# Computing force over a range

I'm building a murphy bed. I've build a box out of plywood that holds the mattress (the box is shaped like a sandbox. See image below). I plan on putting 5 different 25lb springs across the long side of the bed frame, but want to know if the frame can withstand 125 lbs of constant force.

So, what I did was build three different L-shaped test pieces, joined the same way I did the box (rabbit joints + dowels + screws + glue), to test their breaking force. (I'm going to use a similar setup to http://woodgears.ca/joint_strength/).

Here's my question. Does each of those L-shaped test pieces need to withstand 125 pounds of force? Or do they need to withstand only 25 pounds (assuming the L-shaped pieces are the same length as the average distance between springs)?

• A diagram of the planned bed frame would be very helpful here. I have some concerns based on what you described.
– mac
Feb 13, 2014 at 20:34
• Good idea, mac. I've included a quick sketchup image and edited the post. (Sorry the "springs" don't look like springs. I'm not too savvy at sketchup). Feb 13, 2014 at 21:08
• thanks for the diagram. I still have some questions/concerns. 1) What is the purpose of the springs? 2) When you say "25 pound spring" do you really mean a 25 pound-per-inch spring, or are you saying that each spring will be guaranteed (by some other design feature) to exert 25 pounds of force on the bed frame?
– mac
Feb 14, 2014 at 17:12