Countersink Drilling with CNC Equipment

A custom-made one-piece step drill bit is your best bet for countersinking success. May 16, 2005

I have limited success getting good countersinks on fused melamine on MDF. I'm using various diameters with countersink attachments that screw onto fluted bits. Have varied vertical feeds (rotation 5000 rpm). Have tried CMT, Freud, even had diamond made, but they broke where cs met drill. Drilling a lot (millions) of holes.

Forum Responses
(CNC Forum)
From contributor M:
Are you drilling with a boring block (as found on some point to points and routers) or are you using the router itself to drill? Usually breakage is an excessive feed issue. If that is not the case, you could find a good local tool sharpener and have him grind you a custom drill or "drop back and punt" and use two tools, one for drilling and one for countersinking (wouldn't be quite as big an issue if using a boring block, because they could be set up to be used simultaneously).

From the original questioner:
I'm using a boring block (Biesse). Fixed spindle rotation is 5000. I've adjusted feed rate faster and slower. Boring with two separate bits takes twice as long. Boring about 12 counter sinks (and counter bores) per panel in lot sizes of 10,000 pieces, can't afford to double bore.

From contributor T:
If you are drilling millions of holes, you should look into getting custom made step drills. We went through a similar situation and it made all the difference in the world.

From contributor G:
Contributor T is correct in suggesting a custom one piece drill. We (Courmatt) have provided thousands of these tools for the wood industry. Whoever built a PCD C/S that attached it to a drill… Well, I won't comment. The drills can be made with a thru-bore, brad point, with a countersink or counterbore.

From contributor C:
If the drills are breaking where the countersink and drill come together, it will normally mean that the chips are clogging up in the gullet of the countersink. This can be eliminated by lining up the flutes of the drill with the gash/gullet of the countersink. You can also pull the center drill out to the transition of the flute towards the shank and again line this up with the gash/gullet of the countersink. Max RPM 1750. Using carbide tipped countersinks will help.

From contributor H:
We (Southeast Tool) have had many of the one piece countersinks and counterbores special built for our customers. Most if not all metric boring bits are made overseas now. This will be your only problem (time). I am not aware of anyone that actually builds these here in the US.