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Torsion Kitchen Scale Prototype

 
pollinator
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Things haven't been going well for your marauding band of savages lately.  The last two raids have come up with very little food and the war boys are running low on silver spray paint.  As the cook, you are catching a lot of blame for the situation and you are starting to worry about getting sent to Valhalla earlier than expected.  You have one last chance to get on the good side of the war chief, Thok'gar, and fortunately you stored away the supplies to bake him a nice cake for his birthday; Thok'gar loves cake.  Unfortunately, the recipe you have has all the ingredients listed by weight, and electronic kitchen scales are a thing of the distant past...

Sound familiar?  Well worry not, a reasonably accurate kitchen scale can be made from some stuff you already have lying around.  I used a strip of the inner tube from the handle bar grip project, a round of wood cut on a miter saw, some string, and two wooden dowel pins carved down from serviceberry sticks to make this prototype.

The scale is accurate to about 2 grams with a max weight of 100g.  Nothing amazing, but not terrible for a first pass at it.  I installed a stick on the wall with the graduations on it so that it can be replaced and recalibrated if the torsion part of the scale changes in any way.  For calibration, I used a handful of pennies and quarters, which way 2.50g and 5.67g respectively.  I had enough to get up to the full 100g, and I made a lot of marks at various test weights because the scale is pretty non-linear.  It is quite repeatable though, so with lots of calibration points it works alright.

The scale operates by twisting the elastic element at the top and unwinding a thin string from the upper wooden pulley.  A large-ish diameter pulley is good because it increases the sensitivity of the scale.  In place of the rubber strip, some thin rope or braided string would work too (sort of like the old rope-powered catapults).  The elastic element is pulled through slots on the dowel pins and pinched tight, I also added a couple dabs of hot glue for security.  I made a small hook from baling wire to hang the scale cup from, and then pinched in a piece of zip-tie and hot glued that as well to act as an indicator for readout.  The cup is the bottom of a tin can with a short loop of baling wire holding it on.

I was going to make a large free-standing version of this that has more range and more accuracy, but I'm not sure I'll have time to get to it, so prototype it is for now.  Because of the non-linearity of the scale, it is good to approach the weights from the bottom.  In other words, it is good to pull the scale down past its reading, and let it gently spring back up, otherwise there are certain points on the scale that are a bit unstable.

This is part of the MoPID series of permaculture innovations that I am working on during my time at Wheaton Labs.  Check out the thread if you'd like to follow along.
IMG_20220916_163758220.jpg
The scale in action
The scale in action
IMG_20220916_155125796.jpg
Attaching the pulley to the spring by pressing a wood piece in through the center hole
Attaching the pulley to the spring by pressing a wood piece in through the center hole
photo_2022-09-18_11-44-21.jpg
A shot of the whole scale, still needs more graduations added at the higher weights
A shot of the whole scale, still needs more graduations added at the higher weights
 
pollinator
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I like this thing! If ever I need a 'kitchen scale' in my garden shed, I'll try to make my version of your prototype shown here. Or if the 1960s kitchen scale I have here decides to end its life ...
 
steward
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David.  This is cool.

Wanna come back next year for the PTJ and tag-team some gravity-powered lighting with me?
 
Rusticator
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This is VERY cool, David!! Congratulations on saving your own neck from the much too early trip to Valhalla!!
 
David N Black
pollinator
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Beau Davidson wrote:David.  This is cool.

Wanna come back next year for the PTJ and tag-team some gravity-powered lighting with me?



Heya Beau,

Yes!

Schedule permitting, pencil me in for that.  I'll keep an eye out for some tiny gear boxes.
 
My pie came with a little toothpic holding up this tiny ad:
GAMCOD 2025: 200 square feet; Zero degrees F or colder; calories cheap and easy
https://permies.com/wiki/270034/GAMCOD-square-feet-degrees-colder
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