Using a three-bin composting system is a great way to compost your leaves and garden trimmings. This particular three-bin design features three distinct sections with removable wooden slats that provide easy access to each bin. Construction of this design requires basic experience working with tools and lumber.

Supplies
materials
tools 

Construction Instructions
build dividers
set up and connect dividers
attach hardware cloth
attach front and back runners
make slats 

ALSO SEE:
lid for a 3-bin composting system
outdoor composting
indoor composting
other ways to recycle food scraps
using your compost 

Materials

• eight seven 12' cedar 2x4s
• three 8' cedar 2x2s
• two 6’ cedar 2x6s
• five 12' cedar 1x6s
• 31’ of 36” wide ½” hardware cloth
• twelve 1/2" carriage bolts, 4" long
• twelve flat washers and twelve nuts to fit bolts
• 2 lbs of 3 1/2”  screws
• 1/2 lb of 2 1/2”  screws
• 2 lbs of 3/4" poultry wire staples

Tips for using materials:

• Read through instructions for each section before ordering and cutting materials.
• Order extra lumber to compensate for cutting mistakes, knots, and warped boards.
• Less expensive alternatives to cedar, (such as fir or hemlock), can be used, but are not as durable or rot-resistant. Avoid treated lumber since chemicals may leach.
• Galvanized or coated hardware for outdoor use is recommended as it will last longer.
• Use a carpenter's square to check that the cut ends of boards and all places where they connect to other boards are square.

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Tools

• handsaw or circular power saw
• drill/driver with 1/2” and 1/8” bits
• hammer
• tin snips
• 3/4" socket or open ended wrench
• tape measure
• pencil
• carpenter's square
  safety glasses, ear protection, and dust mask
• Tools
• c clamps (for lid)

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Build Dividers

Use the following materials:

• four 12' cedar 2x4s
• hardware cloth
• 3 1/2”  screws
• poultry wire staples
  

Instructions:

• Cut eight 31 1/2" cedar 2x4s for the vertical uprights.
• Cut eight 36" cedar 2x4s for the horizontal connectors.
• Cut four 35" lengths of 36” wide hardware cloth. 
• At both ends of each 36” board, mark two spots for the screws. Each mark should be about 3/4" in from the end and sides. Pre-drill holes for the screws with a 1/8” drill bit and avoid drilling into knots.
• Butt two 31 1/2” boards between two 36” boards to form a square.
• Check corners with carpenter’s square.
• Use 3 1/2” screws in the pre-drilled holes to secure.
• Make a total of four dividers.
• Clip extra wire off ends of hardware cloth to make a smooth edge.
• Stretch the hardware cloth across each divider. Attach tightly by hammering poultry staples hammered in every 4" around the edge. (36" width of cloth is attached to 36" horizontal connectors).

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Set up and Connect Dividers

Use the following materials:

• three 12' cedar 2x4s
• 3 1/2" screws
• twelve 1/2" carriage bolts, 4" long
• 12 washers for bolts
• 12 nuts for bolts

Instructions: 

• From the 2x4s, cut three 108 1/2" lengths.
• On the narrow side of these boards, mark 1 3/4" in from each end.
• Make another mark 36 3/4” in from each end to indicate the position of the centers of the middle dividers. The space between these centers should equal 35".
• On the 4 dividers, mark a line down the center of the cut edges of the 36" boards.
• Stand the dividers parallel to one another and spaced 36" apart.
• Place one 108 1/2" marked board on top of the dividers, flush against the outer edges of the dividers.
• Line up center lines of middle dividers with marks on the board.
• Use a screw to temporarily hold the board to each divider.
• Place second marked board on top of the dividers and repeat process for attaching it.
• Using the 1/2" bit, drill a 1/2" hole through each junction 1" in from the inside edge of 108 1/2" boards and centered over the divider.
• Insert carriage bolts through the 108 1/2" boards and centered over the divider. Secure with washers and nuts but do not fully tighten yet.  
• Turn the unit over so the 108 1/2" boards are on the bottom. Attach the last 108 1/2" board. (This board will be at the top and back of the bin.)
• Use the carpenter's square or measure between opposite corners to make sure the bin is square.
• Check that the dividers are at a 90^o angle to the top board. Tighten the nuts on this board securely.
• Turn bin over and check to make sure bin is square and dividers are positioned properly. Tighten all nuts securely.

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Attach Hardware Cloth

Use the following materials:

• one 2x4
• two 9' lengths of 36" wide hardware cloth
• poultry wire staples
• 2 1/2" screws

Instructions:

• Cut two 9' lengths of hardware cloth.
• Along dividers, measure the gap between the two bottom 9’ boards. Cut 2x4's to fit.
• Use 2 1/2” screws to secure to dividers.
• Fasten a 9' length of hardware cloth to the bottom of the bin with poultry staples every 4".
• Attach a 9' length of hardware cloth to the back of the bin.

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Attach Front and Back Runners

Use the following materials:

• one 16' cedar 2x6
• four 8' cedar 2x2
• 2/12" screws
• 3 1/2" screws

Instructions:

• Cut four 36" cedar 2x6s.
• Cut six 34" cedar 2x2's.
• Center the 2x6 boards on the front of the dividers, flush with the top edge.
• Use three 2 1/2” screws to fasten each board securely. To stabilize the bin, one screw should go through each 2x6 into the bottom 9’ board.
• Set the 2x2s parallel to and 1" behind and front runners. (The 1” gap will hold the slats.)
• Use 3 1/2” screws to attach the 2x2s to the inside edges of the dividers.

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Make Slats

Use the following materials:

• Five 12' cedar 1x6s

Instructions:

• Each section of the three-bin requires six slats.
• For each section, measure distance between dividers. Cut a slat 1/2” shorter than that measurement.
• Test slat by sliding into gap between runners. It should slide smoothly and not pop out of runners.

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