You should be skeptical of "progressive" springs - some force curve measurements

[Pylon]

Hi all,

As many of you may know, SPRiT, Thic Thock, and others have advertised and sold progressive springs for a while. These springs claim to be nonlinear, having a lower spring constant before the approximate actuation point, and an increasing spring constant after, to provide a more cushioned bottom out. SPRiT, on his website, provides the following image for what the force curve for his progressive and complex springs should roughly look like:



These springs are wound tighter on one side than the other. SPRiT's springs look like this, for instance (image from his site):



Nonlinear springs are known to exist - for example, this article from an industrial spring manufacturer describes some of them, including buckling springs, conical springs, springs of varying diameter, and "dual rate" springs that have a tighter winding on one end. So far the "progressive"/"complex" springs sold by SPRiT, Thic Thock, and others have all been of the last variety, which have a constant diameter but a varying winding pitch on one end of the spring. In theory, these springs work by the tighter end compressing first, and the coils on the tighter end bumping up against each other, which provides nonlinearity. A seller of industrial springs has a nice animation of how these work.

However, as implemented in a keyswitch these don't really seem to be very nonlinear.

As some of you may know I recently designed and built an open-source force curve meter, the files which are published on Github here. The curves of various switches, frankenswitches, and springs I've measured so far are published in a directory on the Github, here.

Windows Dump (I don't believe he's on Geekhack, but he goes by that on Discord) recently lent me a gBoards.ca SPRiT spring sampler, and also various Thic Thock DL and MP springs. I measured the 63.5g SPRiT complex and progressive springs from the sampler, and the Thic Thock 68g MP springs. The SPRiT springs I placed in a Gateron Yellow (one test with the leaf, and another test with the leaf removed), and the Thic Thock spring I placed in a JWK Alpaca "V2" / "B" that Slowshi lent me (the Thic Thock spring is a bit wide diameter wise, and tended to catch on the stem in the Gateron Yellow stem, so I used the Alpaca instead). I did the leafless Alpaca tests using a "V2" / "B" bottom housing from a JWK T1 from which I removed the leaf.

The results are here - I compared the SPRiT springs to the stock Gateron Yellow spring (which is nominally 63.5g), and I compared the Thic Thock spring to a Durock 67g spring when installed in an Alpaca switch. For the leafless measurements, I also plotted them against a theoretical perfectly linear line, which I made by plotting the measured values at x=0.1mm and x=3.8mm and drawing a straight line between them.






Obviously these don't look very nonlinear. The Thick Thock 68g MP pretty much looks linear and very similar to the Durock 67g spring when installed in an Alpaca switch.  The SPRiT springs deviate about 1-2gf from linear, and also don't seem to behave nonlinearly by very much compared to a regular Gateron Yellow spring. The SPRiT springs are also much lighter than the 63.5g claimed.

I don't know if this is an implementation issue with these particular "progressive" springs (the tighter wound sections on the SPRiT and TT springs are relatively short compared to the regularly-wound portion of the spring, and seemingly too short to have much of an effect), or if keyswitches just inherently don't provide enough travel and compression for progressive springs to really enter their nonlinear regime. I also haven't had a chance to test other progressive springs, and it is possible that some of them in fact behave nonlinearly as expected.  But in any case, you should probably be skeptical about purportedly nonlinear "progressive" springs for the time being, until you see measurements that validate their claims.

(edit - fixed a typo on a URL.)
(edit Feb 26 2022 - fixed broken URLs)

[Ranger_Trivette]

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.

[Leslieann]

If you want to test springs, it needs to be done outside the switch.

No matter how much you think you're keeping the results fair there's just too many variables you can't control when trying to nail down the spring variables which will be subtle.

[Pylon]

If you want to test springs, it needs to be done outside the switch.

No matter how much you think you're keeping the results fair there's just too many variables you can't control when trying to nail down the spring variables which will be subtle.

Why test springs that are marketed and sold for installation inside keyswitches, marketed as making a difference while installed in keyswitches, without installing them inside keyswitches? Why would that be useful?

Here's some other spring measurements. Here's a comparison between a 12mm long ~90g MX Clear spring, 13nn long 89g Novelkeys spring, and a 15mm Kailh Speed Pale Blue spring - the difference in spring rate and initial preload is pretty apparent:


Here's a measurement of an MX Clear switch with the Kailh and Cherry springs, with the spring measurement (done without the leaf) overlaid on top:


Here's also a chart I did of a Gateron Yellow with and without its leaf and using its stock spring - the leafless measurement looks pretty dead straight to me:


I don't see issues with measuring springs inside a leafless switch.

[Pylon]

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

Show Image

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.

[AJM]

Thanks for these tests Pylon!
Very interesting and it confirms, what I have been suspecting.

[saltimate]

ngl i was pretty disappointed when i tried some out...
was it always just a scam or do they really believe if its noticeable in high precision instruments (or in theory? idk how they evaluate their springs...) it will have a meaningful impact on switch feel?

[N8N]

For what it's worth, I am familiar with progressive springs in an automotive application.  However, I learned over xmas break that BMW does it differently - when I replaced the struts in my car I found that the springs were very soft (relatively speaking) and extended quite a bit when removed from the struts.  The car actually sits on the bump stops at rest, meaning that the bump stop (basically a piece of closed cell foam slid over the strut shaft) is acting as an additional spring.  I'm not sure why they do it this way but I suspect it is because it offers more "progressiveness" than a single coil springs with coils that go into bind when the increased rate is desired.

Unfortunately, they don't last, and often need to be replaced before the struts wear out - I thought I could let this go and hit a bad pothole one night, I now have a chunk of my RF fender missing (it's plastic) and the RF strut was completely blown when I replaced it.

[HungerMechanic]

I never expected much variance between Progressive and regular springs.

But the difference between 68 P and regular 68 G springs on Ergo Clears seems pretty significant to me.

I can barely stand typing on regular 68 G stainless in MX Clear housing. But with 68P, it actuates around 45 G, near MX-Brown level, and bottoms-out closer to 68 G, allowing good functioning. 68 P felt bouncier and less rigid than 68 S.

My 63.5 P Ergo Clears are crazy-light at actuation, maybe lighter than MX Brown, but they seem to function fine with Clears.

[Pylon]

My 63.5 P Ergo Clears are crazy-light at actuation, maybe lighter than MX Brown, but they seem to function fine with Clears.

Have you tested the bottom out weights of each by any chance(using nickels for instance, or the fairly crude "kiss test"?). The 63.5 P I got is bottoming out at 50g on a Gateron Yellow, which has the full 4mm travel. It is possible that gboards.ca included the wrong springs by accident in the sampler, but it visibly has the varying coil spacing, and it's  also possible that they're just much lighter so that they appear to feel different.

[HungerMechanic]

Sadly, I don't have the ability to test.

What are you describing, 50 G bottom-out, probably shouldn't even work with an MX Clear! And yet I have a board full of these. Very interesting.

Incidentally, a thread on KeebTalk may have reached similar conclusions:

https://www.keebtalk.com/t/sprit-progressive-springs/4055/4

[Pylon]

Actually I just counted the number of coils on the 63.5 P I have on hand and it matches SPRiT's pictures.

Here are the pictures of the springs I have:

[Pylon]

What are you describing, 50 G bottom-out, probably shouldn't even work with an MX Clear! And yet I have a board full of these. Very interesting.

Huh, I just put an ergo clear together with the 63.5 P spring and it returns fine. I also tried the 45g spring out of the gboards.ca sampler and put it in an ergo clear and it returns just fine (I did not measure the 45g in my force curve meter, but I can)

[Leslieann]

Why test springs that are marketed and sold for installation inside keyswitches, marketed as making a difference while installed in keyswitches, without installing them inside keyswitches? Why would that be useful?

I don't see issues with measuring springs inside a leafless switch.

Yes, they are sold for use in switches but every switch is different, even the same switch from the same batch, even re-using the same switch introduces variables.

You don't compare engines in cars, valve springs in heads, and suspension springs in the car. They do test that way but it's (usually) done for determining overall performance, not the performance of a particular item to compare one specific part against another specific part. And yes, this is a switch, it's simple but simple also means it's simple to mess it up.

A leafless switch is better, but housings don't always  align the exact same every time, lube and dust gets wiped and added, scars develop, springs don't settle the same, especially depending on lube. You can say all these things are minor but they matter, particularly if you're trying to find a subtlety in a benchmark.

[HungerMechanic]

Huh, I just put an ergo clear together with the 63.5 P spring and it returns fine. I also tried the 45g spring out of the gboards.ca sampler and put it in an ergo clear and it returns just fine (I did not measure the 45g in my force curve meter, but I can)

Interesting. The guides always said best not to go below 55 G bottom-out [they meant the linear springs], and even that's iffy and may require careful lubing. So the actuation weight of 63.5 P would be close to that metric.

Of course, they are thinking of spacebars and other large modifiers, and a high desire for consistency in the switches.

63.5 P will work fine with Clears, I have 64 of them in a board. It's just lower in the actuation than you would want, ideally. Clears really want about 50 G actuation, and I doubt 63.5 P provides that. [In fact, I think it actuates around what a 55 G linear spring would. Which I guess makes it borderline for Ergo Clears.]

With regard to the original discussion in this thread, I think it's true that sub 72 G Progressive springs aren't nearly as 'ramping-up' as MX Clear springs. However, there is a difference. Specifically, lower actuation than the regular version of the spring, and it does slightly ramp up towards the bottom-out weight at the end.

This effect is particularly noticeable among tactiles, in my experience, from Ergo Clears to Holy Pandas and derivatives.

[Leopard223]

This is why I love this site, thank you for this post!

[Leslieann]

Interesting. The guides always said best not to go below 55 G bottom-out [they meant the linear springs], and even that's iffy and may require careful lubing. So the actuation weight of 63.5 P would be close to that metric.

55g is just the point things stop being easy.

I have some tactiles that took 39g springs with only minimal effort and medium lube while another tactile simply does not work properly below 45g regardless of the type or viscosity of the lube you use.

[tp4tissue]

it's also not always the case that the outer fingers are weaker.  for example, it's possible that depending on your technique with an axe, your pinky and ring finger gets stronger than middle/index

[Faceman76]

it's also not always the case that the outer fingers are weaker.  for example, it's possible that depending on your technique with an axe, your pinky and ring finger gets stronger than middle/index

It's safe to assume, that for most of us, the inner two fingers are stronger. 

I've played with various Captains of Crush grippers over the years,  my middle and index fingers are still the strongest. 

Sent from my SM-G975U using Tapatalk

[Ranger_Trivette]

Makes sense - thanks for this. The difference in pitch needs to be sufficient that the tighter wound coils "bottom out" against each other right?

correct.

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.

if you don't modify the pitch in a "dramatic" way, you will never see a difference in the graph.

in the spring the pitch move from 6,5 to 15.5.
the graph change the inclination from 20° to 28°.
and the difference is barely visible.

i think you will never see any difference in a graph if you test the springs you have posted before.

[Pylon]

Ok, so here's my hypothesis as to why the "progressive" springs I tested aren't  behaving nonlinearly, or are very minimally nonlinear.

The equation for the spring constant of a coil spring is the following:


k = spring constant (higher = stiffer spring)
G = shear modulus of the material the spring is made out of
d = wire diameter
D = Mean diameter of the spring (outer diameter - wire diameter)
n_a = number of active coils

Most springs are made of steel so G (shear modulus) tends to be fairly constant, and this is also fairly consistent across different alloys and tempers of steel.The overall diameter of the spring (D) tends to be constant for all MX-format springs, though if you had a conical spring (e.g. Topre) it would vary over the course of the travel. d (wire diameter) varies between different springs, but is constant for a given spring.

What a progressive spring is trying to do is to lower n_a over the course of the travel, by causing coils to bottom out against the inactive coils at the end of the spring over the course of the travel. As individuals coils "bottom out" against the end, they become inactive coils, and so n_a should go down, increasing the k of the spring as you push the switch down. This is done by making some of the coils spaced closer to each other so that they bottom out first.

The main issue that springs are already compressed when you install them in an MX switch. A typical MX-format spring is ~15mm long naturally, but becomes ~8mm long when installed in a switch. When the switch is pushed all the way down to bottom out, the spring is shortened to 4mm long (typical MX switch has ~4mm of travel). So the entire action of an MX happens between spring lengths 4mm to 8mm.

The issue with the progressive springs is that when you install them in a switch, virtually all of the "tight" coils have already compressed simply from installing the spring in the switch. When you go push the switch, the remaining coils left that area all evenly spaced, and so you  have little to no non-linear "progressive" effect over the course of the travel of the switch.

See this picture of the Thic Thock MP 68g spring comparing its natural state, and compressed to 8mm (which is what happens when you install it in a switch). When compressed to 8mm all of the tight coils have already bottomed out, and all of the remaining active coils are evenly spaced apart, so there's no tighter-wound coils left to provide nonlinearity when you go push the switch.

[tp4tissue]

it's also not always the case that the outer fingers are weaker.  for example, it's possible that depending on your technique with an axe, your pinky and ring finger gets stronger than middle/index

It's safe to assume, that for most of us, the inner two fingers are stronger. 

I've played with various Captains of Crush grippers over the years,  my middle and index fingers are still the strongest. 

I must emphasize, DO NOT play with captain of crush grippers. The hand ligaments are very delicate and we have evolved very far from the days where extreme grip force is a necessity in our lives. Exercising grip can cause carpel tunnel. It is an excess with no purpose and high probability of damage.

[Faceman76]

it's also not always the case that the outer fingers are weaker.  for example, it's possible that depending on your technique with an axe, your pinky and ring finger gets stronger than middle/index

It's safe to assume, that for most of us, the inner two fingers are stronger. 

I've played with various Captains of Crush grippers over the years,  my middle and index fingers are still the strongest. 

I must emphasize, DO NOT play with captain of crush grippers. The hand ligaments are very delicate and we have evolved very far from the days where extreme grip force is a necessity in our lives. Exercising grip can cause carpel tunnel. It is an excess with no purpose and high probability of damage.

Was up to the 195lbs gripper for a bit, but backed down to the 140 for the reasons mentioned above. Been 15 years+ and no issues so far.

Sent from my SM-G975U using Tapatalk

[The0rigina1]

I never expected much variance between Progressive and regular springs.

But the difference between 68 P and regular 68 G springs on Ergo Clears seems pretty significant to me.

I can barely stand typing on regular 68 G stainless in MX Clear housing. But with 68P, it actuates around 45 G, near MX-Brown level, and bottoms-out closer to 68 G, allowing good functioning. 68 P felt bouncier and less rigid than 68 S.

My 63.5 P Ergo Clears are crazy-light at actuation, maybe lighter than MX Brown, but they seem to function fine with Clears.

Are you using 63.5p from sprit? According to my samples, they are only 13mm, one mm shorter than normal springs.
So the actuation point is almost at 1mm, which rendered them unusable for me.

[HungerMechanic]

Yes, so what I did in that case was purchased Ergo Clears made by someone else using 63.5 G Progressive Spirit springs, switches lightly lubed with 3203.

They work surprisingly well compared with what I expected, although they are light.

My keyboard is in the shop right now, but when it comes back I'll check the actuation feel. I don't recall having any functioning problems or other issues with the switches [aside from noise from insufficient lubing].

63.5P Spirit so far seems like a viable spring for very-light Ergo Clears. I'm going to continue testing them, they are like alternate Browns that could be made to sound better.

[Pylon]

So I was sent samples of a spring that hasn't been released yet. I didn't post it out of confidentiality, but the person that sent me it ended up posting the redacted force curve anyways on a public Discord server, so I'll post it here. This springs has an ~4gf deviation from linear. I'm not sure if I'm at liberty to discuss the technical aspects of the spring so I won't for now. But it seems that progressives are possible.



This was measured in a Gateron Yellow with the leaf removed.

[Ranger_Trivette]

it doesn't seem soo progressive to me...

[Pylon]

I mean angle and degrees is not a measure of spring rate, and changes depending on what aspect ratio I make the graph. But you're showing a ~2.4x change in spring rate. It's going from around 4gf/mm to roughly 10gf/mm.

Whether you can feel that is another matter.

[Faceman76]

it doesn't seem soo progressive to me...

Show Image

Wouldn't different scaling affect these angles?

Sent from my SM-G975U using Tapatalk

[Ranger_Trivette]

it doesn't seem soo progressive to me...

Show Image

Wouldn't different scaling affect these angles?

Sent from my SM-G975U using Tapatalk

Yes. But it doesn’t matter.
A graph with two different angles is not progressive.
Two springs combined, or a spring with two different pitch, give you a graph like that.
Not a progressive spring.

[Leslieann]

it doesn't seem soo progressive to me...

How much were you expecting on a spring that has only 15-20grams difference from start to finish? There's not a lot of room for a large curve.

A graph with two different angles is not progressive.
Two springs combined, or a spring with two different pitch, give you a graph like that.
Not a progressive spring.

That is exactly what a  progressive spring is.
Two different ratings, they change the angle depending on how close or how far apart the two springs are, the closer they are the more gentle the curve the further apart they are the sharper the curve.

Go look at car/motorcycle/mtn bike progressive springs (or wikipedia or any other encyclopedia about this topic), this is exactly how it works.

[Ranger_Trivette]

a progressive spring has a curve as graph.
this is obtained moving gradually from a pitch P1 to another one, P2.

if you have half spring with a pitch P1 and the other pitch P2, you get two straight lines, with 2 angular coefficients, like the last graph.

(instead of changing the pitch you may use different diameter of the spring, sickness of the wire etc etc)

[Pylon]

Just measured Gazzew's 55g, 65g, and 72g springs. The 72g is showing decent nonlinearity (~5-6gf maximum deviation from linear). The 55g and 65g are significantly less nonlinear, though it's still there.

[Ranger_Trivette]

the 72gf look pretty not-linear!

[nataku411]

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."

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.

[Pylon]

I measured the springs from two linears that claim to have progressive springs:

The first, from a Tecsee Ruby V1, looks pretty progressive!


The second, from a KTT Kang White, does not.


In their respective housings:



I also photographed the springs - the Tecsee spring on the right, the KTT Kang White spring on the left.

[Pylon]

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

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.

[Leopard223]

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

The second, from a KTT Kang White, does not.

Show Image

In their respective housings:

Show Image

Show Image

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.

[HungerMechanic]

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:



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 wonder if this analysis of the Halo True also applies to the Kailh Pro Purple. Some say it is a lighter Halo True. It has a smaller 'tactile bump' than the Halo True, but also a lighter spring. People seem to think the spring is a little heavier towards the bottom, so maybe it too uses a 'short' spring that feels somewhat progressive. Because there were questions about it having such a spring.

I'm not sure I fully understand the implications of the 68 G Progressive Spirit spring. It's just sitting there in the housing getting compressed too much standing-still? Basically, some of the theoretical spring travel in compression / decompression is being wasted, because the denser part of the spring gets compressed before the tactile process begins? So it doesn't reach full designed progressive potential.

[solo-act]

Resurrecting this again because I just started thinking about progressives in a tactile to reduce bottom out.

The photo of the "pre-loaded" progressive spring in the caliper, showing the progressive aspect is wiped out once installed makes a lot of sense, and so does the idea that a shorter but strong resistance non-progressive spring could actually be more progressive because of the physics. 

Has anyone gotten anywhere with this in terms of real-world experience and figuring out recommended progressive spring length for a tactile in order to actually have progressive compression and less bottom out?

I'm currently testing Gateron V2 Cap Golden Brown switches that have a longer, 18mm non-progressive spring that could use less bottom out while retaining the lighter actuation.

Any new/recent insights/thoughts?

[Mikhail]

I think progressive spring is bad idea itself. It's link our to Cherry MY or OKI switches, that feels disgusting.
In opposite slow curved springs feels nice, more like gentle tactile. Closer to Blue Alps.
The naming itself is misleading. Slow curved actually gives a quick press which occurs when a certain pressure is reached.
Progressive, on the contrary, gives the effect that button starts moving with little effort and then it takes more and more, and pressure get slow, fingers get bogged down like in a swamp.

[HungerMechanic]

Can you give an example of a Slow Curve spring weight that you would use with a particular spring?

I think I have heard of people using 63.5 G Slow springs in MX Browns.

[lewisflude]

Thank you