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<title>1990: Cambridge Underground report</title>
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<center><font size=-1>CTS 91.1327/g: Cambridge Underground 1991 pp 32-34</font>
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<h2>Drill Report</h2></center>
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<p align=right>Wookey
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<p>As part of this year's techno-overkill we succeeded in getting ourselves
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sponsored by the nice men at Bosch to the tune of one cordless hammer drill.
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This, actually a GBH 24VRE, soon became named Geraldine B. Heronworthy, and
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was affectionately known as just Geraldine.
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<p>First a bit of spec: the drill has an SDS chuck which allows easy changing
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of bits by hand with no chuck key to lose underground. It comes with a 1.2
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amp hour battery which fits into the handle.
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<p>The first thing we did was adapt the drill for underground SRT use. We
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added a chain handle with which to hang it from a harness. Tony produced a
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wooden insert to plug in instead of the normal battery which had a curly
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cable attached so that an external battery could be used. Animal's Photon
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Cannon battery was ideal for this as it was 24V and designed to be caveproof
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so a connector for this was fitted. On testing in Settle carpark one weekend
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the drill seemed to go slower than with its own battery but this didn't seem
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likely to be much of a problem. Also a protective baggy was constructed by
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Julian to allow Geraldine to survive the caving experience.
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<p>In order to test the drill to determine both it and the battery's
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performance we procured a kerbstone from some roadworks and proceeded to
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drill holes in it. This also ensured that the battery had been given its
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first few discharge cycles to get it up to full capacity in accordance with
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Bosch's instructions. True to form the number of holes (30mm deep with the
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13mm bit provided) went from 14 to 19 over five charge-discharge cycles. We
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also compared the drill with a standard mains powered Black and Decker drill
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with hammer action and it proved to be able to drill holes about five times
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as fast (taking between 20 and 45 seconds depending on how hard the user
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pushed).
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<p>One problem with using a power drill for SRT bolt holes is that the holes
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drilled have conical ends and so it is very dodgy putting the standard
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self-drilling anchors in as their strength depends on the wedge (cone) being
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driven in by the end of the hole. If this end is not flat the wedge may move
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further into the hole rather than properly expanding the spit. It is also
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difficult to drill the holes to exactly the right depth with the drill, where
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only about 1.5mm of error either way can be accepted. Both these problems can
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be dealt with by finishing off each hole with the standard self-drilling
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technique but this means that a complete normal bolting kit must be carried
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along with the Drill bolting kit, which means yet more gear and is not a very
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pleasing solution.
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<p>A better solution is to use different anchors, specifically designed for
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use in conical holes. Discussions with Messrs Cordingley and Carter one night
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in Green Close about their aven bolting activities produced a recommended
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anchor - the Hilti HDK. These are also quite happy in holes which are too
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deep as they don't use the end of the hole at all.
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<p>We found the Cambridge Hilti distributor and boogied on down with grubby
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surveys clutched in our sweaty paws with intent to scrounge/buy some anchors.
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The Hilti man was astounded to discover that we were using spits around their
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maximum stated loads, carefully ignoring the usual safety margin! Having
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decided that we were nutters he was very helpful, demonstrating the HDK spits
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with their internal wedges which are driven out with a special driver, and
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photocopying the spec (see later). We even got a 15% discount out of him. We
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would have liked to buy stainless anchors in the interests of longevity, and
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thus indirectly safety and conservation, but at 28 quid for a box (100) of
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galvanised and 109 quid for a box of stainless we decided that we couldn't
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afford to be altruistic.
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<p>Tony provided a block of limestone which had been destined for someone's
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rock garden to further our experiments as all the Hilti figures were for
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concrete, as were our kerbstone holes. We had expected to get many fewer
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holes per charge but only actually got about 10 to 15% fewer. We now changed
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to using a 10mm bit to correspond with the new HDK spits. These spits have
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the same 8mm thread as the old spits (so all our hangers would fit) but can
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have thinner walls as they don't have to be strong enough to be hammered
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whilst drilling.
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<p>With this smaller bit we got significantly more holes per charge although
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there was significant variation in how many we actually got (between 34 and
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22). We assume that this variation was caused by different duty cycles,
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temperature and technique. We tried drilling holes with heavy pressure as
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fast as possible which resulted in both drill and battery becoming very hot,
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and drilling with lighter pressure and a 5 second gap between holes which
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gave a cooler drill and more holes.
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<p>We also tried placing a couple of bolts and found that when setting them
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the driver wouldn't quite go all the way in, as it had when demonstrated in
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the shop (in air), and when used on KK. We wondered about this but didn't
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realise that it was to become more significant in Austria.
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<p>A limited rock surface, the time consuming nature of the tests, and the
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complaints about noise and vibration from three floors up (the rock was
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living on Del's Churchill windowsill) all conspired to limit the total amount
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of testing, making our conclusions somewhat tentative.
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<p>It seemed from our experiments that the supplied battery had sufficient
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capacity to be useful so only one spare would be required for recharging back
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down at base. Also some practise in drilling the holes and placing the spits
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before trying it underground is beneficial.
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<p>So out in Austria Geraldine and a couple of BDH's, each containing bit,
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driver and some spits, were transported up to the cave, along with all the
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rest of the rubbish. Her first job was re-rigging Checkout (the third pitch)
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yet again, and putting in bolts for the Dreamtime traverse (wielded by Dave).
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The next day she was taken down to attempt the Yapate climb, and used to
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re-rig Bungalow Pitch on the way (Jeremy taking three attempts to get a bolt
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set properly as he hadn't practised it before).
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<p>Unfortunately the battery went flat after just half a hole at Yapate. This
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meant that despite the 30-odd holes on the surface, we were only getting nine
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holes underground - bloody typical. This sort of performance continued
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throughout the Expo, although the total use was not that high for reasons
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which will become clear shortly. Unfortunately there was never an opportunity
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to just use a whole battery in one go so the discharge always took place with
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at least one night's sitting around between start and finish. We came to the
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conclusion that a combination of the low temperature reducing the battery's
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dischargeable capacity, and a high self-discharge rate whilst not in use gave
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us this reduction in effective capacity.
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<p>After the flat battery episode Geraldine sat around for a bit until a
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tourist trip near the entrance started down Checkout. Mark Scott was the
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unfortunate who tried to abseil from one of the rebelays rigged with the new
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spits when it fell out. This, not surprisingly, led to some distrust of our
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amazing new technology so Geraldine lay disused for a time until Wookey and
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Dave brought her back up to the surface.
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<p>The fact that it seemed to be impossible to set the spits according to the
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instructions, (ie. getting the driver shoulder flush to the head of the
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spit) was primary suspect for the spit not holding properly. The problem with
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this was that if Dave couldn't set them then no-one else stood much chance.
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The testing took the form of putting bolts into boulders, tying them to
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something and throwing them off a nearby cliff. The first bolt split its rock
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so we tried a bigger one (estimated at 40 kilograms). A ring hanger was used
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as it could be loaded outwards, and about 2 metres of 10mm Edelrid attached
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that to a sling hooked over a suitable projection.
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<p>A fall factor one test went off fine so we tried a couple of Fall Factor
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2s and still failed to even damage anything. We then tried throwing the rock
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downwards to get a fall factor higher than two but on the second attempt at
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this the sling bounced off and the rock bounced down the mountain. It was
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retrieved but snapped in half across the bolthole as it was being dragged
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back uphill. The set spit could thus be examined and it could be seen that it
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really didn't expand very much at all inside the rock.
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<p>Next we searched for a really big rock which was sufficiently close to the
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edge that we could slide it off. The one chosen was estimated to weigh 150
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kilograms. This did the trick and snapped the tape with what was probably
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slightly less than a fall factor one fall. The rock shattered in the fall so
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we were able to retrieve the remaining 30 kilogram bit with the hanger in it
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to put on display as testimony to the strength of Hilti spits. The rope
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sheath had melted just above the Figure of Eight through the ring hanger, and
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it was probably this which had caused the burning smell we had noticed as the
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rock fell. We assume that the rope must have been slightly nicked or damaged
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at this point as one would expect it to melt or snap at the knot in this sort
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of test.
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<p>This testing convinced us that the new spit and drill combination was fine
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as long as the driver shoulder goes to within at least 2.5mm of the spit.
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However, it shed little light on the reason for the bolt failure. We can only
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assume that it was not set well enough, and users should make an effort to
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belt them as hard as possible to ensure reasonable setting. This attitude can
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be taken too far, as was demonstrated by Del and Dave on the very last day's
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pushing when they sheared one of the drivers off whilst attempting to ensure
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that the spit was properly set.
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<p><center><a href="hilti1-300.png"><img alt="before setting - 1k png"
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width=530 height=90 hspace=10 vspace=10 src="hilti1-100.png"></a><br>
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<b>Hilti HDK spits before and after setting.</b><br>
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<a href="hilti2-300.png"><img alt="after setting - 1k png"
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width=220 height=94 hspace=10 vspace=10 src="hilti2-100.png"></a></center>
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<p>Geraldine was next used down at the bottom of Endless to rig the Hasta La
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Vesta/Captive Wedge/Half Shaft series over a couple of trips. This allowed a
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couple of silly rebelays to be rigged which would have been practically
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impossible to do by hand. It also demonstrated just how fast rigging can be
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done with the aid of a drill.
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<p>Overall the drill was used much less than it could have been due to lack
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of confidence, lack of experience, and poor battery logistics. Despite the
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fact that we had two batteries no-one could be bothered carrying Animal's big
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one underground as it promised no more power than the standard battery.
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Inefficiency also resulted from the battery's habit of discharging itself if
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left waiting in the cave. Hopefully these problems can be resolved next year
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to make better use of Geraldine. A new battery will be constructed and some
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more thorough tests done to discover how we can get the best out of it. A new
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baggy will also be made as the original is damaged, and needs a bit of
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redesign anyway. Also, anyone who expects to use the drill next year should
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have a practice above ground first. And finally, discussion with Hilti will
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hopefully produce some solution to the problem of insufficient expansion in
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limestone.
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<hr />
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<!-- LINKS -->
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<ul id="links">
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<li><ul>
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<li>Photo of the <a href="../../bosch.htm">drill in use</a></li>
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</ul></li>
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<li>Cambridge Underground 1991,
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<a href="../../../jnl/1991/index.htm">Table of Contents</a></li>
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<li>1990 Expedition info:
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<ul>
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<li><a href="index.htm">Index</a> (more detail than in this list)</li>
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<li><a href="log.htm">Logbook</a></li>
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<li><a href="report.htm">Expo Report</a> (Diary)</li>
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<li><a href="cavegd.htm">161 Description</a> to date (ie. 1990)</li>
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<li><a href="162163.htm">Entrances 162 and 163</a></li>
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<li><a href="newent.htm">New Entrances</a></li>
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<li>Surveying Report:
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<ul>
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<li><a href="svy1.htm"> 1: Calibration</a></li>
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<li><a href="svy2.htm"> 2: Survey Production</a></li>
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</ul></li>
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<li><a href="sponsr.htm">Sponsors</a></li>
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</ul></li>
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<li><a href="../../pubs.htm#pubs1990">Index</a> to all publications</li>
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<li><a href="../../index.htm">Back to Expeditions intro page</a></li>
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</ul>
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