When a bore comes out oversized, pressing in a thin-walled bushing can save the part. The process involves boring the damaged hole to a larger diameter, pressing in a bushing, then boring or drilling the bushing to the original size. I have used this technique on hydraulic cylinder barrels, pneumatic valve bodies, and machine tool housings. It is a reliable repair method when done correctly, but the details matter a great deal. ...
Gun Drill Entry Bushings: Selection, Clearance, and What I’ve Learned About Getting the Start Right I have been working with gun drilling systems for long enough to know where the real problems hide. After years of chasing burrs, wander marks, and scrapped parts, I can tell you this: the entry bushing gets blamed for nothing and causes everything. I have traced more straightness problems to a worn or mismatched bushing than to anything else on the machine — coolant pressure, spindle alignment, even drill geometry all get more attention, but the humble bushing at the start of the hole is where the cut is won or lost. This article covers what I have learned about choosing, fitting, inspecting, and maintaining them so you stop fighting the first few millimeters of every hole. ...