Product to secure trim pots against vibration - Page 1
Forum section: electronics / projects

author: ivan747
author_rank: Super Contributor
timestamp: December 13, 2019, 06:41:12 pm
content: Hi guys, Do you happen to know of a product designed or commonly accepted by the industry as a locking compound for trim pots? I have some tiny trimmers I need to fix in place. I have a product that must be baked at around 70 degrees C and is subject to vibration.

author: MT
author_rank: Super Contributor
timestamp: December 13, 2019, 06:56:42 pm
content: I was to say your mom's or girlfriend nail polish is splendid. If you dont have a mom or girlfriend you go to those "1 dollar stores" and buy some cans for 2 dollar who will last a life time. The nail polish have the properties of being stiff without cracking. But i dont think it withstand baking at 70 deg, so instead you can use transformer isolation lacquer that is designed for baking process stage in rewinding transformers. This can be had for free from train/power station transformer repair shop.

author: jhpadjustable
author_rank: Frequent Contributor
timestamp: December 13, 2019, 07:00:20 pm
content: Loctite SF 7400is formulated for this application. You might want to ping Henkel and ask how well it stands up to a bit of heat.

author: tggzzz
author_rank: Super Contributor
timestamp: December 13, 2019, 07:01:39 pm
content: Quote from: ivan747 on December 13, 2019, 06:41:12 pmEven if you lock the screw of the trimpot to the housing, you still have to consider whether the contact will bounce when vibrated. If it is operating while being vibrated, that would be equivalent to introducing noise.

author: JackJones
author_rank: Regular Contributor
timestamp: December 13, 2019, 07:11:51 pm
content: Quote from: jhpadjustable on December 13, 2019, 07:00:20 pmQuoteThe linked page says up to +145°C, should be plenty of headroom for baking at +70°C

author: mzzj
author_rank: Super Contributor
timestamp: December 13, 2019, 08:38:52 pm
content: Quote from: tggzzz on December 13, 2019, 07:01:39 pmMultiturn trimpots are especially suspicious as threre is considerable slop between the actuating screw and the sliding contact. Gluing the screw wont secure the internal parts against vibration.I usually give multiturn pots couple of light taps with a small screwdriver in hopes to settle the sliding contact to ”neutral” position.

author: coppercone2
author_rank: Super Contributor
timestamp: December 14, 2019, 07:05:27 am
content: if you use threadlocker, do not use the one meant for metal.it can make plastics brittle and mess with them, if you think you can exploit the fact that the shaft is often brass. normally for this, you can either use superglue, which is brittle, or a special threadlocker meant for plastic, which is a bit gummy that does not offer such a mechanical impedance discontinuity. as usual you need to clean everything with alcohol before usehttps://www.vibra-tite.com/threadlockers/low-strength-threadlocker/vibra-tite-325-plastic-threadlocker/The electronics product might be better because there is not much room for contact area in the potentiometer head vs a plastic bolt, so it might be formulated differently to add strength in the fillet rather in the thin contact region.

author: Zero999
author_rank: Super Contributor
timestamp: December 15, 2019, 07:57:57 pm
content: I try to avoid trimpots in designs wherever possible. I prefer to connect a precision resistance box, set the value to the one which gives the best performance/correct circuit parameter and solder a suitable resistor network in place. There are also ways of achieving a similar thing which chains of resistors which can be removed by cutting the track or shorting with a jumper/solder, until the circuit works properly.

author: Gyro
author_rank: Super Contributor
timestamp: December 15, 2019, 08:32:04 pm
content: Quote from: Zero999 on December 15, 2019, 07:57:57 pmAn approach illustrated nicely in the old National Semiconductor Linear Brief No 46 by Bob Pease for adjustable voltage regulators...https://www.ti.com/lit/an/snva582/snva582.pdf

author: IconicPCB
author_rank: Super Contributor
timestamp: December 16, 2019, 12:56:45 am
content: Try liquid paper

author: tooki
author_rank: Super Contributor
timestamp: December 16, 2019, 02:46:44 pm
content: Quote from: IconicPCB on December 16, 2019, 12:56:45 amCorrection fluid has practically zero mechanical strength. I don’t think it would help against vibration one tiny bit.