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  1. #1
    Join Date
    Apr 2018
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    Drouin Vic
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    79

    Default Disc sander build

    I've been thinking that a disc sander would improve my pattern making, I'm not particularly well set up for woodworking and making a decent pattern seems like a basic requirement for casting.
    I made a bicycle-powered potters wheel for my daughter's birthday earlier this year, the throwing head is 12" diameter so I decided to use the same pattern and make a 12" disc for the sander.
    sander disc casting.jpg

    After machining the rough-as-guts casting, I made an arbor and set it up on the balancing rail for my surface grinder wheels. Had to drill out a fair bit of material from the heavy side to get it nicely balanced.
    sanding disc balance holes.jpg

    Used the shaper to cut the internal keyway; I drilled a hole at an angle to intersect the bore near the bottom, so the slotting tool has somewhere to run out at the end of the cut.
    cutting disc keyway.jpg

    When I bought the vice for my shaper, the previous owner had it bolted down to a piece of .600" thick plate that has a machined surface both sides. This piece of plate was just the right size to become the table for the disc sander.
    I milled a recess in the plate so that the sides of the plate extend forward of the disc face; this enables the pivot point for the table to be close to the same plane as the front edge of the table so the gap doesn't become change too much as the table is tilted. I then rebated the underside of the table to 45 degrees as the table will be able to tilt to that angle. Setting up to rebate the plate took a bit of imagination as I don't have any kind of tilting fixture; fortunately I have a dirty great angle plate and plenty of room in the Z-axis of my mill.
    setup for table bevel.jpg

    I needed a 1/2" wide by 1/4" deep slot in the table to accept the mitre guide from my cheapy bandsaw. I found a 1/2" x 5" side-and-face cutter amongst my collection; it looks like it's ready for the bin
    rusty side & face cutter.jpg

    but a visit to the surface grinder with my almost-finished sharpening jig and it was good to cut.
    side & face cutter sharpened.jpg

    milling table slot.jpg

    The table is now ready to go.
    table bevel finished.jpgtable top slotted & bevelled.jpg

    I'm using a 3hp 3-phase motor that has been hiding under a bench for a few years. I have a RPC but I want this sander to be more portable than the 3-phase wiring in my shed will allow. I put together a static converter, mostly with bits left over from my RPC build although I had to fork out for the capacitors and the plastic box.
    3 phase starter.jpgstart-stop station.jpg

    I don't know how much power a 415v 3 phase 3 horsepower motor will put out when it's being fed 240v single phase power but hopefully it's about right for a 12" disc sander. Given that every other build I looked at on the internet was running 3/4 to 1hp, I reckon it should do.

    My least favourite metalworking activity would have to be fabrication. After a lot of cutting, grinding, welding etc I got the frame together and gave it a couple of coats of ford tractor blue.
    disc sander frame painted.jpg

    I had to fit the vertical head to my mill to slot the tilt adjusters. This is one of those times when two crappy mill vices are better than one good one. I left the stock long so I could cut the two slots between the vices, gripping the 10x40 bar stock where the slots aren't.
    slotting adjusters.jpg

    I got the thing assembled today. I'm waiting for a couple of sanding discs to arrive in the mail as no-one seems to stock anything bigger than 9".
    Also I put a ground finish on the tilt adjusters, I'm going to have to give them some kind of anticorrosive finish.
    nearly finished.jpgnearly finished 2.jpgnearly finished 3.jpgnearly finished 4.jpg

    The table can tilt about 10 degrees upward and 45 degrees down. It pivots on M8 socket-head capscrews, the diameter of the heads of these means they are below the surface of the table.
    table pivot.jpg

    still to do are add feet to the underside of the frame- I'll probably use discs cut from some delrin stock- and screw a sheet of 19mm flooring to the top of the frame members. The feet will enable my fridge trolley to easily get under it for portability and standing on the flooring to use the sander will anchor it when in use. Once in use I'll be able to decide whether it needs a shield and dust extraction; the main reason to keep it portable is to be able to take it outside, or by the door in bad weather- I've never actually used one of these things so I guess I'll find out how much mess it makes once my sandpaper arrives.

  2. #2
    Join Date
    May 2011
    Location
    Murray Bridge S Aust.
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    66
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    3,626

    Default

    Are you using hook and loop to hold the disc on? I found it easy to change discs with it.
    You'll need some form of dust collection on it, they will throw a lot of dust about.
    Kryn
    To grow old is mandatory, growing up is optional.

  3. #3
    Join Date
    Apr 2018
    Location
    Drouin Vic
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    79

    Default

    Quote Originally Posted by KBs PensNmore View Post
    Are you using hook and loop to hold the disc on? I found it easy to change discs with it.
    You'll need some form of dust collection on it, they will throw a lot of dust about.
    Kryn
    I wasn't planning on using hook & loop, in fact I went into Hare & Forbes the other day and they had discs with hook & loop but none without so i came away empty handed. I didn't want to spend the extra 25-odd bucks for the conversion kit. Perhaps some time down the track I may do that. Will see how often I end up changing the abrasive.

  4. #4
    Join Date
    May 2011
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    Murray Bridge S Aust.
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    I use the hook and loop and takes about 3 minutes to change discs. I have an old thin cutting board that I slide in between the two, slide out the used one and then slide in the new one, handy when you're using several different grits.
    No need to remove the table either.
    Kryn
    To grow old is mandatory, growing up is optional.

  5. #5
    BobL is online now Member: Blue and white apron brigade
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    Feb 2006
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    Perth
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    Quote Originally Posted by Pete O View Post
    I'm using a 3hp 3-phase motor that has been hiding under a bench for a few years. I have a RPC but I want this sander to be more portable than the 3-phase wiring in my shed will allow. I put together a static converter, mostly with bits left over from my RPC build although I had to fork out for the capacitors and the plastic box.

    I don't know how much power a 415v 3 phase 3 horsepower motor will put out when it's being fed 240v single phase power but hopefully it's about right for a 12" disc sander. Given that every other build I looked at on the internet was running 3/4 to 1hp, I reckon it should do.
    Running a 415V motor on 240V will produce about one half that produced by 415V power, then the use of a static converter will only allow the motor to generate 2/3 to half of that power so the final max power will be at most 2/3 x 1/2 x 3HP =1HP and could be as low as 1/2 x 1/2 x 3 or 3/4 HP.

    This is probably enough for your casting pattern making but I've used the Woodfast 1HP 12" disc at the mens shed and while its OK for smaller pieces of wood, it struggles with larger pieces compared to the 3HP 12" disc I have at home. Sometimes I wonder if it really is a 1HP motor on the Woodfast.

    Have you checked to see if the motor can be converted to 240V 3P. This happens automatically if the motor is a 415V "Y" and is converted to "∆"
    Then your available HP would be between 1.5 and 2HP.

    My disc is on a 1m long belt sander and has a 240V VFD connected to it and has been converted to ∆ so it can develop full power and can run at up to 3600 RPM. I used about half speed for final sanding of wood and higher speeds with the blue Ziconia discs on metal. I also have the hook and loop disc exchange system and find it works great. Wheeling is right about them throwing dust around. Here is my setup for dust extraction..

    Linisher.jpg

  6. #6
    Join Date
    Apr 2018
    Location
    Drouin Vic
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    Thanks Bob. Re-wiring motors is outside my knowledge- there's no mention of star / delta windings on the plate on this motor and inside the cover there are just 3 tails of wire. I'll see what it's like once I get some abrasive on it- if worse comes to worst and it is completely gutless, I guess I can buy some 3-phase cable and run it off the rotary converter which would give it the full 3 horsepower but that would reduce it's portability.

    As an aside, an amusing bit of history on that motor- it was the original motor on my lathe when I bought it. The pulley had a very severe wobble that went through the whole machine, it seemed obvious that the motor shaft was bent so I picked up a second 3hp 3ph motor for a song off ebay. When I pulled the pulley to do the swap, I discovered the motor shaft was straight but some goose had bored the pulley not only off-centre but also not at 90 degrees, it must have had close to half an inch of runout. The second motor fortunately had a bigger shaft so I was able to bore the pulley straight at the bigger size and add this motor to the pile under the bench.

  7. #7
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by Pete O View Post
    As an aside, an amusing bit of history on that motor- it was the original motor on my lathe when I bought it. The pulley had a very severe wobble that went through the whole machine, it seemed obvious that the motor shaft was bent so I picked up a second 3hp 3ph motor for a song off ebay. When I pulled the pulley to do the swap, I discovered the motor shaft was straight but some goose had bored the pulley not only off-centre but also not at 90 degrees, it must have had close to half an inch of runout.
    You do have to wonder about where some people are coming from sometimes.

  8. #8
    Join Date
    Apr 2012
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    Healesville
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    Nice job there Pete.
    I reckon it would be a good idea to stick to 1400 rpm with that cast alloy disc as it could become a hand grenade at high rpm's.

    cheers, shed

  9. #9
    Join Date
    Aug 2011
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    Melbourne
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    That's a really nice piece of work Pete. I'm thinking you will enjoy using it once you're finished.

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  10. #10
    Join Date
    Apr 2009
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    Ballina N.S.W.
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    Pete O,
    A nice build on your face plate and tilting table, you will not have any flex in that plate. I have a 3HP single phase 3000rpm motor on my set up to enable me to size the pulleys to run the belt side at high surface feet. The face plate is the opposite, sized to run at a maximum of1200 rpm. You will enjoy using it.
    Bob

  11. #11
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    Apr 2018
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    Drouin Vic
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    Thanks for the comments Bob, I saw your combination setup in the thread on the other forum, looks terrific. I've got a little use out of this so far, it absolutely eats wood, sure as heck makes some dust though. Looking for something else the other week I came across a 3ph reversing switch I was sure I had somewhere, that will be added to the disc sander when time permits.

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