Expected wood movement

[Guest]

I'm in SW FF. Lots of humidity. I have 2 boards, of what I think is cedar. 3/4 thick x 11" x 10 feet, that I am using for short sides on my new lumber hauler.?
Going to bolt to angle iron sides, near the edge, at each angle upright.
Plan on top edge with 1/4" hole for 1/4" but and bolt.
Then on the bottom one enlarge the hole, to allow for movement.
Question. How much larger does the hole have to be to allow for enough movement?

[Steve N]

You live in southwest french fry??????

Could get answers all over the place here, but if both wood, and metal are involved I usually go up 2 drill sizes, but I always use big honking fender washers too.

Maybe a bit more work, but can you weld? Make up some squared off U's with a bottom in them, and weld them on. Or no weld, and just drill them out, and bolt them on? You can make them the size of a 2x4, and you can pull the sides off quick as a cat if you find a load where they would be in the way. The more universal the tool, the greater the use.  
 

[Admiral]

For that application, I wouldn't worry about wood movement, cedar is soft, and will take care of itself IMHO.... just bolt it up.

[TomFromStLouis]

"Cedar" covers many species. If it is the aromatic eastern redcedar then it is the most stable domestic there is, shrinking only 3% green to dry IIRC. We don't even kiln dry our fresh cut boards. Other "cedars" will have different rates of movement, all of which is on the US Forest Products Laboratory site under domestic softwoods.

Shorter answer is that an extra 1/8" or so - Steve's two drill sizes - sounds about right. Big washers sound good too.