why are panel-mount sockets often flattened on two sides?

[carl0s]

as per title really. Why is it done? Surely it just means it's a PITA to drill/mill a suitably sized hole?

I get that it means the socket won't rotate, *IF* you have exactly the right panel cut-out. But..  oh I suppose that's just it isn't it. If you can do a perfect cut out, you get the benefit of it not spinning in place. If you can only drill, then there's no difference. Guess I answered my own question.

Next question: Are there any tricks to making the cut out in a plastic project box? Perhaps you drill under-sized and then there's a special file or broach?
Maybe I'm overthinking it. I should just drill it and put a dab of glue to stop any potential spinning.

[TimFox]

Flats on male threads for BNC connectors, etc., are to stop the body from rotating when mating/unmating the cable.
The nut, even with lockwasher, eventually gives way due to the torque from the mating connector.
Expensive hole punches are available to make a perfect hole, and CNC mills can be programmed to make them.
A cheap solution is to merely use a center punch on the panel at the appropriate location around a round hole to collapse the wall a bit inwards.

[Kim Christensen]

For many common connectors, like D-sub, you can buy special punches for them.

For one off hobbyist projects, a set of files of various shapes and sizes will serve you well. Use needle files for really fine work. Simply drill the largest hole possible and file the rest.

[tooki]

It's done to prevent rotation. Milling off the flat sides of the thread is easy. And you must remember that the vast majority of devices aren't made by hand, they're mass-produced. In a plastic or die-cast metal enclosure you just mold the right shape hole to begin with. In sheet metal cases, the holes are punched as part of the stamping process for the sheet metal parts. And in modern CNC milled or laser-cut stuff, the CNC or laser takes care of it.

They are a PITA for prototyping. Yeah, you basically drill undersize and then file away at it. You don't need a "special" file, just a curved file with a reasonably appropriate width and curvature.

When possible, I try to find switches, potentiometers, and connectors that use alternative methods to prevent rotation, like an orientation pin or notch that is outside the main hole. Then you can just use a small file to file a notch for it, or a small drill to make a second hole, as the design requires.

There do exist, for some connectors/switches/pots, adapter washers that are punched with the flattened hole, and then have a pin to locate in an anti-rotation hole as above.

[tooki]

For many common connectors, like D-sub, you can buy special punches for them.

Why oh why must those things be so damned expensive? ::sigh::

[Kim Christensen]

Yea, those specialized dies are much too pricey for hobbyists. Had them at work and they were great for punching out metal panels.

One other option for the OP is to use aluminum PCBs from places like JLCPCB as faceplates and backplates with aluminum extrusions. Then you can have perfectly labeled front/rear panels with precisely milled out holes.

[tooki]

Yea, those specialized dies are much too pricey for hobbyists. Had them at work and they were great for punching out metal panels.

Heck, they're too expensive to justify getting at work, since we wouldn't use them that often.

[carl0s]

Thanks for the replies and thoughts/ideas everyone.

Yes the wobbliness of the nut is also a huge P.I.T.A.

I want to use these in some project box things that are actually used in production in a factory for something (just a computer terminal..), so I'd like to have them not fall apart within a year. I'll work something out based on all your ideas. cheers!

[langwadt]

you can also get washers that have a flat on the inside and a knob on the outside

https://ccsukltd.co.uk/INSULATING-WASHER-BNC-TNC-MOUNTING-PAD-10221-ST100539

[tooki]

Thanks for the replies and thoughts/ideas everyone.

Yes the wobbliness of the nut is also a huge P.I.T.A.

I want to use these in some project box things that are actually used in production in a factory for something (just a computer terminal..), so I'd like to have them not fall apart within a year. I'll work something out based on all your ideas. cheers!

Why do you think something would come apart in a year?

For pots and switches you’re not normally putting significant rotational stress on them. For connectors, when possible I get ones with square flanges. You have to drill 3 or 5 holes instead of one, but they’re all simple round holes.

[Doctorandus_P]

Apart from the rotation prevention, there is another reason. It makes the connectors themselves easier to make. Injection molds are made out of different sections that have to be separated to release the parts, and the seem between the parts usually leaves a small ridge on the part. This ridge interferes with the thread, but if it's on the flat sides it does not matter much, and the mold has a longer life span before it wears out and has to be replaced.

[mikerj]

They are a PITA for prototyping. Yeah, you basically drill undersize and then file away at it. You don't need a "special" file, just a curved file with a reasonably appropriate width and curvature.

A Dremel and a small HSS or carbide burr is faster, but also easier to mess up if you slip.