4PDT Toggle Too Tall So Pots Won't Stick Out Far Enough

[aviherman5]

Hi,

I'm having an issue where I have board mounted 9mm potentiometers and toggle switches. The 4PDT is too tall so much so that the pots won't go through the enclosure to the other side.

Any tips?

Thanks!

[ElectricDruid]

Errrm, "Don't" ?! 

Sounds like you might have to put the 4PDT on wires to the PCB.

More seriously, if you're going to board mount all the components, you *have* to make sure they're all of compatible mounting heights. That is usually a complete PITA in my experience, so I feel for you. Either the pots or the switches or something aren't available in the same height as the other thing, and you finish up putting padding washers on things to help level it up so it doesn't stress the board when you tighten the panel nuts down. Nightmare, honestly.

[soggybag]

Without a picture it's hard to tell the extent of the problem.

That said, if the gap in height not that great try putting the pots and switch in the PCB and do not solder! Put everything in the box with nuts on. Then solder!

Doing this will allow the pots to stand up off the board without their leads being pushed as far as possible into the PCB.

I have some pictures in this blog post: http://www.super-freq.com/bobtavia-by-bob-starr/

[Kevin Mitchell]

Is this for your own PCB design?
When I don't hand wire I put foot switches on a separate PCB and connect to the main board with a ribbon cable.

Also you don't want the strain of an actuating foot switch to be shared with the main PCB. Potentially asking for trouble. You may think it looks level, but if goes loose at all you may snap the PCB.

Edit:
Just noticed you said toggle switch and not foot switch. I assumed footswitch because my experience is different.
In my experience they mount fine with 9mm pots, just doesn't look great as the bushing sticks out a bit. Though I haven't tried a low-profile/short busing type which would be more ideal.

Pics? I'm curious.

[anotherjim]

Depending on the diameter of the pot shafts you might find an engineering/hobby metals supplier stocking tubing with an internal diameter that slips on the pot shafts with a good fit to make an extension. The trouble with rounds is size is super-critical for a good fit. 6mm won't ever fit over 1/4" even though the difference is only 0.3mm although you can slit an undersized tube to expand over the shaft.

[aviherman5]

Thanks for all the replies and suggestions!

As asked, I'll attach some pictures tomorrow.

This definetly is a complete PITA

[Processaurus]

For this one, board mount the toggles, but put the 9mm pots on wires. Or solder heavy hookup wire to the pot legs to extend them down.

As far as the pcb design, go back to the drawing board. The 16mm Alpha pcb mount pots are ok with the Taiway toggle switches. I've used 1/4" washers to space the pots down if the height isn't right, but then you barely have enough thread on the collar.

[Kevin Mitchell]

Okay let's just spit out some details in reference to Alpha 9mm pots & a typical 4PDT Taiway toggle switch.

The pot allows 10mm from PCB to top of the body/start of the threaded bushing. With the height of the threaded bushing you have 15mm. The nut is 1.2mm thick, so you have 13.8mm to work with.

Hammond enclosure is ~1.8mm thick. So now you have 12mm to work with.

The toggle has a body height of ~11mm.
Some toggles have extra plastic to separate the lugs/leads. Some also have a slight bevel on the top of the body before the bushing (avoid those).

So it looks like it's a close call. What can we do to maximize this allowance with the 9mm pots?
-Raise the pots slightly so they're not soldered flush to the PCB
-Assure the toggle is firmly pressed down.
-Avoid toggles with the extra features that I had noted

[amptramp]

There used to be long radio and television knobs that were designed for controls mounted at the side of a chassis so that when you wanted to pull the chassis straight back, you took off the knob and the pot shaft cleared the cabinet so you could pull straight back.  The part of the knob that fit on the shaft was long enough that you could use a short pot shaft and the part that you put your hand on started some ways above the shaft.

In the radio shown here, the tuning knob is at the side and the only way the chassis can pull out is if the knob extends into the cabinet and is long enough to use a short shaft on the tuning capacitor so the chassis can pull straight back without the cabinet interfering with the shaft:



Knobs like this were made for volume controls as well and extended knobs may be available but they used to be used far more than they are now.

[duck_arse]

The toggle has a body height of ~11mm.
Some toggles have extra plastic to separate the lugs/leads. Some also have a slight bevel on the top of the body before the bushing (avoid those).

always fit a nut under the panel on toggle switches. that way, the mounting stresses are taken on the bush/nuts/threads, as designed. with no under-nut, the switch body rides against the panel and the body-to-bush joint is stressed - there is many a switch with a crappy joint design out there.

[Kevin Mitchell]

The toggle has a body height of ~11mm.
Some toggles have extra plastic to separate the lugs/leads. Some also have a slight bevel on the top of the body before the bushing (avoid those).

always fit a nut under the panel on toggle switches. that way, the mounting stresses are taken on the bush/nuts/threads, as designed. with no under-nut, the switch body rides against the panel and the body-to-bush joint is stressed - there is many a switch with a crappy joint design out there.

Per usual, you share valid facts. But this will only make the OP's problem worse.
Sometimes you have to do the ill-advised to make use of what you have. Even if it'll upset an engineer or two 

What this means is that these traditional toggles do not jive with 9mm pots at all. But obviously that doesn't stop folks from trying & most of the time getting away with it.
Learn now, do it better the next time.

[Processaurus]

Side note about PCB mounted parts, while it is tempting to solder the controls to the pcb and then assemble to the box, it is much better to fasten the parts in the box loose finger tight, then wrestle the pcb in. Then tighten the nuts down, then solder. Everything comes out perfectly, microscopically the right height and there is better reliability by having no built in stress on the solder joints from being under constant tension.

[ElectricDruid]

Side note about PCB mounted parts, while it is tempting to solder the controls to the pcb and then assemble to the box, it is much better to fasten the parts in the box loose finger tight, then wrestle the pcb in. Then tighten the nuts down, then solder. Everything comes out perfectly, microscopically the right height and there is better reliability by having no built in stress on the solder joints from being under constant tension.

+1 agree. I sometimes go with a slightly-easier-to-manage halfway house: tack solder one leg of each pot to keep it in the pcb, then fit the whole thing into the enclosure, then resolder properly. I find trying trying to fit a PCB onto the legs of several upside down pots at once to be a total nightmare, so this avoids that problem.

The key point though is to avoid that stress on the joints by having done the joints after the parts are in the box, as you said.

[Ben N]

That said, if the gap in height not that great try putting the pots and switch in the PCB and do not solder! Put everything in the box with nuts on. Then solder!

Doing this will allow the pots to stand up off the board without their leads being pushed as far as possible into the PCB.

In my experience this works better with 16mm pots than 9mm, just because of the bends in the pot legs, but with a bit of creativity and your needle nose pliers you can finagle a bit more flexibility out of them.