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Thread: Low speed for 12" disk sander

  1. #1

    Low speed for 12" disk sander

    Okay so I have been happily using my Harbor Freight 12" disk sander for a few years. I never really gave it much thought, but it is really hard to not burn cherry when sanding it.

    I developed the habit of doing some small sanding operations when the sander was spinning down and realized that I'd really like a lower speed sander, maybe really low speed. That got me wondering about variable speed options or maybe just a lower single speed than the Harbor Freight comes with (1725 rpm I think).

    I see that other 12" and even 20" models tend to run at the same speed so maybe I am crazy, but it seems to me as if a lower speed would be nice. Is there a chance that different abrasives would be less prone to burning cherry lumber (I have been using the 12" disks from HF since they are cheap and locally available)? Even if that is the case I still think that a low speed option would be nice.

    Adapting an EVS lathe motor and controller would be really nice, but more expensive that I want to spend. Is there some kind of speed controller that would work with the existing motor that wouldn't break the bank?

    I might consider taking the sander it apart and seeing how hard it would be to convert it from direct drive to belt drive and using a stepped pulley setup.

  2. #2
    Join Date
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    Use a three phase motor and a VFD to control speed. The center speed is lower then the rim.
    Bill D.

  3. #3
    Join Date
    Mar 2018
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    Orwell, NY
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    My 12" disk sander is part of a Shopsmith, so I have variable speed. I do find that I use a low speed, sometimes as little as 700 RPM, when sanding end grain, or when the sanding disk is getting worn and I want to get the last bit of sanding out of it. I don't know what the higher speed is that I also use, it is shown on the speed control knob but not with a number. The downsides to the Shopsmith are that is has no dust collection ability, and the table doesn't tilt, but for my needs it is very handy. I tend to have more trouble burning when sanding maple than cherry, but it likely depends on the individual board's density or something like that.
    Zach

  4. #4
    Join Date
    Dec 2005
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    Can’t help you with yours but I have a vfd on my 20” and I love being able to slow it down.

  5. #5
    Join Date
    Apr 2019
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    Would it be possible to use the HF router motor speed controller?
    “Pay no attention to what you cannot control..” Epictetus, 100 A.D.
    It costs nothing to be kind to others

  6. #6
    Join Date
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    Quote Originally Posted by Mark Daily View Post
    Would it be possible to use the HF router motor speed controller?
    No. Those only work with "universal" motors...the ones that scream. You cannot use them on induction motors.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  7. #7
    Quote Originally Posted by Matt Day View Post
    Can’t help you with yours but I have a vfd on my 20” and I love being able to slow it down.
    The VFD solution sounds great, but will undoubtedly cost several times the cost of the sander. It may be worth it though.

    If I understand correctly, I'd need to find a three phase motor that fit in place of the original motor or could be adapted to fit and buy an appropriately sized VFD. I may price out the options. I have a feeling sticker shock may set in.

    I could use my lathe instead, with a platen and table set up on it, but then I'd have the setup time and it wouldn't be easily available when a project was in the lathe. I guess the set up time could be pretty minimal if it was designed well.

  8. #8
    Find a 5/8" shaft, 1750 RPM motor, and add the Shopsmith sanding disk. One word of warning, shaft has to run absolute true - no run out. I have the Delta 3450 RPM and a nicely made (by a machinest) 1725 RPM disk sander. When I got the latter, I needed to up grade motor for more power. Took a couple tries in stash to find a motor that didn't have run out at the shaft. There are many you tube videos of making a disk sander

  9. #9
    Mine is already 1750. I am looking for slower and variable speed would be a nice plus. I am considering keeping the current sander and getting or making a disk (maybe a shopsmith?) to run on my lathe (with a banjo mounted table) to get low/variable speed.

  10. #10
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    Quote Originally Posted by Jim Becker View Post
    No. Those only work with "universal" motors...the ones that scream. You cannot use them on induction motors.
    Rats- thanks Jim.
    “Pay no attention to what you cannot control..” Epictetus, 100 A.D.
    It costs nothing to be kind to others

  11. #11
    Join Date
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    You could belt drive the existing motor with any type of 3 phase motor and vfd. A vfd will cost around 100 from the bay. Or use a single phase motor and reduce the speed with the pulley ratios. run one motor at a time for a two speed setup. I have actually seen such a two motor setup on bandsaws.
    Bil lD

  12. #12
    Quote Originally Posted by Bill Dufour View Post
    You could belt drive the existing motor with any type of 3 phase motor and vfd. A vfd will cost around 100 from the bay. Or use a single phase motor and reduce the speed with the pulley ratios. run one motor at a time for a two speed setup. I have actually seen such a two motor setup on bandsaws.
    Bil lD
    I like the two motor idea. I'll have to look at the sander to see is there is access to some portion of shaft that would allow adding a pulley. I am not sure there is, but if so it seems like something that I might be able to cobble together fairly inexpensively.

  13. #13
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    I suppose you could belt drive or wheel drive the rim of the sanding disk.
    Bill D.

  14. #14
    Quote Originally Posted by Bill Dufour View Post
    I suppose you could belt drive or wheel drive the rim of the sanding disk.
    Bill D.
    Upon checking it looks like a very easy setup. There is a little plastic impeller that would have to move or go, but I think I can manage to get a pulley on and save it by narrowing the hub of the impeller and moving it more inboard on the shaft. Belt access from below is wide open.

    Honestly the placement of the impeller and the air shroud look like it does pretty much nothing to cool the motor. So if it was to need to come off I don't think I'd worry. I could add a muffin fan, but don't think I'd bother unless the motor seemed to run particularly warm.

    I'll have to start shopping/scrounging for a motor, belt, pulleys, and other incidental parts. I am excited about this solution.

    Harbor Freight claims that it is 1-1/4 hp in the current configuration. I figure that it is really comparable to a smaller motor. Also since I will be effectively "gearing down" with the pulleys I figure less hp will suffice. Do you think 1/2 hp will do the job running the disk at half or one quarter the normal rpm? Or will it take more to get all that iron started going?

  15. #15
    Join Date
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    1. The 2 motor solution is interesting but to run the faster motor you need to take off the belt or you will overspeed the slower motor.

    2. A VFD will only give you about 50% turndown so figure on that.

    3. The disk in the lathe is a good approach but don't follow my method. I made a wooden disk which changes shape with the weather.

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