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What is the biggest size metric drill bit you can use before you need to use a pilot hole? Answered


if you are very against pilot holes, you can always make sure you are center punched and use a rotabroach with a center pin. Looks like you can get up to a 39mm hole. You may also need to purchase a mag drill (magnetic base drill) starting around $1000

I always use pilot drills when I want accurate location (unless I'm using a milling machine). As to "ruining" drill bits, erm, that what drill bit sharpeners are for. I'd rather have to sharpen my drill bits occasionally than have often expensive materials getting made into trash by worries over a drill bit. And a Drill Doctor is a sound investment for anyone who drills a lot. I bought one several years back and have never once had buyer's remorse over the purchase.

I never pilot hole anything smaller than 3 or 4 mm BUT I always centre punch for a starting point even in wood if accuracy is critical.

It depends on the way the tip of the drill is ground.

If you look closely at a drill tip, the cutting edges join at the centre ALMOST. There is a tiny piece joining the edges called the chisel tip. This is the part that doesn't cut, and is the part that makes a drill spin off the centre mark when you do drill.

You should always PILOT bigger than the drill's chisel tip.

Some modern grinding methods for drills reduce the chisel tip and can automatically centre the drill, rather than causing it to spin out. Look for these "Split Point" drills in preference to "ordinary" drills.


Its always best to start with a smaller bit and work your way up to the large bit. This helps ensure your hole placement is accurate and your getting a good clean hole. So technically you should always have a pilot hole.

Ok but ive heard going up through the drill bit sizes wrecks your drill bits because it grabs in the undersized whole and wears out your drill bit.

Don't make small steps up. You can do a 1/8" hole then step up to your 1/2 or larger bit. The small hole isn't going to cause any more wear on the bit then drilling without a lead/pilot hole. As long as your using cutting, not putting too much pressure on the bit and not spinning the bit too fast you won't put excessive wear on the bit.

Course a hole punch only makes a small dimple and its easier to stay on that mark with a smaller bit to start. Then you can move up to the bit you want to use.

Thanks yeah makes sense. The whole purpose of a pilot whole is to guide the tip of the drill bit. Is that right or wrong.


Or in the case of a hole saw it helps guide the saw part of the bit through the right area.

The spinning tip wants to automatically stay center over the hole in front of it.