Gap between keys

[mrbobbles]

Gday, I'm designing my first keyboard, to be CNC'd from plywood. I'm currently designing in Fusion 360, trying to lay out the keys correctly.

From what I understand, the keys have standard sizes (multiples of a "unit"), so, for example, a 60% keyboard is 15 units wide. However, there is a different number of keys on each row. Therefore, the gaps between keys on each row must be different. Otherwise, each row would have a different width.

Is my understanding correct?

It doesn't seem right though, since it would mean that the gaps in the bottom row are more than twice as large as the gaps as the top row, since there are fewer gaps. Any help would be much appreciated!

[ErgoMacros]

Hi,
1U (1 standard key width and height) = 0.75 inch.
Keys some in sizes like:
  1U
  1.25U
  1.5U
  1.75U
  2U
  etc...
6+ U for most space bars.

The spacing between the keys is, for planing purposes, 0.0. The keycaps are a bit less that 1U in both directions so the don't rub against each other.
Enclosing a typical 60% keyboard. The top row is a total of 15U side to side.
As are all the other rows.

Some keys are wider than 1U so fewer fit on a row.

So, in order to get the alpha, number, and modifiers all to come out even (15U) some keys are wider, some narrower. The spaces between are the same.

[mrbobbles]

Ok, thanks. So, the number of units is not actually the width of the key *cap*. It's more the space taken up by the key, with the actual cap being smaller to provide a gap.

So, I can create a grid of rectangles, with no gaps between them, and each rectangle being it's proper unit size.
Then if I place the centre of the switch at the centre of each rectangle, it should all work out?  (the gaps will be even, and the edges of the rows will line up)

[Findecanor]

Precisely. The edge of a keycap is about 1/2 mm in from the rectangle's edge. If you measure a 1×1u keycap's width, you will find that it is not 0.75" (=19.05 mm) wide, but rather very close to 18 mm.

BTW, in your case design, if you have a border around the keys that is raised above the mounting plate) then you should widen the opening by 1/2 mm in every direction so that you would get similarly spaced gaps around the keycaps as between them.

[mrbobbles]

Great, thanks! That makes perfect sense.

[funderburker]

I recommend using something like plate generator so you don't have to struggle with the measurements yourself. First, make a layout in KLE (keyboard layout editor) and then use the raw data (or download it in JSON) and just import that into something like swillkb or ai03 plate generator.

That'll help you with getting the right dimensions for switch cutouts, distance between switches and it'll add the "default" gap between keycaps as well.

Just some measurements I've written down for my own designs are:

• standard MX cutout - 14×14mm
• distance between switches (center to center) - 19.05mm (both vertically and horizontally)
• distance between caps - 0.95mm
• distance between cap and case side - 0.475mm

Calculation example (60% case):
width of a case: 6 + (19.05 * 15) + (0.475 * 2) = 3mm bezel on each side, gap between case side and caps on each side, 15 keys in row.

Edit: 19.05mm distance between switches are only correct if they are two 1u keys. So for something like a 1.5u and 1u key distance between their centers would be (19.05 * 1.5)mm.

[nevin]

@funderburker - well done.

[funderburker]

@funderburker - well done.

Thank you, I keep a "cheat sheet" so I don't forget these things.

[mrbobbles]

Thanks funderburker, that's really helpful!

I've seen the online layout generators, but I'm trying to do it from scratch to make sure I understand everything.

Also, since I'm cutting out of wood, to give it enough strength, I'm leaving a lot of material behind the "plate". So it won't just be a flat plate, it'll have a profile on the inside to make way for the switches, wiring, controller, etc. If that makes any sense...

My next mental roadblock is the spacebar cutout. More specifically, what is the distance between stabiliser cutouts for a 6.25U spacebar.

[Tom_Kazansky]

horizontal distance between two switches (vary size, center to center)

19.05 * (A + B) / 2

A: size of switch 1
B: size of switch 2.

the same apply for vertical distance.

I think you should use plate generator, I use swillkb's a lot. 

[funderburker]

Thanks funderburker, that's really helpful!

I've seen the online layout generators, but I'm trying to do it from scratch to make sure I understand everything.

Also, since I'm cutting out of wood, to give it enough strength, I'm leaving a lot of material behind the "plate". So it won't just be a flat plate, it'll have a profile on the inside to make way for the switches, wiring, controller, etc. If that makes any sense...

My next mental roadblock is the spacebar cutout. More specifically, what is the distance between stabiliser cutouts for a 6.25U spacebar.

Yeah, I totally get the idea behind a thicker plate with thinner cuts where switches clip in. With wood that's probably best. Mmm, a good place to start and just to double-check everything is by using a Cherry MX datasheet.

[Findecanor]

Mmm, a good place to start and just to double-check everything is by using a Cherry MX datasheet.

Hmm.. That datasheet lacks the specs for a 6.25u space bar.

The centre of each stabiliser mount is 0.5 units from the left and right edge of the space bar's rectangle respectively. (key, not keycap )
You could fit a 1×1u key on each stabiliser mount and either would be right next to its corresponding Alt key.
This rule applies to all space bars from 3.0 units and up to 8 units.

Stabiliser mounts for 2u, 2.25u and 2.275u keycaps are all 1.25u apart.

[mrbobbles]

Thanks everyone. I'd measured the length of the space bar wire, and got 100mm.

Using the rule provided by Findecanor, I get 5.25 x 19.05 = 100.0125, which is pretty much the same. This kind of information should definitely be more easily found!

I made a test cut for a regular non-stabilised key with a 1/8 inch bit, and it came out really well. I had to push the bit into the corners, to make the switch fit, which made some gaps near the corners. However, the lip of the Gateron switch just covered up the gaps, so it looks really good. I anticipate having more trouble with the stabiliser mounts though. I might need to do some manual cutting in the corners...

[Sintpinty]

But at the same time You don't want the gap to be too short, because that could make you accidentally type a key you didn't want to press.