BUE

What Built-Up Edge Looks Like in Practice Built-up edge in aluminum gun drilling happens when the material welds to the cutting edge instead of flowing away as a chip. The welded material changes the effective geometry of the drill and causes poor surface finish. When I pull a drill out after seeing BUE, the cutting edge has a matte silver buildup that looks like cold-welded aluminum. The bore surface shows scratch marks and torn metal rather than the clean burnished finish I expect from gun drilling. ...

Problem Description Built-up edge in aluminum gun drilling shows up as a ragged, torn surface finish on the bore wall. I’ve pulled a 10 mm gun drill from a 7075-T6 block and found aluminum welded solid to the cutting edge, changing the effective geometry of the tool. The bore looked like it had been chewed out rather than cut, with surface finish readings jumping from 1.6 Ra to over 6.3 Ra. ...

Problem Description Built-up edge forms when workpiece material welds to the gun drill cutting edge. I see this most often on aluminum alloys and low-carbon steel like 1018. The welded material builds up layer by layer, changing the effective cutting geometry. A drill with BUE cuts differently with every pass, and the results are unpredictable. The results show up immediately. Surface finish jumps from 1.6 Ra to 6.3 Ra or worse. Hole diameter drifts as the buildup changes the drill’s effective size. I’ve measured bores opening by 0.08 mm as BUE accumulated during a single cut. On critical jobs, that kind of variation means the hole is scrap before the drill reaches full depth. ...

Why Aluminum Is a Different Animal Aluminum looks easy on paper — soft, gummy, low melting point. I’ve seen plenty of guys run it like mild steel and end up with packed flutes and a scrapped part. The problem is chip formation. Aluminum produces long, stringy chips that wrap around the drill shank and clog coolant ports if you don’t get the parameters right. Thermal conductivity works in your favor. Aluminum pulls heat away from the cutting edge fast, which means I can push speeds higher than I ever would in steel. But that same softness creates built-up edge (BUE) when the cutting edge isn’t sharp enough or the chip load falls too low. ...

I have spent years running deep hole drilling operations across a wide range of materials, and aluminum consistently surprises newcomers. Steel is forgiving in predictable ways — you manage heat, you manage feed, and the chips mostly cooperate. Aluminum fights you on a different front. The chips are long and stringy, the material wants to weld itself to your tool, and a perfectly sized bore can turn into a scratched mess in seconds. This article covers the three problems I run into most often with aluminum and exactly how I fix each one. ...