Blu-tak used in metal cased PSU assembly?

[Faringdon]

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?

[Bassman59]

You're kidding, right?

[Gyro]

Sadly, Faringdon never kids.

[themadhippy]

lick the washer,that should keep it in place long enough

[jc101]

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.

[Faringdon]

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.

Thanks 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.

[Kean]

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.

[nali]

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.

Thanks 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.

Wow, 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

[TomS_]

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.

[jpanhalt]

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/

[Kean]

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?

Hmmm... I missed that.  It makes no sense as described.  I assumed he needed them as a spacer.

[Faringdon]

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?

Thanks...it must be flush with the base...nothign jutting out externally....so its counter sunk screws, and washer inside.

[jpanhalt]

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?

Thanks...it must be flush with the base...nothign jutting out externally....so its counter sunk screws, and washer inside.

A 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:

Faringdon is again on the "other side of the world" train.

Not at all.
Read the top post, this is no fault of the other side of the world.

In fact, as soon as i found out the pilot was in good health, i , with my pals, actually toasted and celebrated that F-35 getting sunk to the bottom of the sea!
...You forget that i myself operate a Far Eastern Electronics importation business, so do many of my pals.
Last year i made £35.4 million profit for myself (not anywhere near as much as my mates though)...not bad for sitting about and placing a few orders now and again.....i dont even have to see the products....just get them sent straight to customer.
Thats why, when we found out the pilot was good, we toasted the sinking of the F-35....after all, the situation surrounding it (the destruction of the Western general electronics industry) ...is the reason i get minted for doing very little! All legal!
Most westerners thank me for bringing in  "cheap products" for them...but they dont realise that i take a huge chunk of the money involved all for myself...as much as i can get away with.....and as general electronics in the west diminish's further, and as western manufacturing facilities get further reduced, i, and my pals, stand ready to ratchet the prices up as high as we possibly can. Cheers!

I wonder why you haven't just assigned the problem to someone else.

[nali]

I love working on mechanical puzzles, but in light of this post:

[snip fantasy stuff]

Wow... 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.

[jpanhalt]

WRT the washers - sounds like they're using counterunk screws too large for the panel thickness.

If 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.   

[thm_w]

I love working on mechanical puzzles, but in light of this post:
...
I wonder why you haven't just assigned the problem to someone else.

That is clearly sarcasm, he hates undercutting from chinese vendors.

[jpanhalt]

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.

[lscw]

Blu-tac absorbs moisture and gets very soft when hot. Perhaps BigClive.com should see what electrocuted blu-tac looks like