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DIY Motorized Compost Sifter Construction & Demonstration

As our garden grew, we discovered we needed a more efficient way to sift the massive amounts of compost we were using and so we designed and built this DIY motorized compost sifter.

Motorized Compost Sifter Picture
This is the third and final version of the DIY motorized compost sifter.

Table of Contents

Necessity is the Mother of All Invention

Gardeners understand the need for a constant supply of compost and most will tell you that they never have enough. We decided that we were going to get serious about composting and generate enough material that we could actually have as much as we desire.  Of course, we need to compost much more material, and this usually means larger tools (unless you really want to do all that manual labor).  While a tractor may have to wait, at least we now have an efficient compost sifter.

Like many, we searched and searched Youtube looking for ideas and there were many good ones.  Many of the sifters we saw were manual, and they were great, but they were still slow.  We saw several that were motorized using anything from drills to jigsaws to tractors.  Some of the sifters using tractor power looked like they worked well, but we don’t have a tractor, and the size of our garden is not quite big enough to warrant such a large compost sifter and the cost of the tractor. 

It would seem that we needed something between the tractor-powered models and the small, arm (child)-driven style.  Not being happy with the options using the various power tools (and there were some clever ideas), we settled on the electronic vibrating motor to do our work for us.  The draw back to this is, of course, that it must be connected to electricity.  We decided that, of the options we had, this was the best suited for our situation.

The Manual Compost Sifter

This old compost sifter worked just fine.  It has a 1/4 inch hardware cloth screen.  The children can shake it back and forth easy enough.  However, children get tired of shaking and they would begin to slow down.  Adults faired better, but if you want wheel barrels (plural) of compost for a large garden, clearly, there must be a better solution for volume.

The Improved DIY Motorized Compost Sifter

Construction Notes

The main components are the simple wooden sifter frame with a plexiglass chute, a vibrating motor, a hardware cloth screen and a frame to hold the spring-suspended sifter.

We used the GlobMarble Concrete Vibrating Motor 0.28 lW Power (110v, 220v) and the GlobMarble Variable Speed Controller for Electric Motor.

After some time using the a-frame legs for the original sifter (see below), we decided they were too unconventional and difficult to work with and so we built a more conventional frame.  This new and improved version works much better.

The new sifter design is very similar.  Notice that the sifter frame is missing the 2×4’s (not necessary without interchangeable screens, we simply weren’t using the 1/2″ screen) and the side runners are no longer hinged (eliminating all those hooks).  The new frame is smaller, lighter, more simple, more solid and less prone to vibrating into pieces.

Choosing the rights springs was a little tricky and we spent quite a bit of time researching them.  You want them to be extended just a bit with the empty weight and you don’t want them completely decompressed (or bouncing closed) during sifting.  The springs we chose were adequate.  We used:

Top – Century Spring Corp. Extension Spring 5552

Bottom – Granger 4″ Carbon Steel Utility Extension Spring with Zinc Plated Finish

Dimensions!

Note that these dimensions are designed to fit a large wheelbarrow nicely and to leave room for adjusting the angle of the sifter body.

Sifter Body Frame

  • Two long side pieces are 2″ x 2″ x 48″
  • Top plate holding the motor is 1″ x 8″ x 23″
  • Bottom plate holding the chute is 1″ x 4″ x 23″
  • The chute is made out of 1″ scrap & plexi glass
  • There is a 1″ scrap spacer between the bottom plate & the chute
  • The side rails are 1″ x 4″ x 38″
  • The top rail is 1″ x 4″ x 21.5″
  • The hardware cloth is 36″ by 48″

Sifter Stand - The Legs

  • The tall legs are 2″ x 4″ x 50″
  • The short legs are 2″ x 4″ x 44″
  • The rear brace (motor) is 1″ x 8″ x 37″
  • The bottom of the rear brace is 38″ high
  • The front brace (chute) is 1″ x 8″ x 37″
  • The bottom of the front brace is 18″ high
  • The side braces are 1″ x 8″ x 51.5″
  • The side braces are in the middle of the long legs

Pictures

Note that in the first few pictures of the new sifter frame, the 2 x 4’s are simply temporarily holding the 2 x 2’s in place and are removed once all the pieces of the frame are in place.

Initially, we used the original sifter body frame with the new conventional legs.  When the screen wore out, we re-designed and constructed an improved version of the sifter body frame.  The old sifter body has a 2 x 4 frame with the 2 x 2 screen holders clamped to the outside.  With the new sifter body, the 2 x 2’s are the frame.

Some pictures are of the old sifter body frame with the new legs and the others are the improved sifter body frame with the new legs.

Design & Demonstration Video

The sifter body frame is more simple and lighter.  The legs are much more practical and simple.  We are very happy with this design and it is performing well. Wow!  Doesn’t this just take your breath away? wp-monalisa icon

The Spider DIY Motorized Compost Sifter

Construction Notes & Pictures

Look closely and you can see that the 1×4 runners are hinged on one end and latched on the other (the original design had interchangeable screens).  Simply unlatch the runners and lift, unlatch and remove the 1/2 inch course screen and put on the 1/4 inch fine screen.  Then, lower and re-latch the runners.  The original hinges we used for the runners were way to small.  It wasn’t long before they broke from the vibration.  We simply replaced them with larger hinges and the problem was solved.  There are hooks at each of the four corners which are used to suspend the sifter from the legs.

The A-Frame Base ("Spider Legs")

UPDATE:  The original design using the a-frame spider legs seemed like a good idea at the time.  We wanted to be able to setup over compost bins.  In practice, it didn’t really work very well and so the a-frame legs were abandoned.  Nevertheless, our original comments follow.

We wanted to devise the simplest set of legs as possible and settled on a pair of a-frames.  After using this sifter for a while, we have wondered whether some sort of aluminum pipe construction with connecting joints might work better (we found many such systems online that would need to be adapted for this application, and are much more expensive), and be more easily adjusted, but the 2×2 legs serve their purpose well enough.

Tricky to Adjust Legs

In order for these legs to be stable, they must be spread apart until the bolts connecting the legs to the cross members are put in a bind.  Once they are bound, they become fairly stiff.  If the legs are not bound enough, they will wobble and collapse.  It doesn’t take long to get the hang of it. 

Initially, we used 6 inch bolts.  However, as the bolts bent and sagged under the vibrating weight (as we knew they would) and formed themselves nicely to the cross member (no longer straight, but more u-shaped), we found there was much more slack in our system and we needed to tighten the bolts.  Unfortunately, there were not enough threads on the 6-inch bolts (only about 5/8 of an inch or so on the end of the bolts), so we replaced them with 5-1/2 inch bolts (again, about 5/8 of an inch of thread on the end).  The legs are stiff now, but we know that over time, as the new bolts break in, they will be just right, and we still have room for adjustment.

The height of the compost sifter is determined by the placement of the legs.  To lower the sifter, simply spread the legs out a bit more.  We designed the sifter in this fashion so that it would be tall enough to fit over our tall DIY Compost Bin Made From Recycled Pallets, yet low enough to fit over a simple wheel barrel.

First Demonstration Video

Here is a short video of the spider in action in our old compost yard.  We are using the 1/2″ screen to sift mulch from the county recycling center.  The spoils are going into the next bin for further composting.  We use the 1/4″ screen for final sifting.  The new sifter design does not have a 1/2″ screen.

Second Demonstration Video

After we realized how popular the original video was, we made a second, longer video that demonstrates the 1/4″ fine screen.