DIY Compost Sifter, Dubbed “The Spider”

Update! (4/29/2018)

Wow, we are shocked to see that our Youtube video has received over 5,000 views!  We are so sorry that we did not post this accompanying blog post sooner…

They say that 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.

The Old, Boring 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 and it works just fine.  However, they were soon complaining about their arms hurting and the shaker was slowing down.  Adults faired better, but if you want wheel barrels (plural) of compost for a large garden, clearly, there is a better solution for volume.

Introducing the Spider DIY 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.

Here is the actual sifter.  The main components are the simple wooden frame with a plexiglass chute, a vibrating motor and a hardware cloth screen (actually a set of them).  Look closely and you can see that the 1×4 runners are hinged on one end and latched on the other.  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 relatch 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.

We used the GlobMarble Concrete Vibrating Motor 0.28 lW Power (110v, 220v) and the GlobMarble Variable Speed Controller for Electric Motor.  During sifting, while the motor is vibrating, the power chords hanging over the side rubbed against the frame and rubbed off some of the rubber insulation.  You will need to prop up the wires some how to keep them from hanging on and vibrating against the frame during sifting.  We tied the chord loosely to one of the legs.

The Spider gets its legs

Of course the compost sifter is not equipped with any anti-gravity devices, so we needed some legs.  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.

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.

You can see the springs that we use to hang the sifter from the legs.  We spent quite a bit of time researching spring sizes, lengths and stiffness in order to find the best springs to support the motor at the top and the wight of the compost sifter at the bottom.  Unfortunately, we missed the mark just a bit.  The springs at the top are just a tad too stiff and do not spring enough and the springs at the bottom are a bit too soft, and spring a bit too much.  Ideally, when the weight of the sifter is suspended from the springs, they should all extend just a bit (maybe a quarter of an inch or so).  Then, when the weight of the compost is added, they should extend a bit more so that  during vibration, the springs should never be totally decompressed (or bounce closed).  When ordering your springs, you need springs a bit softer than our top springs, and a bit stiffer than our lower springs.  Please note that we were close (maybe 10% to 15% off on each), so don’t vary too much from our specifications. Ours still work, but our next set of springs will be slightly different.

We used:

Top – Century Spring Corp. Extension Spring 5552

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

See why this DIY Compost Sifter is dubbed “The Spider”?

What else is there to say?  Doesn’t this compost sifter look fabulous?!?  We discovered that, on a windy day, the finest (best) compost that was falling through the screen was blowing away.  Not wanting to fabricate a wind block, we simply waited for the wind to die down.  The total cost was about $370, about $176 of which was the motor, switch and shipping.  The overall cost was more than we had hoped and we think we could have done better, but we suspect it will still be well worth it provided we get the longevity we expect.

All setup and ready to go!

This is our old compost yard (we have since moved it to an area with more room).  We get a lot of recycled wood chips from the county recycling center to use in our garden.  When we first get the chips, we screen them with the 1/2 inch hardware cloth screen.  Before we use the compost, we screen it again [or are supposed to] with the 1/4 inch screen.  Here, you can see the two piles of compost material we generated from the wood chips: the pile of finer material that has been sifted through (1/2 inch screen) and the pile of the course material that was too large and traveled down the chute and into the waiting bucket.  We will keep turning the pile with the course material and eventually screen it again.

And finally, let’s see The Spider in action!

Wow!  Doesn’t that just take your breath away?

And here is a second page that demonstrates the Spider in action with the fine screen. 

“Spider” DIY Compost Sifter, Fine Screen Demo