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Looking for a captive nut of a different variety
4

Looking for a captive nut of a different variety

Looking for a captive nut of a different variety

(OP)
I have an application where I am joining two plastic panels around the perimeter. We're using bolt,nut, lock washer, and plastic washers but it's way too many pieces. We've tried using u-nuts but in this application we don't like the gap between the panels created by the leg of the u-nut.

(To be clear, a U-nut looks like this: http://www.trfastenings.com/pages/multi+thread+u+n...)

I'm looking for something similar that is sized to slide over both panels together and would allow me to finish the joint with a single wing screw without separate washers. For what it's worth, in this case I'm looking for an M6 nut, stainless material, and 6-8mm thickness of the two panels together)

Does this widget exist and have a name? If so, who might supply such a widget at 2000pcs / year?

Thanks in advance,

David

RE: Looking for a captive nut of a different variety

Get a u-nut for twice thickness of one panel and assemble it over both panel.

Ted

RE: Looking for a captive nut of a different variety

(OP)
That thought occurred to me but I have not yet found a u-nut that fits over the whole 8mm thickness. With M6 size hardware, U-nuts typically stop at 4mm thickness.

Going along that line of thinking, it could be done with a custom u-nut.

David

RE: Looking for a captive nut of a different variety

A U-nut over the edge of two panels with a wing screw through two mating holes is not functionally different from a cable tie over the same panels.

Mike Halloran
Pembroke Pines, FL, USA

RE: Looking for a captive nut of a different variety

(OP)
Mike,

That is an interesting idea. However I don't see a cable tie as functionally same, at least in this case.

A cable tie might keep the panels together but it will not hold preload and it will be more prone to wear/tearing if the plastic panels flex. In my case we are exposed to outdoor environment where heavy winds are present and I need a rugged connection.

An additional factor is the cover must be readily removable in the field for maintenance and the fastener is expected to be re-useable. Cable ties do not meet that expectation and would have a poor appearance.

RE: Looking for a captive nut of a different variety

Well, they're still universally ugly and the preload is limited, but cable ties are available in releasable reusable and UV-resistant versions.

Mike Halloran
Pembroke Pines, FL, USA

RE: Looking for a captive nut of a different variety

(OP)
I'm glad you put that idea out there because in the field our customers often replace this hardware (after warranty) and our outside sales guys could make the cable-tie suggestion.

David

RE: Looking for a captive nut of a different variety

we use anchor nuts (eg AN366), rivet a nut retainer to the back-face of the plate.

you can also use adhesive nut-plates, "Click bond", but they can be fussy about surface treatments.

RE: Looking for a captive nut of a different variety

PEM makes broaching-type captive nuts that can be installed in fiberglass and polycarbonate panels; you never mentioned what type of plastic you have.

RE: Looking for a captive nut of a different variety

is riveting out of the question ?

RE: Looking for a captive nut of a different variety

(OP)
My material is ABS or ABS with static-dissipating Acyrlic coating, 2.5-4mm thick per sheet. It may be tough enough to consider a broaching-type nut as long as it has a nice wide washer profile to prevent it from pulling through, and that it won't fall out or get knocked out after it's been disassembled. That's another good idea, thanks.

rb1957: yes, I am not considering it for reasons of reassembly and the fact that the dirty side of the rivet will remain exposed to operators.

badservo: A t-nut could work but my gut tells me those prongs might be too severe. It warrants a test however, and a design with mild enough prong engagement could work nicely.

RE: Looking for a captive nut of a different variety

Kenat's suggestion of bonded inserts gives me another idea, since it's ABS: bond a washer-shaped piece of ABS to the nut side sheet, to build up the thickness of that sheet to better support a heat-staked/ultrasonic-staked/bonded or similar insert designed for molded plastics.

RE: Looking for a captive nut of a different variety

Was the idea of a recess for the U-nut material thickness abandoned because these are existing parts? That's probably where I'd start if I had an option of adding it to the tooling.

Or you might look at rack nuts. http://www.google.com/search?hl=en&q=rack+nuts...

RE: Looking for a captive nut of a different variety

(OP)
I spoke with PEM today and given the thickness and that ABS has such limited cold flow, and the fact that I would prefer to allow these fasteners to fit existing covers, they recommended one of their self-broaching inserts designed for PCB applications. I'll have my samples very shortly.

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