Tuesday, February 7, 2012

Tech Tip Tuesday

Probably one of the hardest things to get across is how to select good stock.  Students making canoe paddles in my class are looking for one thing, students making oars and Greenland Style paddles are looking for something else and those making double-bladed paddles are looking for both!  Those who are going to make one-piece canoe paddles are looking for flat or plainsawn wood.   That is clear.  That has no grain run-out.  Harder still is trying to explain the grain of the boards and why it is the way it is.

With words.

Yeah.  Doesn't work so well.

So, we're going to take another approach.

To wit, pictures.

Pictures are worth at least a thousand words. 

For example, let's start with this diagram looking at a cross-section of a tree:

This gives you a basic idea of the structure of a tree - simple.  You have to know how the growth rings run in a tree to understand why the next bit of information is important.  Now, let's look how a sawyer will slice that tree into boards:

On the left,  you can see how the boards are sliced from a tree for plainsawn stock.  This leaves the growth rings running side to side on the ends of the boards, with the exception of the slices through the middle which are actually quartersawn. Ideally, for paddle blades and single board paddles, we want them to be from about 3/4 of the way out from the center of the tree so the curve of the grain as viewed from the end of the board is gentle.  The plainsawn piece has flat grain on the wide face - like this:

Why are we so picky?  It has to do with strength and dimensional stability and flexibility.  If we were to thin out a vertical grain board, it is weak along the growth rings and is liable to split from the end.  Dimensionally, once seasoned, it should be relatively stable.  The shaft will exhibit some flexibility in the direction we're going to be pulling the paddle - which is good, as a paddle that is too stiff can be tiring to use.  Blades should be made from plainsawn stock, so a single board paddle should be as well.  A wide variety of materials can be used as you can put a protective tip on the paddle.  Some paddle-making woods are found below:

·       Basswood
·       Yellow Cedar
·       Douglas Fir
·       Spruce
·       Cherry
·       Birch
·       Maple (Soft or Hard, but Soft is a bit less dense, so lighter)
·       Ash
·       Mahogany
·       Walnut  (Peruvian is lighter than American if you can find it)
·       Sassafrass
·       Butternut
·       Cypress

For oars and Greenland style paddles, I want just the opposite - I want rift or quarter-sawn stock with vertical grain running on the face of the boards for a bit more rigidity.  Oars and double-bladed paddles are long and will flex a bit just because they are long and slender, so I'll use the board that has the grain running in the other direction for stiffness.  These boards should look like this:

I recommend good vertical grain dimensional lumber for oars and Greenland style paddles if you can find it - a 2x6 or 2x8 of spruce, cedar, redwood or douglas fir.  light, but strong.  For a Greenland style paddle, these materials work and a 2x4 provides just the right amount of stock.

For the traditional double-bladed kayak paddles, I usually recommend getting the shaft out of the same materials that are used for oars or Greenland style paddles - with a vertical grain in the direction you're pulling the shaft (i.e. looking at the vertical grain as you use the paddle) to avoid making a "whippy" paddle.  For blades - either flat or laminated curved blades, I want the same plainsawn stock that I'd use for a one-piece canoe paddle.  

If I were making a multi-piece canoe paddle, I would tend to use different woods to take advantage of their best properties - light weight, stiffness, hardness, rot resistance, etc.  Light, flexible material for the shaft and plain sawn hardwoods for the grain.

Don't forget that you can be selecting pieces of wood for aesthetic purposes, too - contrasting grains and colors.

Above all, you're looking for the straightest, clear grain stock without knots, checks or wild grain.  You also don't want the grain lines to run diagonally across the board (side-to-side or front-to-back) as it will create a weak area in the paddle - particularly the shaft.

It can take a while to find good wood.  Hopefully, your local lumberyards are like mine and will let you sort through the stock rack.  If they're kind enough to let you do that, be sure to neatly re-stack the stock and don't handle it roughly as you're sorting it or they won't be happy to let you (or others) sort through stock in the future.  Often, if you tell the folks who are in the yard what you're looking for and why, they can be fantastic resources to find those odds and ends that are either not out yet, or squirreled away that are perfect for the paddle you're going to make.

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