Blu-tak used in metal cased PSU assembly? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: December 01, 2021, 08:21:11 pm
content: I just had to dis-assemble, and then re-assemble, a power unit with a metal base. This power unit has very low sales volumes. Screwed to this metal base, were three other internal PSUs (each internal PSU had 4 screw holes for fixing to the base). The screw hole in the base, was too big, so washers needed to be used. The problem was, when you put the 4 washers round the 4 holes, and then rested the PSU on top of them, it was then the devils own job to screw in the screws without the washers slipping away from the screw hole that they “surrounded”.I thought of kind of sticking the washers in place with superglue, or even thermal paste. However, these would be messy solutions.And in fact, blu tak would have been ideal to kind of stick and hold the washers in place whilst I mounted the PSU on top of the washers, and then fiddled about trying to screw the screws up through the holes. Can you think of any problems with blu-tak for this use?.....some of the blu tak would inevitably get stuck in the product and stay there….could blu-tak eventually corrode the metal? The unit gets hot as it’s a PSU…..what is the max temperature that blu-tak can withstand without catching flame?If Blu-tak is no good for this, then is there something similar?

author: Bassman59
author_rank: Super Contributor
timestamp: December 01, 2021, 10:11:18 pm
content: You're kidding, right?

author: Gyro
author_rank: Super Contributor
timestamp: December 01, 2021, 10:23:55 pm
content: Sadly, Faringdon never kids.

author: themadhippy
author_rank: Super Contributor
timestamp: December 01, 2021, 11:51:25 pm
content: lick the washer,that should keep it in place long enough

author: jc101
author_rank: Frequent Contributor
timestamp: December 02, 2021, 09:09:57 am
content: If the screw goes into the power supply and is accessible, put the screw through the hole enough so the washers can sit on it. Hold the screws in place on the outside with Blu-tak until you're ready to do up the screws. Then remove the Blu-tak as you tighten them up.I use Blu-Tak quite often to temporarily hold something in place but never leave it behind.

author: Faringdon
author_rank: Super Contributor
timestamp: December 02, 2021, 08:07:40 pm
content: QuoteThanks but Sorry , this cant be done. The washers are inside the outer alu enclosure.Youve got to put the washers round the holes, then lay the PSU over the washers, then kind of overhang the unit over the table edge, and get under it to screw the screws up ...without dropping the screws.....The wires into the PSU tend to pull it about and the washers end up misaligning.

author: Kean
author_rank: Unknown
timestamp: December 03, 2021, 02:50:14 pm
content: Instead of using loose washers, talk to your metalwork supplier about getting some self-clinching standoffs added to the mounting holes.If you cant get a suitable standoff in the right size/height, then a self-clinching nut with oversized thread should allow the thread of your fastener to pass through.

author: nali
author_rank: Frequent Contributor
timestamp: December 03, 2021, 04:08:44 pm
content: Quote from: Faringdon on December 02, 2021, 08:07:40 pmWow, why is it that virtually everything you deal with is a kludge?Have you tried something like these?https://www.essentracomponents.com/en-gb/p/retaining-washers

author: TomS_
author_rank: Frequent Contributor
timestamp: December 08, 2021, 09:22:38 am
content: I don't understand why the washers are going between the PSU and the base if the screw holes are too big. Surely they should be going between the screw head and the base? What am I missing here? Maybe a picture or diagram would help.But anyway, why not use a tiny dab of Loctite around the edge of the washer to hold it in place? At least it doesn't have the janky vibe of super glue or blutak.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 08, 2021, 11:48:43 am
content: It doesn't look like you (Farington) looked very far for washers. There is a large variety, including cup and sleeve/hat for holes that are larger then the screw. Fender washers may be a consideration. They have a proper size hole for the screw but are larger in diameter. There are also screws that incorporate a washer with the head (aka, flange head), have a retained washer, or an enlarged head (e.g., pan head, binding head).Here are some examples, but the listings are not exhaustive:https://www.mcmaster.com/washer-head-screws/https://www.mcmaster.com/fender-washers/oversized-washers-9/https://www.mcmaster.com/washers/

author: Kean
author_rank: Unknown
timestamp: December 08, 2021, 11:59:34 am
content: Quote from: TomS_ on December 08, 2021, 09:22:38 amHmmm... I missed that. It makes no sense as described. I assumed he needed them as a spacer.

author: Faringdon
author_rank: Super Contributor
timestamp: December 08, 2021, 07:35:38 pm
content: QuoteThanks...it must be flush with the base...nothign jutting out externally....so its counter sunk screws, and washer inside.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 08, 2021, 08:38:17 pm
content: Quote from: Faringdon on December 08, 2021, 07:35:38 pmA hat washer (rim inside the enclosure) or presses nylon bushing will do that. Can you post a drawing so we aren't guessing what you want?I love working on mechanical puzzles, but in light of this post:Quote from: Faringdon on November 30, 2021, 11:03:17 amI wonder why you haven't just assigned the problem to someone else.

author: nali
author_rank: Frequent Contributor
timestamp: December 08, 2021, 09:44:22 pm
content: Quote from: jpanhalt on December 08, 2021, 08:38:17 pmWow... I hadn't even bothered reading that thread. In an earlier post I wondered about OP's motivation for some of his posts. Now I'm sure - definately a Walter Mitty.WRT the washers - sounds like they're using counterunk screws too large for the panel thickness.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 08, 2021, 09:58:00 pm
content: Quote from: nali on December 08, 2021, 09:44:22 pmIf that's the case, get undercut CSK screws. Are they sure the correct angles are being used. There are several possibilities from about 82° to 135°. I believe 82°, 90°, 100°, and 110° are most common.

author: thm_w
author_rank: Super Contributor
timestamp: December 08, 2021, 10:58:34 pm
content: Quote from: jpanhalt on December 08, 2021, 08:38:17 pmThat is clearly sarcasm, he hates undercutting from chinese vendors.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 09, 2021, 11:35:05 am
content: Just to be clear here is an example of a countersunk screw with undercutting.Their intended use is for attaching thin materials where the thickness of the material is less that a standard CSK head depth. They can be had with different included angles. One can sometimes find undercut screws that are severely undercut (or make them yourself). If you go DIY and can't thread the undercut part, just neck it in to clear the mating threads.Two other approaches are to dimple both surfaces or add contersink to the thread part too. It is too late for the former, but the latter might work if the metal is thick enough.

author: lscw
author_rank: Contributor
timestamp: December 24, 2021, 07:47:38 pm
content: Blu-tac absorbs moisture and gets very soft when hot. Perhaps BigClive.com should see what electrocuted blu-tac looks like