deskthority

Some switch types, such as most Alps designs and clones and Futabas, transfer the keystroke force directly against the switch contacts, via the slider.

Comparatively, Cherry and SMK switches, and SMK copies (e.g. KPT) are the opposite: when the slider is pressed, it clears out of the way of the movable contact, which closes under its own power. When the slider is released, the movable contact is opened under the power of the return spring. This means that, at no point, is any force from the user's finger ever transferred to any sprung part.

Is this likely to make any difference to switch longevity?

I think the direct type will experience more variations throughout its life because the user stroke varies. The non-direct type allows more control for the engineers when designing it as the stress on the contact parts will have less variation since they designed it. Take for instance a case where there are slight vibrations. The contacts of the direct switch will experience these, while the indirect type will not because of hysteresis. It will just trigger once, like normal. This allows them to design the contact to be perfect for one scenario with far less variations. It also provides contro over that scenario by allowing them to adjust the strength of the spring acting as a middle man between the slider and the contact parts. That spring will be more consistent towards the contacts than a finger is what I am attempting to get at I guess. In the case of the MX, their contacts still experience variation because of its design, but far less than a direct design would have. My 2c

Edit: If it wasn't clear, I believe that the indirect types will last more cycles in general.

Edit: Holy crap, that was fully of grammatical errors and was pretty incoherent, couldn't even understand it myself after reading it just now. Fixed it somewhat.

The reason I wonder, is that Alps switches get a bad rap for poor longevity — it makes me wonder if this was the bad decision on their part that most commonly leads to this failure?

My post was mostly theoretical. I think there are other factors which contribute far more to their longevity. They want to keep the costs down so they try to have as little excess as possible. Strengthen all parts a few percent and you could further decrease the risk of something breaking. They have reached a point though where the extreme amount of cycles eventually changes the material properties enough to cause failure.

I once read a bout a switch which employed self-cleaning from oxidizing and debris between the contact surfaces. It was as simple as making the contact surfaces meet a bit off axis. This caused them to grind slightly upon contact which removed anything which would have otherwise increased the resistance and eventually caused them to not get a conduct sufficiently. I found this an interesting theory as most are just a pure orthogonal movement and contact. I guess you would have to use the correct amount though, as too much would risk them grinding through eachother eventually.

The GRI KBM-LP switch has self-cleaning contacts:

http://www.grisk.com/pushbutton/kbm-lp.html

I'm not convinced that they designed that switch — it's based on Futaba switches. I never did manage to obtain any samples from them (just chased the distributor I was in contact with). If it's the same as the one in the BBC Master Series, then the longevity is rather suspect. From the photos posted by HaaTa (not sure if GRI or "real" Futaba, as Futaba never branded their switches), it appears to be a reduced size version of the [wiki]Futaba simplified linear[/wiki], which has a weird design with two contact leaves that sit atop each other. I never could figure out any of Futaba's design principles. I guess that the larger one is also self-cleaning, if it's the same as the smaller one.

I didn't mean that Alps switches completely fail — rather, that the switch feeling degrades with time. I don't know whether the springs are failing, or whether it's a problem with plastic wear.

I believe that the issue with Alps is that they are sensitive to dust interfering with the sliding action.

Daniel Beardsmore wrote:I didn't mean that Alps switches completely fail — rather, that the switch feeling degrades with time. I don't know whether the springs are failing, or whether it's a problem with plastic wear.

Findecanor wrote:I believe that the issue with Alps is that they are sensitive to dust interfering with the sliding action.

I believe that this is a theme that started as theories about why some Koreans were lubricating their Alps or why some particular beat-up board didn't feel so well, about 5 years ago. There is a chance the originals are not less or more sensitive to wear than other switches, but that old hearsay, anecdotal evidence and theories have been echoed and bounced for so long and so many times that it entered common wisdom. It could be correct. But this is probably the first topic where I read some deeper technical theory behind it. And the real problem is that there is no evidence from people using a new old Alps boards consistently for a couple of years, or I must have missed it.

Man, I seemed to have edited my post so much that it all became jibberish. I couldn't even understand it myself.

Anyway, these speculations won't yield much without knowing what type of failure is most common. I have too little experience there, as I mostly know of switches failing early because of a traumatic event, rather than those failing "naturally" around their expected lifetime.