# What type of glue would you use on set potentiometer screws on a PCB?

I want to set my potentiometer screws and then glue them in place so they will not be readjusted by the end user and I have seen green adhesive on them before? Any suggestions as to what is best to use on this type of application? Thank you.

• Place it in a box and leave the variable in case there is a reason to "recalibrate" whatever you had to calibrate. Why does it matter if an end-user breaks a device you sold them. They either have to pay you to fix it or to buy a new one. Even better, they easily resolved a malfunction and are impressed that you allowed your product to easily be repaired. This is not meant to say you may not have a reason, just something to think about. – Kortuk Jan 12 '12 at 19:34
• Nail varnish...? – Majenko Jan 12 '12 at 19:45

Loctite is often used. However there are many types. In general you hear people talk about blue, green and red (242, 290, and 271). Blue prevents inadvertent movement due to vibration and such. With moderate force the pot could be turned. Green is stronger, usually you need to apply a little heat before it can be turned. Red requires a lot of heat and would probably destroy the pot.

• +1 -- thanks; I wasn't familiar with the individual product #s. – Jason S Jan 12 '12 at 22:57
• Unless I am missing something, 242, 290, and 271 are completely unsuited for this task, they require an airtight metal to metal contact to cure, which you don't get by just putting a drop on a potentiometer. They'll also can damage plastics. Loctite 425 and 7400 on the other side mentions locking/tamperproofing potentiometers specifically in the datasheet, so those should work. – Grumbel Sep 30 '20 at 11:13

Hot glue might be your best bet, since it can be removed if one ever has to readjust the setting for some reason. You can get inexpensive guns like this one at any hardware store.

• Might want to add that a big advantage is, the hot glue adhesive does not wick into the innards of the potentiometer. – Frank Hileman Jun 12 '14 at 16:05
• But hot glue can leave strings of material attached to the circuit board. Some large company best known design methods absolutely prohibit the use of hot melt glue anywhere near electronic circuit boards. – Michael Karas Jul 27 '16 at 14:01

On trimpots I use automotive touch-up paint, available inexpensively in a variety of colors, and it comes with an appropriate applicator brush.

I'm really not worried about the pot moving by itself in most cases, I'm more concerned with detecting some dufus fiddling with the calibration settings (often to make up for something external that is wrong, such as a bad sensor or improper compensation).

In the instrument business we refer to such a change in calibration as "screwdriver drift". Have a unique color helps ensure that the fiddling can be reliably detected.

• I like the term "screwdriver drift". I've also seen whiteout used to similar effect – Adam Head Jan 31 '14 at 19:07
• Whiteout has the additional advantage that it's probably (almost) safe enough to drink, with minimum volatiles and a fairly benign MSDS. – Spehro Pefhany Jan 31 '14 at 19:19

If you want something temporary, hot glue is fine.

If you want something permanent, the canonical brand name for threadlocking compounds is Loctite. Not sure which Loctite compound to recommend -- they're usually not cheap ($40-$50 per 50ml bottle), but they're designed to retain mechanical screws despite vibration & temperature cycling. For a potentiometer, you could probably get away with general-purpose cyanoacrylate (aka Superglue sold in most stores).

Something to be aware of though: Whatever you use, make sure it's not corrosive. From Murata's website:

The only products which can be thread-locked are hermetically sealed products whose wiper and resistive element are not exposed.

Use thread-locking adhesive which does not contain substances that can corrode metals, such as chlorine and sulfur. When using thread-locking adhesive, carefully evaluate its performance on an actual potentiometer.

Don't use loctite! I purchased an amplifier with red loctite on a tiny pot with no sealing. This pot was to adjust bias, so I needed to move it when I changed power tubes. I managed to get the pot moving without breaking it by securing the body with pliers while I turned the moving part. Unfortunately, that loctite went right into the pot conductive area, and screwed up the pot completely over one half of its range. I can no longer use that range on the pot.

This is just one example, but there is more information available from the manufacturers of potentiometers and adhesives.

One solution is a good quality pot that does not turn easily by itself. Or you can use a pot with a smaller range in series with a fixed resistor, if you are worried about users choosing a bad range.

Another option is to use a sealant specifically designed for potentiometers. "Red" Locktite, and other commonly available sealants known by the name "Locktite", is for wicking into mechanical threads. However, the name "Locktite" is a brand name and not a specific product. The same company produces many types of adhesives, some of which are appropriate. According to the manufacturer, the product Locktite 425 is appropriate for sealing potentiometers.

A thicker product probably has less potential for damage. According to Murata, a trimmer potentiometer manufacturer, "The only products which can be thread-locked are hermetically sealed products whose wiper and resistive element are not exposed.."

• I believe your exercise was diametrically contrary to the purpose of the pot being sealed. Therefore your answer is not just invalid, it is outright wrong in the context the question applies to. -1 – Anindo Ghosh Jan 31 '14 at 19:37
• @AnindoGhosh The post did not state the pot was sealed. Locktite destroys unsealed pots. My experience provided a useful answer; you are incorrect. – Frank Hileman Feb 2 '14 at 20:58
• From the question in case you missed it: "I want to set my potentiometer screws and then glue them in place so they will not be readjusted by the end user". From your answer in case you missed it: "I managed to get the pot moving". You moved something that had had Loctite applied to it, which would not be done unless end user adjustment was undesirable. That's what people do to idiot-proof an adjustment setting. As per your post, they failed. I wonder why. – Anindo Ghosh Feb 2 '14 at 21:05
• It is foolish to assume a tube amplifier will not need its bias adjusted when the power tubes are replaced. Yet is is common practice to use locktite in these amplifiers. I believe the original designers assumed, as reflected in the discussions here, that locktite is harmless. – Frank Hileman Feb 5 '14 at 0:50
• @FrankHileman - It's foolish for you to assume that the OP is asking about making tube amps tamper proof. There are LOTS of places potentiometers are used. – Connor Wolf Jun 11 '14 at 22:24