Re: Skid plate theory and practce

[jlandry@domain.elided (John A. Landry)]

In a brilliant stroke of genius, Christopher Eveland
<eveland@domain.elided> blurted out:

>	So what I would like are some tips about making them.  Seems like a
>simple enough part, but I'm new to off roading, so it seems wise to ask
>a few questions.  How big do I want it to be? The most obvious thing to
>me that needs protecting is the xfer case pan, what else?  How should it
>mount?  I take it the smoother the bottom, the better, are bolt heads OK
>to be down there, or should I weld mounting tabs on or something?  How
>think should it be?  The jeep guys seemed to think 1/4" would be ok. 
>Should I try to bend up the edges somehow, or is flat OK?

Chris,

I'm not an experienced off-roader by any means, but I have seen a few skids
plates over the years and the design follows a simple common sense
approach.  They usually are used to protect *vital* parts hanging low under
the truck... like the engine and automatic transmission oil pans, the fuel
tank and sometimes the differential pumpkins.

Keep in mind that a skid plate could easily be asked to support the entire
weight of your truck, and maybe a lot more if you slam down on it.  So,
thicker is better.  Most I've seen are made from something like 1/4" thick
steel plate and I certainly wouldn't go below 10 gauge to be effective.

When designing the mounting system, I'd avoid having bolt heads sticking
off the plate's underside.  If you absolutely must, you might get away with
using plow bolts or carriage bolts.  A plow bolt has a flat recessed head
and a carriage bolt has a rounded head.  A rock scraping across the surface
of the plate will likely shear off any protruding bolt head or nut.  Heavy
mounting tabs welded to the upper side of the skid plate are normally used
to bolt to the frame.

In many cases brackets or braces have to be used to secure one end of the
skid plate to the frame or cross members.  When fabricating these pieces,
remember how much weight they must bear.  Using something cheesy like
threaded rod as a standoff bracket is next to worthless when the skid plate
is smacked with 5000+ of weight.

The plate should also be designed so that the edges can't be caught by
trail obstacles.  Normally a skid plate will have the leading (and possibly
trailing edges) rolled or bent up to facilitate this.

When you start taking about bending 3/16" or 1/4" thick plate, the services
of a metal fabrication shop are likely to be required.  You have them cut
and form the pieces and then you could weld and install them.

Good luck,

John
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