High Production Threaded Holes: Drilling Performance

I enjoy learning about advancements in science and technology. During the 50-plus years of my metalworking career I was not involved in high-volume part production. A few months ago, I wrote two columns about thread milling. During that time, I had correspondence with an EMUGE-FRANKEN USA engineer who lives in the high-volume part production world. He introduced me to tools that shine when making threaded holes in large quantities.

First a little background about myself. The highest part volumes I have been involved with were in the 1990s when I manufactured a line of chrome-plated accessories for custom V-twin motorcycles. Chromeplated billet aluminum was the rage so I made a lot of chips from 6061- T6 alloy. I recall a taillight housing that had four blind holes with 6-32 threads 3/8″ deep. That alloy will make long stringy chips. The housings were machined from 2″ x 2″ bar stock on a vertical machining center except for the threading operation. That was done on a drill press with a Procunier tapping head.

Why?

Drilling a 0.65″ deep hole with a #29 twist drill and a G81 drilling cycle will produce one chip going up each gullet of the drill that will wrap around the drill and cause trouble. The solution to that problem is to use a G87 peck drill cycle. That cycle drills at a prescribed feed rate for a short distance, then makes rapid moves up and down to break the chip, and repeats until the depth of the hole is reached.

When using a tap to thread a blind hole it is best to use a spiral flute tap. Those taps are shaped like a twist drill in that they have helical gullets to pull the chips out of the hole. The problem is you can’t peck with a tap.

So, tapping this hole produced long stringy chips wrapped around the tap. I tapped the holes manually on a drill press and cleaned the chips off the tap after every hole. Kind of slow, but better than breaking a tap and scraping a part that had 15 minutes of machining time into it. There is a burr caused by the tap entering the workpiece. I cleaned that off with an abrasive disk in a right angle die grinder.