Building a Soil Sifter / Rotary Trommel

Intro: Building a Soil Sifter / Rotary Trommel

Spoiler alert! If you can't wait for the final scene in this instructable, check out this video for the completed trommel.

This instructable is a companion to my previous Bike Spoke Forged Knife. In that instructable I used the bicycle spokes, here I've used the wheel rims.

Back story

Earlier in the year I processed a ton of apricots and discarded the stones in the compost heap. Months later when my wife wanted to use the compost, it was apparent that the stones were decades away from naturally decomposing. And I knew I needed a method to remove the stones (and other detritus).

I did some research and found a rotary trommel was the way for me to solve this problem. There are many examples of rotary sifters on the web but this instructable chronicles my build where I re-purposed most of the material. The only new components were castors, wire mesh and the vee pulley (which I barted for with some beer).

STEP 1: Building the Mesh Tube

I cut a length of sheet metal to attach to the inside of the wheel rim. This probably helps to support the mesh but you may be able to get away without using it. I cut it 4 inches (100 mm) wide* then carefully removed the burrs with a file. I used the existing spoke holes in the rim to temporarily attach the sheet metal using lacing wire.

I calculated the inside circumference of the wheel rims and cut the mesh with 6 inch (150 mm) overlap**. Stand the mesh on its end and drop two wheel rims over it. At the top fix the third rim in place with clamps*** then begin to fix the rim to the mesh using the existing spoke holes. You should aim to use every hole twice and I found it useful to drill out the hole a little to fit in my 5 mm cable ties. At this stage, decide where the 'head' of the cable tie will be...inside or out. I chose inside so it wouldn't interfere with the castors (but since discovered the castor rides above the cable tie). It would be better to have the head outside of the chamber...one less thing to block material.

Fix both ends with cable ties then begin work on the center rim. I used a length of timber to ensure this rim was evenly centered in the tube. It helped to have a second person assisting placing the cable ties from the outside while someone is reaching into the chamber...it's quite awkward. Pro tip: Begin your first cable tie at the edge of the mesh then continue around the mesh. I didn't do this (I began in the middle) and ended up with the mesh pulling in slightly. Happily it hasn't affected performance.

With all three rims cable tied into place, begin lacing the mesh overlap together. A second person here will also help.

Trim off the excess cable tie tales.

Changes I would make:

* If you install a sheet metal liner beneath the rim, keep it to the width of the wheel rim and no wider. Any wider (as I found out) blocks filtered material from passing through. See the exception to this below ***

** Limit the mesh overlap to maximum 2 inches (50 mm) as this double layer hinders filtered material from passing through.

*** While using the trommel I wish I had just a little more of the mesh protruding from the frame so that I could more easily place a wheelbarrow beneath it where it catches the junk. I would suggest installing this rim about 6-8 inches (150-200 mm) back from the end of the mesh, and this should be braced with a wide section of sheet metal that is attached to the rim and extends to the end of the mesh.

STEP 2: Building the Supporting Frame and Attaching Castors

Measure your mesh tube and cut steel to suit. Plan for the tube to be contained within the frame, although I would suggest the exit end (where the rocks and waste come out) protrudes 6-8 inches beyond the frame.

Weld up the frame and place the tube inside so that mount points can be established for the castors.*

I placed my castors in such a way that if I want to remove the tube, I can easily wind the threads into the frame, thus opening up the gap and allowing the castor to be eased from the bicycle rim.

The box steel I used was thin walled so I welded nuts in place for the castors to thread into. There is no need for an additional locking nut as once the castor is embedded in the wheel rim, it cannot turn. It is unlikely that the thread would wind itself up or down over time.

Pro tip: it's useful to hang the large drive vee belt around the tube prior to installing all of the castors. If you don't, you'll have to loosen your castors to install it later.

Changes I would make

* After I had completed the frame, I realized one end rim did not line up with the frame, hence in the photos you'll see I made small weld-on extensions that the castors were fitted to. It hasn't affected performance but took more effort to rectify. It would have been much simpler to mount all castors in the frame.

STEP 3: Mounting the Motor and Vee Pulley

This motor is 1/4 hp and cost me $15 bucks, with the previous owner gifting some used vee belts and a 2-sided pulley housing. The motor rpm was too high so I found a large vee pulley that geared the belt right down to a usable speed. Your motor and vee pulley combo's will infinitely vary so some trial and error will be required.

I placed the motor and housing on a bench to establish direction of motor and size of belt I needed.

I then (precariously) clamped the motor and vee pulley housing on timber blocks while I figured out placement and position to obtain belt tension from the motor to the housing, and from the housing to the tube.

My large drive belt (about 2 m in circumference) needed the pulley housing to be lifted (to take up excess slack) so I made up a steel frame. To create tension, I fitted a sturdy hinge to one end and bolted (rather than welded) this to the frame. To recess the nuts, I drill a large hole into the frame, hover the nut flush then carefully weld and grind it flat. Use a sacrificial threaded bolt to hold the nut in place so you don't mess up your good bolts with weld splatter. You may need to tap the thread if any weld sneaks onto the threads of the nut.

The motor was mounted independently so I could adjust the motor-housing belt tension, again by using a hinged mount. At the other end of both mounting frames, I fitted a long bolt that lifts or lowers the frame to adjust tension. Note a simple way to make a turning knob out of a bolt.

STEP 4: Mounting the Bicycle Wheels and Rear Support Legs

Considerations:

Plan on a height that will allow a wheelbarrow to sit underneath from either the side or the rear (exit).

You also want to plan a gradient for the soil etc to drift down. I can't tell you the exact angle I mounted my frame but it's probably 4 inches (100 mm) lower at the exit end. If you don't have a gradient, your sifted siftings will sit in the sifter!

You don't need to make this a mobile trommel (though I highly recommend it). It's not too heavy so two people could carry the trommel and place it on saw horses or similar at the job site. However, mounting it on wheels means one person can easily move it from place to place.

Yes, stub axles would have been tidier and prettier, but I took the simple option of welding the forks to the frame. This worked just fine. Place some timber under the frame to figure out your tipping/balance point and place the forks a little in front of this. Otherwise it could tip forward when being wheeled around or during use.

The rear legs I made to swivel in three positions: pointed down with feet on the ground; pointed horizontal where they act as handles (think wheelbarrow); straight up for storage (though in hindsight this position probably won't be used).

Mount a solid sheet of something (I used ACM) to the frame to stop soil etc being sprayed out the side of the trommel. I mounted this panel on one side only but it could be useful on both sides. Definitely needed on the drive side though! If you had access to those soft plastic hanging industrial door entrance strips, they'd make great curtains.

STEP 5: First Trial Was...successful!

With a bit of trepidation, I wheeled the trommel out to our compost heap. Those pesky apricot stones were about to be dislodged!

I really didn't know how the machine would perform. Was the mesh too small...the rotation speed wrong; the angle of the frame incorrect...lots of decisions I'd made were about to be tested.

Well it was a brilliant feeling to see the trommel operational and doing a most excellent job of sorting out the good from the bad. Looking at the video and photos, you can see how efficiently it removes rocks, bits of plastic and glass, apricot stones and even weeds. The bad stuff ends up in the wheelbarrow, while the rest piles up beneath the trommel.

STEP 6: Final Tidy Up

The machine was now worthy of a paint job so I applied a protective rust converter then a top coat to the frame.

Aint she a beaut!

About the legs/handles. I planned to wheel the trommel by adjusting the legs into a horizontal position then wheeling the trommel around. But it wasn't long until I realized a broom handle and wooden dowel slotted nicely into the frame and became great handles. No longer any need to adjust the leg position. Use what you have lying around.

STEP 7: The Trommel Enters Production and Creates a Family Event

This freshly rotary hoed section of lawn needed sifting so bring out the trommel (to be honest I wouldn't have even considered doing this job without the sifter).

You can see how much junk and large rocks lay beneath the surface of our grass. We ended up with about 8 wheelbarrow loads of rocks, stones and glass fragments from that one strip of lawn.

This is an amazing machine and I'm very pleased to have it available. It should give long service and working parts are easily replaced.

Thanks for watching.

Comments

[JohnR476]

I followed your instructions and built my frame from wood. I really struggled to find an appropriate motor and vee belts so I just had to make a manual version. It's good but not as good as yours. Well done!

[bpark1000]

Safety first! This machine has numerous pinch points between the drum and the casters, and between the belts and the pulleys. These points need to be guarded!

I was especially paranoid when in the video I saw kids with their hands inches from the caster pinch-points!

[Minnear Knives]

Oh yes I can see how that looks! The little peoples’ hands were over a foot away as they were separated by the barrow. But you’re correct, guards should cover the castors and something over the flywheel pulley would be best too.

[jandyk]

or train kids young to think-nothing is ever safe enough for the fearful. great project-I just scored 3 rims today

[GrahamK5]

Excellent build! I have an allotment with all sorts in the soil, and a load of bike wheel rims (received free!). This is something I plan to build and use in spring.

It occurs to me that the type of open-frame litter bin I've seen (designed to hold a plastic liner), which has a cylinder of large-size (about 2-inch squared?) wire mesh, could be repurposed instead of using bike rims, if lined with a finer-grade mesh.

Also I suppose if successive wraps of different mesh were attached along the length of the sifter, and a row of bins placed beneath, you could obtain soil sorted finest-to-coarser, suiting different uses, all in one pass.

[Minnear Knives]

Good luck with your spring build. I like the sound of a graded soil in one pass, I'll be interested to see how your build goes. All the best.

[tedtol]

Another thought on this theme is to build one or two of these barrel screens, using the same bicycle rims and finer mesh (depending on needs) and swapping out the barrels, assuming that the frame could be made to exchange the screens. In this way you could keep the size of the machine manageable so that it could be easily transported, and for storage when not in use. I have seen commercially purposed trommels that were more or less permanent installations because of their large size with screens that were graded to produce finer and finer soil.

[Soose]

I've been looking at trommels and the easiest idea I've seen to allow different screening sizes is to use a harder wire fencing on the outer drum, then just have sections of inner screens of different sizes that ride on the inside of that outer drum. Search "Gary and Robbie' on youtube, and look for his compost trommel. He shows his build with the inner swappable screens.

[KonaGirl1961]

I am so impressed with your creativity. This will prompt me to learn to weld. I wonder if there is a way around the need to weld? I’m good with my drills, even thru metal... any ideas?

[srilyk]

If you're in the US, head to your nearest pawn shop and look for a 110V wire-feed or stick welder. Offer them $50 or 50% of the marked price for it. I wouldn't pay more than $50 for one. Or make them throw in a welding helmet or something. Then just head to your nearest hardware store and buy some cheap flux core wire or electrodes, and go watch some weld.com YouTube videos, and spend a couple of hours welding on some scrap metal.

Alternatively, you could drill and bold everywhere that was welded on this cart, but you'll probably spend that much in fasteners anyway!

[VinceW11]

I agree! Welding is all about trial and error. I did exactly what is described above, and I'm now an avid welder. The only different advice I would give is to forgo the flux-core wire and utilize a shielding gas with standard welding wire. The welds are much cleaner, stronger, and there's much less spatter. Happy welding!

[bpark1000]

Instead of welding, bolt and braze. Brazing can be done with good propane torch, and the metal is not subject to the high heat shock so it doesn't crack later.

[Tsu Dho Nimh]

I built one with no motor and only wood and the sifting part. The barrel rests on the wheels, the wheels are mounted to 4x4s (old fence posts), and the 4x4s bolt to some sawhorses. It comes apart for storage, and the sawhorses are usable elsewhere.

http://lazygardens.blogspot.com/2015/05/diy-trommel-sifter-for-compost.html

[Minnear Knives]

Hi, go for it! I don't see why you couldn't build it with a timber frame. You'll need some brackets to mount the motor and pulley wheel. But a course in welding would get you started and 2nd hand welders are cheap. Thanks for your comments.

[Iamm1ckser]

Can not get a suitable cheap motor could I use an old 2/3 speed drill instead ?

[amachinetech]

Easiest place to find a perfect motor for the job is a old swamp cooler. You can also use the giant pully inside to gear down the motor RPM

[tedtol]

An old washing machine motor seems like an option, too.

[Minnear Knives]

I’m not sure. There is a bit of load when a shovel full of material is thrown in. Your motor will need enough torque to keep turning. Hopefully you’ll find something...maybe an old washing machine motor?

[tedtol]

Thanks for sharing this informative build. I have looked at several home made sifters on Youtube and the barrel design I think would be the most efficient for my needs. I'm not yet skilled enough to weld a metal frame together, as shown in this build. Can you imagine one made out of dimension lumber and if so do you have any thoughts or suggestions in building one? Thank you millions.

[jeanniel1]

Perfect! I didn't realize how much GRAVEL and rocks are under my soil in my front and back yards! No gold nuggets yet.