The major dimensions are pretty basic all quoted dimensions are what I have measured on Cherry caps, others may have different measurements for the same caps, this is the nature of the real world. The heights and pitches of all faces vary from row to row, however, there are some constants.
A single caps footprint is 17.7x17.7mm and they're arranged on keyboards at 19mm centres. Thus a 2x key is 19+17.7=36.7mm, not 17.7+17.7=35.4mm just to clarify.
The sides of a given row are identical regardless of key width.
The radius of curve on a cap varies depending on it's width, the curve has a constant depth of 0.5mm at its centre regardless - I've taken "down" to be in line with the front face, and the rear face at the respective edges of the top, rather than straight down in the Z-axis, I don't know if this is correct, but it's much easier to draw!
The stem is always centred on the footprint not the top and is 0.7mm higher than the bottom of the cap.
Wall thickness is 1.45mm (OEM I have measured out at 0.8mm)
Included in the file will be two sets of caps. One which looks like Cherry caps, whilest the temptation is simply to scale one of these to the correct size, it will give you a key with too narrow a top, and sides which are too steeply sloping. One has to start with the second set of caps, which are the outer profile pre-chamfering, from this create a cap of the appropriate footprint by moving one side face across. Keep this as a group and work outwith it so as not to muddle your faces.
Create two arcs from either pair of top corners, front and back with a drop of 0.5mm at the centre, play join the dots first by parallels then by diagonals within to make a face make the face a group. Congratulations, you now have all four faces, or so you think, next comes the first tedious bit.
Pick one side face, and on its top front and back corners make a 1.5mm radius circle with a 1.5mm offset from each edge, it should be "flat" to the plain of the original uncurved top. Trim off the inner three quaters, join each point of the remaining quarter to the corresponding bottom point. Join the bottom corners, and the inner ends of your arcs, this won't give you a face; I sub divide these lines by mid-points four times (i.e. halved, quartered, eighthed and sixteenthed) then diagonals to make a face. Group the face and the chamfered corners.
Hide the template cap. Intersect the side group and the top group unfortunately ungrouping and telling SketchUp to intersect won't work, it's to complex a geometry for it. You'll have to intersect the two groups separately. Once complete, duplicate the side group, mirror it and position it opposite it's original and repeat the intersection on the top. You can work with half a top, and duplicate and mirror this it's quicker, but I prefer an unbroken face to a merged pair... it just seems neater.
Ungroup the top and the sides, draw in the last two bottom lines, this should complete the front and back faces, if not you've done something wrong, but probably not very, and if you make a triangular array then it'll never show
That's how to make the outer form. I'll type up how to do the inside once I've done a stem and etcetera.
