Tuesday, October 13, 2015

Waterjetting 37c - A Drilling Diversion

I was asked some questions about waterjet drilling of holes the other day, and it is amusing to remember where it all started, more than 30-years ago. My apologies again for the quality of the video, which has been transferred from 16 mm film, to half-inch tape and thence via a DVD to its current form, losing a little in each transition.

video

Figure 1. The Cygnet Project part 1.

Perhaps one of the more memorable parts of this was that we arrived on site on the Monday, and spent the afternoon setting up. Since there really wasn't that much to the rig we were done quite quickly, and were then faced with an hour before the end of the day. The overall object was to drill a hole 50-ft long, and we had arranged the camera crew to come for the filming on Thursday, so that we could work out all the snags first. But we had a pleasant surprise.

We put our first test nozzle on the lance, and started drilling - it drilled the full length with no problems, we added a second length - same result, and third . . . and then the fourth and within the hour we had achieved the goal for the week. (And run out of drill lengths).

We had the same sort of experience some years later in trials I helped with that were run by the University of Queensland in Australia, although this time we were self-propelling the drill head, so that when we ran out of the outer rigid frame we attached a length of hose, and it kept on drilling, until we had run through that also. Problem was that the drill was then pulling itself forward without any advance rate control, and if it went too fast it did not drill a large enough hole for some of the following structure (we had backward pointing jets for propulsion and hole cleaning).

So somewhere I have a photo of three of us holding the hose back to slow the advance as the drill moved forward, so that it would maintain the 15-cm diameter IIRC. And again we accomplished the goal well before we had expected, and without the need for a lot of sophistication in the design.

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