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 IC 9047 
 
 Bureau of Mines Information Circular/1985 
 
 NOV 27 i9C: 
 
 , OOPY_.. ^,.<$'' 
 
 Lightweight Fiberglass Feed Leg 
 for Hand-Held Pneumatic 
 Percussion Rock Drills 
 
 By Ellsworth R. Spencer 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
 T5J 
 
 AMINES 75TH A^»^ 
 
■tt iaiafMgaCT? ff*ptU- 
 
 Information Circular 9047 
 
 Lightweight Fiberglass Feed Leg 
 for Hand-Held Pneumatic 
 Percussion Rock Drills 
 
 By Ellsworth R. Spencer 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
 Donald Paul Model, Secretary 
 
 BUREAU OF MINES 
 Robert C. Norton, Director 
 

 Library of Congress Cataloging in Publication Data: 
 
 Spencer, Ell 
 
 s worth R 
 
 
 
 
 
 
 Lightweigh 
 rock drills. 
 
 fiberglass 
 
 feed 
 
 leg for hand-held 
 
 pneumatic percussion 
 
 (Informatior 
 reau of Mines ; 
 
 1 circular / 
 9047) 
 
 Unite 
 
 d States Department of the 
 
 Interior, 
 
 Bu- 
 
 Supt. of Docs, no.: I 28.27: 
 
 9047. 
 
 
 
 
 1. Rock drills. 2. Boring — Equipment and supplies. 
 Series: Information circular (United States. Bureau of Mines 
 
 I. Title. 
 ) : 9047. 
 
 ll. 
 
 ^mm^^xiA^ 
 
 [TN2791 
 
 r)22s[(T21.9'45l 
 
 85-6( 
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iiw;gai>iiHBag aicaitja3»H ir.>iWtes)HcT.i»~r a::4^.— ;-- 
 
 ^ 
 
 CONTENTS 
 
 Page 
 
 k 
 
 y Abs tract i 1 
 
 Introduction 2 
 
 \'^ Rationale 2 
 
 ^ Design 3 
 
 -^ Testing 5 
 
 Summary 6 
 
 ILLUSTRATIONS 
 
 1. Standard aluminum feed leg on hand-held percussion drill 3 
 
 2 . Components of fiberglass feed leg 4 
 
 3. Overall dimensions of fiberglass feed leg 4 
 
 4. Offset stoper version of fiberglass feed leg 5 
 
 5 . Standard version of fiberglass feed leg 5 
 
 TABLES 
 
 1 . Comparisons of rock-drill and feed-leg weights 3 
 
 2. Approximate costs of feed legs 3 
 
 
 

 UNIT OF MEASURE ABBREVIATIONS 
 
 USED IN 
 
 THIS REPORT 
 
 dBA 
 
 decibel (A-weighted network) 
 
 Ibf 
 
 pound (force) 
 
 fflbf 
 
 foot pound (force) 
 
 pet 
 
 percent 
 
 in 
 
 inch 
 
 psi 
 
 pound per square inch 
 
 lb 
 
 pound (mass) 
 
 
 
LIGHTWEIGHT FIBERGLASS FEED LEG FOR HAND-HELD 
 PNEUMATIC PERCUSSION ROCK DRILLS 
 
 By Ellsworth R. Spencer^ 
 
 ABSTRACT 
 
 A lightweight fiberglass feed leg for hand-held pneumatic percussion 
 rock drills has been fabricated and tested by the Bureau of Mines. Its 
 lighter weight facilitates easier handling of the rock drill apparatus, 
 thereby reducing the potential for back injury to the driller and in- 
 creasing drilling productivity. Current hand-held feed leg drills of 
 the same class are 50 pet heavier than the Bureau-devised feed leg 
 drill, which is comprised of a reduced-noise drill and the fiberglass 
 feed leg. In-mine tests of the fiberglass leg showed that its perform- 
 ance and cost are comparable to those of standard aluminum feed legs. 
 
 1 
 Physical scientist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
 
INTRODUCTION 
 
 Hand-held pneumatic percussion rock 
 drills, called "stopers" (for vertical 
 holes) or "feed leg drills" (for hori- 
 zontal or angled holes) are thrust into 
 the rock by means of an air-powered cyl- 
 inder called a "feed leg" (fig. 1). 
 They are heavy (over 100 lb), bulky, and 
 must be set up and operated by hand. 
 Basically, a feed leg consists of two 
 tubes, an outer tube usually made of 
 aluminum for lightness and an inner tube 
 made of aluminum or steel that is con- 
 nected to the underside of the rock 
 drill. The inner tube is fitted with a 
 piston at its lower end that slides in- 
 side the outer tube when air pressure is 
 applied. At the bottom of the outer 
 tube is the stinger, a steel point that 
 digs into the ground for support of the 
 
 feed leg and rock drill. A steel bushing 
 fitted to the top end of the outer tube 
 guides the inner tube when it is extend- 
 ed. Pressurized air is passed through 
 the center of the inner tube and piston 
 and forces them to slide forward, therby 
 providing thrust to the drill. 
 
 The feed leg provides vertical and hor- 
 izontal thrust while the drill operator 
 provides the needed directional thrust. 
 During drilling, the weight of the rock 
 drill must be balanced between the forces 
 being exerted by the feed leg and the 
 driller; otherwise, the drill will "hang" 
 on the steel. As the hole gets deeper, 
 the inner tube slides out until it is 
 fully extended. More drill steel is then 
 added, or the inner tube is retracted and 
 the feed leg repositioned, or both. 
 
 RATIONALE 
 
 Although standard aluminum and steel 
 feed legs do not present serious health 
 and/or safety problems by themselves, 
 they have received attention from the Bu- 
 reau of Mines because they are used on 
 hand-held mining drills, which do present 
 such problems. Noise is the greatest 
 health hazard associated with these 
 drills; noise levels of standard drills 
 commonly range from 115 to 120 dBA or 
 greater. Because Federal regulations do 
 not permit continuous noise levels above 
 115 dBA, the mere startup of these drills 
 can result in operator overexposure. In 
 addition, the excessive vibration of the 
 drill handle can lead to Raynaud's 
 ("white finger") disease, an affliction 
 characterized by severe damage to ar- 
 teries and tissues of the fingers. The 
 frequent manual repositioning of the 
 drill can cause muscle pulls and other 
 injuries because of the weight (over 100 
 lb) and awkwardness of the drill-leg 
 configuration. 
 
 In conjunction with Bureau efforts to 
 devise "quiet" hand-held mining drills, 2 
 a lightweight fiberglass feed leg has 
 been fabricated. The major advantage of 
 fiberglass as the feed leg material is 
 that its high strength-to-weight ratio 
 
 results in a lower overall drill weight. 
 In fact, the combined weight of a stan- 
 dard drill with an aluminum leg is 50 pet 
 more than the combined weight of the fi- 
 berglass leg and the quiet drill develop- 
 ed by the Bureau (table 1). Miner ac- 
 ceptance of the quiet drill is increased 
 due to the presence of the fiberglass 
 feed leg, and the likelihood of injury 
 while repositioning the drill is reduced. 
 The lighter weight could also lead to an 
 increase in miner productivity due to a 
 reduction in hole-to-hole repositioning 
 time. Another potential but unproven 
 benefit of the fiberglass feed leg, even 
 when used on standard drills, is a reduc- 
 tion in the noise and vibration emanating 
 from the feed leg itself. 
 
 ^Creare Products, Inc. Development of 
 Commercial Quiet Rock Drills. Ongoing 
 BuMines contract J01 771 25; for inf., con- 
 tact W. W. Aljoe, TPO, Pittsburgh Re- 
 search Center, BuMines, Pittsburgh, PA. 
 
 Creare Products, Inc. Development of 
 Prototype Quiet Hard Rock Drills. Ongo- 
 ing BuMines contract HOI 1 3034; for info., 
 contact W. W. Aljoe, TPO, Pittsburgh Re- 
 search Center, BuMines, Pittsburgh, PA. 
 
Another area of consideration for com- 
 parison is cost. The greatest difference 
 is in the tubing; the inner components 
 are similar and are low in cost, so 
 they have little effect on the total 
 costs. The fiberglass tubing costs are 
 considered high because they represent 
 small-order pricing, not large-volume 
 discounts. The final price at production 
 level is arbitrary for the fiberglass 
 feed leg because of this and other vari- 
 ables, and is reflected as a wide price 
 range in table 2. 
 
 TABLE 1. - Comparisons of rock-drill and 
 feed-leg weights, pounds 
 
 
 Bureau'' 
 
 Standard2 
 
 Feed lee» •••••••••••• 
 
 18 
 50 
 
 30 
 
 Hard rock drill 
 
 73 
 
 Total 
 
 68 
 
 ^103 
 
 
 
 ^Fiberglass feed leg, "quiet" drill. 
 ^Aluminum feed leg. 
 
 ^51 pet heavier than Bureau feed leg 
 drill. 
 
 TABLE 2. - Approximate costs of feed 
 legs, dollars 
 
 FIGURE 1. - Standard aluminum feed leg on 
 hand-held percussion drill. 
 
 
 Feed leg 
 
 
 Fiberglass 
 
 Standard Al 
 
 Tubing cost 
 
 Total cost 
 
 Selling price*" . . 
 
 200 
 
 475 
 
 575-800 
 
 100 
 
 375 
 
 600-700 
 
 ^Estimated. 
 
 DESIGN 
 
 The construction of the fiberglass feed 
 leg is similar to that of aluminum feed 
 legs. Figure 2 shows the individual com- 
 ponents of the fiberglass feed leg; the 
 drawing in figure 3 shows its overall 
 dimensions. The outer fiberglass tube 
 provides containment of the pressurized 
 air for extension and force. A piston 
 with leather seals is connected to the 
 inner tube, also made of fiberglass, 
 which slides relative to the outer tube. 
 Aluminum is used for the piston parts, 
 bushings, end cap, and bearing sleeves. 
 
 To provide the thrust required for a 
 hard rock drill (over 600 Ibf), a special 
 
 fiberglass-wound tube developed for hy- 
 draulic cylinders and pressure vessels 
 was selected for the outer and inner 
 tubes. These new fiberglass cylinders 
 are available in the required dimensions 
 "off-the-shelf." A cross-weave fiber- 
 glass tube has ultimately been selected 
 over a single-weave tube used for prelim- 
 inary testing. The newer tube has the 
 better flex and strength characteristics 
 that are a concern in the rock drilling 
 environment, even though the earlier tube 
 has performed well under very stressful 
 conditions. The material properties of 
 
FIGURE 2. - Components of fiberglass feed leg. 
 
 Guide bushing cap 
 
 Nut 
 
 Outer tube 
 
 Inner tube with brake 
 
 End cap 
 
 rt'»fl«*>Vl^*'Vi^ 
 
 WW^ 
 
 
 Stinger 
 
 FIGURE 3. - Overall dimensions of fiberglass feed leg. 
 
 this fiberglass include a high strength- 
 to-weight ratio and high internal 
 damping, double that of aluminum. Ten- 
 sile strength is 65,000 psi, compressive 
 strength is 50,000 psi, and the charpy 
 impact rating is 5 fflbf,3 Comparable 
 aluminum tubing of 2024 alloy has 70,000 
 psi tensile strength and a charpy impact 
 rating of 3 fflbf. 
 
 A return spring with rate of extension 
 brake is also built into the leg. This 
 return spring and brake fit inside the 
 outer tube to provide a retraction force 
 and limit the rate of leg extension. The 
 
 limiting of extension rate is needed as a 
 safety feature if the drill steel fails 
 or the leg stinger slips, a major hazard 
 with these drills. 
 
 ■^Charpy impact is a pendulum- type, 
 single-blow impact test in which the 
 specimen, usually notched, is supported 
 at both ends as a simple beam and broken 
 by a falling pendulum. The energy ab- 
 sorbed, as determined by the subsequent 
 rise of the pendulum, is a measure of the 
 impact strength or notch toughness. 
 
TESTING 
 
 To verify the potential value of fiber- 
 glass feed legs on both the standard and 
 the Bureau devised quiet drills, Tech En- 
 terprises, Inc.,'* a small manufacturer of 
 hand-held rock drills agreed to design, 
 build, and test a prototype for the Bu- 
 reau. Tech Enterprises' expertise in 
 this area and the initial testing at the 
 Colorado School of Mines Experimental 
 Mine provided valuable information that 
 led to the final design of the leg. Two 
 different drill-mounting methods were 
 used, an "offset stoper" version (fig. 4) 
 and a standard feed leg version (fig. 5). 
 
 ^Reference to specific manufacturers 
 and materials does not imply endorsement 
 by the Bureau of Mines. 
 
 During initial testing, the feed leg 
 provided enough thrust (about 200 to 400 
 Ibf) to stop drill steel rotation; how- 
 ever, several minor modifications were 
 made to counteract problems that arose. 
 First, the mounting clamps failed and 
 slipped on the outer fiberglass tube. To 
 eliminate this problem, the outer tubing 
 was threaded, and a new mount was design- 
 ed to reduce the bearing pressure needed 
 to hold the clamps firmly to the tube. 
 Second, a Nylatron bearing caused stick- 
 ing and scoring inside the leg; an alumi- 
 num replacement bearing eliminated this. 
 Third, elastomer seals were replaced with 
 leather seals because of sticking and 
 bonding problems between the elastomer 
 and the fiberglass. 
 
 FIGURE 4. - Offset stoper version of fiberglass 
 feed leg. 
 
 FIGURE 5. - Standard version of fiberglass 
 feed leg. 
 
In-mine testing showed that the thrust 
 capability of the feed leg was unchanged 
 after the modifications were made. Im- 
 pacts of rocks during drilling and trans- 
 port of the drill with feed leg attached 
 did not damage the fiberglass surface. 
 
 Further testing is planned with produc- 
 tion mines in Canada, South Dakota, Colo- 
 rado, and Wyoming that have expressed in- 
 terest in the new drill and fiberglass 
 feed leg to ensure that the new materials 
 will perform over an extended period. 
 
 SUMMARY 
 
 The fiberglass feed leg has performed 
 as expected and shows potential as a 
 lightweight, highly damped, and lower vi- 
 brating alternative to the standard alu- 
 minum and steel feed legs; drill opera- 
 tors consistently have preferred the 
 lightness and balance of the fiberglass 
 feed leg. About 80 holes have been 
 drilled using the fiberglass feed leg 
 with the usual minor problems in proto- 
 type equipment being found and 
 corrected. 
 
 During early testing for noise attentu- 
 ation, comparisons between the fiberglass 
 feed leg and an aluminum feed leg indi- 
 cated little or no noticeable noise re- 
 duction. This can be attributed to the 
 much higher noise level of the rock drill 
 during operation. While actual use dem- 
 onstrated no obvious noise reduction, the 
 
 vibration damping and weight advantages 
 support the continued development and use 
 of the fiberglass feed leg. 
 
 More testing is required to determine 
 compatibility and durability of the fi- 
 berglass tubes and aluminum bearing com- 
 ponents. A commercial firm plans to man- 
 ufacture and test the lightweight. Bureau 
 devised quiet rock drills with fiberglass 
 feed legs in several mines. Preliminary 
 reports indicate the company's willing- 
 ness to produce the feed leg for commer- 
 cial use when tests are sucessfully com- 
 pleted. Although the cost of the proto- 
 type fiberglass feed leg was higher than 
 that of an aluminum feed leg, the cost of 
 the commercial fiberglass feed leg is ex- 
 pected to be much lower. 
 
 vSrU.S. CPO: 1985-505-019/20,107 
 
 INT.-BU.OF MIN ES,PGH.,P A. 28)03 
 
■TIRS? 
 
*»fifiMnim}ifM"»<i»<'Tni^m!Hiitii!i»T)mir>fTfTr'''"*^'r 
 
U.S. Department of the Interior 
 Bureau of Mines— Prod, and Distr. 
 Cochrans Mill Road 
 P.O. Box 18070 
 Pittsburgh. Pa. 15236 
 
 AN EQUAL OPPORTUNITY EMPLOYER 
 
 OFFICIALBUSINESS 
 PENALTY FOR PRIVATE USE. S300 
 
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