Threadmaking

Tapping and thread milling can both produce internal threads in a variety of sizes, pitches and materials. This article discusses the factors that will dictate which process makes the most sense for a given job.

For many in the machining community, tapping is the preferred method of threadmaking on a CNC machining center. Yet others contend that thread milling is better. Kip Hanson breaks down the long-running argument.

Spindle bolts are made from difficult-to-machine, high-strength superalloys. They have very tight dimensional tolerances, which makes thread cutting a challenge. As a result of facing several thread-cutting problems during process development, we have learned important lessons at Mitsubishi.

Thread cutting is as close to artistic expression as one typically gets in a machine shop. Watching a machinist or toolmaker peel off perfectly formed chips with a precisely ground tool is mesmerizing.

According to Autonetics LLC, automated gaging units (AGUs) for threads are hot. The Cary, N.C.-based AGU manufacturer reported that it shipped 10 systems in the third quarter of last year to U.S. pipe mills that produce oil country tubular goods. No shipments occurred in the fourth quarter because the industry experienced a downturn, so capital expenditure projects got cut or delayed, noted Jeff Heath, COO of Autonetics. However, he said, the projects are starting to receive funding again. “We have about four in the build phase.”

The Look Ahead department includes a combination broaching and tapping tool for thread forming in the January 2017 issue of Cutting Tool Engineering.

Before CNC lathes, single-point threading was a pain in the neck. Fast reflexes were needed to engage an engine lathe’s lead-screw dial at precisely the right time and disengage it before crashing into the shoulder. Around the time of the U.S. Bicentennial celebration, tape-operated lathes made all of this headache obsolete. No more fooling with clumsy gearboxes or levers. You simply programmed where you wanted the tool to go and the machine control took care of the rest.

With the right tools, threadmilling large bore diameters doesn't have to be daunting. Read the article and check out a brief video of several threadmilling demonstrations offered by Allied Machine & Engineering Corp.

When accuracy counts, thread grinding shines. It may not be a new twist, but thread grinding is still one of the most accurate ways to produce internal and external threads.