I'm not too interested in gardening, but I like composting. I'm not going to discuss how to compost - you can find that on the web. I have a couple of big bins (about 1000l each), but wanted a tumbler, so I made one:
The starting
point was a 150 litre grey plastic barrel with a screw lid. This was
second-hand, having previously held unspecified food product, from
ibcextreme
on ebay (who also has an ebay shop. I don't
know about the rest of the products, but the barrel was delivered very
quickly, was exactly as specified and in excellent condition. I chose the
seller simply because they had the barrel I wanted, but I'd have no hesitation
buying from them again.
The points I wanted from the barrel were:
Unfortunately, I forgot to photograph the barrel as a whole before I
started carving it up, so this photo is stolen from the ebay listing (I'm
guessing he won't mind).
The plan was for an axle through the middle (with the barrel upright). A tube vertically up the middle (supported by the axle) vented out the bottom with air-holes in the tube to let air in, and some small holes under the lip of the lid to let air out. As (if) the contents heat hopefully convection will drive air circulation. The top holes, being under the lip, will avoid most rain getting in.
I chose this plan because it meant minimal holes in the outside of the
barrel, so neat appearance, less prone to scattering its contents (because the
material inside will mostly fall away from the middle as tumbled, not out the
holes). I also thought it would make the whole thing easier to rodent-roof
(squirrels and presumably less savoury furry things chew on my compost bins)
Step one is the tube up the middle. I had
some remnants of plastic downpipe and fittings, and some bits of aluminium
mesh. This is a socket used for joining two pipes, which was good because it
had a lip at one end. Cut a square of mesh and bend it to a tight fit by hand.
The mesh is jammed into place, then
liberally glooped with hot-melt glue.
Hole-saw through the bottom of the barrel. This was
harder than expected - the hole-saw bit at first, but then seemed to polish
the bottom of the groove and progress ground to a halt.
It turned out the bottom was about 10mm thick, and I
eventually got through by laying the barrel on its side and crawling in to cut
from the other side.
Once through, the socket was dropped into
place, and liberally glooped (from both sides) with more hot-melt glue.
Socket in place at the bottom of the barrel...
into which a length of down-pipe simply
slots. This is plastic 68mm (I think) down-pipe. As you can see from the
accumulated dust, it's a piece I had lying around from something I did some
years ago.
Drill holes for 8mm threaded rod (bought
from hardware shop) and 3/4" OD (1.5mm wall thickness) steel tube to be the
axle. The tube was another ebay purchase - from
10gbottles ebay shop. Again, accurately
described, quickly delivered, and I'd buy from the same seller again.
The axle and rod pass through the central
tube to support it (with the addition of some nuts and washers, not in this
photo). The threaded rods are intended to break up the compost as
the barrel is rotated. Also, the downpipe has been trimmed to length here.
Air circulation holes drilled in the
central pipe.
Threaded rod cut to length ...
and capped with penny washers and dome
nuts. There are also some T-nuts I had which went on the top threaded rod
either side of the central pipe in order to restrain it. I had to
buy the nuts, the rest was bits-and pieces lying around.
A couple of steps were not photographed:
I made a cap for the central pipe
out of a socket, some scrap plastic sheet and silver duct tape.
I drilled the top air holes in the barrel, three each side above the axle
tight under the lip of the lid and pop-riveted (plus hot-melt glue) aluminium
mesh on the inside to screen them.
That's it for the tumbler itself, which was three evenings work after my daughters were in bed, and required the purchase of the barrel, the axle, the threaded rods, and the dome nuts. Obviously, if I had to purchase all the other bits, it would have been rather more expensive - probably as much as just buying a cheap commercially-produced unit.
To tumble it needs a support frame.
I made one out of 90x25mm decking boards and some bits and pieces. It's
screwed with deck screws and glued with weatherproof adhesive, then painted
with some dark wood preservative. The wood I used was already
pressure-treated, but I wanted it darker (to make it less conspicuous in the
garden). The frame was a Saturday morning's work, with assistance from my
four-year-old elder daughter.
The bearings are 50mm lengths of 22mm
copper pipe a tight push-fit into holes drilled in the timber frame legs. The
axle protruding from the barrel is a reasonable fit through the copper pipe.
More 8mm threaded rod passes right through
the axle ...
and is capped with penny washers and
wing-nuts, which hold the axle in the frame.
Fully complete, the unit is installed in
place at the end of my garden, behind a row of trees and some trellis fencing, which
is why I wanted it all dark - it disappears into the shadows viewed from most
of the garden.
There's a spacer bit of timber between barrel and support frame legs
on each side so the
barrel is held away from the legs, to prevent the assembly acting like a
guillotine on (especially little people's) fingers.
So, now I need to see if it works, and the first thing is to see how well it mixes, so:
Add some compostables - in this case
kitchen vegetable scraps and a big handful of shredded paper. Shredded paper
is what I use when a heap gets too wet, but here I'm using it as a bright
indicator.
There's a step not described in the construction sequence visible in this
photo - the barrel doesn't just hang on the axle, the axle is a tight push fit
through a hole in a length of the same timber used for the support frame,
and then there are a
number of short but fat screws through the barrel wall from the outside into
this timber on the inside.
Cover with a couple of shovels-full of
half-made compost from another bin. Note that vegetable scraps and paper are
now concealed.
Put the lid on, two complete revolutions, and open up...
Excellent! Even the quick two turns of
the tumbler seems to mix it all up, and now there's a fairly uniform mixture of
scraps, paper and compost. I'm very pleased with this.
When it's more full, I expect it will mix less quickly and easily, but
we'll just have to wait and see how it performs in practice.
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