Clearance size for buttons in panels?

[intellijel]

So I am in the process of designing a PCB that will have a bunch of tact switches on it. Each tact switch has a square cap that is 10mmx10mm and they have a geometric tolerance of +/-0.2mm.  So if I am designing the openings for these on a panel design the squares have to be bigger than 10.2mmx10.2mm but what should the ideal size be? e.g. How much clearance should I design in?  0.1mm? 0.2mm? ??

thanks,

Danjel

[Wilba]

It depends on who is making the panel.

If it is Front Panel Express or Schaeffer, you can't make a perfectly square hole, since it is routed with a minimum 1mm diameter "cutter" bit, so the square hole will have rounded corners of a minimum of 0.5mm radius. So I think it would be a good idea to make the hole 10.5mm x 10.5mm so there would be a 0.5mm gap around the cap, and the corners of the cap would then be in the centre of the rounded corner. If you make it any less than 0.5mm then it might have enough clearance on the edges but not the corners.

This is only a suggestion, I have not yet ordered square holes from FPE to fit a switch cap to give first hand experience, but I do know their 3mm and 3.5mm round holes are so close to exactly 3mm and 3.5mm that I can't measure a difference with my el cheapo digital calipers.

[seppoman]

it also depends on the possible sideways travel, i.e. if and how much the switch top can be moved horizontally or be tilted. If the buttons are slightly unstable in these directions, then take that into account, too. You don't want the buttons to scrap along the border or get stuck when you press them. Most buttons are at least slightly unstable, so depending on that 10.5x10.5mm or even 11x11 mm holes can be reasonable. If your buttons are 10.2, that still means the gap would be only 0.2mm or 0.4 mm per side, which is perfectly acceptable in my opinion.

S

[intellijel]

yeah I was figuring 11x11mm to account for slop but also to account for possible alignment issues with he PCB (I forgot to factor in those tolerances). Just for an example the buttons on my Nord Lead 2 have almost a 1mm gap around them.