mounting potentiometer - Page 1
Forum section: electronics / beginners

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: May 20, 2019, 05:30:54 am
content: Does this small tab need to be entirely on PCB or need to protrude out and contact wall onto which it will be screwed onto?https://www.digikey.com/products/en?keywords=P091S-QC15BR50K

author: Dundarave
author_rank: Regular Contributor
timestamp: May 20, 2019, 05:40:03 am
content: When inserted into a small corresponding hole in the panel it’s being installed in, it acts to prevent the torque caused by the nut tightening from twisting the pot out of the circuit board.

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: May 20, 2019, 05:54:06 am
content: But that slot making contact with panel would cause it to be mounted unevenly.

author: floobydust
author_rank: Super Contributor
timestamp: May 20, 2019, 05:56:32 am
content: It's supposed to go into a cutout (hole) on the front panel.Tightening the nut, or cranking the knob can otherwise rip the potentiometer off the PC board. The pins can't really stop the body from rotating.You can buy some without the anti-rotation tab.I mount the green body at the PCB edge, so the cast portion sticks out.

author: Zero999
author_rank: Super Contributor
timestamp: May 20, 2019, 08:22:40 am
content: Quote from: LaserTazerPhaser on May 20, 2019, 05:54:06 amThe tab doesn't take up much space, just drill a small intent in the panel. The drill should be a little wider than the tab and be careful not to drill too deep: the hole should be blind, i.e. not go all the way through the panel.

author: Gregg
author_rank: Super Contributor
timestamp: May 20, 2019, 09:51:33 pm
content: Another way is to file a slot from the hole in the panel to accommodate the tab so it won't twist and cover the slot with the washer

author: james_s
author_rank: Super Contributor
timestamp: May 21, 2019, 12:26:18 am
content: You can also just break the tab off if you're mounting it to a panel that lacks the slot. Obviously it won't get the additional strength the tab provides but it will work as well as a pot lacking the tab in the first place.

author: Brumby
author_rank: Unknown
timestamp: May 21, 2019, 12:44:33 am
content: I would not break off the tab. Preventing the pot body from turning is not really a "nicety" in my book. It is a necessity, especially for PCB mounted ones.If your front panel is too thin and/or you don't want to try putting a hole in the back of it, then I would suggest a secondary panel between the front panel and the pot, with the appropriate holes drilled right through it. To stopthispanel from rotating, all you need is another pot, switch, etc mounted on the front panel and/or have at least one edge of it resting against the body of the enclosure.This approach can be taken further, in that you can have all the pots, switches, etc. mounted to such a panel which is part of the chassis and just have the front panel as a "dress" panel, having nothing mounted on it - just the labels, logo and livery. My HP5381A frequency counter does exactly this and the concept is quite common.

author: james_s
author_rank: Super Contributor
timestamp: May 21, 2019, 02:07:53 am
content: I've broken the tab off numerous times, it works fine for the most part, I mean you can in most cases buy the same pot without a tab on it in the first place, the tab is an optional design feature. If you get the nut snug enough then it won't go anywhere, there should not really be a tremendous amount of force on a pot. If it is likely to be abused then the tab provides additional strength.

author: tkamiya
author_rank: Super Contributor
timestamp: May 21, 2019, 02:20:34 am
content: I always clip that off....

author: wraper
author_rank: Unknown
timestamp: May 21, 2019, 02:28:38 am
content: Quote from: Zero999 on May 20, 2019, 08:22:40 amThere is no reason why it should not go through the panel unless you use tiny knob.

author: wraper
author_rank: Unknown
timestamp: May 21, 2019, 02:32:10 am
content: Quote from: james_s on May 21, 2019, 02:07:53 amAnd after some time, nut becomes a bit loose and problems start to happen.QuoteAnd abuse pot/PCB even before device was made.

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: May 21, 2019, 07:58:03 am
content: Quote from: wraper on May 21, 2019, 02:32:10 amWould a few drops of cyanoacrylate onto potentiometer threads under nut prevent it from becoming loose?

author: Zero999
author_rank: Super Contributor
timestamp: May 21, 2019, 08:06:13 am
content: Quote from: LaserTazerPhaser on May 21, 2019, 07:58:03 amYes, but then undoing it will be virtually impossible.

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: May 21, 2019, 12:04:58 pm
content: Quote from: Zero999 on May 21, 2019, 08:06:13 amPliers should take it off quickly after initial turn breaks adhesive.

author: james_s
author_rank: Super Contributor
timestamp: May 21, 2019, 04:33:19 pm
content: If you have trouble with it loosening up, use a drop of threadlocker, it takes only a very little. In practice I haven't really had problems with that, just tighten it reasonably snug and it will be fine.

author: Nominal Animal
author_rank: Super Contributor
timestamp: May 22, 2019, 11:16:42 am
content: The part with the nub is typically zinc, and will easily snap off cleanly using pliers or side cutters.Instead of thread locker or supergluing the potentiometer to the front plate, I suggest gluing or screwing in small brackets to the front plate on either side of the potentiometer, to stop it from rotating wrt. the front plate. If you have a 3D printer, you can print a small collar with a square (rectangular) hole, and glue that to the face plate. It does not need to be thick at all, a couple of mm suffices. Larger face plate area means the forces will be spread to a larger area, and glue will hold better. It only depends on what you have next to the potentiometer on your face plate.