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Fresh Roast base made from aluminum.
I had the glass set deeper in the base increasing the area for the silicone
to adhere to for a much better bond.
So far dissimilar expansion between the base and the glass roast chamber has not
been a problem,
I have heated and cooled the roast chamber many times and have run it very hot
for much longer than normal.
Aluminum expands and contracts more and faster than glass so with close
tolerances potentially
the glass could be broken as a result. Because the aluminum base is on the
outside of the glass
the expanding part should not be a problem, what I was worried about is having
the aluminum base cool faster
than the glass roasting chamber putting excessive pressure on it breaking the
glass.
As it turns out the base stays hot much longer than the glass so this condition
should not be a problem unless
the base is rapidly cooled while the glass is still very hot, like being put in
cold water or being set
on an extremely cold surface.
The next base I have made will have a slightly larger inside diameter where the
glass sits for a little more cushion.
I have had the lower inside ledge of the base where the screen sits cut a 1/4
of an inch higher than the stock base.
This has helped reduce scorching considerably moving the coffee beans away from
the heat, this changes the bean level in the roasting chamber so you need to
adjust it accordingly.
The first run of aluminum bases had the lower inside ledge of the base where
the screen sits the same as the original base.
The picture below is one of the first aluminum bases that were made.
Two chambers end to end with aluminum base.
I successfully roasted 160 grams of coffee in one batch with the double
chamber and the VariAC.
I had to stir the beans until they started to change color, but once they
started moving on their own
I put the chaff collector on and they continued to agitate. As the roast
progressed I turned down the voltage
a little at a time so the beans continued to move but not blow up into the lid.
160 grams is the max and I think is too much coffee to do on a regular
basis, I had to try :-), roaster failure
would be eminent after very many 160 gram batches in a row, it pushes the
roaster to the limit.
120 grams works much better, it still needs stirring at first but only a little,
the results are quite good and the roaster seems to handle it without
straining at all.
130 grams out in one batch !!
The roast came out quite even.
120 gram batch start. The unevenness in bean color is from decaf beans
in the mix.
120 gram batch finishing.
120 grams of coffee going into first crack. 1.3 meg MPG
http://www.coffeewisdom.com/freshroast/firstcrack120g1.MPG
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High temperatures and sharp implements can be hazardous,
modifying your roaster voids your warranty, USE THIS INFORMATION AT YOUR
OWN RISK.
Now that's out of the way.
A few pointers on repairing your roast chamber using the aluminum base.
The aluminum base and double length glass chambers are available at http://www.coffeewholesalers.com/fr-arcb/freshroast-rcb.htm
I have had a few people ask about assembling the roast chambers with the aluminum base so I came up with this procedure. Some of you may have few tips of your own, additions and corrections are welcome.
You need 100% Silicone. Any color will work as long as its 100%
Silicone.
The first thing you need to do before assembling anything is wash the roast
chamber parts thoroughly including the aluminum base.
Be careful the rough end of the glass is sharp on the edges, this is also the
most likely place the glass will break if hit or handled rough.
Apply a small bead of silicone to the surface of the base where the screen sets, use enough to make the silicone squeeze out when you put the screen in place but don't over do it, it should only squeeze out a little.
Let this set long enough "several hours" to bond together before you handle it to do the glass.
You can put the base in the oven at 150 to 175 degrees to fast cure the silicone, not to hot or you will weaken the bond normally 30 or 40 minutes is enough then you need to let it set for an hour to cool and cure.
You can also use the roaster to heat the parts "if your wife won't let you stink up her oven and the kitchen" just make sure not to get the wet silicone extremely hot, you can run the roaster till the parts are hot then put it in cool mode, do this several times then let everything set for a while before you go to the next step.
If you just cant wait, you can use the roaster heating / cooling method repeatedly to fast cure the silicone, do this until the bond is strong enough to handle the pieces without falling apart. You can do this after each application of silicone.
Be careful when doing this the aluminum base and glass get EXTREMELY HOT
the roaster can generate 600+ degree temperatures.
You should clean any excess silicone from the inside of the base with an X-Acto knife or razor blade.
I have found that the cheap $1 snap blade knifes that are available at
hardware stores work very well for trimming silicone out of the inside of the
roast chamber.
Once that is done apply a bead of silicone to the surface of the base that the glass will touch when it is set in place, again not too much because you will have to clean the excess silicone from the inside of the roast chamber when you are done.
Now very carefully set the glass in the dead center of the base, once you have it lined up try not to move it too much, you can do the heating now or let it
set until it has bonded, if you feel especially confident you can hold the base and the glass together while it is wet and fill the gap between the base and the glass with silicone, again not too much silicone, just enough to fill the gap around the
glass with a slight bevel up on to the glass.
Now this needs to cure before you put the handle on, or if you left the handle on be careful not to pick it up by the handle before the silicone is cured. It may be easier to leave the handle on the roast chamber, you need a special wrench to tighten the metal band once the handle is on the glass.
Now you need to slide the handle up on the glass enough to get the silicone applicator tip into the gap or right against it, between the handle and the glass, don't try to slide the handle too far up,
1
to 2 inches should be far enough. Fill the space between the handle and the glass about 1/4
to 1/2 inch of the way up into the lower part of the handle
"if you can get that much in there" so that there is enough silicone to bond the two pieces, slide the handle down into place make sure there is a bead of silicone where the handle and the aluminum base touch.
At this point you will most likely have silicone on everything and everywhere, a role of paper towels is a must.
Wipe off excess silicone with paper towels and make sure the handle is set in place and square,
let this set at room temperature at least 24 hours before you roast or your coffee will have a distinct vinegar character.
Excess silicone can be trimmed with an X-acto knife and pealed off after it has partially cured, but try to keep from getting silicone on too much of the roast chamber especially the inside where it is much more difficult to remove.
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