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29. Folding

29/07/2012

Phew! It’s been a busy time.

After coming home with a large boxload of welded bits, I managed to fit in a trip to Fabrite to get the last few metal parts waterjet cut, and also to undertake a really tricky piece of metal bending.

It may not look all that spectacular, but believe me, this is a critical part and I really sweated over it.

It’s the front engine mount; the engine fits into the big round hole in the middle. So obviously it must finish up exactly the right width and height, and perfectly flat.

Fabrite’s posh computer-controlled hydraulic folding press (you can see a bit of it on the right of the picture) has a sort of ‘knife’ on the top and a vee-shaped groove underneath and the metal is forced into the groove by the knife.

You would think that getting the folds in exactly the right place would be a doddle; mark a line on the metal where you want the fold to be, pop line it up exactly with the point of the knife, and Bob’s your uncle.

But unfortunately it’s not that simple. the line will end up in the middle of the bend, and it’s odds-on you wanted the dimensions to the inside or outside edge of the folded bit, which will be somewhere else – not by much, but enough to be important; possibly very important.

The discrepancy can be affected by the bend radius – obviously a wide bend will cut more of the corner than a tight bend – and the type of material is critical too, but if you do things in the proper order – tell the folding press what finished dimensions you want, and let it tell you what size to cut the piece – everything’s more or less straightforward.

But we hadn’t done things in the right order, and Fabrite’s Mark Ethelstone had to sort of best-guess what settings the machine would come up with and allow for them. It was a sweaty moment – you only get one go at this, since you can’t straighten the metal out once it’s folded – but everything went well, and the top and bottom folds were perfectly placed so that the inside dimension was exactly 400mm.

The observant among you will have spotted that doing the top and bottom folds is pretty straightforward, but that bending the sides is trickier since the first folds will get in the way. It’s called box folding, and it’s no problem for Mark and his press. The ‘knife’ comes in a whole range of lengths, and you simply make up a ‘knife’ that just fits inside the earlier bends, and the job’s a good ‘un.

Well, we did those, and I have to say I was gobsmacked how well it turned out.

There’s a second, smaller frame that we also bent, and while it wasn’t quite as perfect as that first one, it was very good, and well within tolerance.

It may not sound much, but it took most of the day to get those jobs done, and there’s a bit more work yet to finish them off, including another trip to Allen Haseldine to get them welded up, but I was very happy with the day’s progress.

The following day, I headed off with parts of the control system to Briggs Brothers (who did such a good job on other machining work) to get that under way. I took along two of the original parts – the joystick and rudder bar – that form part of the control system – so that they could be measured up. Of course I couldn’t leave them there; they are far too precious!

Then it was off down to Theo’s for the next stage of assembly work!

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