Proper way to mount binding posts in a metal front panel? - Page 1
Forum section: electronics / beginners

author: ledtester
author_rank: Super Contributor
timestamp: December 10, 2018, 05:04:17 am
content: I am mounting a pair of 5-way binding posts into a metal front panel, and I'm concerned about the shafts shorting with sides of the hole I've drilled.For now I'm using heat shrink to insulate the first centimeter or so of the screw threads, but I was wondering what the standard solution is.

author: RobertHolcombe
author_rank: Frequent Contributor
timestamp: December 10, 2018, 05:20:51 am
content: There are similar style panel mount which are designed with isolation in mindhttps://www.pomonaelectronics.com/sites/default/files/styles/product_image__500px_x_450px_/public/products/slideshows/2143.jpg?itok=aFdDx7yrOr more commonly the individual panel mount jackshttps://uk.farnell.com/productimages/standard/en_GB/1654713-40.jpg

author: beanflying
author_rank: Super Contributor
timestamp: December 10, 2018, 05:27:40 am
content: Not use the one you have. Most of the ones I use have a raised washer to keep it away from the metal. Even the very cheap and nasty ones.The one on the right is Beryllium Copper and if you have to ask the price you don't need itYour heatshrink is sort of OK but maybe look at an alternate.Better - Make or 3D print some stepped washers then over drill your holes to suit.

author: Ian.M
author_rank: Super Contributor
timestamp: December 10, 2018, 06:48:44 am
content: A cheap and dirty way that's only suitable for low voltages is to put a close fitting O ring over the stud, slightly thicker than the panel and drill the hole to just clear the O ring OD, measured when its on the stud. For high voltage work, you need proper insulating shoulder washers (aka: 'Top Hat' washers) with a bush long enough to provide enough creepage distance + a thick back washer to support the long bush. I would be very reluctant to trust 3D printed ones a they really need to be a solid piece of plastic with no micro-voids or other defects. Such washers are commercially available, but you may have difficulty finding them in the flange and bore diameter combo you need.

author: beanflying
author_rank: Super Contributor
timestamp: December 10, 2018, 06:58:21 am
content: Quote from: Ian.M on December 10, 2018, 06:48:44 amSo what you are saying is a void or 'Air Gap' is an issue or may be lower resistance than fully formed plastic, show me the data?Typical 3D printing done properly has no defects on a well setup machine but like any manufacturing process including injection molding can have flaws done badly. Where it may lack a little is strength but PETG, Nylon or even Poly Carbonate will take care of that at a doddle.O'Rings are simply WRONG!

author: brucehoult
author_rank: Super Contributor
timestamp: December 10, 2018, 07:15:27 am
content: Quote from: beanflying on December 10, 2018, 06:58:21 amWhat about rubber grommets?Of course just getting the mounting posts that already come with insulation would be better.

author: beanflying
author_rank: Super Contributor
timestamp: December 10, 2018, 07:16:44 am
content: Please indicate to me the micro voids and defects on this 0.2mm thick single layer washer let alone using multiple layers that would be required for a stepped washer? I have even back lit it to make this easier.Quote from: brucehoult on December 10, 2018, 07:15:27 amBiggest issue with rubber is it rolls or gets pinched by nuts and washers and can roll out of the way completely under pressure.

author: Ian.M
author_rank: Super Contributor
timestamp: December 10, 2018, 07:18:00 am
content: A micro-void is fine till the combination of plasticiser migration, environmental contaminants and humidity leaves it with a somewhat conductive surface film. There's also the risk of stress cracking starting at the void (or sharp interior corners).Yes, O-rings are wrong (I did say 'cheap and dirty'), but for low voltages, they do the job - providing insulating gap filling - more reliably than sleeving the stud with heatshrink. . .

author: beanflying
author_rank: Super Contributor
timestamp: December 10, 2018, 07:24:02 am
content: If you use that logic then ALL plastics will get a somewhat conductive film not specific to 3d printing. As I said show me the void! It is extruded as a circular filament there is NO sharp interior corners on small 100% infill items like washers.As to porous/trapped moisture or similar with modern 3D printing have a look at this.https://youtu.be/WNvXFYG-C2s

author: Brumby
author_rank: Unknown
timestamp: December 10, 2018, 07:37:52 am
content: Quote from: ledtester on December 10, 2018, 05:04:17 amThe standard solution is that the insulating pieces that clamp against the panel have a raised section that sits in the hole through the panel. The terminal/conductor/thread then passes through a smaller hole.Something like this:That set of terminals is the sort that could be used in a non-conducting panel - but if you want to use then in a metal panel, then you are going to have to provide something to keep the thread right away from the panel.The O-ring idea is one approach - but I'd be more in favour of a plastic washer type solution. If you can't find one, make one. Find a plastic sheet about the same thickness as the panel and cut a disc from it. Put a hole in the middle for the thread. Drill the hole in the panel big enough for the washer to fit. Assemble and done!Check dimensions before committing. You don't want the washer so big it will be visible and you don't want it thicker than the panel.

author: Jeroen3
author_rank: Super Contributor
timestamp: December 10, 2018, 07:52:10 am
content: Shorting to chassis is not a problem with proper binding posts. Stop buying that cheap stuff.930103101 - Binding Post, PKI 10 A SeriesThis one has plastic bushing in and around the hole on both sides.Look for yourself in thisthis model.

author: David Hess
author_rank: Super Contributor
timestamp: December 10, 2018, 06:38:38 pm
content: Binding posts intended for a metal panel include an insulating flange. Hardware kits for some power packages like TO-220 also include an insulating washer with a flange to isolate the tab from the mounting hardware.I like Ian.M's o-ring idea but have not used it myself. I think o-rings would be more reliable than heat shrink tubing and as good if not better than a small insulating washer that fits inside the hole in the chassis.

author: Gyro
author_rank: Super Contributor
timestamp: December 10, 2018, 07:22:17 pm
content: I've never seen terminals with absolutely no locating flanges. It will be very difficult to make themlookstraight unless you introduce some form of rigid insulating spacers - that probably rules out anything flexible (rubber).@OP: You say 5-way binding posts, the ones you show are 2-way, any pictures of the actual ones? Is it a case of the end terminals having flanges and the intervening ones not? (You didn't trim them off so you could use smaller holes did out?)EDIT:You want someting like these, designed for the job...https://uk.rs-online.com/web/c/fasteners-fixings/spacers-standoffs/screw-insulators/

author: Brumby
author_rank: Unknown
timestamp: December 10, 2018, 11:31:42 pm
content: The only problem with things like this:is the flange at one end.There's no room for them without lifting one side off the panel, cutting the flange off or some other mechanical modification.Edit: By cutting off the flange, you create the plastic washer I mentioned above.

author: Nusa
author_rank: Super Contributor
timestamp: December 11, 2018, 12:03:29 am
content: Quote from: Gyro on December 10, 2018, 07:22:17 pmDepends on how you choose to count the ways:(Fromhttp://www.ietlabs.com/pdf/GR_Experimenters/1952/GenRad_Experimenter_June_1952.pdf)

author: vk6zgo
author_rank: Super Contributor
timestamp: December 11, 2018, 12:53:03 am
content: Over the years, I've seen a lot of such binding posts with moulded bits which are supposed to sit in the hole in the metal panel.In all but a few cases, that part is either too long or too short to work properly, so you still end up trying to use "workarounds".Usually, the best such terminals are ones salvaged from properly made equipment from HP, Marconi, or the like.I would suggest cutting a rectangular hole in the panel, fitting some strong insulating material inside the equipment to cover that hole, & attaching the terminals to that.

author: Gyro
author_rank: Super Contributor
timestamp: December 11, 2018, 10:39:18 am
content: Quote from: Brumby on December 10, 2018, 11:31:42 pmThe idea is that theyreplacethe rear plastic plate (if as shown in the OP photo). The nuts and washers then clamp down on the flanges. There are many sizes of bore and flange available.

author: Brumby
author_rank: Unknown
timestamp: December 11, 2018, 01:07:22 pm
content: OK. That could work ... but I'd be looking for some decent flanges then.