Published 8/22/2012

Tapping Oil Field Parts

Emuge’s Rekord DZBF taps promote the uninterrupted flow of chips out of the cutting zone to protect oil field components during hole-threading operations.

Mark Albert

Editor Emeritus, Modern Machine Shop

Emuge’s Rekord DZBF series of taps is designed to produce discontinuous chips with a short curl that flow readily up and out the wide-open flute when threading the grades of stainless steel and other alloys frequently used in oil field applications.

Long, stringy chips that wrap around a tap during hole threading operations can degrade the workpiece and decrease tap life. Avoiding these conditions is especially urgent in critical oil field components.

Thread connections are common—and critical—on many oil field parts such as blow-out preventers, valves, pumps, pump jacks, compressors and gears. Tapping operations on openings in these components can be complicated by problematical chip evacuation. To address these difficulties, Mark Hatch, product director—taps and thread mills at Emuge Corp. (West Boylston, Massachusetts) offers these observations and product recommendations.

For example, he notes that the size and complex shape of components make it a challenge to monitor and clear taps of chips that tend to “birdnest” around the tap’s shank. To withstand the harsh environment of the oil field, many of the parts are manufactured in 4140 and 4340 grades of steel, which produce long, continuous chip formations when tapped. Stringy chips of this type are likely to wrap around a cutting tool to form the birdnest-like tangles. In addition, the most common thread diameter range is from 0.5 to 2.0 inches, with coarse pitches of UNC and 8-UN. Coarse pitch threads have a thick cross-section that can compound the problems associated with evacuation of long, thick chip braids. Mr. Hatch adds that many parts are also safety-critical components, which demand true-to-gage threads with high surface quality, so there is little room for error.

Emuge’s answer to these challenges includes its Rekord DZBF taps that now feature
Emuge CBTz, the company’s latest development in chip-breaking technology. It is designed to promote the uninterrupted flow of chips out of the cutting zone. This eliminates the potential
for tap failure due to chip packing in the flutes or chips birdnesting around the shank, Mr. Hatch says.

The taps are produced with a cutting face geometry and spiral flute form, which combine to affect chip flow, chip curl and chip length. This design produces short, broken, controllable chip formations that prevent flute clogging and potential failure of the tap due to chipped cutting teeth or breakage. Mr. Hatch says this technology contributes to higher reliability of the threading process, eliminates machine downtime required to clean chips, improves tool life, produces a better surface finish and also increases operator safety.

The Rekord DZBF series taps are made of premium cobalt high speed steel and ground with eccentrically relieved threads that feature full pitch diameter relief. In this series, the tap surface is coated with titanium nitride (TiN) to reduce friction between the tap and workpiece, which improves thread finishes and increases tool life in carbon and alloy steels, cast and forged steels, tool and die steels and 300 stainless steel as hard as 35 HRc.

Mr. Hatch points out that these taps are ground with an increased pitch diameter, designated 2BX, which enhances the gage tolerance for a 2B class-of-fit, to add ample wear allowance for extended tool life. The taps are made with DIN-length shanks for extra reach, improved chip evacuation, effective cooling and lubrication, he adds. The taps can be used in both horizontal and vertical machining applications. This reduces tooling change-over time and eliminates the need to stock two lines of taps in the tool crib. As a final note, he adds that modified bottom chamfer on these taps improves performance in blind holes.