hold the bowl.
     
  13. Gary Beasley

    Gary Beasley

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    For sure it will, but with all the little leaks at the joints and turbulence that causes a vacuum reading with the port wide open the low values on this rig are quite suspect. I do open the bypass some after it gets a good grip when drying so the pump can move some air through to help cool it.
     
  14. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Just guessing that the bowl might be about eight inches inside diameter which would say that the inside area is about fifty square inches. If you were to apply a vacuum of 20 inches of mercury which translates to 9.8 pounds per square inch then the force exerted by the atmosphere pressing the bowl against the disk would be about 490 pounds. You could use a tenth as much vacuum and still have far more force than necessary.

    That must be a real whopper of a vacuum pump to have that much air flow capacity and still be able to pull a usable vacuum. :D
     
  15. Gary Beasley

    Gary Beasley

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    It has an inside diameter of 11” which according to the chart puts it at 900 lbs at 20”. I have serious doubts all that 20” of vacuum makes it to the area under the bowl, Id bet it loses a fair amount. The gauge is built into the control box I stole off an old graphic arts contact frame. It originally had a much smaller pump, maybe a 5 cfm but the motor died and the one I found to replace it is much more powerful.
     
  16. Bill Boehme

    Bill Boehme Administrator Staff Member

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    You're right about the gauge location being important. Ideally it ought to be as close to the headstock as possible. Even then, leaks through and around the bowl have a really big impact on the actual vacuum. My gauge isn't anything to brag about. It came off a refrigerant manifold set so the vacuum side of the scale is a little tiny arc. One of these days I might get a real vacuum gauge or maybe not.
     
  17. Dwight R Rutherford

    Dwight R Rutherford

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    3960704E-7F85-4216-BBFA-BCC16D0329CF.jpeg Here is a chart you might find handy.
     
  18. Gary Beasley

    Gary Beasley

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    Ive already printed that out, it was my reference for my earlier figures, thanks.
     
  19. Gary Beasley

    Gary Beasley

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