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Behmor Mod #2 – Bean Temp Probe

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  • Behmor Mod #2 – Bean Temp Probe

    After much brain scratching here’s my simple approach that didn’t require a lathe or the drilling precision of a dentist.

    Cut off spindle, drill hole, insert hollow threaded fitting and secure with backing nuts. Enlarge slot holding the spindle and .....
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  • #2
    …. and then drill through both inner and outer panels for probe access. Fit a cable gland and an offset bolt to prevent the probe from spinning in the drum. Cut small section off the drum vanes to ensure the probe doesn’t foul them. Bend probe, insert and job done!

    (Instead of the fitting, next time I’ll just use a hollow threaded rod used to make lamp stands, cheaper, easy to find and more clearance for the probe. And looking at it now, it doesn't seem cutting the vanes was actually needed but better to be safe that sorry I guess.)

    In the temp charts, bean temp is the dark green line.

    ps. To those who have a stake in Behmor, what do you think if they pre-drill the spindle and panel holes? They could then sell bean temp probes as optional extras.

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    • #3
      Well done
      That profile looks spot on!

      Cheers Matt


      • #4
        Originally posted by DesigningByCoffee View Post
        Well done
        That profile looks spot on!

        Cheers Matt
        Thanks, I'm new at this so I need any feedback, good, bad or otherwise.


        • #5
          That looks tip top. I'm wondering how it will help you with your roasting, as in how will you use it to improve your roasts? I have installed a heatsnob in the way suggested on my behmor (up the back/top) but am pretty new to roasting so at this stage just collecting data and seeing what affects what. Since I'm not getting bean temp I'm really just hoping that the relative data (comparing roasts) will help, as I can only see what's going on in an indirect way. I'm hoping this is good enough. I'm unfamiliar with graph you've posted and the legend is too small to read, what are the other colours?

          What is the minimum roast size with your setup that the probe sits inside the bean mass? Is 200g enough?


          • #6
            Hi Agrajag

            The colours are:
            Red - measures the heating elements. The thermocouple is positioned directly between the two elements. I’m using it as a lead indicator. It tells me exactly what the unit is doing heat wise before it is felt elsewhere.
            Dark Green – Bean Temp (BT)
            Light green – Rate of Rise (ROR) for BT (on the right axis). I’m using this to help predict where the BT is heading. I want a slowly decreasing BT that doesn’t flatline or kick up. Artisan has a really useful projection function that extends the BT curve out to the future based on your current ROR. I rely on that a lot. It’s much easier than doing mental ROR calculations.
            Pink – internal air temp. This is Andy’s Heatsnob, positioned where he recommends so it should be the same as what you’re getting. I’m only using the temp probe bit and not the little HID box as Artisan doesn’t recognise HID devices (GRRRRR ) To be honest I’m only tracking this cause I already had the probe installed.
            Blue line – this is the power setting. This is especially useful for replicating previous profiles. I ramped up at 100% and dropped to 50% at 150C BT which allowed a gentle cruise to FC at 9min with a final development ratio of 17%. Previously I’ve tried coming in hotter to FC but FC happened at 195C which I wasn’t happy with. For my next batch I wanted to do a longer slow roast so I dropped to 50% sooner at 100C BT. This gave me FC at 12min but with a similar development ratio of 18%. Without knowing BT, all you can go by is time, eg dropping to 50% 3 mins in. This however doesn’t factor in changes in ambient temp or humidity.
            Brown line - This tracks drum speed. Currently only using slow which is set at the beginning and left alone.

            I think your roasting style will determine if BT is necessary. There is no right or wrong way. I know a professional roaster who has no temp measurements at all. He roasts purely by experience, constantly pulling bean samples to judge what is going on. I also know roasters who have a myriad of metrics. I prefer data based decision making hence my preference to quantitatively measure. It also allows me to be incredibly more consistent. As a newbie myself, it is also easier as I don’t have the experience to simply look at a bean and tell what’s going on.

            Hope that helps

            Edit: yes I'm using 200gm. Not sure if 100gm would have enough bean mass to shield it from its surroundings. hmmm. I might have to do an experiment to find out....


            • #7
              Wow that is really cool. Thanks for the detailed explanation. It is interesting to compare the internal air temp (pink) to your bean temp, seeing how bean temp keeps rising after air temp falls. How are you measuring the power % (blue line)?


              • #8
                Yeah, the beans go exothermic so start giving off their own heat which is difficult to pick in the air temp curve.

                The power is just buttons I made in Artisan. When I change the power on the Behmor I press the corresponding button in the software. Not perfect but close enough.

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                • #9
                  Nice work. Care to share the details on the threaded tube that you fixed to the drum? Dimensions and where you got it from would be handy.

                  And that bean temp profile looks tasty


                  • #10
                    I found the fitting in my father's tool tray. Been there for 20+yrs. Length was 45mm x 10mm but I ended cutting it down to 25mm. I drilled out the internal hole to 6mm. We're not sure of it's original purpose but it's stainless steel with compression olives at either end if that helps.

                    10mm diameter is important as that is the distance b/w the two rods traversing the drum door. If you go larger you will have to either cut chunks from the fitting so it fits or cut those traversing rods.

                    As mentioned, if I was to do it again, I'd just get a hollow threaded rod and nuts like these ones. Hollow Threaded Rods. Buy Threaded Rods Online - Mica Lighting

                    You'll also need at least 2 backing (hex) nuts to secure the new spindle. I actually don't think the flange I have on the very left hand side of the spindle is necessary. The drum can't slide to the right anyway due to the drive side spindle.

                    btw I have a 200mm MIMs thermocouple but any insulated one should work (Note, a non insulated/grounded thermocouple will not work unless you find some way of electrically isolating it from the roasting unit. This caused me quite a bit of grief before we figured this out. And 200mm is just long enough to fit a cable gland though I've seen are other ways to secure the probe.
                    Last edited by MrFreddofrog; 9 December 2015, 05:30 PM.


                    • #11
                      Where is the fluffy dice


                      • #12
                        Hey MrFreddofrog, I'm pretty keen to install a BT probe as you have here, just wondering how happy you are with it now that you've had it installed for a while? Also can you point me to the right kind of thermocouple to buy, I don't know anything about the different types and want to make sure I get one that's the right type/insulated/length/etc. Also the cable gland, is this the right kind of thing? EPA 20mm Nylon Cable Gland | Bunnings Warehouse



                        • #13
                          Hi Agrajag. Sorry for the delay in replying, was out bush giving the aeropress a good workout.

                          The probe works perfectly, no issues with it at all.

                          I got my thermocouple custom built from who are a Perth engineering company. Really nice guys. I called a lot of suppliers and there was nothing premade that was suitable. And the ones that were supposedly premade were made to order anyway. We did a few versions before we came up with one that worked well. If you speak to them and tell them what you are doing they will know exactly what you want which is a Type K TC 3mm x 200mm MIMS TC c/w 2 Mtr Teflon lead and plug. (ie probe is 3mm diameter, and 200mm long, "K" type MIMS). I'm assuming you are using a Behmor. It cost around $80-100, not exactly sure but given they have already done the R&D it may very well be cheaper by now. Btw that is relatively cheap given some of the other quotes I received.

                          How do you plan to connect the thermocouple to your computer? Andy's Heatsnob HID box or a multimeter?

                          I got my cable gland from Altronics as it is rated to 100C. And you need something that will hold 3mm. That bunnings one is way too big and has no temp rating.

                          Good luck!


                          • #14
                            Thanks for the detailed response, very helpful. I'm using a behmor with a heatsnob at the moment but am pretty keen to get BT going as well as I'd like to know a bit more about what's going on with the beans. I could either keep using the heatsnob with the new probe (if compatible) or get a phidget or similar.

                            I'll have to have a think about going down this route vs. upgrading the roaster (Huky/Aillio/something else. Huky looks pretty great for $ at this stage, doesn't seem to get mentioned much here) that will give me more control.


                            • #15
                              Holy smokes, still learning Artisan and from this thread learned that you could make power buttons. I was writing down values and then entering them manually after the roast. THANK YOU SO MUCH.