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  • Need help with soil sifter

    Discussion in 'The main mechanical design forum' started by Medic7594, May 31, 2013.

    1. Dana

      Dana Well-Known Member

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      10:2 reduction gives you 350 rpm, or 5.8 cycles per second. That's still pretty fast to [try to] move something as big as your shaker frame, unless you're only moving it a small fraction of an inch (like you jigsaw did). I have no experience with soil sifters, but I suspect you need to be going something under 60 rpm at the final crank pulley.

      The pulley broke because the spokes aren't made to take loads in that direction.

      You probably need the motor with its 2" pulley driving a 10" pulley on an intermediate shaft, then another 2" pulley on that shaft driving the existing 10" pulley on the existing shaft. On that shaft, make a crank arm (you could modify a steel, not cast iron, pulley or gear, or make it from scratch) to connect to the connecting rod.

      The crank is your existing 10" pulley. The crank pin is where you attach the connecting rod.
       
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    3. Medic7594

      Medic7594 Member

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      Hi Glen,

      I'm trying to clean mulch beds and an area that I removed a bunch of brush and trees. I purchased a house last year and the prtevious owner neglected the property. The much beds are 12" high and the area I cleared (20'x20') has all sorts of debris burried there (tiles, plastics bags etc).

      The goal is to shovel the mulch and other dirt into the sifter and basically seperate the garbage and rocks from the actual soil. I saw similar sifters to the one I built on Youtube and Google. All seemed to work well. Unfortunately I'm having problems.

      Your idea sounds good. I'd love to see a picture of it. Like you, my sifter is for home use and small areas.

      I am using a 1/4 horse washing machine motor.

      This morning I though about trying a washing machine transmission. From what I read, it will give me that agitation motion I want. I'm not looking for high speed or long travel. I need just enough movement to shake the soil.

      Any additional ideas or suggestions is greatly appreciated.

      I'll PM you with my email address for the pics.
       
    4. Medic7594

      Medic7594 Member

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      Dana,

      I agree the current setup is way too fast. 50 - 60 RPM's would be ideal.

      I don't need too much travel. Just enough to shake the material. That's why I copied the jigsaw model I saw online. Quite frankly it did wonders until it broke.

      What do you think about using a washing machine transmission? It would provide minimal movement, reciprocal motion and would be smoother.

      I'm also going to try your intermediate pulley idea.

      Thanks again. I really appreciate it.
       
    5. ChrisW

      ChrisW Well-Known Member

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      This type of sifter is often hand operated and will very efficiently sieve small volumes of materials. It also allows hand picking of weeds, archaeological artifacts etc.
      The combination of long travel and slow speed will not stress the frame or cause rapid erosion of the screen mesh.
      Stroke of 5" and speed in the range 60-120 rpm should give acceptable results and not break the frame.
      A variable speed washing machine motor would be practical if you can figure out which connections energize the slow washing cycle, running at the spin speed would be bad!
       
    6. Medic7594

      Medic7594 Member

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      ChrisW,

      Thanks for your response. I agree the speed is too fast. I am going to shoot for a target speed of 60 RPM's.

      You stated a steoke of 5" would be ideal. I understand this as the travel of the sifter. Does the connecting rod length matter? Reason being, when the sifter is all the way back, it is about 5 inches from the pulley. Hence I would need a 10" connecting rod to allow for a 5" stroke. Is this correct?

      I currently have a 1/4 horse 1750 RPM washer motor. From what I understand the speed of the motor can't be regulated. I am going to have to use intermediary pullies to regulate the speed. Perhaps a washing machine transmission?

      What do you think?
       
    7. ChrisW

      ChrisW Well-Known Member

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      It isn't that 5" is ideal, it's a value which is in the range for a good sieving action and when run below 120rpm it will have a peak acceleration below 1g, which your structure should survive. 4" or 6" would be just as good;)
      To achieve the speed you will need to use a secondary shaft and set of pullies as Dana outlined earlier. The length of the linkage doesn't matter (within reason!)
      With such a simple structure as this, I am a great believer in trying it out to see what works. Disconnect the linkage, drop a spade of soil on the mesh and re-create the action by hand. You could see if it works ok without modifying the drive, this is the no-cost reality check. If it looks good then make up the drive and you know it won't be wasted.
      Possibly a washing machine transmission would work if it has variable speed, European washing machines have variable speed motors so I'm not familiar with the transmissions you may have available. Otherwise using a 2" drive pully, 10" driven pully on a layshaft connected to a 2" drive pully finally driving another 10" driven pully. This will give you a double reduction and final speed of 70rpm which is ideal.
      Only other thing which may help is to fix a few small bars across the screen mesh, only 1/4" or 1/2" high. This would help break up clumps of soil by giving a small impact.
      Hope this helps.
       
    8. Medic7594

      Medic7594 Member

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      Chris I completely understand what you are explaining. I now understand the logic.

      I'm going to keep it simple and do the layshaft as you and Dana suggested. I'll keep you guys updated.
       
    9. Medic7594

      Medic7594 Member

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      Well I finally finished the soil sifter.

      I ended up using a 10" and a 9" pulley. It works but does not sift. Seems like it is too slow to produce enough of a jerk to move the soil. I attached a video of omit looks.

      Do you think it will produce more of a motion if I replace the 10" crank pully with a 5" pulley?

      [video]View My Video[/video]
       
    10. Medic7594

      Medic7594 Member

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      I think I had the video links incorrect.

      Try these:
      [video]http://www.flickr.com/photos/[email protected]/9006904588/[/video]
      [video]http://www.flickr.com/photos/[email protected]/9006867013/[/video]

      From what I figured on my own, if I replace the 10" crank with a 5" crank, I'll get 189 RPM's. will this be too fast?

      Would there be more of a jerking motion or shake if I were to keep the 10" crank but make he connecting rod shower? What if I moved the connecting rod to the outer rim?
       
      Last edited: Jun 10, 2013
    11. ChrisW

      ChrisW Well-Known Member

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      Nice job, you can see the soil is just starting to shear but not quite yet.
      Quite a few options you can try, moving the con-rod to the outer periphery is going to double the effect, that might be enough so worth trying first.
      Speeding up to 189rpm might be a bit high, but you could then move the con-rod closer to the centre to slow it down a bit. Changing the speed has a greater effect than changing the travel or stroke.
      Guessing the exact numbers, you are getting about .5g acceleration. Moving the linkage to the periphery will double to 1g while doubling the speed instead will raise to over 2g. Doubling speed or stroke don't give the same results.
       

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