Multi-Hole Patterns: Drilling Sequence and Strategy
Why Sequence Matters The order I drill holes in a multi-hole pattern affects the final accuracy of the part. Each hole relieves residual stress from the workpiece material, and the part shifts as the stress redistributes. Drilling in the wrong sequence can distort a flat plate by 0.5mm or more. I learned this the hard way on a job with a 300mm square plate of 4140 steel that needed 16 deep holes in a 4x4 grid. I drilled from the top-left corner to the bottom-right, one row at a time. The plate curled 0.3mm across the diagonal. I had to re-machine the reference faces and re-drill four holes that moved out of position. ...