How to Read a Force Curve

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#1

When you’re looking at switches, one term that almost always comes up is a force curve.
Why you ask? Well, when read correctly a force curve allows you to visually interpret what a switch will feel like.

But what if you don’t know how to read a force curve? :cry:

For those that don’t know me, I became so obsessed with switches I built my own force curve tester, which I chronicled in The Problem with Mechanical Switch Reviews.

Reading a Force Curve

To read a keypress from a force curve, you read the graph from left to right, and then if there is data for the release it is then read from right to left.


The X-axis (bottom) going from left to right shows how far you have pressed the switch. Starting at 0 mm (switch is not pressed at all) and ending at the maximum travel of the switch (e.g. 4 mm).


At each X position, the Y position represents how much you have to push on the switch at that part of the keypress. So at 0 mm, it makes sense that it takes no effort to press the switch, because you’re not pressing it (hah). At the end of the press (bottoming out the switch) the force will sharply increase.

In the case of a Hako Violet Switch there are 3 other notable force/distance positions on the graph.

Bottom-out Force vs. Actuation Force

When someone mentions a switch is 45 gf, what do they actually mean? Is it bottom out? Is it actuation? Is it at the tactile bump?

The truth of the matter, they probably don’t know either, lol (or at least misinformed).

Instead, you should be talking about how much work it was to press the switch
(using force to talk about how heavy switches are is perfectly ok, just remember to specify what you’re talking about :smiley:).

Force vs. Work

Work is just force x distance, or more easily visualized, the area under the force curve (Total Force is the sum of all the force, which is the same as Work).
For convenience I calculate the work (gfmm, also known as joules) for each switch I measure. And if I have the press/release data, I also measure the actuation work as well.


Conclusion

When talking about how heavy a switch feels, be specific!

  • X switch bottoms out at 55 gf.
  • Y switch activates at 40 gf.
  • Z switch takes 57 gfmm to activate.
  • W switches uses 68 gf springs (this is ok, but we should specify the length of the spring as well…).

And don’t do…

  • Q switch is 80 g. (Does Q weigh 80 g!?)
  • Hako True switches use a 95 gf spring. (Yes it does, but the spring is also 12.3 mm long, vs. 14.5 mm in typical Box switches)
  • Use g (weight) when you actually mean gf (force). g can mean weight of the object, while gf is always about applying force.

I hope this guide was useful, please feel free to add any suggestions or comments. I’m always trying to improve how I explain switches :smiley:


Novelkeys Cream Switches Force Curve Graph
#2

One of the most important/first things any keyboard enthusiast should learn :slight_smile:


#3

This is probably one of the most impactful guides in this community! I think the only minor issue I have is that the work done isn’t provided by the manufacture for switches (afaik), so it would be hard for people to talk about switches without that data. At the moment that exact data only comes from you which is good, but I think it great if we could have someone (whether it be from the manu. or another independent source) be a secondary verification like how you are to the manu. for the rest of the data.

Otherwise, I do like the idealology of talking about switches in terms of Work. I think adding how it should be discussed in more concrete terms would help the conclusion.


#4

Updated the conclusion a bit.


#5

Great write-up. We also tried to build our own force gauge to help quantify and validate the crispness of IBM’s buckling-spring mechanism after restoration. We wished we had your good “explainer” before we started the endeavor

ibm-model-m-force


#6

I’m so pleased that this exists, genuinely one of the most informative things I’ve read in a while.


#7

Very informative. Thank you for doing what you do for us!


#8

Thank you Haata for your wonderful science, everybody should read this first berfore decide which switch they one to purchase


#9

Everyone talks about how Cherry MY feels like typing on wet newspaper. Well, I’d like to get a force curve for wet newspaper one of these days. Also for anything that you come across in daily life that has an interesting clicky response. A bottle cap. A pen cap. Some particularly satisfying metal latch. Could be fun.


#10

Oh yeah, like how people say typing on Topre feels like typing on boobies. Well?

This is in the interest of SCIENCE.