How much spacing do I need inbetween each keyswitch?

RadikulRAM

04 Sep 2016, 12:30

I'm looking to make my own KB, and now to design the PCB I need to know how much spacing I need. Does the size of keycaps vary greatly? I've got Vortex PBT double shots right now, would they be a different size to DSA keycaps in width?

These keycaps are roughly 18x18mm.

I'm guessing that I need to create 19mm squares (1mm on right side of key cap), to be able to put on the keycaps with 1mm of spacing in between them.

Are there any sample PCB designs I can use here, or do I have to make mine from scratch? I need to make a layout like this:
http://yager.io/keyboard/1a.png so I can print it and make the PCB.

Edit: Here is the layout I'm looking to make: http://i.imgur.com/DTN559x.png
What program can I use to make it? I found an online pcb viewer: http://3dbrdviewer.cytec.bg/

I used it to load the PCB (found here: https://github.com/wyager/micromechboard). I'm looking to create that type of PCB, not this type w/images/d/d0/KiCAD_tutorial-Complete_schematic.png

Findecanor

04 Sep 2016, 13:39

The standard spacing, I.e. one "key unit" is 3/4 inches square, which is 19.05 mm. 0.05 mm is so small, so I think that you could use 19 mm if that makes it easier in your design tools.
All keycaps for Cherry MX are made for that spacing. All keys are in multiples of a quarter unit, I.e. 1u, 1.25u, 1.5u, 1,75u etc. All keycaps have the switch in the centre of the key (not on 1/4 unit intervals..), with the exception of 6.25 and 6 unit Space bars on keyboards made by Cherry itself.

There is a KiCAD keyboard PCB design guide in the Wiki. Besides KiCAD you would also need the footprint files for Cherry MX switches. Links are at the bottom of the Wiki page.

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matt3o
-[°_°]-

04 Sep 2016, 14:42

as per cherry specs: side to side is 5.05mm. center to center 19.05.

1u full size (including keycap) would be 19.05x19.05. So --for example-- 1.5u would be 28.575x19.05.

PS: I know .05 might seem nothing but on a 6.25u unit becomes 0.3125 which is quite something.

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lot_lizard

05 Sep 2016, 04:16

19.05 applies to IBM legacy switches as well. As a person that has fought to retrofit the legacy designs... .05 is MASSIVE across the entire board (x 15+ keys even on a TKL). Cherry inherited the IBM spacing. 19.05mm is the universal truth.

HuBandiT

05 Sep 2016, 09:50

If you are fitting into an existing case, measure the spacing for yourself, I seem to have met some (admittedly somewhat exotic) European boards that actually used a 19,00 mm pitch.

as mentioned above, 19,05 mm comes from three quarters of an inch (25,4 mm) - which might help you set up a grid easier in PCB layout software that allows using inches (which I guess most do :) ).

so if you design from scratch for yourself, use 19,05 mm, if you design into an existing case, measure, measure, measure. :) but even in that case most probably 19,05 or 19 mm. :)

HuBandiT

05 Sep 2016, 10:09

matt3o wrote: PS: I know .05 might seem nothing but on a 6.25u unit becomes 0.3125 which is quite something.
Are you thinking 0.3125 inches (about 8 mm - almost half a key)? Because my math says it comes out to 0.3125 millimetres (about 12,5 mil or thousandth of an inch - less than the size of a dot on your semicolon key) which might look a little ugly/crooked, but in the big picture should not really hurt much functionally.

Oh, the fun of mixing multiple units of measurement in the same conversation. That or your aesthetical tolerances are much tighter than mine. :)

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matt3o
-[°_°]-

05 Sep 2016, 10:52

I never use inches

Findecanor

05 Sep 2016, 14:00

Yes, it adds up. I was thinking only of smaller keys, sorry.
If you are making or refitting a case with side-borders then measurements should be more exact. Do add a 1/2 mm gap between a group of keys and its border so that the spacing from keycap to border becomes the same as the spacing between keycaps themselves.

pomk

05 Sep 2016, 14:37

HuBandiT wrote:
matt3o wrote: PS: I know .05 might seem nothing but on a 6.25u unit becomes 0.3125 which is quite something.
Are you thinking 0.3125 inches (about 8 mm - almost half a key)? Because my math says it comes out to 0.3125 millimetres (about 12,5 mil or thousandth of an inch - less than the size of a dot on your semicolon key) which might look a little ugly/crooked, but in the big picture should not really hurt much functionally.

Oh, the fun of mixing multiple units of measurement in the same conversation. That or your aesthetical tolerances are much tighter than mine. :)
Although 0,35mm might not sound like much, it may be enough to cause chafing between the keys, as they are designed with the 19,05mm in mind. I.e. nU key is 19,05 x n wide minus some margin. If the margin is close to the max(n) x 0,05 you will have chafing issues.

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kbdfr
The Tiproman

05 Sep 2016, 16:06

pomk wrote:
HuBandiT wrote:
matt3o wrote: PS: I know .05 might seem nothing but on a 6.25u unit becomes 0.3125 which is quite something.
Are you thinking 0.3125 inches (about 8 mm - almost half a key)? Because my math says it comes out to 0.3125 millimetres (about 12,5 mil or thousandth of an inch - less than the size of a dot on your semicolon key) which might look a little ugly/crooked, but in the big picture should not really hurt much functionally.

Oh, the fun of mixing multiple units of measurement in the same conversation. That or your aesthetical tolerances are much tighter than mine. :)
Although 0,35mm might not sound like much, it may be enough to cause chafing between the keys, as they are designed with the 19,05mm in mind. I.e. nU key is 19,05 x n wide minus some margin. If the margin is close to the max(n) x 0,05 you will have chafing issues.
Most probably not, because it is a matter only of the keycaps and not of the switches,
and you cannot add the 0.05mm difference over the whole keyboard but must always consider two adjacent switches.

Measuring not with laboratory equipment but with a simple graduated ruler,
I find 10 original Cherry keycaps in a row (not on switches) to be something like 18.25 cm,
i.e. a cap would be approx. 18.25 mm wide.
If your switches are in a 19mm instead of 19.05mm grid,
the interval between two caps will be 0.75mm instead of 0.80mm,
which is a negligible difference in terms of physical interference.

The same conclusion obtained not from mathematical considerations, but by simple observation:
as the difference between 19.05mm and 19mm (for the switches, i.e. for the keycap stems) is 0.05mm,
look at the space between two caps on a standard keyboard and diminish it by 0.05mm,
i.e. a twentieth of a millimeter. No way caps would interfere.

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matt3o
-[°_°]-

05 Sep 2016, 18:38

guys do not derail. the specs say 19.05mm why would you want to do anything different?

(not to mention that laser cutters already have a margin of error)

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OleVoip

05 Sep 2016, 19:24

lot_lizard wrote: Cherry inherited the IBM spacing. 19.05mm is the universal truth.
HuBandiT wrote: If you are fitting into an existing case, measure the spacing for yourself, I seem to have met some (admittedly somewhat exotic) European boards that actually used a 19,00 mm pitch.
In Germany, the spacing was standardized in 1927 to be 19±1 mm (DIN 2111), copying the 3/4 inch that was found on american typewriters of the era, which ruled the market (no IBM, yet). In 1976, the tolerance was reduced for alphanumeric computer keyboards to be ±1 mm between any keys of the alphanumeric section (DIN 2139), meaning that 11 u must equal 209 ± 1 mm, still allowing for 1 u being 19.05 mm. After DIN 2139 was withdrawn, this specification eventually found asylum in DIN 2137-2:2012, waiting to be superseded by an ISO standard for it, which doesn't exist anymore. ISO 1091:1977 used to specify 19 ± 1 mm as the vertical and horizontal spacing between key centres of adjacent letter keys, but it got withdrawn 1994 in favour of the ISO 9995 series, which AFAIK lost that spec.
Last edited by OleVoip on 16 Sep 2016, 10:51, edited 1 time in total.

pomk

05 Sep 2016, 21:46

kbdfr wrote: Most probably not, because it is a matter only of the keycaps and not of the switches,
and you cannot add the 0.05mm difference over the whole keyboard but must always consider two adjacent switches.
You fail to take long keys into account, where the adjacent switches are actually quite far apart. Also should you use a manly 8U spacebar, you will encounter problems at least with cherry stabilizers being in the wrong position when compared to the stems in the keycap.

Edit: of course you are correct in a sense that if the keycap manufacturer decides to force some other dimension for 1U, things change.

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