Why are drill bits often too short for a pilot hole

Question

It seems that my drill bits are often a bit too short to drill the full pilot hole to cover the whole length of my screw. The screws I use aren't particularly thin, they are regular width.

I fix this by redoing the drilling in my secondary board. But that is annoying, I just want to clamp everything down and do the pilot hole through the two boards in one go.

Is this normal that the drill bits are a bit short to cover the length of a screw? It's just a vanilla Bosch drill and the drill bits that came with it.

I have seen special long length drill bits but I don't want to go out and buy exotic drill bits if there is a simpler solution, or brands with slightly longer drill bits, I miss just a tiny bit of length, not much.

Thanks.

Answer 1

A "tiny bit of length" difference between the depth of the pilot hole and the length of the screw shouldn't be a problem in most cases.

Notes:

1. The harder the wood, the more critical this may become, as hardwoods can split more easily if you just drive a screw without a pilot hole. However, even in hardwood, if your pilot hole is just shorter than the screw, it shouldn't be a problem.
   1. If you're spending money on hardwoods, it may well be worth the investment to buy a few longer bits for pilot holes anyway.
2. Make sure that you're actually drilling a clearance hole through the top board. A clearance hole is the same size as the screw threads, not the screw shank. This will allow the screw to clamp the two boards tightly together as the head of the screw will act as the clamp for the "top" board and the threads won't be biting into the top board.
3. If you countersink the hole to allow the screw head to sit flush with the surface or even below the surface so you can put a plug in to hide the screw head, you can redrill the pilot hole and the jaws of the chuck will sit into the countersink giving you just a bit more depth to the pilot hole.

Answer 2

I just want to clamp everything down and do the pilot hole through the two boards in one go.

The holes in the two boards should be different sizes:

1. a clearance hole sized for the screw's unthreaded shank in the first board (the one closest to the head)

2. a smaller pilot hole sized for the minor diameter of the screw's thread in the second board

The threads should normally only bite into the second board. If you use the same bit for both holes, you're probably using one that's both too large for the threads to bite fully, and too small for the shank to fit, making the screw hard to drive and more likely to split the first board.

Two holes aren't always necessary if the material being attached is soft, or if the screw is designed to be driven without a pilot hole. For normal wood screws in hardwood boards, though, it's a good idea to drill the holes properly.

There are tapered drill bits that are designed to drill both the clearance and pilot holes at once, and you can even get them with countersink cutters so you can save the countersink step too. The bits are sized for wood screws (#8, #10, etc.), and each size should be long enough to handle screws in the range of lengths for the corresponding size.