Making the piano hinge ruler accurately
I purchased a digital vernier caliper and set it to 1/4" and used it to put a scratch on the aluminum ruler as it is shown.Anywhere will do ,it is just going to be used for a reference for the marking tool next
A woodworking marking tool
You can pick these up at just about any lumber store such as Home Depot .It has steel marking pins prortuding out of it and you simply guide it along the side of the rule using the steel pin to put a scratch on the ruler setting it at that scratch you made with the vernier.
The scratch leaves an indentation in the aluminum(thats why it's important to buy an aluminum rule) that the center punch will catch .Now it is simply a matter of center punching at the inch marks all along that scratch.You will feel the punch fall into the scratch.Buy a good quality center punch with a very fine center .Just hammer enough to leave an indent that your drill bit will easily reference.As you punch along the rule it will begin to curve the ruler.When the holes are drilled to 3/32" you can turn the ruler over and center punch down the middle and it will take the curve out
The Onex tail calls for the vertical stab hinge to be pilot drilled 19/64"from the edge so the pilot holes on the rule will be 13/64" from the edge so that when the ruler is tucked up against the hinge you will wind up drilling the hole 19/64" from the edge as per plan
The horizontal hinges pilot holes are at 1/4" from the edge so the other side of the ruler I did at at 1/4".The digital vernier gave me that accuracy with no problem and the scratching tool gave me a consistent indent for the center punch to fall into.
Don't scratch the hinge as it will create a stress riser .(see problems avoided)Use painters masking tape instead to give your center punch something to rest against.
I have removed that scratch tool from my tools .
The horizontal hinges pilot holes are at 1/4" from the edge so the other side of the ruler I did at at 1/4".The digital vernier gave me that accuracy with no problem and the scratching tool gave me a consistent indent for the center punch to fall into.
Don't scratch the hinge as it will create a stress riser .(see problems avoided)Use painters masking tape instead to give your center punch something to rest against.
I have removed that scratch tool from my tools .