I purchased a set of KEO M42 (cobalt) center drills, which is a countersink combined with a small drill point that’s typically used to produce a center in the end of long material that will be turned between centers on a lathe.
I use them a lot for spotting holes in metal that will be drilled on a drill press or even drilled by hand. The traditional method is to mark the hole, center punch it and then attempt to center the drill bit and start drilling the pilot hole, the usual result is that the drill bit “walks” off of the center punch and tries to drill at a slight angle. It mucks up the starting hole and it mucks up the drill bit geometry.
The reason for this is the combination of the large point/lip size and the small diameter of the drill bit shank along with its long length. The wide lip skates off of the center punch mark and the long drill bit flexes/bends.
With a center drill, the drill point is small while the drill body is large and short. It’s an extra step in the hole drilling process but if you need straight, accurately placed holes in metal it’s worth the extra effort.
These also work well on wood if you need extreme precision for hole locations. I can draw something up in CAD, print 1:1, use that as a template, attach it to the wood and then center drill the hole locations with the small diameter center drill. The hole locations will all be within .005” if you’re careful.
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Just to give you an idea of the drill body diameter vs the drill point size, it usually runs around 2.4:1.
#1 = 1/8” body = .046” hole dia
#2 = 3/16” body = .078” hole dia
#3 = 1/4” body = .109” hole dia
#4 = 5/16” body = .125” hole dia
#5 = 7/16” body = .187” hole dia
As I mentioned, these are 60º cobalt while HSS is standard but TiN coated and TiAlN coated HSS and solid carbide are also options. Optional angles are both 82º and 90º.
And finally here’s a photo of a standard length #4 body (5/16” diameter) center drill vs a 4" long length #4 body center drill usually referred to as a #4 x 4. This is a 4” version and they’re offered in lengths up to 8” long to reach into difficult areas.
If you’re interested in just trying one for your projects, I’d suggest the #4 is probably my most used size and that’d be a good way to evaluate its usefulness
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