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01/29/2023 4:55 AM
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New 1kg drum roaster build
Hello all! I haven't been very active on this forum lately, but I've built a few versions of an air roaster that has roasted hundreds of pounds of coffee for us. I took a bit of a break from roasting coffee, but I'm getting back into it, and I've decided to finally build a drum roaster. I've wanted to build one since I started roasting coffee, but I haven't had the means to do so until now. I'm a welder by trade and I build custom bicycle frames: https://mythcycle... So now that I have my own shop, I feel really ready to take on this project and do it justice.

So anyway, the plan is to build a 1kg (most of the time 2lbs) drum roaster that can be our weekly workhorse, but I'd really like if it can roast just 1lb as well. The air roaster can only do about 14oz of green beans, and it works great as our weekly roaster. But I really love giving coffee to friends and family as gifts, so I'm looking forward to the ability to do bigger batches, and hopefully with a little more consistency.

I was originally going to use electric heat, but I've decided to go with propane because I don't want it to require a high amperage 240v outlet to roast. I have visions of being able to take it places for special events, but who knows. I'm excited to try out propane however.

Anyway, on to the build! I started with the drum. A friend of mine had a piece of 8in stainless tubing that had about an 1/8" wall thickness, so I figured that would be perfect. He let me have 8in of it, so the drum is 8 x 8 which seems like it should be just right for 2lbs.

The band saw only cuts 7in round, so I had to rotate it and cut twice.

I made 6 arms out of some flat stock, and made them all the same length. By sheer luck I had an old lathe chuck laying around that had grooves that fit the flat stock perfectly, so I had a jig to hold the three arms in place while I welded them!

I did my best to calculate a helical vane at 30 degrees of twist on the computer. Then I printed it out to scale, cut it out of the paper, and traced it onto the stainless sheet I had and cut it out with the bandsaw. I later found a thread where folks were mentioning that 20 degrees would have been more than enough. Too late, I made them and they were welded in.
Twisting the vane.

I taped the perforated stainless to the back as a temporary setup to test bean movement. Then I chucked it up in the lathe and put it to 53rpm which is as slow as it goes.

I'm really happy with how the bean movement looks! I looked in the back through the perforated, and I was happy to see that quite a few beans were piling up there as well, so I think I'm getting good back and forth movement, and at 53rpm, I'm getting a lot of beans being tossed through the air. This is one of my goals with this roaster, as I'd like to be able to turn up the venting air and pull lots of hot air through the beans to get a brighter, air-roaster-like roast if I want to.

I also tested the drum with a 1lb charge, and the movement was great for that as well. My only concern was that so many beans were airborne that I'm not sure how well the BT probe is going to contact them. Maybe at a slower rpm like 45 or so could work well.

I'm not sure how to embed a video, but you can watch it here:

So at this point I'm calling the drum done! I welded the perforated stainless to the back and finished all the other welds. I'm really happy with how it turned out.

The next step is the plates. I don't have a good way of cutting the 3/16 stainless plate I want to use for the front, mid, and back plates, so I'm going to get them laser cut. But this means I have to know what drive motor I want to use, what bearings, and how I want to lay out the front plate, including the bean dump/air vent setup. So I'm going to work on getting those things figured out so I can design the plates around them. Once that's done, I can send off the order to the laser cutter.

Here's a question I have for for the drum roasters out there: How often do you change the speed of the drum? I like the idea of having that as an option, but I sort of see it as one of the things I would just set to a good speed and never change it after that. I know that many people use the "makermotor" gear motors for their drum drive. I'm hesitant to use them since I really like sourcing USA made motors and parts if I can. I've found a nice Bodine gear motor that has a fixed rpm (I've found both 49 and 56 rpm) that is 115v AC which makes my wiring pretty simple.

Thanks! I'm excited to share this build with you all, as I've learned so much reading over the years.
Nice bike frames and roaster!

Boy, you have the setup to fabricate drum roasters.
Always wanted to try a drum roaster but welding was always the stopping point for me.

I wish I could answer some of your drum roaster questions. There are many members here who have built so you should have some answers soon. I think most stay at one speed that tumbles things properly for the size of the drum.

KKTO Roaster.
Hi Tom. Nice fab work and envious of your shop capabilities!

My drum is 7" dia. and around 7" deep and at 1 lb I've found the sweet spot for getting the beans adequately airborne so that they arc high enough to land at around the 4:30 clock position, I needed around 75 rpm. Less than that lessens the ability with my roaster to allow enough air contact. This is with 4 vanes. With 3, you may need a bit more rpm than that. The slowest rpm I've seen commercial drum roasters run at is 65 rpm. Some may go slower than that but would need additional vane height to make up the difference.

On being able to vary drum rpm, I personally don't see any benefit and to me, would add one more thing to worry about fiddling with. But, there may be some who have done A-B tests using different rpms and seeing differences in cup quality.
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
Thanks guys!

Allenb, I'm actually surprised at that drum speed. The lathe also does 73 rpm, but I didn't even think to try that out. I'll go ahead and load the drum again and try that speed with both a 1 and 2 lb charge. Thanks for the info.

I agree with what you're saying about variable drum speed. I think it's a neat idea, but I think I would either fiddle with it too much or just be worried it was contributing to variances in my roasts and leave it at one speed anyway. We will see, I'm leaning towards a fixed speed motor.

I have been roasting on mine for awhile now. Drum is 8.5" dia and 12" long. I usually roast a 3lb batch and for that I run between 75 and 80 RPM. depending on which bean I am roasting. I have found that different bean size needs a different speed. Bean load makes a difference (on mine anyway) and smaller beans take up less space volume wise.

Your work is really very well thought out and fabbed great! Nice work!
Edited by BobbyS on 09/29/2019 4:12 PM
it looks pretty awesome mate! what grade of stainless steel you used for the drum?


plyshag wrote:

it looks pretty awesome mate! what grade of stainless steel you used for the drum?

No idea, since it came out of a friend's personal scrap pile. Pretty good chance it's 304. It wasn't that hard to cut so I'd be surprised if it was 316.
Nice work BBQ grill. Drum looks great
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