Thanks,
The 1 lb'r drum is 7" dia x 7" deep. It's the top half of a halon fire extinguisher which has close to a 3/32" wall thickness. I chose this so I could do a single-end shaft mount. The threaded fitting that screws into the top of the extinguisher had close to a 1/2" bore so it was easy to bore it out and setscrew mount the shaft to the fiiting. This really saved a lot of fab time. They are perfectly round to boot. Your local fire sprinkler company will usually have a couple dozen of these laying around that failed the hydro test and can't be used as an extinguisher. If you choose to use one you will want to thoroughly boil it out then bake it to make sure no chemicals remain in the pores.



From what I've seen of the Quest its a very robust solidly built machine with a very hefty front plate assembly. It would probably better survive a drop test over mine.

In most drum roasters the front of the drum is in very close proximity with the front plate to avoid bean fragments getting jammed in the gap (mine is around .015" gap). In a typical Probat shop roater as in the L-12 the lower portion of the charging funnel has an oval shaped duct attaching to it and runs back to the rear of the roaster underneath the exterior skin (same as the Quest but hidden). This duct is an exhaust path leading to the chaff collection area and exhaust fan.
The path of combustion gasses is from under the drum (burner), around the drum, back to the rear entering the perf metal back plate of the drum, through the drum and out via the charging funnel/oval duct. There's a few inches between the back of the drum and the next sheet metal partition otherwise there would be no air path.

The Quest is built differently in regards to air path but Jim or Rafael could much better answer that question as I don't have a good understanding of it yet.

Allen

On the Quest, the air path is similar. The difference is that the air enters at the rear of the drum chamber, rather than through the combustion chamber as on gas roasters. After that the airflow is roughly the same (through and around the drum from rear to front, then out of the exhaust). This system was originated by Probat but has been widely copied by all manufacturers of solid drums. The Probat L is different from all other roasters in that the drum rear can be sealed for short periods allow the beans to roast with no airflow.

However, my impression is that the magnitude of the effect of airflow is quite different on different solid drum roasters. On the Quest, If I hold drum temperatures constant for all air flow settings, (using more heat for higher airflows), a constant 500F drum temperature produces 11 to 13 minute first pops of the second roasts with 1/2 pound and maximum airflow, about 14 to 16 minutes one with minimum airflow.