Posted by Sherman in Idaho [24.32.202.166] on Monday, March 04, 2013 at 19:46:12 :
In Reply to: How to crib up the power wagon posted by junoir copey [174.35.241.51] on Monday, March 04, 2013 at 15:51:28 :
I agree with everyone about jackstands not being safe to trust your life to. They're okay for holding the axle up while you're working outside the truck, like on the brakes or wheel bearings.
Ideally, I have a stack of 6x6s 18" to 2' long to stack up criss-cross as proper cribbing, with a single piece at the top perpendicular to the axle. It's never safe to stack single pieces of wood one on top of the other, although in a pinch I've done it if all the other wheels are on the ground and chocked. Other larger dimensions are good as well, if you can get them. 6x6s are common in pole barn construction and usually there's a foot or two cut off of the top of each pole. A few 6x8s are nice because you can turn one on edge on the top if you need a couple extra inches. Wood is good because if overloaded it will crush and fail gracefully rather than breaking like a bad Chinese weld, cast iron, or a cinder block.
There's nothing wrong with firewood rounds either if you stand them on end and they are larger in diameter than they are tall.
The key to stability with any sort of support is to make sure that even if things shift around the worst possible way, the point where the load is applied to the top of the stack will never be outside of the base of the stack. That's where jackstands are risky even if they don't break. The top piece is usually a very wobbly fit in the base, the whole thing can be extended at least twice as tall as it is wide, and the top can bend over quite a bit. Add in slightly irregular ground and it's easy for the point where the load is applied to the top to end up being outside of the periphery of the base, at which point the only thing keeping it from falling over is whatever happens to be blocking up the other corners of the truck. Jack stands have their place, and they're safer than crawling under a rig supported by nothing but a jack, or by cinder blocks, but that's not saying much.