I found myself needing to separate a pile of excavated dirt into three piles:
- Large rocks, chunks of cement, and broken glass - to be thrown away
- Small rocks and dirt - to use in the garden and planters
Fine topsoil - for scattering over a low spot in the lawn without introducing rocks to the grass
Rather than build two separate sifters, I built one that can sift one shovel-full of dirt through two increasingly fine screens at the same time, cutting my sifting time in half. The sifting screens are designed so they can be used independently if needed.
I made mine at TechShop.
- Saw - to cut the lumber to the proper size for the frames
- Staple gun - to attach the screen to the wooden frames
- Wire snips or metal shears - to cut the metal screen to size
- Drill & bits - to attach the metal brackets to the frames
- Lumber for frames - Pressure treated pine is cheap and resistant to moisture in the soil
- Coarse screen - 1/4" aluminum garden screen was easy to find and pulled out big chunks quite well
- Fine screen - Aluminum window screen creates a very very fine result
- Metal angle brackets - to mount to the corners of the sifter screens so the screens interlock
- Thick dowel - to use as a roller underneath the sifter. The thicker the better. Three inch diameter would be a good ballpark size.
Step 1: Build Three Frames
This project requires three rectangular frames: a coarse sifter, a fine sifter, and frame with no mesh that will simply act as a smooth surface on the bottom of the whole contraption so it can roll smoothly across a dowel.
The outside dimensions of the rectangular frames should be identical, but the system will work a little smoother if the inside opening of the frames gets slightly wider as you go down the stack. This lets dirt fall through each subsequent screen screen without getting hung up on the sides of the frame below it.
I planned to sift dirt into a wheelbarrow, so I made my frames somewhat smaller than the barrel of my wheelbarrow so that I could collect all of the dirt as I shook the sifter back and forth.
I constructed the frames using a box box joint, so each piece of lumber used in the frame will be the full measure of the side it will create since the pieces will overlap at the corners. I cut the fingers using a tenon jig. It is important to make sure that all of the lumber is exactly the same height and width or the fingers will not match up properly once they are cut.
If you don't have access to the equipment needed to make accurate joints, you can use brackets purchased from a hardware store. If you use brackets, be sure to attach them to the inside of the frame joints so as to not interfere with the additional brackets that will be used to nest the frames together.
If you opt to use an oh-so-easy butt joint, but be sure to use at least two screws at each corner to prevent the rails of the frame from twisting. The screen we attach later will pull only on one side of the frame, and can apply quite a bit of torque.
Step 2: Attach Screen to the Frames
I was able to acquire mesh of the appropriate size from my local hardware store. I used gardening mesh with 1/4" square holes for the coarse filter and aluminum window screen for the fine filter.
To make the coarse filter, lay the mesh across your frame and cut the mesh so it is just slightly larger than the frame. Use metal shears for this. I, being right handed, recommend the shears designed to cut to the left. This will help keep the pointy bits away from your fingers as you cut.
Fold an entire row of the mesh back under itself around the entire border of the mesh. This will keep the points out of harms way while you are using the sifter. The mesh should now be just slightly smaller than your frame.
Use a staple gun and staple the mesh at the middle of the bottom of one edge of the frame. Move to the opposite side of the frame, pull the mesh taut across the middle, and staple one staple in the middle of that frame.
Do the same for the other two sides, stapling in the middle. Once you have a staple in the middle of each frame, start adding staples working from the middle towards the corners of the frame. Add staples to each side in turn instead of finishing an entire side before moving on to the next. This will prevent the screen from buckling and will leave you with a tightly strung screen.
If you push too hard on your staple gun it is easy to accidentally cut through the mesh with the staple. This can happen a couple times without weakening the mesh, but if it happens too many times the screen can become significantly weakened and tear along the edge when loaded. Be careful and reinforce any tear throughs by adding a staple to either side.
Attach the fine mesh to a second frame in similar fashion. If you anticipate heavy loads it may be best to apply a layer of the heavier mesh after installing the fine mesh to help hold the weight of the soil and protect the finer strands.
The third frame receives no screen.
Step 3: Add Brackets to the Frames
The frames need to be able to nest together so they stay aligned with each other while being shaken around. We will use metal brackets at the corners to accomplish this. The way I set things up, either the coarse or the fine screen can be used on top of the screenless frame, or the three can be stacked together with the coarse screen on top, the fine screen in the middle, and the screenless frame on the bottom. There are various ways to accomplish this, but I opted to add brackets extending downward from the coarse frame and brackets extending upwards from the screenless frame. Only two opposing corners are needed to accomplish this for each frame, meaning four brackets total are all we need. By staggering the orientation of the brackets we can keep them from interfering with each other if the coarse frame is set directly on the screenless frame.
I'm sure that appropriate hardware can be purchased at a hardware store, but I just repurposed some scraps of mild steel, added a 90 degree angle and drilled two holes in each big enough to accommodate drywall style screws.
Using the brackets as a template, line the holes up with the middle of the height of the frame at an appropriate corner. Use a pencil and scribe the position of each hole onto the wooden frame.
Pre-drill holes for the screws at the positions marked. Be sure to avoid having the screw holes intersect each other. You may have to angle one or both pilot holes up or down slightly so the screws can cross by each other.
Step 4: Stack the Frames
If everything has been assembled properly, the outsides of the frames should all line up exactly on top of one another, and the metal brackets that were screwed to the frames should snugly cradle the corner of the adjoining frame.
All three frames can be used at once, or either of the filter screens can be used with the bottom screenless frame as a stand-alone one-size sifter.
Lay a large dowel across the top of your wheelbarrow, place your frames on top of the dowel, and you're ready to start sifting.
Step 5: Sift!
Dump a shovelful of dirt onto the top screen.
Push the sifter back and forth, letting the dowel support the weight of the frames. The dirt will slowly separate out into different grades of sediment.
You may need to use your hand to break up large clods on the top screen.
After each shovelful, empty the screens of their contents. I find it easy to keep two five gallon buckets next to the wheelbarrow and collect the large and medium grades in those, allowing the fine dirt to continuously accumulate in the wheelbarrow.