What's a good way to measure key travel?

Makerspace
1

I was thinking about getting some calipers for measuring miscellaneous keyboard things.

Does anyone have a suggestion for measuring key travel on a switch? The standard is usually rated at 4.0mm, but many long pole switches reduce this travel to 3.7 or even as low at 3.00mm at times.

I’m thinking I will take a single switch, put the caliper teeth on the top of the stem and the bottom of the pole shaft for baseline reference. Then measure distance when pressing the switch all the way down and subtract the difference?

I’m not sure if there are any switches where the stem gets completely recessed inside the housing or not. If so, maybe I could do this with a keycap installed?

Any suggestions or pointers?

Also, anyone have suggestions for a reasonably priced set of calipers that they happen to like?

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I don’t have a caliper to try but wouldn’t measuring length of stem protruding above top housing before and after keypress be enough?

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3

I think most calipers have a reset option to reset the value to 0. At least my really cheap chinese caliper have it. Despite that, I belive that whouldn’t be enough for really precise measurements.

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Yeah, maybe with the bottom depth gauge slider. Good idea

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Does anyone have a suggestion for measuring key travel on a switch? The standard is usually rated at 4.0mm, but many long pole switches reduce this travel to 3.7 or even as low at 3.00mm at times.

I’m thinking I will take a single switch, put the caliper teeth on the top of the stem and the bottom of the pole shaft for baseline reference. Then measure distance when pressing the switch all the way down and subtract the difference?

I’m not sure if there are any switches where the stem gets completely recessed inside the housing or not. If so, maybe I could do this with a keycap installed?

You can measure this using two ways, clamping the entire switch with the jaws on the top of the stem and on the outside of the central housing pole, or using the depth gauge slider. Either way will work fine as long as you zero the caliper at the first contact with the stem (if inside jaws) and housing (if you place the caliper end on top of the housing and use the depth slider), although I would personally prefer to clamp the entire switch using the outside jaws. Using a Durock Medium tactile and a Durock Sunflower I measured both at 3.8mm and 3.5mm respectively. Both match the measurements that Pylons has in terms of switch travel.

Disclaimer: I work in the manufacturing industry and use calipers, micrometers and depth gauges on a daily basis. I also have a Mitutoyo 6" digital caliper that has been previously calibrated using reference gauge blocks which I used to test this.

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Thanks for the feedback. Any recommendations in the sub $100 range for digital calipers?

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Honestly not sure, I’ve never touched one myself for serious use. The last time I tried using that cheapest Adoric digital plastic caliper from Amazon it seemed reasonably accurate. I’d probably pick any one of the metal calipers and try to measure things that you know to be a specific thickness/dimension and use that as your “reference” to estimate the caliper accuracy.

If you’re really serious about accuracy then I’d suggest you get a Vernier scale caliper in the sub $100 range if you don’t trust the digital calipers. As long as the manufacturer made the vernier scale correctly then they’re impossible to drift in accuracy.

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As for calipers, I know a few people purchased Mitutoyo calipers and they look to be very happy with them.
They are unfortunately a bit above your max price range, at around 130-150$, but the brand and their products are praised all around the world.
You don’t need the extreme precision (±0.01mm error range) for your current application.
But this is something you keep your whole life, a worthy investment.

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I have this caliper and it works great for me:

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You may be able to use the step measurement or the depth bar on a Mitutoyo caliper for this purpose, with the upper “step” being the top of a non-depressed key and the lower “step” being the top of a depressed key in the same row? Here’s a demonstration video from Mitutoyo (step measurement at 1:53; depth bar at 2:14):

agree with @Rico that a Mitutoyo caliper is a worthy investment. They are a buy-it-for-life tool if stored properly, especially the vernier caliper models (I personally prefer vernier over the digital models)

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I am one of those people :grin: Recently got mine from ebay. I have had more affordable ones — I couldn’t be happier now.

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