PCB - cuttling hole in half. Safe or not?

[temol]

I've designed a pcb for 1590a enclosure and it turns out that potentiometers outermost mounting holes are located at the edge of the board. I know that some of the Chinese fabhouses have an  option for this - castellated holes. But the price goes up from 5$ to 20$ per order. Do you think it's possible to cut ordinary plated hole in half, without damaging it? If cutting isn't an option, than maybe sanding it down?

[Juan Wayne]

For 5 bucks an order? I'd give it a try on a couple boards, you know, for science. If you're gentle enough and use proper tools, I think it'll be just fine.

[vigilante397]

If you're gentle enough and use proper tools, I think it'll be just fine.

+1 Especially if it's just a mounting hole, I wouldn't worry too much about it. A nice sharp saw or a cutting wheel on a dremel should make quick work of it and I wouldn't anticipate any problems.

[diffeq]

If you add a V-cut line right through the hole, you might be able to snap it cleanly. Or not.

Just a thought: why not make outer pads just an outline and simply not soldering those lugs? A house stands on four corners, surely a pot will stand too.

[vigilante397]

why not make outer pads just an outline and simply not soldering those lugs?

Also a reasonable option. They're going to be soldered on the 3 pins and one of the mounting pins, plus they already sit flat on a PCB. Leaving of the pin also shouldn't be a problem.

[R.G.]

It depends on what knobs you're using.

No, seriously. If you are using knobs that have 18-tooth knurls, the knobs can go on the shaft in nearly any rotational position. This means that the knob pointer position isn't tied to a shaft flat, and so the pot can be an any rotation on the board without damaging the looks of the front panel.

And that gets you to where you can rotate the pots a bit on the PCB (maybe) and move the mounting leg hole back onto the board. The pots won't be in a nice horizontal/ vertical orientation, but the soldered pins will be solid.

As an alternative, make the half holes be unplated. Soldering a pin into a half hole on an edge is not a good idea because the solder joint is highly exposed to cracking unless the part is constrained to the PCB very well in other places. You're counting on using the solder as glue, and solder is a very poor glue. When the part is in place and the board is tested, dab a bit of epoxy on the half-hole and pin. Epoxy, used properly is a good glue. This setup reinforces the other solder joints.

[temol]

Thank you all for the replies.
I'm not going to use knobs this time. Those are tone stack potentiometers, 9mm size, plastic shaft, board mounted. And I've just realized that with potentiometers like this, without mounting nut, one solid mounting leg may be ok or may not..
It's not possible to mount this potentiometers in a different orientation unless I'd make new pointer on the plastic shaft. Another option is to move LOW and TRE lower and away from the edge.

T.

[LiLFX]

PCB fabricator checking in...

Castellated holes are a cost adder because cutting the board outline can tear the plating out of the hole wall. You need a brand new really sharp contour router, but they dull out quickly, and it's likely they will use multiple new ones on your project. If you don't want the cost adder you can always modify the part in your library to exclude the holes that will be castellated or you can modify your board outline to include that pad within PCB.

[R.G.]

So make the hole a notch and use JB Weld.