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Homemade 12" disc sander

Discussion in 'Grinders' started by dancom, Mar 17, 2015.

  1. dancom

    dancom Dust Maker Best Shop Tool

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    Homemade 12" Disc Sander
    One of the things I use most in the shop is the little disc sander on my combo 4x36" belt / 7" disc sander. It's pretty lightweight and when I saw some examples on YouTube of others making a 12" size out of wood, I started thinking about my scraps and wondered if I could put something together for cheap.


    The Motor

    [​IMG]

    Never one to pass on a motor, I bought a 1/2 horsepower 1730 RPM motor at a garage sale for $5. A steal for $5, but then both the seller and I never knew if it worked at the time. I took it home and put power to it and it worked! It may be slightly under-powered, but a 1/2 horse should do most of my lightweight work with ease.

    I had to swap the starter capacitor leads to get the motor to run counter-clockwise (when looking at the shaft).

    The Disc

    I bought a piece of 1/4" thick aluminum from the metal supermarket. This is probably going to be the most expensive item in the build at around $25 for a square foot. The piece I have is roughly 12-1/2" x 12-1/2". If you get something larger, you can cut it down to size with a jig saw. I used a steel cutting blade, some masking tape and clamped the piece down good before cutting. It's slow going but doable.

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    I found the approximate centre point.

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    Punched a dimple at the intersection.

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    Then using a divider set to 6", I scratched a circle. I then went over the outside of the circle with felt marker.

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    On the portable band saw, I cut the circle out. This was done in 8 small sections. I am staying outside the line as I will true the circle after it's mounted.

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    Voila! A "roughly" 12-1/8" circle of 1/4" aluminum.

    [​IMG]
    I found this at the hardware store. It's unique because it has a has a flat face. It is 5/8" bore (to match the motor shaft), has a set screw and is about 2-1/2" outside diameter.

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    For mounting the sheave, I used four 10-24 flat head machine screws. Although these seem small in diameter, they are strong with about 720 lbs. of clamping load and a shear strength of over 3000 lbs. each.

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    I placed the sheave directly on centre and drilled one hole. This one screw and nut will help keep this in place while drilling the other holes.

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    On the face, the holes are countersunk with a standard 82° countersink. The idea here is that no part of the screw head is above the surface. Try to get them perfectly flush.

    I used a little nail polish for thread locking of the machine screws to keep the nuts from working loose.

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    Here I have mounted the disc and have it ready for the spin test. You'll want to clamp or screw the motor down. At this stage we really don't know how much vibration will be present when it's spinning.

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    Once it's spinning, I put my shield on and used a rest and the edge of a file to true the outside of the circle.

    Now the motor and disc are looking good, it's time to build a frame to mount the motor and allow for a dust port and table mount. To be continued...
     
  2. FORGE

    FORGE Maker of the Year Best Knife

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    Dan I would like to know ........ When do you sleep or work ??????

    Anyway I will add to your post with a box that I made for my 12 inch disk.
    This is one of the beat tools a knifemaker can have and you don't realize how much you would use it until you have one in your shop.
    [​IMG]

    [​IMG]

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  3. dancom

    dancom Dust Maker Best Shop Tool

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    That looks sweet man! I like how you drop the disc down the front of the bench to reduce the table height. I was going to raise up the motor, but may change my mind now.

    Did you bring out the motor capacitor wires to a switch for FWD/REV?

    I get up usually before 5AM and head out to the garage. I live out in the country so I can make all the noise I want. I upload pics and drive to work. On my coffee break I do some write up to go along with the pics. Before noon, we're all good for the day.

    Dan
     
  4. FORGE

    FORGE Maker of the Year Best Knife

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    I made two of these simply because it is a pain to rip off the paper to change grits. I have 36 grit one one and 120 grit on the other.
    I made one fwd/rev and the other is only fwd.
    I never have had the need to run them in reverse, so I would only make then single rotation.
     
  5. dancom

    dancom Dust Maker Best Shop Tool

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    One other thing, did you make some kind of brake?
    Just thinking if that is 5/16" steel, she probably stays spinning for a minute after you power off.

    Dan
     
  6. FORGE

    FORGE Maker of the Year Best Knife

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    Just my finger....... on the back side, stops it.
     
  7. dancom

    dancom Dust Maker Best Shop Tool

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    LOL! Ya not the front side eh?

    The 1/4" alum "flywheel" stays going for about 30 seconds after power off.
    Thinking I am going to try adding a brake. Using a double throw switch and putting a load on the motor (which is acting like a self-exciting generator) when the power is switched off.
    I am sure the big guys use DC injection or something, but I reckon I'd try it and see.

    Cheers!

    Dan
     
  8. doublehelix1

    doublehelix1 New Member

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    lookin good.

    what did your materials cost you? how was the balance?
     
  9. dancom

    dancom Dust Maker Best Shop Tool

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    The alum was $26, the motor was $5 (garage sale roulette), sheave and screws means it's closing in on $40.

    The balance was pretty rough until I trued the round. I used the tip of the mill file and before long it was touching continuously.
    I will have to accept that it won't be precision balanced, but it's nice and quiet when running clamped to the bench. I did "flatten" the sheave face on the belt grinder so as to not have too much wobble.

    Dan
     
  10. FORGE

    FORGE Maker of the Year Best Knife

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    If you look on the last picture of mine you will see where it was precision balanced and then I filled the holes with epoxy because
    my hand brake was getting a beating on the holes.
     
  11. dancom

    dancom Dust Maker Best Shop Tool

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    Yes, I saw the balancing holes. Must have been killer on the fingers until you filled them in.
    Was the disc statically balanced?

    Dan
     
  12. FORGE

    FORGE Maker of the Year Best Knife

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    No dynamically, a buddy of mine worked at the IPSCO steel mill R&D Lab we did it there.
     
  13. dancom

    dancom Dust Maker Best Shop Tool

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    The Frame
    The frame needs to account for holding the motor and providing attachment points for the dust barrier.

    (I don't want too much steel dust inside an ODP motor.) The frame also needs to hold a mount for the table and a pedestal for the power switch.
    [​IMG]

    I always try to re-use as much as I can.
    In the scrap pile I have some salvaged 1-1/2" channel. It comes as bracing for large cardboard shipping boxes to keep them rigid.
    It's folded up 18 gauge so not the strongest thing, but when it's tacked together in a web it will be quite strong.

    Welding alert - welding 18 gauge steel is a bit of an art.
    Please excuse my beads, as I was trained in electronics. LOL

    [​IMG]

    The basic frame measures 13" x 12-1/4" The 12-1/4" is to get us close to the diameter of the disc so we can add pair of vertical supports to hold the table on either side.

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    The motor needs to be raised 3" from the bench so the disc will spin clear.
    I welded 4 x 1/4" NC x 1/2" bolts to the underside of the motor mounts.
    The spacing for the mounting studs is 3 x 5" on centres.

    Oh yes it looks kind of Frankestein. Most of this contraption will be hidden by the disc guard and dust barrier later.

    [​IMG]

    Reusing some 3/16" x 4" plate, I made these two vertical supports for each end of the table.
    I drilled and welded a 5/16" NC nut to each of them.
    The other holes will accept a length of 5/16" threaded rod for support and precise adjustment.

    [​IMG]

    The motor and disc fit on there nicely. I want the table to be adjustable over about 50° (+5° to -45°) from right angle.
    Next is to weld on the table supports and true them up with the threaded rod and 4 nuts.

    To be continued...
     
  14. dancom

    dancom Dust Maker Best Shop Tool

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    The continuation of the grinder build.

    Reusing some 3/16" x 3" plate I made these two vertical support for each end of the table. I drilled a hole and welded a 5/16" NC nut to each of them. The other holes will accept a length of 5/16" threaded rod to act like an adjustable truss.

    [​IMG]

    I welded the supports on to the frame and cut and installed some 5/16" threaded rod.

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    Here I have attached the angles to hold the hood and the post to put the switch on. The angles are hardware store inside braces and the post is some 1" square tubing, about 16" long.
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    Here's the table. Some 3/16" plate cut to 16" x 8" with a 1" notch at 12-1/8" for the disc to fit in.
    [​IMG]

    I cut two 5-1/2" pieces of 1-1/2" angle for mounting the table.
    These heavy angles , along with the truss rod, will allow me to tighten the table at the correct angle without flexing anything too much.
    [​IMG]

    Two 11/32" holes are drilled in each angle to pass the star knob or threaded handle to pass through.
    The star knob will thread into the nuts that I tacked on to the vertical supports.
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    With some temporary bolts in, I can check the range of table tilt angle. Looks good.
    [​IMG]

    Time to slap some paint on the frame, start on the hood, make some star knobs and do a little electrical.

    To be continued...
     
  15. dancom

    dancom Dust Maker Best Shop Tool

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    More work on the disc sander...

    Here's the frame after some Royal Blue rust paint we're looking good to go for final assembly.
    I chose this colour as it closely matches the motor (not because Cal's is blue ;))

    [​IMG]

    While the paint was drying, I started on the hood.


    The Hood

    To build a hood I opted for something easier to work with than steel.
    It's main purpose is to keep the dust out of the motor and doesn't need to be so heavy-duty.
    I had some 1/2" plywood and cut it to 12-5/8" x 12-5/8".
    I drew an arc with a radius of 6.25" and drilled a 3/4" hole in the centre. This will give a nice round curve and 1/8" of wiggle room for sanding the arc.
    I cut on the band saw and smoothed on the sander. Also with the band saw, I cut in towards the hole so this will slip over the motor shaft.

    [​IMG]

    I cut a half circle, again 6.25" radius out of scrap 3/4" plywood.
    Another cut at about 4" radius makes a curved strip about 2" wide.
    I cut this piece into smaller into "wedges."

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    The wedges are drilled, glued with carpenter's glue and screwed with #8 wood screws.
    These are positioned match the radius of the hood.
    1-1/4" long screws are perfect if you don't sink them in too far.

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    Once the glue is dry I cut a strip of 1/8" hardboard at 2-3/8" wide and 19" long.
    It's glued and screwed with #8 wood screws. Starting at one one and working around the curve.
    Any little excess is trimmed off at the finishing end.

    [​IMG]

    I'll do some assembly this week and update with the finishing details.
    Thanks for watching!

    Dan
     
  16. dancom

    dancom Dust Maker Best Shop Tool

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    Continued...

    I painted the hood with black enamel.
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    Hood installed with table.


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    For the switch I used a good old 1110 box. The green and red rectangles are made with coloured Sharpies. :)

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    With a 120 grit AO disc installed.

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    Squaring up the table.

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    Seems to work pretty good for under $70. Now to find a place to bolt it down.

    Dan
     
  17. shadman

    shadman Member

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    always impressive
     
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  18. LeclairKnives

    LeclairKnives Active Member

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    Very nice! A disc sander Is way up on my wish list for the shop. I have some 8" rounds of micarta and a 1 hp motor that I wonder if I could cobble somthing together from.....
     
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