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19. Cutting Metal

07/05/2012

Things are starting to hot up a little bit.

Last week I went to Fabrite Ltd., a small fabricator close to us in Cleobury Mortimer, to get another lot of metal fittings cut.

Just to remind you, we’ve had to get the original 1915 drawings digitised (put into digital format via AutoCad). That’s been done over a copule of years by Derek Walton and Dave Graham.

Once that was done, and I’d ordered the metal sheets from Light Aero Spares, I went to Mark Ethelston at Fabrite who has more software to convert the AutoCad drawings into the instructions needed for the waterjet cutter.

This software is very cute. It identifies all sorts of more or less invisible errors in the AutoCad drawings – places where one line overlaps another; places where a there’s an open line intruding into your cut piece, and so on. Poor Mark found a large number of these problems, and spent ages removing them by hand, before finding a button that would have done it all automatically!

Eventually, it produces a picture of what it thinks you want to cut, and then goes ahead and generate3s the detailed instructions for the cutter. If you want, it will leave the last little bit of the cut undone, so that the part remains attached to the rest of the sheet, and doesn’t drop ignominiously into the large water tank under the cutter. It also decides the best order to cut the pieces out – I was impressed to discover that it cuts all the holes out of the piece first, before cutting round the outside.

the order in which it cuts things is VERY strange. I’m sure there’s a logic to it, but I couldn’t work it out, and watching the cutting, it seemed pretty much random.

Anyway, once all the instructions were done, we went across the yard to the machine itself. there’s a large water tank with metal slats just level with the water surface. Above that is a large and very solid beam, with two cutting heads mounted on it. At the back is a control room with a computer console, a VERY powerful pump and a nice heater- very welcome on an extremely cold day. Mark fired the unit up, and very carefully aligned the cutting head with the corner of the workpiece. Once it was clamped in place, we took a deep breath, and pressed the big green Start button. The effect of 50,000psi water hitting the metal is pretty spectacular; there’s a big splash of water with the first impact, but once it cuts through the metal a fraction of a second later, it all settles down. There are regular upsurges of water from the tank during the cut, and with our very thin metal, it rips through it in no time at all.

It’s pretty unnerving watching the machine moving around; it’s so damn sure of itself!

But everything worked fine, and we managed to get all of the available steel cut in one afternoon, with a pile of aluminium wating for Mark to get round to in due course.

Then all we need is two large pieces of steel for the engine mounts (not that easy to source) and we’re all done with the metal stuff…

Here’s what the waterjet cutting looks like.

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From → Building, Technical

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