custard
Established Member
There's been a few mentions recently about wooden straight edges, every time the topic comes up I remember that mine is getting bit long in the tooth and should be replaced. I had a spare half hour this morning so made one up.
For shorter straight edges, say 150mm or 300mm I tend to use an engineer's quality steel ruler, they're a bit thicker than normal metal rulers so have the stiffness you need for a straight edge. For a longer straight edge, say 2 metres, it's easy to rip off the factory edge from a sheet of MDF and use that. Where wooden straight edges really come into their own is in that middle ground, say from 0.6 to 1.5 meters. The metal equivalents are too heavy and expensive for everyday use, plus they're unwieldy so you can easily damage your furniture with them.
If you're going to make one there are three hurdles that you'll have to cross. Finding a suitable piece of wood, drawing a fair curve on it, and planing a really accurate straight edge. I'm sure there are loads of different solutions to these three problems, but here is how I set about it.
Unless you can get hold of the right piece of timber it's a waste of time making a wooden straight edge, a gnarly bit of wet stuff from a skip isn't going to deliver the stability you need. What you want is a straight grained, quarter sawn or rift sawn piece of completely dry hardwood. That's not so easy as almost all PAR and sawn kilned hardwoods are flat sawn. That's because the market usually wants cathedral grain in the centre of the board, tapering out to rift sawn edges. This is the configuration that delivers most visual grain interest in the centre of the boards, along with straighter grain at the edges that makes it easy to seamlessly joint boards together to make them wider. The ideal solution is to visit a proper timber yard that has through sawn, waney edged boards re-stacked into the original boule or flitch. You can then dig out a straight grained, quarter sawn board and you're pretty much sorted.
But if that's not possible then you still have some options. Oak is pretty much the only timber that's commercially quarter sawn (so as to maximise the distinctive Oak ray figure), so there's a good chance you can get quarter sawn Oak. Alternatively, if you get a board that's 75mm or thicker you can rip off a thin piece from the edge, which is likely to then be rift or quarter sawn. Finally, if all else fails and you're near the south coast in the Dorset/Hampshire area then PM me and I'll sort you out a suitable off-cut!
Here's the board I used,
It's quarter sawn Mahogany, machined to about 1000mm x 80mm x 10mm. Any width from about 65-90mm is suitable, but you want to keep the thickness in the range 9-12mm. Any thinner and it's too whippy for a straight edge, any thicker and it's too heavy and too thick for an accurate read.
The bow shaped item next to the board is how I draw fair curves . It's a lath about 40mm x 15mm that's about 1600mm long. The string runs through two holes at one end and is secured with the same arrangement you might use for tensioning a tent's guy rope.
Normally in a commercial workshop you get someone to help, between the two of you bend a long flexible steel rule to form the curve you want and then pencil it onto the workpiece. But on your own you'll find you're at least one hand short of pulling this off, which is why I use this bow arrangement. The resulting curve is fine for curved aprons, most furniture components, and for the back of a straight edge. But even though it's fair to the eye it's not an accurate section of a circle, the radius is actually very slightly smaller at the ends than in the middle. Absolutely not an issue for this or many other applications, as I said, visually it's fully acceptable. Here's the resulting curve (look closely and you'll see the red line),
Then it's off to the bandsaw to cut down to the line,
Then over to the bench to spokeshave it smooth and knock of the arrises with a nicely spokeshaved round, smoothed off with 120 grit.
For shorter straight edges, say 150mm or 300mm I tend to use an engineer's quality steel ruler, they're a bit thicker than normal metal rulers so have the stiffness you need for a straight edge. For a longer straight edge, say 2 metres, it's easy to rip off the factory edge from a sheet of MDF and use that. Where wooden straight edges really come into their own is in that middle ground, say from 0.6 to 1.5 meters. The metal equivalents are too heavy and expensive for everyday use, plus they're unwieldy so you can easily damage your furniture with them.
If you're going to make one there are three hurdles that you'll have to cross. Finding a suitable piece of wood, drawing a fair curve on it, and planing a really accurate straight edge. I'm sure there are loads of different solutions to these three problems, but here is how I set about it.
Unless you can get hold of the right piece of timber it's a waste of time making a wooden straight edge, a gnarly bit of wet stuff from a skip isn't going to deliver the stability you need. What you want is a straight grained, quarter sawn or rift sawn piece of completely dry hardwood. That's not so easy as almost all PAR and sawn kilned hardwoods are flat sawn. That's because the market usually wants cathedral grain in the centre of the board, tapering out to rift sawn edges. This is the configuration that delivers most visual grain interest in the centre of the boards, along with straighter grain at the edges that makes it easy to seamlessly joint boards together to make them wider. The ideal solution is to visit a proper timber yard that has through sawn, waney edged boards re-stacked into the original boule or flitch. You can then dig out a straight grained, quarter sawn board and you're pretty much sorted.
But if that's not possible then you still have some options. Oak is pretty much the only timber that's commercially quarter sawn (so as to maximise the distinctive Oak ray figure), so there's a good chance you can get quarter sawn Oak. Alternatively, if you get a board that's 75mm or thicker you can rip off a thin piece from the edge, which is likely to then be rift or quarter sawn. Finally, if all else fails and you're near the south coast in the Dorset/Hampshire area then PM me and I'll sort you out a suitable off-cut!
Here's the board I used,
It's quarter sawn Mahogany, machined to about 1000mm x 80mm x 10mm. Any width from about 65-90mm is suitable, but you want to keep the thickness in the range 9-12mm. Any thinner and it's too whippy for a straight edge, any thicker and it's too heavy and too thick for an accurate read.
The bow shaped item next to the board is how I draw fair curves . It's a lath about 40mm x 15mm that's about 1600mm long. The string runs through two holes at one end and is secured with the same arrangement you might use for tensioning a tent's guy rope.
Normally in a commercial workshop you get someone to help, between the two of you bend a long flexible steel rule to form the curve you want and then pencil it onto the workpiece. But on your own you'll find you're at least one hand short of pulling this off, which is why I use this bow arrangement. The resulting curve is fine for curved aprons, most furniture components, and for the back of a straight edge. But even though it's fair to the eye it's not an accurate section of a circle, the radius is actually very slightly smaller at the ends than in the middle. Absolutely not an issue for this or many other applications, as I said, visually it's fully acceptable. Here's the resulting curve (look closely and you'll see the red line),
Then it's off to the bandsaw to cut down to the line,
Then over to the bench to spokeshave it smooth and knock of the arrises with a nicely spokeshaved round, smoothed off with 120 grit.
