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Waterjet planning

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LauraJ

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I'm making progress getting my various sheet metal pieces into CAD for the waterjet, but I was wondering how many extra pieces I should request.

In my theater construction work, I'd usually get 10% extra materials to cover any oops moments, or discoveries that the plan missed out on a couple of 2x4s. I've heard many people say that they make airplane parts three times before they have something they want to put on the plane. Seems like there's a happy medium between 110% and 300%.

My sheetmetal parts fall into four basic categories: those which are flat, those which are bent, those which are welded, and those which are bent and welded. The flat ones (the minority) I'm not too worried about -- 110% seems like overkill.

However, for the bent ones, 110% feels about right: bending is a low-speed operation, and can be done carefully enough that I'm not worried about making each one three times, but I can easily see where I'd make enough mistakes to want that 10% overage on each part, particularly if I need to apply heat to get the bend done.

Where things get more uncertain for me is the welded parts: I'll be doing lots of practice welding, but welding proceeds at a comparatively speedy pace, and I can see myself making more mistakes on airplane parts here. Is this the area where I want more like 200% coverage?

Obviously I can also make parts by hand if I blow up too many of my waterjet parts, but as long as I'm spending the money on the waterjet work, I strongly suspect it won't cost much more (as a proportion of the base cost, anyway) to get extra parts cut out in anticipation of my future butterfingered self.

I still need to figure out who I'm working with and get their opinion on how to work this out, but I feel like the decision on how many extra parts to cut is one I should make independent of cost, so I can at least balance cost and future pain.

I appreciate any thoughts.
 

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