How to make proper pilot holes

Question

This is related to the question about Replacing small drill bits without buying new sets (or preventing breaks) but I wanted to expand on this.

I think I'm just using cheap bits and much like the OP in the above question I am going through them like balsa wood. I also find that when I make pilot holes and countersinks that my wood is still prone to splitting. That and my bits are burning in hardwood (oak I think) so something is wrong there.

Should I always be using brad point bits on wood? It is what they are for is it not? How do I know how big my pilot hole should be? In general I try to use a bit the same size as the shaft of the screw I'm using (width without the threads to be precise).

How can I make better pilot holes. I've seen videos where you clip the end of a nail and use that but that seems more of a kludge than a solution. Worst case this could be a dupe of the other question.

Answer 1

For most hard woods using a pilot hole the size of the shaft of the screw should be good enough to prevent splitting, since it is the shaft that would be 'pushing' out on the wood.

There are some that are hard enough that making the pilot hole larger than the shaft but still smaller than the threads is useful, but these are pretty hard woods and it is mostly to ease the driving of the screw.

The other two issues that could cause splitting would be putting the pilot hole to close to the edge of the board, and/or putting the screw in too tight. when you have pilot holes and counter sinks in hardwoods, you don't need to over-tighten the screws, good and snug is perfect.

It is easy to over-tighten with a power drill and the head of the screw with shaped funnel of the counter sink makes it easy to go to far and split the end of the board.

Comments from BrownRedHawk

Also, if your bits are burning, they could be overly dull and/or not enough feed pressure. Allowing the bits cutting face to slide can cause this. I've also had second hand bits sharpened inappropriately so the cutting face is narrower than the shank of the bit that caused excessive burning and poorly shaped holes.

Answer 2

If the screw has threads that stand proud of the shaft, then it may be necessary to drill two different-sized holes: the base piece receives a hole determined by the size of the shaft (softer woods may receive a slightly smaller pilot than harder woods); the piece being attached requires a hole that will allow the threads to pass through easily, so that the threading action pulls the two pieces together. I have a set of bits that do both at once, but I find them a bit small, so I regularly have to go up a size (use #10 for a #8 screw, etc.). Maybe it's just my kit (Makita); I haven't tried others. Also, make sure you're using a fine thread screw, if you're working with hard woods.

Answer 3

I like to put a piece of masking tape over the wood before drilling a pilot hole. It's not 100% fool-proof, but does cut down significantly on splitting.

Answer 4

I also find that when I make pilot holes and countersinks that my wood is still prone to splitting.

The first thing this suggests is that the holes aren't large enough, however some woods are particularly prone to splitting. The size of the hole in relation to the thickness of the wood is also a big factor.

I've read suggestions that you should slightly over-drill the clearance holes to help prevent this, but this is bad practice. Just shy of the screw's total length is the correct depth.

That and my bits are burning in hardwood (oak I think) so something is wrong there.

Drill more slowly. Some woods are prone to scorching, oak is one, but slowing down is rarely a bad idea anyway.

It's not a huge deal if you get some scorching in screw clearance holes (it is when drilling for dowels as it can prevent a proper glue joint from forming) but it is still best to avoid it if possible.

Also holding the drill as straight as possible can help, so that the shaft of the bit doesn't rub the hole, but you can still get burning when using a drill press so this isn't a sure fix.