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Shop-Built Thickness Sander

Discussion in 'Tele Home Depot' started by Guitarnut, Apr 13, 2012.

  1. bbmyers

    bbmyers Tele-Meister

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    I used MDF to build mine. Painting MDF to stabilize is a must. You've used plywood here but it's still probably a good idea to paint it to minimize movement due to moisture.

    Looks like you're having fun with this build. An excellent addition to your Shopsmith. Can't wait to see the finished product!

    Bb
     
  2. frankentele

    frankentele Tele-Meister

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    This thread is absolute genius!

    I was just looking at a used industrial sander yesterday, and the owner wanted $1000.00. I want to make one like yours too.

    ken
     
  3. Guitarnut

    Guitarnut Friend of Leo's

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    Thanks, Ken. I don't know if it's genius, but it keeps me challenged. :cool:
     
  4. Guitarnut

    Guitarnut Friend of Leo's

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    Motor and Controller Test

    Here's about 3 mins of rambling and some scary motor RPMs. The controller works fine but I had the wrong taper pot hooked up. Still a pretty good run thru. My guy feeling is, this motor is far too dangerous on a feed table with variable speed. I could see an accident happening very easily. but, i have a plan. :twisted:




    Since a pot is a variable voltage divider, and the potential for excessive speed is a real danger, I decided to hook up a linear 500K pot and see where the sweet spot is for feed control. I'll have to test again when I get the final load on it but here's an example.

    I can make a switchable fixed resistance control that gives me a couple of feed speeds. I hooked up the pot and set the speed to where I thought it would work. Then without moving the wiper on the pot, I measured from the wiper to each side of the pot and wrote down the values.

    Hi to wiper was 460K.
    Lo to wiper 80ohms.

    So, I can wire a fixed 470K resistor between the hi side and the wiper and a 100ohm going to ground...making a fixed voltage divider. I can set up values for a few speeds and switch them with a rotary switch. This way, I can safely use the motor with no fear of it running away on me. Infinitely variable speed is really sort of useless in this application anyway.

     
    Last edited: Apr 27, 2012
  5. Guitarnut

    Guitarnut Friend of Leo's

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    Speed Control

    I was thinking this thru last night and it seems like the way to go. I did a few quick diagrams. This one shows fixed values for R1-R4. R1 and R2 make up a voltage divider for the slow feed rate and R3 and R4 make up the divider for a higher feed rate.

    Since the two resistors, R1 and R2 are in series, they divide the 24Vdc input voltage. If I remember how to calculate this, the voltage sent to the wiper would be .05Vdc. On the other side, the different values of R3 and R4 would yield an output voltage of about .15Vdc. You can see that getting the right values for the right speeds would be a bit of trial and error.

    [​IMG]

    So, having some sort of variable resistance is a plus. The external pot is just too risky but having trim pots inside the case with the controller, allows me to have some flexibility in dialing in the speeds and then they tuck away, out of reach.

    [​IMG]
     
  6. Guitarnut

    Guitarnut Friend of Leo's

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    I spent some time drawing up the feed table this morning and got ready to cut when I realized another issue. The motor has to be attached to the table so it will keep drive belt tension as the height of the table is adjusted.

    One big issue with this is the flywheel. I have no exposed armature to pass thru the frame of the sander...so, it's time for surgery. I was thinking I needed a puller to get the thing off but I found a video of a guy using this motor as a generator...he shows it without the flywheel and there are threads on the armature. So, I braced the motor in the vise and with a tug, it came right off...reverse threads as I saw in the video.

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    Since the flywheel is cast, I figured I could cut it off with a hacksaw pretty easily. The pulley portion has one extra groove outside the belt, so I used this as a guide to cut.

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    Another bonus, I just shaved over 3 lbs off the motor. :cool:

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    I ran the motor thru it's speed range to make the lack of a flywheel didn't affect it's balance or current draw. In this shot you can see the 3 LEDS I mentioned before. The 4th...just above the white alligator clip...is the Current Limit indicator. It never came on during the cycle except for a flicker at start up.

    [​IMG]
     
  7. Guitarnut

    Guitarnut Friend of Leo's

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    I set out this morning to get the feed table built. Had the band saw set up, fence in place, hit the Shopsmith switch...nothing. Dang switch just went...no warning. Just stopped working. So, I rewired it. Actually, just a couple of jumpers to bypass the switch until I get a new one in. Classy, huh? :twisted:

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    On to the build! Various stages of the table build.

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    The belt will just clear the frame. The motor should have enough reach with the flywheel removed.

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    I'm not going to have the range I was hoping for if I stow the motor underneath. The main advantage of this is the sander will stay balanced with most of the weight being supported by the top tubes.

    The piece of stock under the drum is a shade over 1.75". It's lifting the pinch rollers but the drum still spins freely. I might be able to get 2" out of it which would be fine since I have a planer as well.

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    Another option would be to mount the motor under the roller. this would give me back the depth I lose with the motor in the middle of the table. But, it would make the sander heavy on that end. It's going to clamp to the lower tubes of the Shopsmith so it may not be an issue. This config would allow me to use the current belt. If i go this route, I'll put the coarse adjustment holes on the heavy end so it is always supported and that will leave plenty of room on the other end for the height adjustment.

    Either way, the sander will sit flat on a bench.

    [​IMG]

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  8. Warnz

    Warnz Tele-Meister

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    Looks like your options are limited there matey, you could always use just a simple clamp arrangement on the underside of the SS tubes if your worried about stability.
     
  9. Guitarnut

    Guitarnut Friend of Leo's

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    Yeah, I had planned to make a set of wooden clamps similar to what I used on the belt sander. I'll put some tee nuts in the bottom of the frame and then bolt in from underneath...not elegant but it will work,

    I think I'm going to go with the motor below the pulley, like in the last few pics above. That will keep it clear for the frame and tubes.
     
  10. macaroonie

    macaroonie Friend of Leo's

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    That looks great Mark , you are quite the bodger. If I were to make one observation my gut says that your feed rate on the lower belt may be a tad high. I'm just guaging that by eye from your motor / pulley vid. From experience of these things I would expect to see about 1 Ft in 5 secs at most in a machine of this power. Big industrial jobbies run a lot quicker obviously.

    PS bodger is not an insult here.
     
  11. Guitarnut

    Guitarnut Friend of Leo's

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    Thanks Mac. You're correct. There's no way I can determine resistance values and speed until I get tension on the rollers and load the motor. The trim pots will allow me to custom tweak the feed rate.

    Keep in mind, the Shopsmith is variable speed as well. I can match the feed rates to the optimal sanding speed. The drum spin test was done at the slowest speed the Shopsmith will go. I should have lots of possibilities.
     
  12. Guitarnut

    Guitarnut Friend of Leo's

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    Moving on to the motor box. I can see form this shot that the original motor mount is just going to get in the way.

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    So, a little time with the hack saw and it's just a memory.

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    I also needed to flatten one side of the casing flange. This is where mt mount for the roller will pass thru.

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    With a few pieces of scrap clamped around the motor, I hung the whole contraption from the belt and leveled it at the other end. This let me take accurate measurements for the side pieces of the motor box.

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    The motor box pieces cut and clamped together to check the fit.

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  13. Guitarnut

    Guitarnut Friend of Leo's

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    One of the ideas I had for trapping the ends of the axle was to make a bracket out of thick PVC. So I glued up some double and tripe thicknesses.

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    Here's the finished bracket. The bottom will screw to the under side of the feed table and pass thru the cut portion of the motor flange. The triple thick portion on the side will be drilled to just smaller than the axle and tapped into place over it. One of the great things about drill bits that are sized by 16ths is you can get a very snug fit.

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    While the cement is drying, I made caps for the free roller. They're made of ply for now but I thick I'll make them out of PVC as well.

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    Here's the PVC bracket drilled and clamped in place. I drove the axle into the bore and it is not going anywhere. No need to pin right now.

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    Here's a video of the roller test. the pulley on the roller isn't seated square the the roller...it has a bit of wobble in it. I can true it up next time i take it apart.

     
  14. Guitarnut

    Guitarnut Friend of Leo's

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    I was going to use the existing threads in the free roller for tension adjustment but the only hardware I had on hand was 1/4" and only had threads on the last 1" of the bolts. I cut threads in them all the way down to thickness of the axle from the heads. Here's one before and one after.

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    After drilling out the axle ends to a touch over 1/4", I slid a bolt thru and put 2 nuts on the back to keep everything in place.

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    Then I made some brackets out of scrap aluminum from my belt sander build. These are also temped...I'll make PVC "L" shaped brackets that wrap around the corners and screw to the side.

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  15. Guitarnut

    Guitarnut Friend of Leo's

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    I took everything apart one more time. While I had it apart, I trued up the pulley, and drilled some cooling vents in the motor box. I also installed the 16" x 48" belt. I wanted to take it for a test run but after adding the belt and rear tensioners, things are in a little bit of a bind. I need to spend some time balancing it out before running the motor with it..

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    The motor box will also house the controller. I'll cap off the end with a DC cooling fan. I can take power from the 24Vdc terminals that the trim pots will be connected too. The AC cord will go out the back of the box...out of the way.

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    While I was searching the top shelf above my bench for a small C clamp, I found this. It came with my Ridgid chop saw. I have no idea what it is, but I know what it will become. It's perfect for the height adjuster. It has a swiveling plate at the end and the lever is a quick thread release that lets the threaded rod slide thru when pressed. That will save some cranking when moving the feed table from one coarse adjustment hole to another.

    [​IMG]
     
    Last edited: Apr 30, 2012
  16. macaroonie

    macaroonie Friend of Leo's

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    Thats a hold down clamp that you are supposed to use when you are chopping something in your chop saw. It's meant to help you continue to have ten fingers. ))
     
  17. Guitarnut

    Guitarnut Friend of Leo's

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    Thank goodness I still have caution and common sense. ;)
     
  18. RogerC

    RogerC Poster Extraordinaire

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    Hey Mark, I was doing some research on a shop-built thickness sander, and I remembered your thread here. Did you ever get it finished up?
     
  19. Guitarnut

    Guitarnut Friend of Leo's

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    Hi Roger,

    Nope. But it taunts me daily...I'm gonna hide it away in a box until I can finish it up.

    I have decided to go with a manual feed vs motorized...at least to begin with. I'm gonna take that hi torque, hi speed motor treadmill I was testing with and use it for my buffing station.

    Mark
     
  20. RogerC

    RogerC Poster Extraordinaire

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    What?! Now you're making another tool that I want badly?! Dang you, Mark. Dang you to heck!

    :D
     
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