Best screw head that won't strip

[krw]

I find exactly the opposite. Torx (star) are much better. I find the screws aren't nearly precise enough for the Robertson (or "square head recess") to work as well as it should.

[whit3rd]

Square drive/Robertson tips are tapered; the harder you push, the greater the drive surfaces contact forces become. So, you can drive them very hard. But when you want to REMOVE a screw, you don't want to apply a push (this hurts you because it increases friction).

Torx/star tips are straight-sided, you get equal torque limits in drive and remove operations. So they're easier to remove.

Philips/crosspoint, like Robertson/square, are tapered, and can be difficult to remove.

[-MIKE-]

I don't get this. Why not push when removing?

[Bill]

For the same reason you lift your feet when you walk.

[-MIKE-]

I don't get that either. A screw is a helical ramp, more or less. You turn it to go in and come out. The farther the screw is in, the more friction/resistance there is in both directions. Most often, I find it necessary to push on a screw when removing it, at least until it's a good deal out.

What am I missing?

[Grant Edwards]

Because the objective is to _raise_ the screw. Pusing down on it makes that harder to do and thus requires more torque to raise it. To get more torque without cam-out yout have to push harder, which then requires more torque to raise the screw, which requires you to push harder...

[Ed Pawlowski]

Theory aside, when the head is buggered, pushing gets it out, not pushing makes the bit slip. One law of physics out does the other.

[-MIKE-]

Yeeeeeeeaaaahh, OK. wow

[Bill]

Well, I should clarify my remark, since there appears to be at least 2 factors:

1. The friction (between the bottom of the screw head, and the workpiece) that I alluded to.
2. The fact that you are pushing "down" when you wish for the screw to come "up", that has been mentioned.

[Grant Edwards]

True. But the point is you're better off using a screw head and bit design that minimizes the amount of pushing required -- especially when removing a screw since the pushing is forcing the screw in the "wrong" direction.

[krw]

That doesn't mean pushing down is making it easier (than it would be were a different head chosen up-front).

[Ed Pawlowski]

In a perfect world. . .

If you are removing screws above you, you can defy gravity and push "up" to get the screws out.

[clare]

I guess there is a difference between the generic "square-drive" now being sold in the USA and the original Canadian Robertson (or Scrulox) screws and screwdrivers. I know I've seen a lot af really crappy square drive screwdrivers recently, and a lot of REALLY crappy screws of all types with Chinese lettering on the boxes.. And the difference between pozi-drive, Reed and Prince (aka Freerson), and Philips screws and drivers causes a LOT of problems because they look so similar but are virtually incompatible.

[clare]

I smell a scarlet colored fish.

[clare]

Anyone with a torque screw driver want to do a test? Drive several identical screws into severel peices of different woods then read the torque required to remove them with no downward force, and with , say,

5, 10, and 15 lbs of force pressing on the screw and tabulate the results? In both hard wood and soft wood - and using both steel and brass screws. I'd be willing to bet the difference in torque required would be within the limits of the torque required to lift the downward force treating the screw as a simple inclined plane. (in other words, insignificant).

[clare]

Like I said - a scarlet fish -(red herring)

[Bill]

Since the amount that you wish to raise the screw head with a twist of the wrist is very, very, small, I think the effect you describe may be negligible. Of course, the wider the threads, the greater the effect. I could probably design a screw that would be difficult to unscrew by pushing down on it! ; )

Bill

[Bill]

I have a hunch this thread isn't over yet! ; )

[jloomis]

Torque drive. octagonal design.

throw away square. john

I can't decide which is better, the square or the star? Which is less likely to strip?

Thanks.

[Grant Edwards]

OK, so square (four sides) is better than slot (two sides), and octagonal (eight sides) is even better than four sides, the logical conclusion would seem to be than the more sides the better.

Take that to the limit as sides -> infinity, and you get what must be the best of all: round drive (or as it is usually known: cheap philips head screws after use with the wrong sized driver).