Use sagulator for bench backrest thickness

[mike mcilroy]

I'm making a bench with a 2 piece back rest between three uprights and was wondering how thin I could go. Could the sagulator numbers be extrapolated for this somehow?
I have 3/8"×3"×30" red oak that I was hoping would be sufficient.

[Jamie Buxton]

You should be able to use sagulator to calculate how much the back would bend. However, you have to know what your load is. Are you going to lean on the back with ten pounds of force? Or twenty, or forty? Sagulator can precisely calculate the bend in each of those cases, but I wouldn't know which load is really what is going to happen.

You's learn quite a bit by mocking up your design, and leaning back into the back the way you think you'll sit on your bench. You should remember that a chair back can flex -- some are designed to do that -- but what you don't want is breakage.

For what it is worth, you can see older dining chairs with thin back splats. They've survived a hundred years or more. The backs may have flexed in service, but that's okay.

[Lee Schierer]

My Grandfather had a porch swing with slats that were white pack that were about 1/4 x 2. They spanned about 2 feet for over75 years with no problems. The regulator will tell you how much one strip will bend under a given load. That will be worst case as there will be several strips supporting the load.

If this is an outdoor bench red oak is not a good choice for a long life.

[mike mcilroy]

Thanks for the replies.
It is an indoor bench. I thought a little flex or bend might add some comfort. The boss looked at it tonight and decided the back rest should be 2 slats and as I don't have enough scrap to get that done I'll be breaking down another piece I will just replace the current 2 with somewhat thicker pieces😃
Invention is the necessity of Mother lol