Tuesday, January 13, 2009
Tech-Tip Tuesday : Pattern Stock
When building a strip canoe, it's necessary to make patterns which are the cross-sectional shape of the canoe. Over time, I've seen a wide variety of materials used for this task. I've seen rigid foam (don't ask me how they did it...), Plywood (of various ilks...), MDF, glued up pine, and chip-board. They all have their ups and downs.
Usually, you are looking for a consistent material with no voids that is flat and thick enough for your purposes - 1/2" to 5/8" thick is usually fine. You want something inexpensive and easy to bevel. It should also resist warp and hold staples well. In the case of my students, I'm usually looking for an additional feature - light weight. (We move our forms in and out of the shop at every class!) While the pine isn't bad if you alternate the grain direction to avoid warping, I tend to prefere sheet goods for cost and ease of use.
Personally, I prefer plywood underlayment with patched voids. It's inexpensive and does the job well. If I wasn't lifting the boat and forms, I'd go for MDF as it's cheaper and very stable, although heavy. Chip-board is about the worst material I've used. It doesn't machine well, has random voids and it doesn't hold a staple well for some reason. One fellow I know prefers MDO for the nice paper face it has so that he can lay out patterns with ease. Unfortunately, it's a bit on the pricey side.
When choosing materials, I think it's very important to talk to the people at your local lumberyard. There are a wide variety of sheet goods out there - some are very similar in function, but can vary widely in price. Very often, they can point you in the direction of a less-expensive substitute if you tell them what you're doing with it.