Dec 2002
 

The start of the construction!

It seemed sensible to start by building the tubular frame, then add the supporting strip for the deck, and then the deck panels until the deck was complete. Once this was complete I could then build downwards, to create the cockpit and side planing panels, then add the floor. I planned to screw most of it together, then do all the welding in one go.
 

Bending

I already had a hydraulic pipe bender which with a little skill, patience, and extra inserts could be used to bend any pipe thickness up to about 2.5" to almost any bend radius. The idea was to bend the outer frame tubing to a smooth curve (around 0.9m radius) to give the front of the craft, and bend tighter curves to form the rear corners (around 0.5m radius).

Using the templates as a guide I then bent the front tubing, and rear corner sections of the outer frame using the Clarke hydraulic pipe bender. The pipe bender is really just a standard car jack, inside a steel frame, with some formers and rollers to press the pipes into the required shape, but itís a nice bit of kit none the less. Although the formers that come with the pipe bender are fixed radius and so would give only a certain bend, the machine can be used for more gentle curves by putting in a series of very small bends at regular intervals along the length of the pipe.

The small bends are done by jacking the formers against the pipe until there is firm contact, and then applying a fixed number of strokes (say about 5 or 6) of the jack handle to put a small bend into it. You then release the hydraulic pressure, move the pipe through by 5cm and after jacking the former into firm contact again, give the same number of strokes another six strokes, then repeat. Once you reach the end of the pipe, you will probably need to repeat the whole curve again to tighten up the bend, but this time itís best to put each mini-bend between the previous runís bends, so the first one starts 2.5cm before or after the very first bend, and the next is another 5cm on.

Bending the initial rough curves is quite easy, but fine tuning the curve so that it matches the template to within about 2mm is much more time consuming, because you donít want to bend it too tight then have to unbend it (metal fatigue problem) so you need to be cautious. With experience the results can be pretty good. You would have to look pretty closely to spot that the curve was made that way.

Sheet metal cutting

I cut out the semicircular bow deck panel, first using a jigsaw to get it roughly right, say to within 5mm, then using the guillotine to trim off the last few millimetres. The guillotine is really handy Ė itís quick, easy to use, and you can get very accurate cuts, if youíre careful, even on a curved edge. It looked like I would be using it a lot, so I drilled holes in the fold away bench so that the guillotine could be bolted in place when required. I also cut out the rear corner deck panels Ė quarter circles radius 536mm.

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