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  • Modifying a grinder with a scale?

    Hey everyone,

    Been having some thoughts re: modifying a grinder to give the right dose consistently using a scale "built-in" to the machine. I was wondering if anyone had attempted this or thought of it.
    I have a Compak K3 touch that I was thinking of doing one of the following:

    1. Put the whole grinder on a scale, prior to grinding, turning the scale on (self-zeroes), then as beans get ground into the portafilter, the weight of the beans actually ground goes into negative values. You can stop grinding once you've reached your desired weight. The portafilter obviously has to be held "in the air" so that it doesn't contribute to the weight of the entire contraption. From what I can tell, the limiting factor would be precision of scales. It seems that to get precise measurements on the orders of fractions of grams, the scale weight range needs to be small. This wouldn't work with a grinder that is heavy. I have yet to find a scale that can accommodate the weight of a grinder and give that much precision.

    2. Build a scale into the portafilter holder (the 2 bars used to support the portafilter). This gets around the above problem by having to support the weight of the portafilter only and of the ground beans. The scale could be adapted to "sit" on the portafilter holder and the portafilter would sit on the scale (perhaps with some sort of cushion or moulding to support the weight?). Once the pf is on, the scale would be turned on, zero-ing the scale with the pf and grinding would begin. The difficulty with this is adapting the scale to sit on the portafilter holder, and ensuring it will give an accurate measurement given that the scale's native feet would not be on a solid surface. Then there is making sure the portafilter stays in place, and that ground coffee makes its way into the basket without having to fiddle...

    If either of those 2 would be feasible, the next stage would be to wire the scale and the grinder to some sort of controller where you set the desired weight of ground coffee and go! Obviously this bit would be much more complex, but was thinking of starting with solution number 2 above.
    Has anyone had any experience or attempts doing such a mod?

  • #2
    Kudos for ambition. Setting any opposing opinions aside for the sake of creativity... you'd be better off developing a portafilter holder of your own to place on the detached scale isolated from the grinder and directly under the grind delivery so that vibrations of the motor wouldn't cause you trouble. That would also make it possible for easily retrofitting into a grinder upgrade down the track if you were keen without needing to do a full rebuild.

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    • #3
      You might want to have a look into the work Decent Espresso are working on with their Decent Doser app. It could save you a whole heap of trouble - it's pretty much along the lines of method 2. Method 1 sounds pretty tenuous, vibrations from a running grinder will play merry hell with a precision load cell. This is why it's so hard to build ACCURATE scales into an espresso machine drip tray.

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      • #4
        Hmm yeah didn't consider vibration...
        Coffee_machinist, the decent doser looks great, but it costs more than my grinder, being $499 USD... just for the mod
        I was thinking more like 30$ budget

        Having said that, the decent doser gave me an idea, maybe a similar contraption, like a "table" (or a stand of some sort) that slides over the base of the grinder without being in contact with it, and has a scale attached to it (very much like the Decent doser). You could even build it to be height adjustable and thus customisable for different grinders..
        Will look into it in the coming weeks and post back if I come up with a decent cheap solution

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        • #5
          You could just do your dosing via timing , that will get you very close once you get it worked out , l'm going to give it a crack on my dosered grinders using a digital timer relay switch I've ordered off eBay

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          • #6
            Kesa the problem I've found two problems with time based dosing:
            1) There is some variation in time depending on the bean freshness
            2) This may only be my issue, but sometimes the beans don't slide out of the hopper at the same rate and need a gentle tap (happens more near the end of a full hopper). The grinder is going, but less beans are running through, resulting in less weight.

            I will attempt a very low tech solution in the next week as a prototype. Here is my idea:
            Parts needed: mini table (dyi or buy from ?), cheap scale, glue, bendable shelving brackets, shelving nuts + bolts
            Steps would be:
            1) Create a U-shaped contraption with the shelving bracket, similar to the Decent doser shape, but lower tech (and uglier). Secure shape with nuts + bolts
            2) Glue said contraption to kitchen scale
            3) Secure kitchen scale to miniature table (method TBD, perhaps clips of some sort, as the scale would need to be removable for battery changes)
            4) Slide table over feet of grinder, rest portafilter on contraption, turn scale on
            5) manually activate grinder until desired weight
            6) rejoice, then think of ways to make it better.

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            • #7
              l love doing my own little improvisations on things too , and l completely agree , weighing is more accurate , especially for home use .
              I roast my own most of the time so a small bit of wastage is acceptable to me ( like retention ) , ld rather none , but it isn't going to happen
              The timer will mainly be helpful to my wife as a push button solution rather than counting in her head as we try to single dose with the dosered machines , unless we are having coffee together of course

              It'll be interesting to see how you go with your project mate

              Cheers

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              • #8
                So a little update on this project.
                Started with an ultra low budget solution, cost me $4.50, using my current scale. It's just an inverted Tupperware acting as a table, with a silicon ice cube tray to hold the pf on the scale. See 1st pic. Using the grinder did not affect the weight of the measured grounds, but the Tupperware did not offer enough structural support for the setup. The ice cube tray was fine enough but the pf didn't sit that nicely in it.

                Evolution on this was to construct a pf holder using a small 10x10cm piece of 12mm MDF with some brackets from bunnings (I think they were just over a buck each) held in by wood screws. I chose 10x10 since that was the size of the scale weighing surface and it also miminised extra weight. See other pics. Still using the upside down Tupperware which I stabilised using the lid.

                Next step is to build a more stable base. I will use MDF with 3 inch 3/8 bolts with rubber legs. I'll use bolts and washers underneath the MDF so that it's height adjustable. Should work nicely

                I'm currently manually actuating the grinder and stopping at my desired weight. I've ordered an arduino, a load sensor, an lcd display, an HX711 (module for the load sensor) and a relay to connect to the grinder. I will be recording the weight using the bits and display the weight on the LCD. After that, will use the relay to connect the weighing circuit to the grinder (hopefully that will be easy). I've never used an arduino before so yeah hope it works! Will keep u posted
                Attached Files

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                • #9
                  Just using a good old Mk1 eyeball here!

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                  • #10
                    Originally posted by danyboy View Post
                    So a little update on this project.
                    Started with an ultra low budget solution, cost me $4.50, using my current scale. It's just an inverted Tupperware acting as a table, with a silicon ice cube tray to hold the pf on the scale. See 1st pic. Using the grinder did not affect the weight of the measured grounds, but the Tupperware did not offer enough structural support for the setup. The ice cube tray was fine enough but the pf didn't sit that nicely in it.

                    I'm currently manually actuating the grinder and stopping at my desired weight. I've ordered an arduino, a load sensor, an lcd display, an HX711 (module for the load sensor) and a relay to connect to the grinder. I will be recording the weight using the bits and display the weight on the LCD. After that, will use the relay to connect the weighing circuit to the grinder (hopefully that will be easy). I've never used an arduino before so yeah hope it works! Will keep u posted
                    G'day danyboy

                    Well done. Looks like a similar setup could work on any grinder that was tall enough. Good luck with the Arduino.

                    Anything that helps the process is a good thing in my view.

                    TampIt

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                    • #11
                      Hi db , your getting there mate ! You don't know anyone with a 3D printer by any chance ? You could make a neat fitting stand for your porta filter.......

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