Can you share what type of screws (length, thread, drive, supplier, etc.) you prefer for installation? I build and install face frame cabs and (I know, I know) have always used 2 1/2" drywall screws to join cabs together through the frames. These have never really been ideal but are easily accessible. I know most of you know what I'm encountering -snapped screws occasionally, rounded out heads, etc. Currently I clamp, drill a pilot and countersink with a quick-change bit, flip the bit around, and drive the screw, trying to be careful not to snap it and still draw them together tight. This usually requires me to run it most of the way in, reverse it back out, then drive it home. I would like to find a screw that is flat-head, self-tapping, not brittle, and probably square drive. As an aside, what type/brand of drill/counter-sink/driver do you like? I usually buy the off-the-rack Ryobi ones at HD and they last 3 or 4 jobs before becoming dull, sloppy, broke, or lost.
From contributor H:
I build frameless, but the best countersinks are carbide from anyone. Amana has a good reputation. I bought a set 6 years ago at a woodworking show for 20.00 and they are still drilling clean, perfect countersinks today without a single sharpening. Get a good stock of matching bits in quantity, as they do break occasionally.
Lastly if you were unable to sink those drywall screws in one shot, your bit was too small. Go to the next higher size and use a decent screw and your life will be much easier.
Certainly the primary characteristic of screws is the strength they develop. In some cases, the screw has a load that is trying to pull the screw out in the same direction as the shank runs. The screw strength in this direction is called the WITHDRAWAL strength. In other cases, the screw is being loaded from the side. This screw strength in this direction is called the LATERAL resistance. (Although it is probably obvious, the strength of a screwed joint can be doubled by using twice as many screws. However, it is important that the screws not be too close together; when too close, the strength will not double.)
Everyone also knows that screws should never be pounded into wood. Pounding damages the threads and tears the wood fibers, resulting in much lower strength.
In general, the withdrawal strength is dependent on the depth of penetration of the threaded portion (L) and the diameter of the shank (D) of the screw and the density of the wood (G at 12% MC expressed as specific gravity). The formula for screw withdrawal strength (p) when the screw is inserted into side grain of dry, solid wood (not particleboard, not end grain) is
p = 15,700 (G x G) x D x L
Because the effect of wood density is squared, if the density goes up 20%, the strength goes up about 36%. Note that with dense hardwoods and medium length screws, the withdrawal strength is so large that the weak link is the screw itself; that is, the screw shank breaks before it is pulled out of the wood.
This strength value is not affected by using pilot holes that are 70% of the root diameter for softwoods and 90% for hardwoods. The strength is also not affected by using a lubricant to aid in insertion.
A series of tests has shown that the lateral resistance for wood in the side grain of dry wood is
p = K (D x D)
The value of K for hardwoods is 3360 for woods with a SG of 0.33 to 0.47, 4640 for SG of 0.48 to 0.56, and 6400 for SG of 0.57 to 0.74. For softwoods, the value of K is 3360 for woods with a SG of 0.29 to 0.42, 4320 for SG of 0.43 to 0.47, and 5280 for SG of 0.48 to 0.52.
Depth of penetration of a screw into the second piece should be seven times the shank diameter. Also, the depth of penetration of the pointed end of the screw into the second piece must be at least twice the thickness of the outer piece. The pilot hole in the outer piece should be equal or slightly less than the shank diameter. The pilot hole in the second piece should be no larger than the root diameter, and maybe even a little smaller in softer species.
The 3" square drive washer head screws are great for hanging boxes on the wall .