Woodworking clamps, does force add up? I was watching a woodworking video about glue, and the guy was clamping two pieces of wood together using a total of 8 clamps. He argued that by doing so he would apply 8 times the maximum force of 150N (a property of the clamp), resulting in 1200N in total.
I think he's wrong. I think the force of 150 N is only working locally where the clamp is and will decline drastically radially from that spot. And so the clamping force on any given spot on the board will never exceed the max. force of the clamp. 
Who's right?
 A: If the area stays constant the pressure will increase as the total force increases when more clamps are used.
The wood is probably flexible and not perfectly flat so the force will only be exerted over a region close to a clamp where the two bits of wood are in contact.
A: Forces add in that way, and the clamps would do the same.  You can prove this to yourself by drawing a free body diagram for the forces that would act upon the beam.  Applying Newton's laws would show that the force you lift with will have to exceed the total clamping force if you wish to move the clamped board.
Obviously, this is extremely oversimplified, and there are many situations where this doesn't really apply.  
The stiffness of the board is extremely important.  A stiff board will even out the load between the clamps better than a flexible one.  A flexible board may be able to cheat the total force rules; because it has less internal forces that resist relative movement this means that just adding the total clamping force and comparing that to the total applied force is not enough to represent the situation.  It is possible to apply the force to one location and have that undo the clamp and bend the board there, but because the board is very flexible, it doesn't transmit enough force to undo any of the other clamps.  You can't reliably treat it as a single object to apply Newton's Laws to anymore, but instead have to consider how the board interacts with itself as well as the clamps.
Basically, the proximity to each clamp is important, and it will be more important the further you are from the point of the applied load.
For the case of clamping wood, if it's a thick piece of sturdy wood, with clamps evenly spaced, you can assume that the forces approximately add.  If you require the clamps to hold a specific force for safety reasons, I would suggest doing some more detailed calculations for your material, and providing some extra allowance for errors.
A: 
And so the clamping force on any given spot on the board will never
  exceed the max. force of the clamp.

This would, quite obviously, be the case, if we assumed that the clamps are evenly distributed around a circle. 
Under these conditions, due to symmetry, any redistribution of the reaction force, which, in total, is equal to the total applied force, would not be possible, so the reaction force applied locally by each clamp would have to be $150$N and the pressure under all clamps would have to be the same.
If the clamps are not placed symmetrically, we can still state that no redistribution of the forces will occur by looking at one pair of clamps at a time and observing that, if that was not the case, the work (the two pieces of wood) would rotate, since two different reaction forces would create a net torque acting against two equal applied forces. 
A: You're both wrong.
Although I would say you are more right than the expert. When you apply a force to an object's surface, the stress (a.k.a pressure) on the object clearly can't be constant across the surface; it must have a maximum closest to the point of contact and then dissipate as distance from the point of contact increases. 
A very simple model of the clamping pressure experienced by a piece of wood might look like this:

The units here aren't important (pressure is in unites of 1 clamp). What is important is that clamping stresses add up:

Here is an animation of what happens when seven identical clamps are taken from clamping at the center of a board to being equally spaced across it's length. Total clamp pressure is just the sum of the seven separate clamps. Some observations:


*

*Only when all the clamps are at same location do you get 7 times the pressure.

*The total pressure however is higher (above any one clamp) everywhere.

*The average pressure doesn't change, only the peak pressure. (note it does dip slightly as the end clamps reach the ends).

*The pressure is very uniform when enough clamps are used. This is probably of greater value to a woodworker than maximum clamping pressure.

A: He's right - the forces of the clamps will add up. You seem to be confusing force and pressure. The pressure from each clamp would reduce radially outwards from each clamping point, as you describe (although adding clamps will increase the average pressure acting across the entire length of the planks, thus increasing the force!).
