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Well, Having played with a popper for a while,
I decided I wanted something bigger than the 80/100 grammes
capacity of the good little popper.
Maybe I didn't want anything this big, but when me and my neighbour Jeff
get started on something it just, well,
grows!
Original plan was for something that would
roast between 1/2 and 1lb, and the pics below record our steps to date
in making a prototype. The design
is a (almost) horizontal can which rotates slowly (adjustable) via a belt
drive from a 24v motor.
Don't ask why 24v, it's what was lying around.
There is a PID-connected thermostat running through the hollow shaft which
will always be in contact with the bean
mass. Heat source is a hot air paint stripper (which has a fan and
can generate 500-600 degrees F in the can. We haven't tested the
actual bean temperature yet. There is another fan for cooling.
(The reason for this is that most of the hot air guns I've taken apart
unfortunately link the fan to the end of the heater element, using it as
a resistor so the inbuilt fan can be 24v). The unit has controls
for roast time, heat on, rotation, cooling, rotation direction (for expelling
the beans at the end of the cycle, all controlled from a cam arrangement.
The roasting chamber is angled 5 degrees from horizontal to keep the beans
in during roast, but they will be expelled at the end of the roast by means
of reverse rotation and the internal blades which act as a kind of Archimedes'
screw.
Well I did say it was a baked bean can!
2nd picture shows mount through which the spindle attaches.
Archimedes screw type arrangement (fins to
move beans around) and aid in expelling beans at end of roast)
made from 10mm copper pipe bent round my
old bakelite coffee table as it was the correct radius!
These are to be soldered in the tin.
The driveshaft for the roasting chamber
(drive belt pulley to fit between the bearing mounts)...
...driveshaft is hollow to allow the temperature
sensor to be routed into the roast chamber
vaguely what it should look like (only slightly
raised at the front end)
Cam-based controller (from a tumble drier,
I think) that has 11 functions we use...
(Jeff sat here for several hours setting
up each cam to the correct angle)
cigarette packet drawing by Jeff (OK - bigger
than a cigarette packet!)
The cats think we're mad (or is it that they
haven't been fed yet?)
Left to right - Scampi, Bodgitt, and Toast
That's it for tonight...
DAY 2 - trial run
Well, we completed the drum today, using
the layout of the picture on the left below.
This had some disadvantages - the capacity
of the drum was limited, even when we raised the open
end by 5/10 degrees, so that we could only
roast 200 grammes (454 grammes is our target) before
beans spilt out the end. We decided
to test it anyway, so Jeff rotated the can by hand (holding the driveshaft)
whilst I pointed a hot air gun in the other
end with one hand, and measured the temperature with a probe in the other
hand.
We got a fairly uniform 250/260C in the
air, and in the rotating bean mass.
However, it took 24 minutes to complete
the roast to the degree shown below.
The can on the left is MKI - and we found
that with this design, the capacity of the can was
limited to 200 grammes, due to beans spilling
out. MKII on the right holds 250 grammes of ROASTED
beans, and with a further modification to
add slots at the end so that the beans can only exit when the drum is in
reverse rotation
we think we can hold the target weight of
500 grammes. This is a true screw, (try bending 15mm copper pipe
like that 1st time! - we couldn't either!)
Not a bad first attempt, but the beans look
a little (lot?) baked more than roasted, even though
we achieved 260C in the chamber in little
time. The trouble was that 1st crack took
18 minutes, 24 minutes total time to beginning
of 2nd, so we also ended the roast a little early.
Day 3 - Microwave day
Yesterday I found a local microwave
repair shop, whose owner was more than happy to provide
old microwave bits for non-microwave
use. Went there today, and he had found a quartz halogen element
(1000w). He also found
a boxfull of old rotating turntable motors. For the princely sum
of £15 I came home
with the element complete
with it's mount and reflector and a couple of motors. I'm now confused
as the heat gun worked OK, but the quartz elements are just crying out
"Use me"!
view of quartz element
switched on and running...(provides 400F
at approx 4 inches below the elements)
and one of the motors. These are 240v
and rotate at 6/7rpm