Deep Hole Counterboring and Spot Facing: Tools and Techniques
I use counterboring for bolt head seats and spot facing for sealing surfaces after deep hole drilling. Both operations are done after the main bore is complete. Getting them wrong means the fastener does not seat or the seal leaks — either one scrapes the part. Counterboring Deep Holes Counterboring enlarges the entry of a hole to create a flat-bottomed recess for a bolt head or cap screw. The counterbore has a pilot that fits the existing hole to keep the counterbore concentric with the bore. I use a counterbore with replaceable pilots so the same cutter body works for different hole sizes. ...