Guide-Bushings

Problem Description Material transfer on guide bushings happens when workpiece material bonds to the carbide bearing surface during deep hole drilling. I’ve seen this most often when running 304 stainless steel and Inconel at spindle speeds above 4,000 RPM. The transfer builds up progressively, scoring the bushing bore and eventually marking the drill shank. Once the transfer exceeds 0.05 mm in height, it creates a hot spot that accelerates further adhesion. The bushing clearance closes up and the drill starts to bind. I’ve had jobs where a single bushing went from clean to scrap in under 200 parts because I didn’t catch the early signs. ...

I use a fixed setup checklist for every deep hole drilling job. It takes five minutes to run through and has prevented more scrapped parts than any other process control I have implemented. A cold machine, a dirty bushing, or a clogged coolant line will ruin a part faster than any programming mistake. Step 1: Machine Warm-Up I run the spindle at operating speed with coolant circulating for at least 30 minutes before starting a job. A cold machine does not drill straight holes because the spindle, headstock, and bed expand as they warm up. ...