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  • Any ideas for improvement before build?

    I have been playing around with one of those convection turbo cookers, and it seems to be one of the best available heat sources for making a coffee roaster.

    After a bit of research and looking at a few other peoples ideas (mainly Farmroasts and Sullos roasters based on these things) I came up with this, as something similar I could make from stuff I had lying around at home.

    The only part I have not got set up is the bean mixing motor (proposed: a 240v exhaust fan motor) but I really want something lower power and 12v (as I have a dual 12v fan controller I can use for this project) I want to be able to get the bean mixers up to 300RPM or so to get them to whirlpool around with the hot air, creating something between a BM/HG and a fluid bed air roaster.

    Here is 15 minutes wasted in paint.

    Does anyone here have any improvements/suggestions before I get the 240v motor tomorrow and finish this?

    Cheers for your input.





  • #2
    Re: Any ideas for improvement before build?

    Here is how I hope the air will flow.

    Also showing you the "bowl" is one of those 30cm safeway ones that are around $10

    Sorry for the sh*tty quality paint drawing again, my mouse has something interfering with it and I cant work it out!

    John :P

    Comment


    • #3
      Re: Any ideas for improvement before build?

      Hey John - nice looking project ...

      Is the lid, or bowl, transparent? Just wondering how you watch the beans as theyre roasting, to monitor darkness.

      Also being a fully enclosed chamber, will this hamper youre ability to hear the cracks?

      My 2c worth ...
      Tony

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      • #4
        Re: Any ideas for improvement before build?

        Thanks for your suggestions.

        The lid around the convection heater is tempered glass, and has a good view of the entire bowl from any angle.

        The oven itself is quite quiet, and has only a thin layer of metal above the fan and element, allowing you to hear inside quite well. In fact you can hear when water boils in it.
        Also the small chaff/hot air exhaust system is another place sound can exit the chamber, not to mention the parabolic shape of the bowl to amplify and direct the sound.

        Im just hoping the sound of the beans flying around hitting the thinnish SS bowl will be so loud it would muffle the cracks.

        I am also hoping if varying the speed of the 12v fan (green) has a significant impact on the temperature, that I can use this as the main way to control it hooked up to my laptop to monitor and control and log the temperature inside the roaster and get away with not buying a nice big expensive variac for the element, and avoid high current switching in the controller altogether.

        John.

        Comment


        • #5
          Re: Any ideas for improvement before build?

          Just out of interest, I am hoping it would have a roast size of about 150g up to 600-700g, as the mixer speed can be adjusted based on the size of the roast as to get them whirlpooling in the right position over the TC probe (slow it down if the beans fling too far up the edges, speed up if they pool at the bottom around the mixer)
          Any reasons this would not work?

          Comment


          • #6
            Re: Any ideas for improvement before build?

            Hi John

            I agree, an interesting project.

            Ill be particularly interested to see how the flying bean aspect works out.

            Ive been thinking of the turbo oven idea also, but with a slower agitation approach. There a heaps of old sunbeam mixmasters unit on evil bay, all with variable speed rotary units, many detachable. Another (slower) alternative.

            Gary

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            • #7
              Re: Any ideas for improvement before build?

              You have to be careful your agitator doesnt pulverise the beans. They really dont need to be "flying" around to take advantage of the convective currents. Keeping them constantly turning over is the idea. You also have to be careful about the distance from the element to the beans. Too close and you stand to scorch the beans, too far and youll be struggling to complete the roast in a decent amount of time.

              Ive found 12v supplied to a wiper motor works fine for me. Id much rather have a variable power supply, but I only had an old PC power supply on hand.

              Try looking for a fairly shallow (~20cm) deep pot that matches the diameter of the turbo oven.

              Comment


              • #8
                Re: Any ideas for improvement before build?

                Hi John,

                Im not sure how the 12v fan would affect the roast temperature in your diagram, if at all? Is the mixing bowl supposed to be floating in the middle, or is it sealed with the TO lid?

                I have a BM/TO setup with a steel bin lid adapter in between the round TO and square BM. Its only 1300W but running it at full blast start to finish produces slightly uneven roasts. Ramping up the temp/starting with a drying cycle always seems to roast more evenly.

                Make sure the TO sits flush with the bowl (or whatever chamber youre using). My roasts are shorter by 1-2mins now that the TO lid sits flat, centered and flush rather than off-center. It used to be off-center cos it would get shaken off by the vibrations of the BM agitator.

                Preheat it all til it starts giving consistent readings at the start and/or end of the deadband. Then try to load your beans at the same point in the heating cycle every time. The start of the heating cycle works best for me.

                Re: temp probe, with my k-type I get the smoothest readings either slightly above or slightly below the surface of the bean mass. At the surface makes it fluctuate too much cos it keeps going from mid-air to mid-bean.

                Immediately after roasts, put the TO on its stand and leave it turned on but with the temp turned all the way down. This seems to cool it down nicely.

                Keep some glass cleaner handy, as the TO glass gets oily and harder to see through, then harder to clean if you leave it for too long between cleans.

                Also, beware of flying, flaming chaff! While Im doing the warnings, make sure you dont electrocute yourself. :P

                Good luck, keep us posted!

                Paul

                Comment


                • #9
                  Re: Any ideas for improvement before build?

                  Have been doing a bit of work on this today.

                  What are the best drills for hardened or SS? I have killed my 6mm viper bit after only 8 or so holes through the bottom of the pot.

                  As for the deadband, I might still bypass the thermostat and manual control the element. Its about 20 degrees, I dont know if it will be too high, but very well could be.

                  The S/S bowl that would contain the beans is about 2/3 the depth of the roasting pot, and sits perfectly flush with the cooker lid.

                  Theoretically, the 12v fan would be able to influence the roast speed, as it is pushing extra cold air into the roasting chamber, forcing more hot air out through the chaff vent. I settled for a nice big 120mm full depth 12v fan connected directly to the bottom of the SS pot.
                  The SS bowl has many small holes around the shaft of the motor, allowing this air in.
                  I am hoping this will lower the deadband (mechanical thermostat will cool faster than it would if it were completely sealed) or even allow me to run it at 250 and have enough fresh air flow that the TS never gets this hot and switches off the element. (This might not work as there is still the radiant heat from the element as the TS is located ABOVE it.

                  It can also be used as a (slowish) cooling function once the roast is complete just by removing the lid. (at least I hope)

                  My risk of electrocution has also gone down a little bit, as I have a smallish 12v motor I can control with the same circuit as the fan controller.

                  I hope this works out, will greatly simplify my roasts (as oppose to a HG, metal bowl and wooden spoon).

                  Comment


                  • #10
                    Re: Any ideas for improvement before build?

                    Originally posted by itsme5k link=1194316186/0#8 date=1194408234

                    What are the best drills for hardened or SS? I have killed my 6mm viper bit after only 8 or so holes through the bottom of the pot.

                    The only drills (or lathe tools ) which will adequately cut stainless steel are carbide tipped (and I dont mean the masonry variety).....

                    You will also need a cutting lubricant to cut effectively..... and a slowish cutting speed.

                    Its tough stuff to work (just been turning some tamper bases myself this morning)

                    Comment


                    • #11
                      Re: Any ideas for improvement before build?

                      Out of interest John,

                      Have you tried roasting with the TO/Bowl combo as is yet, without any extraneous hardware? Would be good to have some empirical data established before you get too far advanced with a lot of additional mods applied...

                      Mal.

                      Comment


                      • #12
                        Re: Any ideas for improvement before build?

                        Originally posted by JavaB link=1194316186/0#9 date=1194408654
                        The only drills (or lathe tools ) which will adequately cut stainless steel are carbide tipped (and I dont mean the masonry variety).....

                        You will also need a cutting lubricant to cut effectively..... and a slowish cutting speed.

                        Its tough stuff to work (just been turning some tamper bases myself this morning)
                        Decent "Titanium Coated" bits would be ok too and probably easier to get than T/C jobs.... Good brands would be "Sutton", "P&N", "DeWalt", etc or if you prefer to go the T/C route, heres a link to a supplier Ive used before who stock a good range of cutting tools of all types. Theyre a bit exy though....

                        Mal.

                        Comment


                        • #13
                          Re: Any ideas for improvement before build?

                          Thanks for the tool advice, ill get some more appropriate bits for my work tonight hopefully.
                          The Sutton "viper" bits I had been using were for softer metals obviously and lost their tip very quickly.
                          I have one of those "As seen on TV" titanium drill sets (which I purchased from a cheap shop for $10 for a set of 24 bits + all other shit) but for some reason I wouldnt even think of using them :P (the reason is probably because they were blunt when I bought them )

                          Maybe I should buy myself one of these: http://www.dealsdirect.com.au/p/diy-inverter-plasma-cutter/ I bet it could cut off your hand and you wouldnt even feel it happening.

                          I have tried the turbo oven and bowl with no additional airflow or bean agitators, and it cooked the beans in about 10 mins on one side and still quite light on the bottom. I expected this as the beans are not moving at all, and the surfaces in contact with the bowl cooked less quickly. Beans towards the centre cooked evenly on both sides but alot slower than the ones on the edges. Some chaff came off the beans and whirlpooled around with the hot air. None the less easily powerful enough to get the temp up quickly.

                          I just need to finish the bean mixer now, and a way to slow the application of heat after FC.

                          John

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                          • #14
                            Re: Any ideas for improvement before build?

                            I wouldnt risk spending that much money on that site.
                            Ive been bitten by them before.

                            Comment


                            • #15
                              Re: Any ideas for improvement before build?

                              Originally posted by Thundergod link=1194316186/0#13 date=1194434274
                              I wouldnt risk spending that much money on that site.
                              Ive been bitten by them before.
                              Really? I must be lucky then. I bought a rabbit hutch from them recently and it was delivered within 4 days of order - as described.

                              Ive found it useful to use a cutting oil with any metal drill bit.

                              Comment

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