Inspection

The paperwork side of deep hole drilling has grown significantly over the years. Customers who used to accept a simple dimensional report now require material certifications, process validation, and full inspection data for every batch. I have adapted my documentation system to meet these requirements without slowing down production. Here is what I document and how. What Customers Typically Require The level of documentation depends on the industry and application. Here is what I see most often: ...

The parts came back from quality control with a bright red rejection tag attached. REJECTED — SURFACE FINISH NONCONFORMING. I picked up the tag and read the reason code: “Surface finish exceeds maximum allowable roughness per print specification. Ra 3.2 micrometers maximum required. Measured value per profilometer: Ra 4.1.” I looked at the parts in the red bin. They were a batch of hydraulic manifold blocks — 4140 steel, with a 16mm hole drilled 300mm deep using a BTA drill. I’d run them myself that morning, and I knew the surface finish was good. Not a mirror finish — BTA drilling doesn’t leave a polished bore — but perfectly adequate for the hydraulic application. The customer had been accepting similar finishes from us for years without a single complaint. ...

Inconsistent regrind quality is a problem that I have dealt with from both in-house grinding and external regrind services. The symptoms are hard to diagnose because they look like machine problems — one drill runs perfectly, the next one breaks after three holes, and the only variable is the regrind quality. I started inspecting every reground drill before it goes into production, and the tool breakage rate dropped by half. ...

I use a tiered safety inspection checklist for every deep hole drilling machine in the shop. The inspections are divided into daily, weekly, monthly, and quarterly checks. Each level covers different aspects of machine safety, and the total time investment is about five minutes per day plus 30 minutes per week. The time is well spent — I have caught loose hoses, failing interlocks, and low coolant levels before they caused injuries or damage. ...

I use bore gauges for most deep hole measurements. I have measured thousands of holes across dozens of shops, and the right tool always depends on the tolerance and the hole depth. Measuring the diameter of a deep hole is not the same as checking a conventional bore. Access is limited. The bore is long and narrow. Standard calipers and bore mikes will not reach past the first 100mm. Over the years, I have settled on five main methods that cover the full range of what I encounter on the shop floor. ...

The Customer Who Refused to Let Me Inspect the Part I’ve been running CNC lathes for about fourteen years now, and if there’s one thing I’ve learned, it’s that gut feelings on the shop floor are usually trying to tell you something. This story starts with one of those feelings, and it almost ended with a fifteen-thousand-dollar chargeback. The job came in through our regular quoting process. Nothing special about it on paper. But from the moment the material showed up, something did not sit right with me. I have learned to pay attention to that feeling. ...