I've just been planing the narrow edge of an approx. 18" long piece of American Black Walnut using a Veritas low angle jointer plane with a freshly sharpened blade. As a straight edge I used a 60 cm long aluminium ruler the long edges of which are about 1/8" and 3/32". After a few strokes with the plane I had the proverbial single shaving so I checked the edge by placing the 1/8" side of the ruler on the wood. This indicated two humps along the length. Plane, check, plane, check. Now down to one hump. Concentrate on that bit, plane until the single shaving is there. Check again. Still got a hump.
Something made me decide to check it with the other side of the ruler. The hump was now a dip! So I checked it with the second ruler (I have two so I can use them as a pair of winding sticks). One side showed that the wood was essentially flat (as expected) and the other showed a minimal dip but not in the same place as the first ruler.
Conclusion: the aluminium rulers are not straight along their edges. I find this quite astonishing as I just assumed that an aluminium ruler was going to be bang on. This means that every time I've checked an edge with these rulers, I've not been getting correct results. Is this the sort of thing which leads e.g. Veritas to go to the trouble of manufacturing guaranteed straight edges? I don't know whether to try to find some super stable tropical hardwood as recommended by Christopher Schwarz in The Anarchist's Tool Chest and have a bash at making my own or just cough up for the Veritas.
But to come back to the aluminium rulers: is it normal for tolerances to not be particulary tight in such things?
Something made me decide to check it with the other side of the ruler. The hump was now a dip! So I checked it with the second ruler (I have two so I can use them as a pair of winding sticks). One side showed that the wood was essentially flat (as expected) and the other showed a minimal dip but not in the same place as the first ruler.
Conclusion: the aluminium rulers are not straight along their edges. I find this quite astonishing as I just assumed that an aluminium ruler was going to be bang on. This means that every time I've checked an edge with these rulers, I've not been getting correct results. Is this the sort of thing which leads e.g. Veritas to go to the trouble of manufacturing guaranteed straight edges? I don't know whether to try to find some super stable tropical hardwood as recommended by Christopher Schwarz in The Anarchist's Tool Chest and have a bash at making my own or just cough up for the Veritas.
But to come back to the aluminium rulers: is it normal for tolerances to not be particulary tight in such things?