Pull Boring Highlights the Capability of Deep Hole Making

Published 6/24/2011

Pull Boring Highlights the Capability of Deep Hole Making

Pull boring enables users to achieve remarkable straightness in deep holes. A variation of this technique is also effective when maintaining consistent wall thickness (in long, cast pipes, for example) is top priority.

Mark Albert

Editor Emeritus, 91��Ƶ��վ��

Although deep hole drilling machines such as this B630 from Unisig are designed for the special needs of creating holes through long workpieces, they have the flexibility to perform a variety of operations such as boring, counterboring, trepanning, roller burnishing and pull boring. The machine shown here is the 10-meter version.

Pull boring is a precision operation in which a cutter is pulled through an existing hole to improve straightness.

Because the ability to make deep holes effectively and efficiently is critical in many applications, deep hole technology is one of the most highly developed sectors in metalworking. It covers a diverse range of processes and methodologies. Unisig (Menomonee Falls, Wisconsin), a supplier of machines, tools and automation for deep hole making, says the list of industries it serves includes aerospace, automotive, defense, hydraulics, mold making, oilfield and energy. Yet deep hole making is largely the domain of shops specializing in this capability, whereas technology suppliers such as Unisig believe that a wider awareness of deep hole making processes would alert new users to valuable opportunities.

As an example of how deep hole technology has mastered some of its most extreme challenges, Unisig points to one particularly interesting technique: pull boring, which enables users to achieve remarkable straightness in deep holes. A variation of this technique is also effective when maintaining consistent wall thickness (in long, cast pipes, for example) is top priority.

As its name implies, pull boring involves pulling a cutter through an existing hole. Pull boring is usually performed on the same machine that created the original hole. In this case, a boring bar is inserted all the way through the existing hole. After emerging at the opposite end, the bar is fitted with a single-point pull boring head. The bar is then engaged in the tool drive mechanism and drawn back through the workpiece. The bar rotates in one direction, while the workpiece is rotated in the opposite direction by the work spindle. The tooling head holds a carbide insert of the appropriate grade and style for the workpiece material. This insert functions much like an ID turning tool, enlarging the original hole slightly as it is pulled into the workpiece. Coolant pumped around the boring bar channels chips up and out through its hollow center to aid metal removal and protect the surface.

According to Sarang Garud, a Unisig applications engineer, hole drift tolerances achieved by pull boring can be less than 0.001 inch per foot (0.08 mm/meter) of workpiece length, if material, tooling and process conditions are favorable. However, reaching this level of straightness may require several passes.

For concentricity, a multi-point pull-boring head is used instead of a single-point tool. A multi-point tool typically has between two and six inserts, Mr. Garud says. Wear pads are located in front of the inserts so that the existing ID of the bore provides support during cutting. In contrast, a single-point head is supported by the finished bore ID, so wear pads are located behind the insert.

Mr. Garud notes that pull boring involves several nuances. For example, it is customary to make the original hole by boring halfway through the part, turning it end for end and boring the second half of the hole. This practice reduces the overall out-of-straightness condition in the resulting hole because each half of the bore will show less drift compared to a hole bored all the way through in a single pass. Thus, pull boring has a “head start” in its straightening action.

Pull boring can be applied to any part that a deep hole machine can accommodate. The only limit on part length is the length of the deep hole machine. Likewise, pull boring benefits from the same qualities of accuracy and rigidity in the deep hole machine that affect the original boring operation. In addition, sensing the rate and pressure of coolant flow, which the Unisig machines do automatically, enables users to protect workpieces and cutting tools by closely monitoring cutting conditions during pull boring.

A special accessory that makes pull boring more efficient is the lantern chuck. A drum-shaped device with openings on opposite sides, the lantern chuck is installed at the workpiece headstock end of the machine. The side openings make it easy to install and align a guide bushing for the pull boring tool. The lantern chuck also eliminates the need to machine a special pilot hole otherwise required so that the pull boring tool enters the workpiece on center.

Advances in deep hole technology will strenghten the capability of specialist shops while widening its use in general metalworking. By providing complete machining systems, tooling, coolant, accessories and process know-how, Unisig says it is ready to support customers following either trend.

Related Content

Quick-Change Tool Heads Reduce Setup on Swiss-Type Turning Centers

This new quick-change tooling system enables shops to get more production from their Swiss turning centers through reduced tool setup time and matches the performance of a solid tool.

How to Accelerate Robotic Deburring & Automated Material Removal

Pairing automation with air-driven motors that push cutting tool speeds up to 65,000 RPM with no duty cycle can dramatically improve throughput and improve finishing.

The Future of High Feed Milling in Modern Manufacturing

Achieve higher metal removal rates and enhanced predictability with ISCAR’s advanced high-feed milling tools — optimized for today’s competitive global market.

Holemaking 18 Dec 2023

Custom PCD Tools Extend Shop’s Tool Life Upward of Ten Times

Adopting PCD tooling has extended FT Precision’s tool life from days to months — and the test drill is still going strong.

Economics

Last Chance! 2025 Top Shops Benchmarking Survey Still Open Through April 30

Don’t miss out! 91��Ƶ��վ��'s Top Shops Benchmarking Survey is still open — but not for long. This is your last chance to a receive free, customized benchmarking report that includes actionable feedback across several shopfloor and business metrics.

Automation

AMRs Are Moving Into Manufacturing: Considerations for Implementation

AMRs can provide a flexible, easy-to-use automation platform so long as manufacturers choose a suitable task and prepare their facilities.

Top Shops

Machine Shop MBA

Making Chips and 91��Ƶ��վ�� are teaming up for a new podcast series called Machine Shop MBA—designed to help manufacturers measure their success against the industry’s best. Through the lens of the Top Shops benchmarking program, the series explores the KPIs that set high-performing shops apart, from machine utilization and first-pass yield to employee engagement and revenue per employee.

91��Ƶ��վ��

Pull Boring Highlights the Capability of Deep Hole Making

Share

Related Content

Quick-Change Tool Heads Reduce Setup on Swiss-Type Turning Centers

How to Accelerate Robotic Deburring & Automated Material Removal

The Future of High Feed Milling in Modern Manufacturing

Custom PCD Tools Extend Shop’s Tool Life Upward of Ten Times

Read Next

Last Chance! 2025 Top Shops Benchmarking Survey Still Open Through April 30

AMRs Are Moving Into Manufacturing: Considerations for Implementation

Machine Shop MBA

Country

Industries Served

Operations Performed

Welcome to 91��Ƶ��վ��!

Pull Boring Highlights the Capability of Deep Hole Making

Share

Heidenhain Corporation

Featured Content

Featured Videos

SMW Autoblok Corporation

Featured Content

Featured Videos

CNC Engineering, Inc.

Featured Content

Featured Videos

T J Davies, Co., Inc.

Featured Content

QualiChem Inc.

Featured Content

Featured Videos

Mikron Corp.

Featured Content

Featured Videos

All World Machinery Supply

Featured Content

Featured Videos

ZEISS Industrial Quality Solutions

Featured Content

Featured Videos

Related Content

Read Next

Country

Industries Served

Operations Performed

Welcome to 91��Ƶ��վ��!