3D Printed Sugar Doser for Controlled Homebrew Beer Carbonation

When bottling homebrew I like to prime with table sugar, this is the cheapest and easiest accessible solution. For a while I used carbonation drops but they were a hassle to get and I dont like to need to think about keeping stock. Alternatively a simple spoon, like https://www.thingiverse.com/thing:116475 works quite well but if you have multiple bottles to fill it becomes a bit tedious and sugar starts to clump and block because of stray drops of water, etc.

So I designed a funnel with a slider that drops in a fixed amount of sugar each time by filling a chamber with sugar and then letting it drop out of teh bottom with a slider mechanism. can be used to easily, neatly and quickly dose when bottling.

STL files in 3 sizes at:

https://www.thingiverse.com/thing:6457377

The original design is available in Onshape at:

https://cad.onshape.com/documents/e61a8f8ede8c25567348c3ee/w/0509d2718368252b104ded8c/e/bd7e102e8508a3d26bb3b983?renderMode=0&uiState=65b6d07d75a8a5702fd8b4c9

I tested several sizes of the design, to get a sense of weiging consistency and quantity for a given doser volume. It is a parametric design so if you want a different carbonation or weird measurements (hello Americans :) it can be easily modified for different sizes. The parameters determine the volume of sugar that gets dosed, then the model is built around this volume. 

It took me a couple of tries to get the quantity right (I was looking to dose about 2.6g into 330ml bottles, which is a medium to strong carbonation). For the granulated sugar I use (generic supermarket cheap stuff) I get a bulk density of ~0.85g/cm3. I expect that number will vary depending on brand, type, etc - maybe even vary over time between different batches. I'd reccomend giving it a test run with the sugar you use to avoid bottle rockets!! 

Eventually settled on a sugar volume of 3.15 cm3 whch gives around 2.65-2.7 g sugar per dose.

Funnel's also parametic in case you have a particularly small printer or just want to save filament.

Once you get the size you want figured out, the dose tends to be pretty consistent, with an accuracy of 1-3%. YMMV! 

3D printer

PLA

TPU (Shore 95)

Sugar

Homebrew beer

Bottles & caps

Designed in Onshape, all based on my own idea/concept.

There are several parts in common to all sizes, and I've uploaded the 3 sizes I printed:

2.8 cm3 (doses approx 2.37g),

3.15 cm3 (doses approx. 2.68g)

3.4 cm3 (doses approx. 3.09g)

Or you can make your own copy of the onshape doc and re-size as you like..

Print the parts and assemble - should be mostly self-explanatory. No supports required! Pay attention to the orientation of the 'slider' part - this has a top (chamfered hole) and bottom (square hole) end. The chamfers are to stop the sugar grinding in the way. Should probably work the other way tround but I didnt try it.

The top end of the dose cell has a slightly wider gap, and this is where the TPU wiper goes.

Glue the funnel to the slider, endcap and nozzle to the dose cell and you're done. Careful not to get glue on the slider, it needs to move freely.

I didn't use food safe glue or PLA, figuring it's only a brief surface contact between two solids so there is very little opportunity for anything nasty to diffuse out of the plastic. Use food safe materials if that worries you, of course!

There is a little square nozzle part called TPUwiper which goes on top of the dose cell, underneath the funnel. I found that the sugar gets inside all the sliding parts and grinds everything together. This was a real problem in the first iterations and made the part more or less unusable, also because there was very little room between the sliding pieces.

I found that widening the gap between the pieces and adding this little flexible nozzle helps to ensure the sugar doesnt get in the way too much, although it still does grind. Every now and then you need to push through, sugar isnt hard and it will grind out of the way.

I havent tried omitting this part or printing it from PLA or other plastic. Might work if you dont have any soft filament handy, let me know if it works without!