• Welcome to engineeringclicks.com
  • Need help with soil sifter

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

    1. Medic7594

      Medic7594 Member

      Joined:
      May 2013
      Posts:
      17
      Likes Received:
      0
      Hello everyone. I'm new to this site and I am not an engineer. I'm more of a backyard tinkerer. Anyway, I have been reading many sites and came up with a design for a soil sifter. Everything looks good on paper but I am having difficulty with the sifting mechanism.

      Since I don't have a photo posted, I give a brief description of the project.

      I have a base which is 30" x 36" sitting on my lawn trailer. Inside the base I have rails which support a 28"x30" sifter which has 1/4" screen on the bottom.

      Initially I had this powered by a jigsaw. It was working well until the jigsaw died 20 minutes later. The sifter was mounted on casters and there wasn't any friction. It moved back and forth smoothly.

      Searching around the house and online. I came up with plan B.

      With plan B I am using a 1/4 horse washing machine motor with a 2" pulley. The 2" pulley turns a 10" pulley via 1/2" belt. The motor is mounted below the 10" pulley and I am using a 40" belt. I then built a crank and slider mechanism to give me the reciprocal motion. It works but man is it rough. I tried to research crank and sliders but most of what I found is way over my head with the math.

      So here is my question, is there a simple way to design or calculate the proper diameter of the crank, slider and connecting rod?

      Currently I have a bolt going through one of the spokes on the crank connecting it to a 1"x1"16". The connect is loose enough to allow the shaft to move freely. The other end of the shaft is attached to the sifter tray and can move freely.

      Does this make any sense to you guys? Any ideas or suggestions on how to make a crank and slider that isn't so rough? Maybe you can recommend another method to provide the reciprocal motion I need?


      I'll try to post pictures tomorrow.

      Thanks.
       
    2.  
    3. Dana

      Dana Well-Known Member

      Joined:
      Sep 2010
      Posts:
      341
      Likes Received:
      3
      The crank diameter should be whatever you need the travel to be. It sounds like your second version would have a lot more travel than the jigsaw! The jigsaw's travel is what, maybe a half inch? You don't say what the crank diameter is, but say it's halfway out on the 10" pulley, that's 5" travel. Assuming a 1725 rpm motor, peak speed is 7.5 ft/sec (5mph), reversing 12 times per second. No wonder it's rough!

      Increasing the length of the connecting link will help, but you need to use a reasonable travel and speed (might need another stage of pulley reduction).
       
    4. Medic7594

      Medic7594 Member

      Joined:
      May 2013
      Posts:
      17
      Likes Received:
      0
      Dana,
      i might be confused with the terminology so please bare with me. I can't attach a pic because I don't have a way to post it.

      i have a 1x1x16 connected to the outer spoke of the 10" pulley.
      tomorrow I pan to remove the 1x1x16 and put a shaft and a 5" pulley. I'll then attach the 1x1x16 to the outer spoke of the 5" pulley. I know this will slow down the reciprocating motion. Will it also ease the rough movement?
       
    5. Medic7594

      Medic7594 Member

      Joined:
      May 2013
      Posts:
      17
      Likes Received:
      0
      Ok so I finally had a chance to post the following pictures of what I am building.

      Below is the Plan B build. Currently I have a 1750 RPM motor with a 2" pulley driving a 10" pulley via 40" belt. When I tested this it was very rough. I don't know if I have the wrong dimentions for the crank and shaft.

      Does anyone have any ideas?

      [​IMG][/IMG]

      [​IMG][/IMG]

      After reading more on this forum and the Internet, I though about adding a shaft with an additional 5" pulley. Will this decrease or increase my RPMs? Will it make the sifter slide more smoothly?

      Here is what I am currently thinking about doing...

      [​IMG][/IMG]

      The 5" pulley will be the crank and shaft. I'll also be adding additional supports for the shaft.

      Once again thanks for the help.
       
    6. Ramana Rao

      Ramana Rao Well-Known Member

      Joined:
      Jan 2012
      Posts:
      47
      Likes Received:
      0
      Keep the 10" pulley, but fix the crank as close to the center as possible, instead of the rim. This will reduce the travel of the sifter and give a smoother action.
       
    7. Dana

      Dana Well-Known Member

      Joined:
      Sep 2010
      Posts:
      341
      Likes Received:
      3
      ^^^ what he said. Basically you're trying to move it too far, too fast. Your jigsaw, which you said worked well, had what, maybe 1/2" of travel? Now you're moving it 10"... it's gotta go a lot slower, or you have to shorten the distance you're moving it. Using the same large pulley but connecting the link closer to the shaft is what you need to do.

      You're also going to have to support the shaft bearing better; the way you have that 2x4 just attached at the end it's not gonna last very long...
       
    8. Medic7594

      Medic7594 Member

      Joined:
      May 2013
      Posts:
      17
      Likes Received:
      0
      Thanks for the reply Ramana Rao and Dana,

      Dana,

      I actually am in the process of better supporting the shaft bearing. I am mounting two 2x4's with two bearings and the 10" pulley in the middle.

      If I understand you correctly and remember physics...

      The inside of the 10" pulley travels slower than the outside so my sifter will travel slower?

      Ramana you said, "Keep the 10" pulley, but fix the crank as close to the center as possible, instead of the rim". Do you mean the connecting rod? I thought the crank was the 10" pulley.

      How much will the slider slow down when I mount it closer to the center of the 10" pulley?

      From what I calculated, a 1750 RPM motor with 2" pulley connected to a 10" pulley will give me about 300 RPM's? Still sounds fast. Do I need to slow it down further? if so, do you have any suggestions?

      As for distance, currently the sifter can slide up to 7" if needed. However I'm thinking 7" of sliding isn't needed.

      Does the length of the connecting rod matter? I assume it doen't matter because the diameter of the pulley is going to dictate how much movement the crankshaft will have?

      What do you guys think? Am i making any sense?

      Once again, thank you for the help and responses.
       
    9. Medic7594

      Medic7594 Member

      Joined:
      May 2013
      Posts:
      17
      Likes Received:
      0
      Hey guys I took your advice and finished the project. Unfortunatley it only lasted 2 minutes.

      i reenforced the 2x4 which held the bearing. I also took 3/4" rod and made an axle for the 10" wheel. I secured it with a cotter pin on each side. As suggested, i moved the connecting rod as close as possible to the center of the 10" pulley. Mounted the motor and adjusted the belt.

      it worked. But it was still way too fast and rough. It wasn't as rough with the connecting rod at the rim.

      The spoke with the connecting rod broke away from the pulley.

      Any suggestions? What is a good way to slow this machine down?

      Do you think a washing machine transmission would work? They have an agitation cycle...

      Here are the before and after pics...

      [​IMG][/IMG]

      [​IMG][/IMG]
       
    10. PWASS

      PWASS Well-Known Member

      Joined:
      Sep 2009
      Posts:
      66
      Likes Received:
      0
      Years ago I was involved in the shakers used to filter the fluid returning from North Sea Oil Rigs.

      The screen was mounted at an angle, about 10 degrees, the large particles travelled up hill and off the top whilst the small particles went through the screen and out the bottom.

      It was driven hydraulically so that the speed could be adjusted and it was non explosive, but it could have been driven electrically.

      The motor was mounted on the screen driving an eccentric weight and the screen was mounted on springs.

      It must have worked well because we manufactured 100's of the hydraulic systems to drive them.
       
    11. Glen Krueger

      Glen Krueger New Member

      Joined:
      Dec 2011
      Posts:
      1
      Likes Received:
      0
      What are you trying to do with the sifter: are you trying to grade soil by size, or are you simply trying to separate rocks from soil and pulverize the soil? I fear your reciprocating system will have a tendency to beat itself to death. I recently designed and built a homemade 'sifter' that separates rocks from soil and pulverizes chunks of clay at the same time. The soil in my yard is half rock, and the balance is clay. Separating the rock was a chore, and pulverizing the clay was also a lot of work. I designed and built a very different machine, based a trommel concept. It has a spinning drum made of a cylindrical screen that's closed at one end and sits at a small angle (10 degrees). It uses a surplus 1/8 HP gearmotor that drives the drum at a speed that produces a centripetal acceleration just below gravity, so the contents fall to the bottom of the barrel just before reaching the top of the drum as it spins. The small stuff falls through the screen, and the rest gets pounded by the remaining aggregate until the clay chunks get beat to smithereens. It works great, and hasn't broken after a few months of use. It's relatively light weight and quite portable: not suitable for commercial use, but fine for home garden use. I can send pictures if you wish. I can provide the Complete SolidWorks model too, if anyone wants it. It cost me about $350 to build it (plus my labor), with the gearmotor being the most expensive component ($125 on eBay).
       

    Share This Page