CTS 87.339: NPC Journal 4(1), Jan 1987, pp 75-77

The Story of a Rock Drill

Ron Bury

The idea of building a rock drill was probably conceived after reading about the ULSA drill, an awkward, heavy piece of ironwork which, I was informed, had an inherent tendency to pack up due to crud in the screw threads.

Action was prompted following a letter from Arthur Champion to the CPC Newsletter, suggesting that the ULSA drill might be improved by using a hydraulic cylinder in place of the screw jack and spring. My reply to Arthur's letter indicated that, to all intents and purposes, a liquid is incompressible and thus if hydraulics were to be used, then some form of spring would have to be retained to make up for lost pressure as the drill bit moved into the rock. I recommended the use of pneumatics rather than hydraulics.

I decided to take up the challenge. My requirements were for a drill that would be of low weight, capable of being used in awkward, dirty places, by one person if necessary, and having a minimum of moving parts capable of being rendered inoperative by crud. A secondary requirement was that the drill should be easily stripped down for cleaning.

A hunt around the fitting shop at work produced a pile of junk with possibilities of producing what at the best could only be described as a prototype.

It has already been stated that the medium responsible for providing the pressure was to be air. At the time, I was regularly being conned by a Mr. Cordingley into carrying for his dives. Calculations showed that his mini-bottle, the first stage of his diving valve and the air cylinder that I had acquired, would theoretically give over twenty full operations of the air cylinder. With a stroke of six inches, this meant that the drill would have the promise of a ten foot deep shot hole with one caving trip - not bad for a hole day's work !

The next two or three weeks saw quite a lot of unauthorised overtime. Soon I was the proud possessor of a weird and wonderful contraption. Would it work ?

The general idea of the use of the drill is that first of all, the drill is assembled. The drill bit is screwed into the drill, the diving bottle is connected and the appropriate extension pieces attached. The drill bit is placed on the chosen spot, ideally with some means of locating the drill bit until it has started to cut its own hole, eg. the centre of a scallop mark. The extension is then adjusted to hold the drill in the required position against a suitable support and the air is carefully turned on.

Experience later proved in no uncertain way that if either end of the drill is not safely located, and there is no restrictor in the air supply, then the drill will slip, and the extension piece will disappear into the distance (rather worrying for a second or so until you realise that the projectile has in fact missed all vital parts of your anatomy and, hopefully, everyone else's as well). The handle is now turned, and all things being equal, a six inch hole is produced. If a deeper hole is required, then it is a simple matter to release the air pressure, change the extension pieces and start again.

With John Cordingley and Pete Seed as independent assessors, a gritstone cobble was removed from an adjacent wall (we don't, unfortunately, have limestone walls in Darwen), placed under the bench, the drill set up between the cobble and the bench and the air turned on. A few minutes later, the cobble had a hole through it. In the excitement, we forgot to measure the drilling speed - we went to the pub and celebrated.

One or two modifications were made and then ... nothing happened - we had nowhere to use it.

Eventually, the rust was scraped off the drill and it was taken down Calcite Way in Sell Gill. Two hours later, two cavers detackled the entrance pitch having left three five inch deep shot holes in a passage around two feet wide and eighteen inches high. The second outing was almost a complete failure. Soon after starting drilling, the bottle fell over, bending the pillar valve spindle, and producing a high pressure leak (NB. a wet rag is no good for repairing a high pressure air leak). With a rapidly diminishing air supply, it was just possible to get a couple of shot holes two or three inches deep.

Several modifications were made at this stage which made the drill lighter, more compact, and more reliable.

It has since been used a few times in another dig. I can't say where, on account that I have heard recently that a certain member is threatening to set loose his dogs on anyone publicising its location. Anyway, in this cave, the drill was used in a narrow rift, the shape of the rift necessitating the use of longer extension pieces. The extensions tended to bend and jam the drill bit in the hole, making turning the drill rather difficult, if not impossible, at times. Another problem encountered at this time was binding of the bit due to water seeping into the hole and making a paste with the dust. It would appear that the hole should either be dry or under running water.

The next stage in the development of the drill will be the inclusion of a smaller air bottle (weight seven pounds, including valves), sealed bearings and generally rebuilding to the specification of the drawing, which includes modifications intended to overcome current problems. Other factors under consideration for the new drill will be: is the drilling pressure optimum ? is the drill bit currently used the best type, or would a core drill be better ? would better efficiency be obtained by changing the cutting angles ?

Whether the new drill will be built is not known, it depends on the success and availability of commercial battery drills, on whether I can warrant the expense of rebuilding with new parts, or whether anyone will want to use it.....

engineering drawing - 16k GIF

Specification :

Drill bit Long Series Mason Master 3/4 inch
Min. Lengtht 26 inches ( with above bit )
Max. Lengtht 53 inches ( could be extended )
Max. hole deptht 8 inches ( also easily extended )
Weightt 12.5 lb ( without diving kit )
Drilling speedt approx 5 min. per inch ( varies with conditions )
Carrying volumet 15 x 8 x 2.5 inches ( without diving kit )
Number of operationst up to twenty 6 inch holes
This latter is based on 15 cubic foot bottle and Kawasaki first stage demand valve. It may be reduced by leakage or aborted operations.

( Rock drill diagram )

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