i've designed some springs for work. the progressive spring exist.
if you create a spring with two different pitches you will have a graph with 2 angles.
(you can have the same effect using two different springs, with they own pitches, stacked)
if you use a variable pitch, you really get a non-linear spring.
in both cases, if you want to feel the differences, the variation of the pitch must be HUGE.
there isn't a linear correlation between pitch and strength.
here is an example that clarify.
when you fully compress the upper part of the spring, you will start to compress the lower part, and the graph angle changes.
Show Image
(https://i.imgur.com/TUCJihT.png)
Show Image
(https://i.imgur.com/KZhgs9G.png)
Makes sense - thanks for this. The difference in pitch needs to be sufficient that the tighter wound coils "bottom out" against each other right? The change in spacing in the coils of the SPRiT and TT springs isn't particularly dramatic (nowhere near as dramatic as in the spring you posted), and only around 25% of the spring has the tighter winding. I suppose that's why they appear to behave mostly linearly when installed in a switch.
it doesn't seem soo progressive to me...
Show Image
(https://i.imgur.com/hdAECNp.png)
Wouldn't different scaling affect these angles?
Sent from my SM-G975U using Tapatalk
In regards to progressive springs, I don't see a lot of people talking about an obvious issue, which is the pre-tensioning of the spring when assembled.
Let me use the Halo True as an example, I'll copypaste a section I wrote elsewhere:
"...It all comes down to the pre-tensioning. I'm not a rocket scientist so I can only use basic terms but essentially a switch spring's tension weight increases dramatically during the first 4-6 millimeters(this is before assembly), and more or less evens out more as it gets pressed towards it's bottom-out weight. By having a longer spring rated for the same bottom-out weight as a shorter spring, you essentially skip most the period of exponential weight increase, giving a more consistent weight across the switches' 4mm or less of total travel. Long story short: long spring = flatter force curve and vice versa. Conversely if we look at the other extreme side for example, a Halo True switch: it has a 12mm spring(pre-compresses only approx. 2.7mm when assembled) rated at 95 grams bottom out, but due to its short length and despite a tactile bump it's only rated at 60 grams actuation weight because the short length allows the spring to remain at a relatively light tension during actuation. I've gone as far as to try clipping the spring length to test, but at 11mm the spring does not have enough force to reliably lift past the tactile bump and reset when used in spacebars. The Halo True's spring is a perfect example of what should be considered a true progressive spring. They feel easy and light to actuate but surprisingly difficult to bottom out when typing."Show Image
(https://i.imgur.com/XwPtUyG.png)
I still think the spring in the Halo True to be the 'best' example of a spring with a 'progressive curve'. It cannot be made lighter and cannot be made shorter, or else the switch fails to reliably reset(this obviously isn't a problem were it using a linear stem). The point I'm trying to get at is that the 68p progressive from Sprit is approx. 13.5mm, meaning the switch (in a Halo True) is being pre-compressed around 4.1mm. As viewed through an assembled clear switch you can spot and see that the spring is being compressed too much. This means that those sections of lighter spring(more dense coils-per-inch) are basically compressed first and are slightly lost before switch travel even begins.
Just some food for thought.
I did discuss preload in an earlier post, and how many springs that claim to be progressive end up not being so because all of the tight coils get compressed and bottomed out once you install it in a switch.
There are short linear springs that serve similar purposes as progressive springs - a providing a light or reasonable actuation weight but a heavy bottom out weight. In addition to the Halo True springs you mention, the 12.5mm springs in a Cherry MX Clear have the same effect (and was in fact what inspired the Halo True spring). I'm not really sure if these linear qualify though as progressive even though they fulfill the same purpose - I believe it has to be nonlinear for it to qualify as a progressive spring, and [early Geekhack discussions on progressive springs](https://geekhack.org/index.php?topic=50254.0) seem to use the definition to refer to nonlinear springs.
I measured the springs from two linears that claim to have progressive springs:
The first, from a Tecsee Ruby V1, looks pretty progressive!
Show Image
(https://github.com/bluepylons/Open-Switch-Curve-Meter/blob/main/Force%20curves/Okay-I'm-Just-Going-to-Calibrate-Every-Day-Now/Springs/Tecsee-Ruby-V1-spring.png?raw=true)
The second, from a KTT Kang White, does not.
Show Image
(https://github.com/bluepylons/Open-Switch-Curve-Meter/blob/main/Force%20curves/Okay-I'm-Just-Going-to-Calibrate-Every-Day-Now/Springs/KTT-Kang-White-spring.png?raw=true)
In their respective housings:
Show Image
(https://github.com/bluepylons/Open-Switch-Curve-Meter/blob/main/Force%20curves/Okay-I'm-Just-Going-to-Calibrate-Every-Day-Now/Tecsee-Ruby-V1.png?raw=true)
Show Image
(https://github.com/bluepylons/Open-Switch-Curve-Meter/blob/main/Force%20curves/Okay-I'm-Just-Going-to-Calibrate-Every-Day-Now/KTT-Kang-White.png?raw=true)
I also photographed the springs - the Tecsee spring on the right, the KTT Kang White spring on the left.
(Attachment Link)
Interesting, can you actually feel the difference when using a progressive spring? I'd love to try a very progressive spring, something really round that progresses slowly and goes up dramatically in the end of the travel if that's possible.