Interesting. I guess I’ll need to measure some switches as well.
Some questions I’ve had about the situation.
- Are these “new” switches as in they’ve never had keycaps on them?
It seems semi plausible to me that depending on what kind of keycaps were used, the POM cruciform mount could be warped just by inserting a keycap.
I’m still a bit of a novice when it comes to materials science…but
ABS (105) seems to be not as hard as PBT (112-120) or POM (69.0-121). Compared using Hardness, Rockwell R.
But, I have no idea which formulation of POM Kaihua is using, so that it’s hard if the ABS is actually less hard or not.
Modulus of Elasticity (again from the above links)
- ABS 2.21 GPa
- PBT 0.420-21.9 GPa
- POM 0.586-11.7 GPa
I’d say from those numbers that ABS isn’t as elastic (more brittle) than PBT and POM. So…ABS keycaps aren’t as durable as PBT or POM and are more susceptible to cracking it seems.
Do any keycap manufacturers actually publish their keycap mounting dimensions? Cherry has in the past it seems (https://deskthority.net/w/images/c/c8/Cherry_MX_1×1_keycap_specification_(1983).pdf). If I’m reading the schematic correctly, I’d say 1.17 +/- 0.02 mm? It has to be less than the stem mount or the keycaps will fall off, lol.
Is it possible the keycap fabs screwed up the melting temperatures and then how it cooled afterwards? Again, I’m not an expert in this sort of thing. Brittle ABS is a thing when dealing with 3d printing at least.
What to do about the situation? Is Kaihua entirely at fault? Is GMK making faulty keycaps? TBH, I don’t know.
Getting Kaihua to manufacture things to their spec shouldn’t be too difficult (as long as keycap insertion warping isn’t a thing). Getting Kaihua to make smaller stems might be doable, but that would require new tooling for every stem Kaihua makes.
Really what would be better: Get keycap manufacturer to give dimensions and tolerances for their keycaps. If they are out of spec, that’s the manufacturer’s screw-up.
I’ve asked Kaihua to check all the molds of all the stems (it seems like they had already started doing this, so at least Kaihua isn’t ignoring the situation).
- Do keycaps fail consistently? As in, for a BOX switch that is known bad, does it consistently destroy keycaps?
Will a BOX switch that is measured to 1.32 mm in the X-Axis destroy any keycaps?
Really, what this situation reminds me of is Matias Alps switches vs. Signature Plastics DSA PBT Alps mount keycaps. Matias tightened the stem mount slightly to better hold onto keycaps (so they wouldn’t fall out during shipping); whereas SP decided to make their Alps mount as tight as possible. And at least in 2014 when I noticed this (when working on the Infinity 60%) tried to get SP to adjust the molds so they would better accommodate Matias switches. Long story short, SP refused to do anything about the situation.
The more data we can get on all the different parts (proper datasheets and possibly even material specs for plastics used) the easier it is to focus on the problem at hand.