September 16, 2018
Since the beginning of this project, I have had reliability problems with the kitchen timer. Sometimes it ran 7 hours without a problem, sometimes it stopped mysteriously after only 20 minutes.
as if by coincidence, there are problems with the only mechanism that it was not me who did it. I'm not criticizing, but I take note.
In reality, it's pretty normal that it does not work well, because I use it largely outside of its specifications. There is a big difference between turning a small dial in the air for an hour and moving gears and springs for 5 hours.
I am not going to list all that I tried to solve this problem but you have to know that I screwed up around fifteen timers while looking in the wrong direction.
For example this thing with mad eyes, you will be nice not to ask me what it is, I don't want to talk about it.
At this point I do not know what to do, so to pass the time we will play doctor.
I made a stethoscope with an old piezo buzzer:
It is practically insensitive to the vibrations of the air but very sensitive to the vibrations of a solid.
In addition, I think it is a little directional given its flattened shape, which should allows to focus on an axis.
Logically, the amplitude of the noise of the ticking should correspond to the force exerted on the pendulum and I will perhaps finally be able to find where it gets hot.
It's not "haute horlogerie", it's made for cooking.
For an unmodified timer, we get this:
To increase the power reserve, I unrolled the spring in double spiral to make one, I put it on the back of the timer and attached it to the axis of the clutch (there is not enough room inside for the complete spiral). The ferrule is taken on another clutch, I do not lack spare parts.
Yes, I know it's not good to tinker with small mechanisms in sawdust, but it's so much warmer.
When the timer does not stop in it's way, we get this:
It's noticeably less clean and there are weird peaks from time to time
Zooming again, we notice that these peaks have a different spectrum and are not synchronous with the ticks, whose amplitude increases just after.
So it's not rubbing, it's more like slipping.
the timelapse allows to see the phenomenon, although it is discreet, actually the spring does not move fluidly but rather by small jerks. It does not slide very well on itself, contrary to foolishness.
Listening is clearer:
If we look at the distribution of tick-tac amplitudes, we see that the standard timer has almost a Gauss curve
while mine has several bumps.
Here it is very clear, the bumps on the left represent the slowdowns before the strike-slips.
In fact I have no idea, but I'm pretending because it would suit me well.
I think it's a bit like an hourglass: there are lots of small collapses and occasionally, an unpredictable avalanche. My problem is when nothing moves before the avalanche.
I tried to polish the spring with emery paste, grease it and everything, but there is nothing to do.
We are in trouble, I think that maybe it was not so smart to build an automaton around a kitchen utensil, and maybe I should accept once and for all that We rarely do a nice thing from a stupid idea.
OK, I did not want to get there but since that's it, we're going to read a little theory about spiral springs.
The spiral is a long steel blade wound on itself.
As the turns do not touch, the force applied to one end of the spring is distributed over its entire length, which allows to have a very long range of elasticity in reduced dimensions. We have a good usable portion with almost constant force.
I dumbly thought that to make a spiral spring it was enough to wrap it around an axis, well no, we must first give the double spiral this confusing S shape.
This is the only way to prevent the turns from touching each other.
Preforming the spring is a little more hardcore than it looks, the people still able to do it properly are counted on the fingers of the hand of a carpenter, the others are missing since the years eighty.
I have an idea: What if I replaced my foolish spring with TWO foolish springs?
By fixing them on the same axis, knowing that the blockages are random, there is little chance that a critical slowdown will occur at the same time on both, and logically the moments of weakness of one should be offset by the other.
So I put the original spring inside, keeping the other one on the outside.
The movable arm, I added it to prevent the curvature of the first portion of the spring from changing,
I think it is useless except it foolishly decenters the spiral, but it works so we will stop touching everything.
The recording is much cleaner
And the distribution almost normal.
isn't it beautiful life?
I add that ticking is also part of the specs for a timer, we are supposed to hear it in order to know at every moment that the time is not up, and the fact of having added a spring makes it even stronger.
Unfortunately I can not measure the decibels, but according to the feedback I received, the sound level is somewhere between "very present" and "a little sucks". Fortunately with the plexiglas of 10 mm we hardly hear it anymore.
The box is now almost finished, I should be able to show it at Lemanmake on September 29th and 30th. This will probably be it's only public appearance because after that it will be in production in my kitchen. It will give me some time to write the 4 or 5 late updates ...