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  1. #1
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    Default 15" Disc Sander build

    Hi All

    I decided to build a 15 inch disc sander after watching a you tube video by Jords Woodshop.
    I liked the idea of using the lathe head as I can change the speed of the sander.

    Mine is built slightly different to Jords and I also included dust collection which works really well.
    I bought the discs from Hare and Forbes, they have a stick on velcro backing disc and 3 different grit sanding discs to choose from.
    I used 18mm plywood as the disc. I would prefer to use an aluminium disc. I may try to chase one up in the future.
    I used 16mm MDF which was lying around my shed and a sheet of masonite to build the rest.

    Cost me about $70 all up.
    I was very happy with the end result. It works great.
    Considering it costs over $1000 to buy a 15 inch disc sander I think i did well.

    Here are some photos of the build process.
    Attached Images Attached Images

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  3. #2
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    Feb 2006
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    Default

    Good job on the build but I think the comparison to the 15" H&F sander is a bit of a stretch..

    There is a good reason the H&F uses a 1.5kW (2HP) motor on its 15" disc sander.
    Using a small motor only permits very light passes otherwise it is too easy to bog the motor down.

    Even if only light passes are taken, using such a large disc on a low powered motor may be overloading/overheating the motor.
    Just the start up current needed to start such a large disc could be causing damage and going to an Al disc could make this worse.
    If you can I would put a power meter or ammeter in line with the motor to see what the currents are while you are using it.
    If these currents are above the currents on the nameplate of the motor this could be a problem

    The other important thing is, does the motor have a thermal cutout switch (TCS) on it?
    If not, given that most of the sander is made out of wood I would recommend that a TCS is fitted and make sure that it works.
    If the TCS can be accessed while the motor is running, a heat gun on low played onto the switch should stop the motor. If you have one, using a resistance meter across the switch is an alternative.
    Once you have done this the TCS should be tested under load and it should not damage the motor if this is done deliberately a couple of times.

    PS. I see you are in Perth. If you want to borrow a power meter you are more than welcome to borrow one from me.

  4. #3
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    There is a discussion on the size of sanding disc that should be used with what size motor in this thread.
    https://www.woodworkforums.com/f11/1-4-hp-motor-disc-sander-184211

  5. #4
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    Default

    Gday Bob

    Thanks for the reply

    I just measured the current draw of the machine whilst in use. (whilst actually sanding something) It draws 2.5A

    I cant get a reading on startup. It is either too high for my meters (10A) or my meters cant pick up the reading quick enough.
    I have a good quality set of Fluke multimeters.
    I dont have a clamp meter.

    I figure the motor is 1/2HP
    The sticker on the side says 380W 2.06A

    So I looks as if I am drawing 1/2 an amp too much.
    Would this pose a problem in the long term?

    I dont have a thermal overload switch either.
    I should be able to sort that out. You can get those reset type with a button on it.

  6. #5
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    Quote Originally Posted by legin View Post
    Gday Bob
    Thanks for the reply
    I just measured the current draw of the machine whilst in use. (whilst actually sanding something) It draws 2.5A
    Good work on doing that.
    Was the test piece typically of the hardest and largest possible piece of wood you would be likely to be sanding and where on the disc were you sanding?
    I was thinking of something like the end grain of a piece of 4x2 jarrah applied to the outer 4" of the disc with about an 80 grit paper..
    How difficult is it to stall the motor by pushing on the wood and does it stall before burning the wood?

    I cant get a reading on startup. It is either too high for my meters (10A) or my meters cant pick up the reading quick enough.
    If you can't get a reading then that should be Ok. I am surprised, but maybe not because it's a MDF disc.

    I have a good quality set of Fluke multimeters.
    I dont have a clamp meter.
    If you don't have a clamp meter how did you measure the current? Did you put the meter in series?

    I figure the motor is 1/2HP
    The sticker on the side says 380W 2.06A
    2.06 x 240 = 500W
    so
    380/500 = .76 or the motor is 76% efficient, which is either optimistic, or a very efficient motor.

    So I looks as if I am drawing 1/2 an amp too much.
    Would this pose a problem in the long term?
    1/2A over the limit should be fine but that depends on my first comment.

    I dont have a thermal overload switch either.
    I should be able to sort that out. You can get those reset type with a button on it.
    Either one with or without a reset button is fine as long as there is something there to protect the motor.
    It can be useful in situations where a small piece of wood gets jammed between the table and disc.

  7. #6
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    Default

    Was the test piece typically of the hardest and largest possible piece of wood you would be likely to be sanding and where on the disc were you sanding?
    I was thinking of something like the end grain of a piece of 4x2 jarrah applied to the outer 4" of the disc with about an 80 grit paper..
    How difficult is it to stall the motor by pushing on the wood and does it stall before burning the wood?
    I went back and sanded some jarrah. It draws just under 3 amps sanding that.
    I have 100 grit paper on it at the moment.
    To stall the motor you dont have push overly hard but I do have it set on the slowest speed. It does stall before burning the wood. If I set it to the next highest speed it doesnt stall nearly as easy. It is just over 3 amps on this speed whilst sanding and 2.4A without sanding. I might leave it on this speed.
    I would say and average current draw would be 3 amps normal use. I am now closer to 1 amp over the rating of the motor.
    Maybe I am pushing my luck on this.

    I do have another motor from a compressor.
    I didnt want to use it as it it is a bit excessive for this job.

    If you don't have a clamp meter how did you measure the current? Did you put the meter in series?
    Yes I put the meter in series.

    2.06 x 240 = 500W
    so
    380/500 = .76 or the motor is 76% efficient, which is either optimistic, or a very efficient motor.
    My guess would be optimistic Bob, after all it is a quite cheap lathe I took the motor from.

  8. #7
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    Quote Originally Posted by legin View Post
    I went back and sanded some jarrah. It draws just under 3 amps sanding that.
    I have 100 grit paper on it at the moment.
    To stall the motor you dont have push overly hard but I do have it set on the slowest speed. It does stall before burning the wood. If I set it to the next highest speed it doesnt stall nearly as easy. It is just over 3 amps on this speed whilst sanding and 2.4A without sanding. I might leave it on this speed.
    I would say and average current draw would be 3 amps normal use. I am now closer to 1 amp over the rating of the motor.
    Maybe I am pushing my luck on this.
    Yeah 3A (or ~750W) is starting to get up there.
    What current does it draw when it is free running? (i.e. not sanding) and does the motor get warm just driving the disc for about 10 minutes?

    I do have another motor from a compressor.
    I didnt want to use it as it it is a bit excessive for this job.
    Is it a 3HP? If so that is probably overkill for a a 15" disc although that is what I use on my 12" disc/6" belt sander combo.
    The reason for this is that my sander is a 3Phase and has a variable speed drive on it so it can run for zero to 3600 RPM (I could run it a bit faster)
    The 3HP is achieved at 2880 RPM, so at 1440 RPM it's only ~1.5HP.
    I never thought I would use it at 3600 RPM but on the belt sander that represents 1200 FPM which is less than the belt speed of the 4" Makita belt sander (1650 fpm)
    An 80 grit belt fair rips the wood off at that speed.

  9. #8
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    Default

    A nice sander build and a good use for one of those GMC lathes. A lot more up market than my mdf disc on a spare faceplate.
    I usually am happy if the motor stays reasonably cool after a fair bit of work so I wont get into the power to disc size dedate.
    Regards
    John

  10. #9
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    Default

    Very good work on reusing and adapting an old lathe.

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