Just posted a discussion in Coffee & Roasting titled "Roaster Mods". Am doing an overhaul on a Samiac 10k am tossing around which mods I am going to make, one of which is variable speed drum & drum exhaust. Would love to hear from anyone who has experience and has made some of these/other mods.
My name is Adam and as a former Diedrich Technician I am curious as to why you would like to vary the speed of the drum, I fully understand wanting to vary airspeed through the drum but in my experience varying the drum speed can cause issues such as bean scorching, most roasters have the ability to vary airspeed through the drum and all of the big Diedrich C.R's have the ability to vary air speed as well as drum speed via variable frequency drives on the three phase motors. The only reason we varied the drum speed was for initial set up and for speeding the drum up during the drop into the cooler at the end of the roast for a faster discharge time in order to stop the exo thermal and get the beans cooling. The bigger the machine the longer it takes to get those beans out. If the drum turns too fastthen the centrifigal force holds the beans to the drum and they scorch, if it moves too slow you dont get proper cycle throughout the drum and again scorching can occur. I suppose that due to the beans becoming lighter throughout the roast it could possibly be beneficial to vary the drum speed although it seems to me that it might be more hassle than it works. We did at one point experiment with this in our automation so that the drum speed varied automatically in accordance with the bean temp. If you attempted this manually with a lot of trial and error you would find the benefits, if there are any, simply aren't gonna be simply would not prove to be that beneficial. Keep in mind that I am no roastmaster but simply a roaster electrical/gas tech but I have built many roasters in my time and as a result have picked up a few things along the way.
If I am way off base then please don't hesitate to call me out, I am all about learning new things and am always willing to help out if ya need any mechanical help. Good luck.