Thread without dread: Drilling Performance

When it comes to threading, don’t be intimidated by titanium. Although it’s notoriously difficult to machine, titanium can be successfully tapped by combining the right equipment with practices that facilitate the process. And if tapping doesn’t measure up to your standards, a threading alternative can help users meet the requirements of the most demanding titanium applications.

To begin with, shops tackling the job of tapping titanium should make sure they have a rigid workholding setup so there’s no workpiece movement during the process, said Joe Gillilan, applications engineer at Tapmatic Corp., a developer of tapping attachments and tapholders in Post Falls, Idaho. He also recommends a modern CNC machine with a rigid tapping cycle that synchronizes spindle rotation to match the feed advance of a particular tap pitch.

Providing much better control over tap position than floating tapping, rigid tapping “keeps getting more and more accurate as machines get better,” he said. “It’s really helped with tool life and thread quality.”

When used to tap tough, long-chipping titanium, benefits of high-relief geometry include longer tool life and better thread finish. Image courtesy of Emuge-Franken

Although the rigid or synchronized tapping cycle is very accurate, it can’t prevent small discrepancies between the machine synchronization and the actual tap pitch. While small, these differences can cause big problems when tapping titanium.

“The tap has to run in a condition where there’s no pushing, pulling or pressure on the flank surfaces,” said Mark Hatch, product director at Emuge-Franken USA, a tool manufacturer in West Boylston, Massachusetts. “If the feed is off, you’re going to get an imperfection in the thread form and uneven cutting forces on the tool that can cause premature failure.”

To solve this problem, both Emuge-Franken and Tapmatic offer tapholders designed to provide a minor amount of positional compensation during rigid tapping. The result, according to both companies, is much better thread quality and significantly longer tap life.

Suitable Taps

When tapping titanium, Gillilan noted, tool life will always be shorter than it would be if the operation were performed on a material that is less difficult to machine — and a worst-case scenario is tap breakage during the process. An easy way to minimize these tool-related downsides is to use a tap made for titanium.

“A lot of job shops might try to use a universal tap,” he said, “which can be done as long as it’s of high quality.”

But Gillilan added that titanium tapping shortens the life of even high-quality universal taps.

“If you’re doing a real short run, that could be OK,” he said. “But if it’s a company that does a lot of titanium tapping, a tap made specifically for titanium is ideal.”

Emuge-Franken makes taps with geometries and coatings aimed at improving tool life and thread quality in titanium applications. Hatch said a major challenge in making these tools is dealing with the high compressive forces produced by titanium tapping. Emuge-Franken does this by giving the taps a high-relief geometry, which increases the space between friction surfaces for improved lubrication and reduced torque load in both the forward and reverse directions.

In addition, he pointed out that taps designed to thread titanium need a flute angle that provides enough core strength to handle the high cutting torque produced by the process. This means that high-helix taps — with higher hook angles to improve shearing action in soft, ductile materials — cannot be used for titanium.

With a precisely machined flexure inside, SynchroFlex tapholders provide small amounts of positional compensation to improve rigid tapping results and tool life. Image courtesy of Tapmatic