|Project by wch||posted 05-16-2010 10:50 AM||3340 views||10 times favorited||20 comments|
This is a straightedge I made from a 1×2” piece of clear pine. I based it on a description of a straightedge from Toshio Odate’s book, Japanese Woodworking Tools.
I’ve made a few other tools. This one is the simplest and yet also in some ways impresses me the most, because it taught me that it’s possible to make something that’s straighter than any object you have to begin with. You do need a hand plane, but it doesn’t have to be a great one; the resulting straightedge can be straighter than the plane’s sole.
The straightedge actually consists of two pieces of wood. They’re placed side-by-side and planed together, and then “unfolded” and held up to a light to check for gaps. If there are gaps, you shave away the high spots in the wood until the gaps are gone.
One property that might actually be an advantage over a store-bought straightedge is that this straightedge serves as a reference for itself. To illustrate, I have a cheap combination square, and I’ve never been sure if the blade was straight, but I had no good reference object to compare it to. If I compared it to another straight object and the two were slightly off, I couldn’t be sure which one wasn’t straight, or if both of them weren’t straight. But with this two-piece straightedge, I don’t need a separate, better reference object; I can just compare the two pieces to each other, and if they disagree at all, then I just plane them flat.
For more information on how it’s made, click here.
Update: From reading some postings on another forum, I realized that if there are any visible gaps, you can use a sheet of paper as a feeler gauge to test the amount of deviation. A sheet of regular 20 lb. paper is 0.004” thick, so if it won’t fit between the two pieces of wood, then the straightedge is good to within 0.002”. Playing with my micrometer, the smallest gap I can see is just under 0.001”, so I think that if there are no visible gaps, the straightedge is probably good to within .0005”. Bear in mind that you have to hold them together lightly—if you press the two pieces together with any appreciable force, you can easily bend them this much and close a gap.