Hey Monito - couldn't attach pics to the PM, so I'm posting them here.
Again, I'm not a fan of CRC drums. RK makes much more rugged and better agitating drums (or at least made, I am not familiar with their newer models).
Here's a couple of snapshots of my current homefab 12# (for realz, finished weight, not what a drum mfr. tells you). 22.5" long, 10.5" diameter. The size was dictated by the size of the BBQ, which is a 45k BTU with an IR back burner (which makes a LOT of difference in the roast quality, especially the high notes). 38RPM direct drive 1/3 HP motor with enough torque to turn a grown pig on a rotisserie, don't wanna worry about wearing it out... The 3/8" axis tube is welded to a 1" expansion with slots for the key-type drive. These welds are accomplished with a couple of washers for spacing, which insulates the drive expansion so well that it can be handled bare handed at the end of the roast. The opposite side uses a drilled 1.5" wood dowel for an insulator.
Welded (heliarc) together out of 304 stainless steel, 3/16" perforated 16 gauge (might be 14). Everything was home fabricated by my ironworker buddy and I, you can see the hinge is actually little 3/4" pieces of 3/8"ID stainless tube welded over a stainless rod so the hatch and the drum end ARE the hinge. If you look at the interior, you can see the 'V' shaped fins (3 o'clock and 9 o'clock) are facing the same way - this allows the beans to alternately cycle from the center of the drum to the outer edges with each rotation - these fins are about 2" shorter than the drum length on each side. The 12 o'clock and 6 o'clock fins are slightly angled and go all the way from end-to-end, which also works to agitate the beans from one side to the other [regardless of which way your motor turns].
The advantages to this design are obvious when you watch the beans agitate. I load 12-14# depending on density, and with removable insulation panels I can hit first crack in as little as 8 minutes if I want (of course I don't). If you try something like that with a drum with less thought put into the fins/vanes/whatever-the-heck-you-wanna-call-em you will certainly see the uneven roasting as you approach the loading limit of the drum.
Here's the experiment to show the degree of mixing: pour in 5# of old roasted beans and tip the drum so they all go to the far end. Then carefully pour in 5# of crappy old greens into the loading end. Put this on your grill and watch how many rotations it takes to mix them into a nice even distribution... I can guarantee you that some of those CRC drums that are too long and have all straight vanes will have an uneven distribution after 30 seconds of spinning, where my design has them fully blended within 15 seconds. If your BBQ has a perfect heat distribution I guess it wouldn't matter, but that never seems to be the case in the real world...
