Material-Variation

A customer sent me a print for what looked like the simplest job I had seen in months. It was a 4140 steel shaft, 600mm long, with a 20mm through-hole drilled axially from end to end. The print had no tight tolerances. The bore diameter was 20mm plus 0.5mm minus zero. The position tolerance was 0.5mm. The surface finish was 3.2 micrometers Ra. I had drilled hundreds of similar holes in 4140 over the previous five years. I quoted it as a standard gun drilling job at $85 per part for a batch of thirty-six pieces. ...

Material Batch Variation in Deep Hole Drilling: What to Adjust When the New Batch Arrives I have been running deep hole drilling operations for over twelve years, and if there is one lesson that has cost me the most scrap, it is this: the same material spec does not mean the same material. A new batch of 4140 or 304 stainless from the same mill arrives with the same certificate, and within the first ten parts I am resharpening tools that should have lasted a full shift. I used to chase those problems by tweaking feeds and speeds blindly. Now I have a routine. This article covers what actually changes between batches, how those changes show up in the drill, and the qualification steps I run on every new coil or bar stock delivery. ...