Screw clamping force?

[Locks14]

Hi guys.

Does anyone have a link to any guides for exactly how much force certain sized wood screws apply? Obviously there are other variables other than size, such as the material being screwed into, thread type, number of screws, etc.

But I'm struggling to find a starting point for numerical information on this subject.

So, for example, a guide that would tell you based on the size of a door hinge, the size and number of screws and the material being screwed into, just how much clamping force is the hinge being fixed to the door with?

Similarly, fixing shelving brackets. Given a size of bracket, the material it's being screwed to and the size/type of screw, just how much force is each individual screw applying to fix the bracket to the wall?

Or an even simpler scenario, if you had two piece of wood (lets say two pieces of 3x2), and screwed them together with how much force would the screw be applying? And if you inserted more screws is the relationship linear and when would you reach a point of diminishing returns when a certain number of screws are inserted...

Many thanks.

Lock.

 

[Birdhunter]

If you Google "screw clamping force", there are several references that might give you a start. Also, look at curiousinventor.com as that site has a tutorial on screw holding.

From a very casual look at one of the references, it looks like there is an assumption that the material is not elastic. The fact that different woods have different degrees of elasticity and ability to withstand crushing force, may affect the calculations. For example, balsa would crush faster than Ebony under a screw being tightened.

As to diminishing returns on the number of screws, as the number of screws increases within a given area, the wood fibers get shorter and the screws would begin to just sink into the wood.

 

[Holmz]

Look at the pitch of the screw... It is an inclined plane.
You can get an idea if you ignore friction.