Possible Friction Rating?

[ArtoriasEdgeworth]

Hello Deskthority.
As a relative newbie, I was struck by the lack of a unit to describe keycap friction.

Is there some way we can develop a way to test the friction of a keycap, and make it easily to replicate?

[HuBandiT]

Are you referring to how smooth/shiny or rough the surface of an injection molded keycap is? In that case I suggest you look into injection molding literature about the smoothness classes they have, they have been doing this for decades.

[ArtoriasEdgeworth]

Thank you. do you have any recommended reading material?

[ArtoriasEdgeworth]

And yes; I was referring to the smoothness of a keycap.

[XMIT]

Hi there ArtoriasEdgeworth! Neat idea!

Do you mean surface roughness, how it feels when you slide your finger along the top? I can think of a few empirical measurements:

- coefficient of friction, µ; https://en.wikipedia.org/wiki/Friction# ... f_friction
- mean particle size or "grit", µm. https://en.wikipedia.org/wiki/Sandpaper#Grit_size_table

I think the latter is better!

[ArtoriasEdgeworth]

Thanks, XMIT. Interesting, I'll see what I can find online.
Is there any way to easily test for either of those units?

[Wodan]

Thanks, XMIT. Interesting, I'll see what I can find online.
Is there any way to easily test for either of those units?

I like the idea a lot, too. But I am pretty convinced there is no way to measure this properly without special equipment for thousands of dollars.

I got myself a cheap, high magnification USB "microscope" for visual examination of keycap surfaces. Since I was experimenting eith sandblasting shiny keycaps, this was very helpful to closely examine the sandblasting results.

If you are planning to do a keycap surface comparison, you could get yourself one of these microscopes and take pictures of different keycap types at the identical magnification/light and create a galery for a visual comparison.

This is probably as close as you can get without spending a loooot more on testing equipment.

[HuBandiT]

Thank you. do you have any recommended reading material?

Hmm, these pages at ProtoLabs might just give enough acronyms to google:

• https://www.protolabs.com/injection-mol ... e-finishes
• https://www.protolabs.com/resources/des ... s/2015-11/

[HuBandiT]

I like the idea a lot, too. But I am pretty convinced there is no way to measure this properly without special equipment for thousands of dollars.

However if the goal merely is classifying the surface characteristics just enough to choose the right option for injection molding - which I suspect it is, considering where we are -, then having samples of the possible finishes available to compare to keycaps by sight and touch should provide just enough information to be able to communicate the right surface finish selection to the manufacturer doing the injection molding. For this the ProtoLabs sample cube (or an equivalent sample object from another manufacturer) should be sufficient.

[Wodan]

I'm afraid the samples we will be seeing are so close together, they will basically all be in one class even thuogh they give a sliiightly different feeling. Like comparing Cherry PBT keycaps with Gateron PBT and other PBT keycap surfaces ... the differences will be incredibly small but noticable.

Maybe we can create some surface standards between SA and DSA surface

Still it will e FAR away from something measured. We will not get a measured value or something we could draw an average from ...

[HuBandiT]

Here some more - apparently from the company that invented textured injection molding: http://www.mold-tech.com/downloads/

[Chyros]

Hi there ArtoriasEdgeworth! Neat idea!

Do you mean surface roughness, how it feels when you slide your finger along the top? I can think of a few empirical measurements:

- coefficient of friction, µ; https://en.wikipedia.org/wiki/Friction# ... f_friction
- mean particle size or "grit", µm. https://en.wikipedia.org/wiki/Sandpaper#Grit_size_table

I think the latter is better!

Grit wouldn't account for the different friction coefficients for different materials though.

[ArtoriasEdgeworth]

Something that I was thinking was a force gauge pulling a sheet of paper with a weight across the keycap. Then say the peak force that the gauge measured. I know you can get a force gauge for pretty cheap, and use a standardized weight?

[ArtoriasEdgeworth]

And having a chart for each profile is a good idea.
Also, isn't the frictional coefficient a constant?