Jacklegs are pneumatic rock drills that are attached to telescoping legs, which push the drill for the operator. The drill is relatively light weight requiring only one person to operate, this feature and their ability to drill in all directions allowed them to replace drifters and in some cases stopers in Bisbee mines. Introduced in Bisbee during the late 1950’s these quickly became the dominant machine in use underground. Several different versions were used, Ingersoll Rand JR38A Thor 390, Gardner Denver S58 and S63F models. The very early type of jacklegs developed in the late 1940’s were pluggers with an air cylinder clamped to them. Bisbee mines were slow adopters of changes in drilling technology and never saw these in general use.
The Jackleg momentously changed underground mining and soon became to a miner what a horse is to cowboy. They are temperamental, tempestuous and spectacular to drill with. Jacklegs are also one of the most dangerous pieces of equipment used in mining. Anyone, who has spent any time operating one will have a story on how it got out of control. The mining culture has established their own jargon which varies from each mining district. The following terms are used with jacklegs in Bisbee.
S63F Gardner Denver
Bisbee term Conventional term
Machine Rock drill
Steel Drill steel
63 S63F Gardner Denver Jackleg
58 S58F Gardner Denver Jackleg
Thor 390 Thor Jackleg
Starter steel 3 ft Drill steel
Bit Rock bit
Face The rock area were the drilling is to be done
Ground Rock mass
Shanking Breaking the drill steel
Jackleg Pusher drill
The basics of drilling with a jackleg are similar between different models. The succeeding guidelines are written for the S63F (presently on display inside the Queen mine tour) and the S83F which is the currently the most commonly used jackleg in Mexico and the US mines.
To drill you will need the following items
Drill steel 5” 7” and others
Knock off rock bits
Bit hammer / axe
In line Oiler
Rock drill oil
Air hose 1” ID
Water hose ½” ID
Safety glasses or eye shield
Ear plug or muffs
Before drilling is started the work area is made safe by barring down loose rock, checking for bootlegs, wetting down and examining for loosened timber. The jackleg is brought close to the face. Before connecting the air and water lines to the machine, blowout any dirt in the air and water line by turning them on a little.
The water hose will be connected directly to the swivel on the machine. Air line will go first to an in line oiler then, leave the oiler to the machine. Note: the oiler should have a shut off valve attached to it this will make it easier to shut the air off instead of running back to the main line. All pressurized air hose connections will need to have a safety chain attached to keep the hose from whipping around in case the hoses come apart. In mining the hose connections are made with wingnut fittings instead of the more common Chicago fittings. The wing nuts are more durable and are secured by hammering one of the ears with a bit hammer.
Diagram showing parts of a jackleg
General specifications ( specs will vary on type of machine and it’s attachments)
Weight machine + leg 84 to 115 lbs.
Air psi (best operating) 90 to 110 psi
Water psi best operating 40 to 70 psi
Safety chain attached from machine to hose
Rock drill oil is used to lubricate the machine using a inline oiler. Inside the oiler, a venturi atomizes oil, sending small oil particles through the hose to the machine. It is a common practice for miners to pour a small amount of oil into the hose that is to be connected to the machine and in the drill chuck before starting to drill.
Miners used the longest drill steel possible to start the hole. This kept steel changes to a minimum, hopefully eliminating them. The longest steel commonly used in Bisbee was 7 ft. which will drill a 6 ft. hole. The chosen drill steel will then be inserted in to the chuck and snapped the steel retainer in place.
The air and water are now turned on; make sure the leg and the drill are turned off. Note if the leg is turned on even just a little it will literally throw the drill. This can be very dangerous.
Lift the drill and place the leg into position. Then pivot drill and steel to the general angle and location were the hole is to be drilled. Move the throttle now to the second or third click this will turn the drill on and should have the drill steel slowly rotating. Grab hold of the drill with one hand on the handle and with the other under the cylinder, start lifting the drill so the bit will touch the rock at the same time turn the leg control on very slightly. This will push the drill towards the rock. Use the leg control carefully and remember it takes a moment before the leg reacts to the adjustments made to it. Misuse of the leg controller will cause the drill to go wildly uncontrollable very much like riding a bull. This will usually bend the drill steel and can severely injure the operator or anyone nearby. When just learning to drill it is best to have another person help collar the hole, they will need to hold steel near the bit and help hold the bit against the rock until the hole is started . Two person collaring will also be done when the ground makes it difficult to collar holes or you need a specific position for a hole. Experienced drillers will usually collar the hole by themselves. Once the hole is collared and about 1 inch deep and secure, increase throttle to the maxim setting. The leg will need some more air. The driller should position themselves on one side of the drill with one hand over the leg control holding it lightly. Always keep one hand on the leg control in case the machine goes wild. Any observers need to stand to the sides at distance never behind or in front. While drilling the hole the drill steel will need to be kept in the center of the hole. This may require having to lift the drill or pushing down on the machine while drilling.
Diagram showing proper position of drill steel in the hole
Chattering of the drill steel indicates that there needs to be more pressure from the leg.
During the drilling the operator will need to pay attention for changes in vibrations of the drill, color changes in cuttings, loss of water circulation and if the machine lurches forward. If these changes occur slow down or stop the drilling and proceed slowly. They indicate that the rock in the hole is changing and the steel could get stuck or plugged. When the hole is finished, shut off the leg and reverse the throttle this will stop the rotation and send a blast of air into the water needle through the steel out the bit, cleaning out the hole. Turn the drill throttle on full and pull the drill out of the hole. In drilling horizontal holes it is usually best to start with the back holes (top most) and work downward to the lifters (bottom most) this will keep the holes clean of drillings from other holes. If this is not done the holes should be sealed with a rag or wooden plug. Holes drilled waist to chest high on the driller are fairly easy once one gets used to the weight of the drill and its controls. Holes drilled lower will require bending over and holding the machine up so the steel does not ride on the edges of the hole. The operator might find it necessary to straddle the leg to do this lifting, which is unsafe. The leg position is also more difficult because of the flatter angle. This causes the leg to try and skid along the floor. Adding cleats or timber might be necessary to hold the leg.
Throttle postions for drilling
Leg feed control knob and emergency leg shut off button
Drilling low holes with S83F note: the dust cause by loss of circulation of water (photo not Bisbee)
Drilling with the machine head height or above is uncomfortable because of the difficulty in controlling the machine with its leg extended this far. It might be necessary to stand on a block or if the leg handle is horizontal you can stand on it ( not advised but done often).
Drilling head height with S83F (photo not Bisbee)
Upward vertical holes, the pivot on the leg will need to be tightened so it will not move. Jacklegs are very effective in drilling upwards the steel retainer makes it easier to pull out the drill steel and helps it from falling on you when coming out of the hole. The drilling will be messy with the cuttings and water pouring on the operator. There are times when drilling vertical, the machine will go high enough to be out of reach of the operator. At these times the control of the machine is done with the air valve on the oiler. The operator standing on the handle of the leg is done in this case also.(unsafe)
Downward drilling can be done, with a jackleg, it is best to detach the leg. The lack of places to hold the drill make hard especially when trying to pull the drill out of the hole. This often will require two people.
Cleaning out drill hole with blowpipe (photo not Bisbee)
Drilling downward with S83F leg still attached (photo not Bisbee)
After the drilling is completed the holes will need to be cleaned of water and cuttings. Blowpipes or drilling spoons are used for this
Blowpipes are pipes hooked up to the compressed air and are inserted into the holes blowing out the cuttings and water. Scrapers (copper spoons) in Bisbee are made from the copper trolley wire with a scoop fashioned at one or both ends. The spoon is inserted into the holes and the muck scooped out.
Some of the common problems that occur while drilling, are plugged steels, Stuck steels, steels breaking, bit comes off steel, leg too long or too short, rocks falling.
Plugged water holes are usually caused by feeding the drill to fast through soft materials like clays. Plugged steels create a large amount of dust and can cause the steel to get stuck. A good way to unplug them is to turn the drill on and let the bit rattle against the rock face. If this procedure does not work change steels and send it to get drilled out.
Stuck steels are caused by material building up behind the bit, drilling through cracks too fast and in Bisbee mines native copper wires wrapping around the steel. They can be removed by putting a pipe wrench on the steel, rocking it back and forth while pulling out at the same time. Another method is reversing the leg direction and putting it against the face, turning the drill and leg on forcing the steel out. This method requires the steel to be stuck where there is enough room to do this and it is dangerous technique. Shift bosses will want you to recover every possible steel, rarely would miners be allowed to leave it for blast (just do not get caught blasting them).
Using wrench to remove stuck drill steel
To help prevent stuck steels, water should be continually coming back out of the hole, if the water stops, a crack has been hit. Back the drill out a little and continue drilling slowly through the crack. This will cause widening of the area around the crack and clean out any material built up in side. When you pull the steel out of the hole the bit won’t hang up on the crack edge or on material. Depending on the ground, to much feed on the leg can cause the steel to get stuck.
Bits can come off the drill steel in the hole sometimes, Cut a taper on a wooden tamping rod and insert it the hole with the bit. Try an get the tapered end in to the lost bit. Once this is done pound the tamping rod in until it is stuck in the bit and remove from the hole. You can use a drill steel in this procedure if it is a knock off bit.
Steels can break, the weak points are just behind the bit and just in front of the shank. Because of the danger of shanking (breaking the steel) a steel never push the drill in to the hole, guide the drill let the leg push. If the drill steel breaks at a point that is not inside the hole the drill will go out of control.
In mining things are never perfect, the length of the leg will often be too long or too short to effectively drill. To defeat this problem Bisbee had Jacklegs made with shortened legs. The single feed legs used here were often to short, so extensions were made for the legs.
Single feed leg with extension
During drilling the vibrations will cause rocks to loosen and start falling, this can be dangerous if not prepared for this occurrence. To help prevent this make sure the back and ribs are well scaled.
Bisbee used for jacklegs is the 1” square drill steel with a tapered end for knock off bits.
Drill steel shank
Tapered end for bit
The drill bits used in Bisbee were knock off cross bits with carbide inserts. The diameters of the bits varied with (1 ¾”dia), common for blast holes. The pattern waterholes in the bit will is important in hard ground a bit with a center waterhole would be used , in soft ground that plug’s the drill steel a bit with holes on its perimeter would be chosen. The bits are attached to the steel by pressure, the bit and steel have inverse tapers the bit will have a small brass insert inside. To seat the bit just slip the bit on the steel and hit the bit end of the steel against a rock face.
bit without center waterhole note bit has been resharpened
Bit with center water hole
Diagram showing knockoff bits
When the bits become dull or lost its gauge (width is to narrow) they need to be replaced. Knock off bits come in resharpenable and throw away styles, resharpenables would be taken back to the surface to sharpen bits that that lost their gauge are no longer usable.
To remove the bits from the steel, place the bit knocker on the steel resting on the bit and hit it with an axe or double jack. The bit will pop off the steel after a few hits.
Bit knocker on steel ready to take off bit
In line oilers use Rock Drill oil, a special vegetable based oil, which is formulated to help prevent icing up of the drill. This oil has a low toxicity from inhalation. The operator will be breathing some in through the exhaust of the machine, never use any other oil because of this it will make the operator very sick. The flow of oil can be adjusted by removing the fill cap on the oiler and turning the adjustment screw.
In shutting down the drilling operation air and water lines are shutoff and disconnected. The intakes on the machine are capped,and the rest of machine is wiped down. Hoses are coiled and their ends covered with rags to prevent dirt getting inside them. Everything then is take to a place out of the way. When storing the machine and steels it is best to stand them verticaly rather than laying them down.
Capped air and water intakes on S63F
Coiled air hose with wingnuts covered with a rag
Miners were able to do some repairs on their jacklegs. Side rods and water needles could be replaced underground. Icing of the drill is caused by too much water in the compressed air this is can be solve by draining the water separator on the compressor or main air line, checking to see if exhaust ports are clogged or blocked and /or increasing the amount of rock drill oil used by the oiler helps.
All other repairs would be sent back to the surface to a drill doctor.
Besides drilling, jack legs are used to install rock bolts. Rock bolts are a used mostly for roof/rib support. The types of bolts used in Bisbee mine were the slot/ wedge, expansion and split set. The basics of rock bolting are drill a hole, insert rock bolt into hole and tighten rock bolt. Expansion type bolts will be tightened by inserting a socket into the jackleg chuck and using the jackleg like a socket wrench.
Split set inserted into the mouth of the hole and hammered in the hole using the split set driver in the jackleg chuck.
Slot wedge style a hole is drilled and the bolt tightened by hitting the nut end with a double jack.
The introduction of the jackleg generated a vast improvement in production of underground mines. Today they are symbol of the modern hard rock miner.
Types of jacklegs used in Bisbee ( left to right)
Thor 390, S58F, S63F, S63F (short leg) JR38 (on Ground)
Code of Safe Practice for Drift Mining 1955, Phelps Dodge Corporation Fig 3
Code of Safe Practice for Stope Mining 1958, Phelps Dodge Corporation pp.73,77
Gardner –Denver Air Line Oilers bulletin LO-2
JR-300 Jackdrill Challenges comparison Form 4219 Ingersoll-Rand
The making of a Hardrock Miner Stephen, M. Voynick Howell-North Books 1978
Models FL58 & TFL58 air leg drills part list, Gardner- Denver Company, Part list FL58-6, April 1960
Henry Hernandez 2010, pers. comm., 2 February
Richard Graeme IV 2010, pers. comm., 8 February
Richard Graeme III 2010, pers. comm., 2 February
Pete Oiller 2010, pers. comm., 8 February
Thor Air tools for construction and mining, Catalog No.44 Thor power tool company p.24-p.26
Timken Carbide Insert Rock Bits suggested User Net Prices, Bulletin 15-64-B,sheet no. 3 0f 8 , April 15 1960
A room for the summer: adventure, misadventure, and seduction in the mines ... Fritz Wolff p114-117 2004 university of Oklahoma press
Glllerstrom A. Hilmer United State Patent Drill Cradle no. 2610030 Sept 9, 1952