Reply To: Fixtures, Guides, Jigs, and Templates – aids to accuracy and precision
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Sven-Olof, sometimes developing the skill levels you describe as out of reach relies on insights on how to work progressively and discovering such methods as needed for yourself. Don’t give up!
As an example, consider paring the shoulders of a tenon after sawing away the bulk. Paul shows putting his chisel into the knife line, pushing, moving across, and then having what he needs. I can get close doing this but found I was usually out of square a bit, especially on the side. What I’ve learned to do is to work progressively towards my knife line. So, that is the first step- Knifing in an acceptable layout all the way around the shoulders. Next, the waste is cut away. Now for the trick. I take a narrow chisel, about 3/8″, put it in the knife line one the narrow edges with the work horizontal in the vise (chisel vertical) and gently tap a couple times. This deepens the knife line. I aim away from the finished plane just a tad, i.e., I’m a little out of plumb, aimed into the waste. Just a hair. Next, I put a 1″ chisel into the knife line along the main shoulder, aim definitively into the waste (out of plumb/square), and remove a sliver of the fuzz about 3/8″ wide. What I’m looking for here is for the deepened knife line to appear from the side. I usually won’t see it on the first sliver, so I take another sliver, a little closer to square, again registering in the knife line, and repeat until the knife line on the side appears. The key observation here is that, because of the way knife lines work, you will see the knife line appear *before* you’ve actually cut down to it. Now that I can see it, I can carefully remove fuzz to be on it. You see what we have now? We’ve worked to two knife lines, one on the face and one on the edge, so we know have a perfectly square corner, about 3/8″ wide and the depth of the shoulder, and it is as good as our knife lines. No magic skills were required. No super-calibrated mystical eye. Now that I have this perfect little shelf, I plop the back of my chisel onto it, apply strong downward thumb pressure to stay registered, and walk a bit further into the shoulder, i.e., I register in the fuzzy knife line while registering on that perfect, square table I just made, and push. At this point, it goes quickly and looks like Paul’s motions, but I’m just extending that trued up surface across the shoulder.
That’s meant as an example. There are other places where this property of knife lines comes in. So, please see that if you aren’t getting the results you want, there isn’t some fundamental weakness or lack in you. With some experimentation to find ways to work iteratively, you can achieve the precision you want, I’m sure.
One of the most useful things a teacher ever said to me was, “Keep at it. You’ll get it.”
None of this is meant to argue against jigs. It’s just meant to encourage. Keep at it. You’ll get it.