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Bolting 2 plates together but keeping them insulated.

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ELS122:
I need to bolt to plates together, they have an insulating spacer between them, but I need to insulate the screws somehow.
what would be the best solution?
using plastic screws
drilling the threaded holes, epoxying them and tapping them
drilling the screw head part plate and epoxying that

or something else entirely?
I dont need to torque the plates much at all, but I'd like to have it robust anyway.

TimFox:
I would suggest insulated shoulder washers, with normal bolts and nuts.
Traditionally, these are made of hard fiber, but nylon and Teflon are available.
They also exist made of ceramic, which are good for high temperatures, but may be brittle.

bdunham7:

--- Quote from: ELS122 on October 01, 2022, 05:19:27 pm ---I need to bolt to plates together, they have an insulating spacer between them, but I need to insulate the screws somehow.
what would be the best solution?
using plastic screws
drilling the threaded holes, epoxying them and tapping them
drilling the screw head part plate and epoxying that

or something else entirely?
I dont need to torque the plates much at all, but I'd like to have it robust anyway.

--- End quote ---

Nylon screws and nuts may work for very light duty uses, but the more rugged method is to use nylon shoulder washers to center and insulate the bolt from both plates.  Depending on the plate thickness and the general stack-up and design, you may use just one per plate or put one on each side.

https://www.digikey.com/en/products/detail/keystone-electronics/3054/16013?s=N4IgTCBcDaIDoBcAEBmAbAWhQBgKwBYMA5AERAF0BfIA

Benta:
Plenty of nylon shouldered bushings available as TO-3, TO-220, TO-247... mounting kits. Cheap too. Normally for M3 bolts.

ajb:
Yep, shoulder washers, or if you need a larger fastener than you can find a suitable shoulder washer for, a regular plastic spacer on the shank of the bolt and a plastic or fiber washer on each side would do. If the OD of the plastic spacer is close to or larger than the OD of the head/nut then you might want metal washers on top of the insulating ones to spread the clamping forces out past the spacer. For heavy loads, you'd want to use heavy structural washers rather than plain flat washers.

Be aware that plastics can flow under compressive loads, so you may not be able to rely on bolt tension alone to keep the fastening secure with plastic washers.  In those cases you probably want a nylon insert or deformed thread locknut to keep it from coming loose, and/or Belleville washers to maintain tension.  It all depends on the materials, environment, and geometry involved.

This all assumes a dry environment, though, if this will be outdoors or otherwise exposed to water then you might need to take extra precautions to ensure that water can't get into the fastening and form an internal conductive part, or can't bead up across the insulating washers

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