#6-32 Retaining Washer

[uwbsme]

Hi everyone,

Anyone have any ideas for retaining some #6-32 machine screws so they won't fall out of a plastic lens? The only solution that I've found, which really isn't a solution since they don't work well, is the following:

http://www.mcmaster.com/#washers/=88exnq

Any ideas?

 

[MintJulep]

Are you threading into plastic?

Use a thread forming screw, or an adhesive that will stick to the plastic, or heat the screws up after you install them to melt the plastic.

 

[CoryPad]

Do the screws loosen and fall out due to external forces? Or do they fall out because you loosen them for maintenance? Or something else?

 

[uwbsme]

MintJulep: We are threading into metal, the plastic lens has a clearance hole for the #6-32 machine screw.

CoryPad: I don't want the screws falling out when they take the lens off for service. The idea is that the service personnel won't take the time to find screws that fall out. We want them to stay with the plastic lens when they are unscrewed from the metal base, so they are all there when the lens is ready to be re-attached.

 

[MintJulep]

Ah.

Something like this:

http://www.mcmaster.com/#captive-panel-screws/=88hjxg

 

[agostinorotondo]

Captive panel screw is probably the way to go, but another possible solution would be to use a bolt retainer...

http://www.mcmaster.com/#bolt-retainers/=88ogxa

...so you can use standard hardware.

This assumes you are using a partially threaded bolt, as this retainer slides onto the un-threaded portion.

There are similar retainers designed for temporary use, sized to hold a standard screw by the threads. Here's one...

http://www.bakfin.com/starlock/screwretainer.html

...they aren't designed to hold much of a load.

 

[uwbsme]

I've ordered some of the captive panel screws and retainers for testing.

I've tried an item like the Bafkin Starlock, but it was plastic. This metal version will probably work better. I will try this also.

Thanks a lot guys.

 

[btrueblood]

Captive screws are what you want, but you will have to change the hardware design to accomodate them. If you have 6-32 tapped holes in the base part, and 6-32 clearance holes in the lens, a 6-32 captive screw won't be captivated. You'll need to go up to an 8-32 or so thread size, and tap the "clearance" hole thru the lens...you'll also need enough relief length under the lens so that the loosened screws have room to disengage from the body threads without starting into the lens threads...

Alteratively, use the captive screws shown on following pages in Mint's McMaster link, i.e. press-fit style panel fasteners.

 

[uwbsme]

You're saying If I have a #6-32 tapped hole in the metal base part, and have a #6-32 tapped hole in the lens, I can use a #6-32 captive screw. The #6-32 clearance hole messes up this concept as the #6-32 captive screw would fall right out, correct? I understand the 'room to disengage' concept.

Thanks for the info.

 

[KENAT]

I think you're getting it.

You have to use a special captive screw which has a 'shank' slightly less than the minor diameter of the thread where it goes through the retaining part. You then have threaded holes of the same size in both parts. The retaining part threaded holes have a counter bore or similar on the mating face to allow room to disengage/float during assy. If you're willing to undo each screw only partway at a time then the c'bore depth can be minimized - but it will confuse some folk.

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[KENAT]

Doh - doesn't have to be the retaining part that has the c'bore - it can be on the other part. Or you can even split it across both parts where you have limited depth.

Posting guidelines faq731-376

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(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​