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Old 09-20-2018, 01:59 PM   #1
Aqua Puttana
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Default Thru Bolt Backing Plates

L-track, seat mount mounting, install, fender washer

The question of what to use for backing through bolts against body metal often comes up. There are commercially available backing plates for wheelchair securing from Q'straint, Sue-lok, and other companies.

For the road salt northeast I have used stainless steel ss fasteners. To be clear, ss fasteners are not graded, but they don't degrade from rust. The graded fasteners and plated fender washers I used for the L-track which I installed in the 2004 have rusted quite badly. I grease them regularly. That has helped. The ss fasteners and ss fender washers that I used for the 2006 have been better. Dissimilar metals (aluminum L-track, steel body, ss fasteners) has not been an issue to date. For a general use L-track installation, a great number of ss fasteners can be as effective as graded fasteners. Be aware that there are specific backing plate sizes and metal gauge regulations which may apply for seat installations.

If larger plates are necessary vs fender washers, these are some backing plate alternatives which I feel can do the job and are more commonly available than purpose specific plates.

Scrap plate from a metal fabrication shop.
The cut off pieces of metal sheet are known as "drops". That term comes from the pieces of metal dropping off and falling after being cut by a shearing machine. Metal fab shops will often sell "drops" at a very good price, or sometime give them away. For a reasonable price they will likely cut some to size for you. When the drops are free I usually stop by at a later date with donuts or cookies for the shop.

Sections of Unistrut, Superstrut or other structural components.
Slotted is shown.

UnistrutSlotted.jpg

There are also various flat plate fittings which can be used, but they can be pricey. The components are available in various depths, gauges, solid, slotted, painted, plated, galvanized, etc. Available at home box stores and electrical supply houses.

Galvanized trailer U-bolt plates.
https://www.etrailer.com/dept-pg-Acc...%7C4_Inch.aspx
https://www.etrailer.com/Accessories...RTP175173.html

Electrical box cover plates. Search round, octagon, 4" blank cover. Available at home box stores and electrical supply houses.

OctagonCover.jpg

Please feel free to add your ideas and pictures of installations to improve the value of this thread.

vic
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Old 09-20-2018, 03:35 PM   #2
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Default Re: Thru Bolt Backing Plates

Simpson Strong-Tie manufacturers a variety of fasteners, etc. here's a small sample.
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Old 09-20-2018, 04:22 PM   #3
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Default Re: Thru Bolt Backing Plates

I used a steel C channel in my installation


Got it from Home Depot
https://www.homedepot.com/p/Everbilt...0187/204325591

It's somewhat cheaper than unistrut, so I used the savings to buy a good drill bit.

I also primed and painted the steel with a couple coats of each from a rattle can. Fortunately, I don't live in the rust belt, so hopefully the paint will be sufficient to keep the rust at bay.
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Old 09-21-2018, 12:56 AM   #4
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Default Re: Thru Bolt Backing Plates

If you have a local tower contractor in your area, you might politely hit them up for scraps. I have a guy not too far away that has become an unlimited source for unistrut, misc galvanized angles, channels, pipe and various fasteners. Hot-dip galv is standard in the tower industry and they often have tons of offcuts and dismantled material that they end up scrapping. I tried to pay for scraps for my projects (like the attached) and the guy says take as much as you want and buy me a beer later.

Unistrut is really good for the application you mention and can easily be configured to support under-body water or air tanks.
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Old 09-21-2018, 01:58 AM   #5
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Default Re: Thru Bolt Backing Plates

Quote:
Originally Posted by radair603 View Post
... Hot-dip galv is standard in the tower industry and ...
That is a great find. So much of the galvanized material found in big box stores is somewhat lacking for corrosion protection even when labeled "galvanized". The towers that I worked on rarely had any failure of the galvanized steel. (Of course my experience was with older equipment which pre-dated environmental regulations getting in the way of proper coatings protection. )

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