I’ve had limited success drilling holes in pieces I’m making on the CNC. I need some 1/4" holes and have been using a 2 Flute 1/4" End Mill Bit, pecking 3.5mm holes with full retraction after each peck. In order to be successful, I need to increase the RPM to 23k!!! If I’m anything lower than about 18k, about 40-50% of the time, the bit will catch and cause a mess of a hole. I’m drilling into 3/4" Birch Plywood. At 23k, the bit suffers a little burning and the sawdust is like a powder, which then passes through the dust collector and into the vacuum.
Should I be using a 1/4" drill bit and if so, how do I prevent tear out to leave a clean cut?
check if the bits you are using are rated to do plunge cutting. you can look at
the bottom of the bit and see if you have cutting edges that go all the way to
the center of the bit. Many bits do not cut at the exact center of the bit.
it’s common that drilling with a drill bit (say an 1/8 in bit) and then going
back with a proper milling bit and going down again works much better (same
reason that when drilling large holes is best done in steps works better)
remember, the cutting speed at any point on the bit is based on rpm * radius,
when you are cutting a slot with a 1/4" bit, your radius is 1/8"
but when you are drilling with that same 1/4" bit your radius ranges from 0 to
1/8", so the closer you get to the center the slower the cutting edge is moving
in relation to the workpiece.
this is why increasing the rpm helped, but drilling a smaller diameter hole
first would reduce the problem towards the center of the hole.