Hello,

I am a coffee lover from Spain and also a lover of DIY and antique machines. That's why I decided to start a project to make a coffee roaster. I have read many of the topics in this forum to get some ideas and find response to some of my doubts. Now I will explain what do I have and which are the main lines of my project. Of course all of you are invited to participate and to tell me when I am wrong.

I got an iron pipe with diameter 200 mm, the wall has a thickness of 4 mm. So i will make the inner drum with this. My idea is to make it of 400 mm long. Would be necessary a thicker wall drum?

To move it I will use a car window motor. I think that will move it fine, I used this kind of electric motors for other issues and work great. I will adjust it for 40-50 rpm.

About the outside walls, my idea is to use thicker iron sheets. Maybe 5 or 6 mm. And insulate everything with ceramic wool. Do you think thas is better to put the wool in the inner of the walls near the drum or can I put it outside over the iron walls?

My doubts with the drum: I would like to make a completely solid drum, without holes. Down of it I will install a propane burner and flames will touch directly to the drum. Do you think that this will give hot enough for the roast? Or do I have to make the air go through the drum too??

I am not planning to install a fan to make the hot air from the drum go out. Is that a good idea or not?

This are my main ideas. Of course, I have to start with it and I will update with pictures of everything. Once I will have clear the main construction questions I will start with it and later I will speak about technical adjustments and issues.

Thank you for your responses.

Hi Luis, your plan sounds very good already. There's a terrific site homeroasters.org that has priceless information on building drum roasters, and it addresses all of the issues you brought up. There are several extremely knowledgeable people who still post there.

Your drum is on the thick side, 2mm is probably recommended, but yours (4mm) will still work. Forced airflow is also recommended through a solid drum, I'm not sure if it's strictly necessary but you need some airflow forced or not. Drum roasters are designed around the air flow path, it's key.

People worry about warping because of heat, but I believe it's not an issue if the plate is not constrained and is allowed to expand. Think of your roaster as a breathing creature that expands and contracts and you can use thinner plates. You can test with a heat gun. (Hah I should try that!)

The key parts of drum roasters are: airflow design for efficient heat transfer; coffee stirring (vanes) design, for mixing and bean separation; getting the beans out of the drum quickly; precise fitting of drum edges to front and back plates, especially accounting for drum lengthening when warm. Drive, bearings, chaff also need working out but are by comparison quite easy. Control of the gas is another bugaboo and homeroasters.org has a great deal of information on that too.

Be sure to search that site for answers to almost all your questions, and go through the projects there, they're a great source of ideas.

Always like to hear about DIY roasters. Your ideas sound good. MJW makes some great points in his post. I designed a small solid drum Stainless Steel roaster in 2013, and enjoy using it over my 1 kilo commercial electric roaster as it is quick. A couple of things that make it fast is it's size of 1.25 qts and the fact that there is no pre-heating with the DIY roaster. I can roast 250 grams in 12 to 15 minutes depending on how much heat (10,000 BTU maximum) is applied to the roaster. The heat source is a propane camp stove. As far as air flow, I can only use passive air flow as I spin the roaster by hand throughout the roast. Profiling is accomplished by varying the temperature of the stove, and I usually keep RPM's to 50. The flame is kept one inch from the roaster body, but can be removed at any time for additional agitation. I use a simple thermometer normally used on the edge of a frying pot. It can take the extreme heat of the 1550 F propane flame.

I am wondering if the thickness of your iron drum might be an issue as iron retains heat well, so when you reduce your heat source it will take time for your beans to cool. My DIY roaster has a wall thickness of .060", so it responds to heat quickly.

My commercial roaster runs at 40 RPM, so you are on target there. The drum on it is perforated stainless steel with a thickness of .100". Sorry about not using the metric system.

hey man, in case your DIY project is ready, let me know. i probably will give it a try. i dont live in spain though so might need to talk about shipping cost. maybe you can try to sell it on ebay and then PM me

I am in the process of building a drum roaster myself, and concur with the comment above regarding the Homeroasters site. You can glean everything there is to know about principles, best-practice design etc. Plenty of active examples and people willing to help.

Specific drum thread is http://www.homeroasters.org/php/forum/v ... rum_id=137