Surface-Roughness

I have spent years chasing better surface finishes in gun drilled holes. The difference between a Ra 0.8μm hole and a Ra 0.2μm hole is not just feed rate — it is a combination of parameters, tool geometry, and process conditions that most operators do not connect. Here is what I have learned about each variable and how much it actually matters. Feed Rate: The Biggest Lever Feed rate is the single most influential parameter for surface finish. Every 0.01mm/rev increase in feed adds visible feed marks. The relationship is direct and measurable. ...

Why Surface Roughness Units Matter In my years of deep hole drilling, I have seen countless specification sheets where the customer calls out surface finish in a unit the shop floor does not use regularly. European prints often specify Rz, aerospace jobs use RMS from the old MIL standards, and medical device prints stick with Ra. If you convert wrong, you scrap parts. I keep this conversion chart posted in the inspection area for quick reference. The conversions here are based on the ISO 1302 standard and verified against actual profilometer readings on gun-drilled and BTA-drilled bores. ...

I use a contact profilometer with an extended probe for measuring surface roughness inside deep holes. The probe reaches into the bore and traces the surface profile along a measurement line. Getting a reliable reading in a deep, narrow hole takes the right equipment and a consistent procedure. Equipment for Deep Bore Roughness Measurement A standard profilometer with a short probe arm works fine on shallow, accessible surfaces. Deep holes need extension rods that carry the stylus into the bore. I use a profilometer with modular extension rods in 100 mm, 300 mm, and 500 mm lengths. Anything deeper than 500 mm requires custom extensions, and the accuracy starts to drop off. ...