Torque dynamics: Slotted screwdriver head

[cube137]

See attached image

I experienced yesterday that when the slotted screw driver head was exact fit to the slotted screw, it was easier to turn the screw into the hard wood. I'd like to understand the physics of it.

Is the bottom (in the picture) easier to turn because there is even contact, while the top (in the picture) is harder to turn because the force is applied to a small area which damaged the screw by shredding the contact region?

But supposed the screw was infinitely rigid and can't deform. Would they give you same effort or force to turn the screws in the top diagram or setup (in the picture)?

(If negative, so even without the small region of metal deforming under the force in the top case, fewer contacts would make it harder to turn it? Why?)

 

[AZFIREBALL]

What do you mean by 'harder'? Do you mean 'more skill' or 'requiring more torque' ?
The number of inch-pounds required to turn the screw should be the same in either case.
The 'feel' would be much different in each case however.
A ridged connection would just 'feel' like less torque was needed to turn the screw because you would not need to apply as much 'down force' to keep the blade in the slot. The true test would be to apply a calibrated torque wrench to the end of each of the screwdrivers to measure the amount of torque (inch-pounds) required to turn the screw.

 

[Dr.D]

Part of "how hard" it is to drive the screw is how much effort is required to keep the screwdriver engaged with the screw, i.e., the axial force. The axial load contributes little or nothing to driving the screw, but it still tires out the person doing the work.

 

[jrmichler]

I experienced yesterday that when the slotted screw driver head was exact fit to the slotted screw, it was easier to turn the screw into the hard wood.

I have seen the exact same thing. @Dr.D is 100% correct. Which is why I splurged some years ago and bought a Brownells 58 bit Super Set: https://www.brownells.com/gunsmith-...t-handle-sku080112804-417-1915.aspx?rrec=true. This set is terrific. It has almost completely eliminated profanity when dealing with slotted head screws.