Ayres Rocks

A run of wet weekends has spoiled our dirt parties over the past few weeks. On the 2 occasions we could have done some work we have been suffering through colds and sniffles our boy keeps bringing home from kinder gym or playgroup. Such is life.

Still we did get up there this weekend and spent a full day organising all the bits and pieces so the next fine break we get we can spend building the actual house. Our neighbour has electrically fenced off our woodlot and the house area and has his cattle happily grazing in the paddock in pic1. We went for a bit of a wander as well to have a look at how our tree plantings have progressed since around this time last year. Some of these trees have grown more than a metre since we planted them and you can see Elise standing amongst them and indicating actual height in pic 2 & pic 3.

The trommel was assembled as in the first pic below and tested for workability and it performed flawlessly. The width of the cage is just smaller than our builders barrow so all that needs to be done is throw dirt in, empty barrow and occasionally empty the barrow of rocks on the other end. I reckon we’re seeing far less rock come out the other end compared to the shaker sift where half the lumps were just compacted dirt and not rock at all. You’ll notice I welded up a quick support stand to keep some of the pressure off of the axle end of the barrel. Second pic is all the formwork on the slab ready to go.

All bolted together the working end of my newest toy looks like thumb 1. By this time I had decided a secondary panel inside the drum to keep things working away was not necessary, and instead I split a length of 100x100x2mm steel to make two large pieces of angle. I used these to both joint the drum ends and the screen together as well as provide agitation in the drum as the material tumbles around. Thumb 2 shows where all the rock eventually tumbles out of the drum. Last pic shows how I attach most materials that are welded end on. Tacked into position first and then a piece of angle iron on at least 2 sides is fully welded to provide extra rigidity.

Since belts stretch and need constant tensioning I added in a simple system to achieve this as seen in the next thumb. To tension the belt all that needs to be done is the 100mm bolt is screwed further into the assembly, pushing the entire engine up. The opposite end is bolted through 2 pieces of angle to act as the pivot point. Last thumb shows how the angle of the drum can be adjusted should it need to be set up on sloping ground, a few cranks on the turnbuckle can raise or lower it quickly and easily.

The earth sift I made works as it was intended. BUT…. it is time consuming and it does take a toll on the body having to bang the sieve screen to get dirt to fall through it. At this time of the year the clays in the soil are also activated and you end up with a “sloppy” rock wobbling around on top of the screen.

Trommels are an industrial machine that are basically a perforated rotating drum on a slight angle. The material to be sifted is dumped in the higher end, the drum rotates with anything smaller than the screen passing through it as it tumbles with the larger particles passing through the lower end and into a spoil pile (or as in mining into a crusher).

So here is the simple outline of how I made a trommel to make my job of sifting soil for the walls easier.

First job was to secure a cement mixer, a quick tour through eBay and their localised subsidiary Gumtree found a suitable cement mixer for sale for $180. I used this as a base since a trommel needs a slow and controlled spin and a cement mixer already has the gearing in place to achieve this. Important note is that mixer had a bowl that was bolted to the gearing. The first thumb below is the mixer I bought. Second thumbs shows bolts cracked and the bowl removed to expose the gearing.

I picked up an ex food 44 gallon drum for $15 and an elcheapo 5.5HP honda knock off engine for $177 from Paramount Browns. The drum I sat in a square frame on casters and used the momentum of the grinder to cut a 100mm lip into the lid and then separate the drum into hoops, roughly a third of the drum per section as in the third thumb.

Also in the third thumb is the most difficult part by far – getting the 25mm galvanised wire sheet ($42 from Senturion Steel) to roll. That took several ratchet straps and a lot of swearing to roll it back on itself. I’ll leave that strapped up until the frame of the drum is complete and then I will unleash it and trim the excess.

Last thumb in this group shows the new axle for the trommel, it’s a very large 1&1/8 x 10 inch high tensile bolt which also happened to be very expensive at $38.

First thumb in this group shows how the gearing works in the mixer. Second thumb shows the axle and gearing in place. The bolt was welded to a 5mm plate with a hole drilled into each corner of it. The most thinking of the job involved working out how to centre the axle in the base of the drum.

I did this by subtracting the diameter of the gear ring from the diameter of the drum, halved the result then used a ruler to mark that measurement in as many places as possible around the rim of the drum. From there I positioned the gearing ring and marked the bolt holes. Once the holes were drilled I scratched a line between opposing sides and that gave me the centre of the drum. Since there are six holes and the bolt head is hexagonal, simply lining up the “corners” of the bolt head with the scratched lines centred the axle assembly perfectly. Holes were drilled, bolts welded to the plate and internally the bolts were secured using a small piece of angle to spread some of the load as shown in thumb 3.

All up this gadget will come in under $500 and since the mixer bowl will be able to be restored I’ll be able to sell it once the project is finished as either a mixer, a trommel or both.