Accuracy vs. Precision


3 boards that are precisely the same length

Age old problem – do you need this to be accurate, precise, or both? If you are not familiar with the question – google it. So how does that apply to this dresser? I am getting the case pieces ready for joinery by planing them exactly the right sizes. This is important if you want the case to come out square.

What is the right size? Close to my desired the dimension and exactly the same size as the opposite board (on the finished case). This is precision over accuracy. I want the depth of the dresser to be about 18 inches – the boards finished up at 17 3/4 inches. I’m fine with that. I wanted the case to be 60 inches long – it is 59 7/8 inches – which is perfectly fine. Why am I ok with this? Because the top and the bottom are exactly the same length. Here is how I guarantee identical lengths – clamp the boards together in the same arrangement as they will be on the case. Think of it as collapsing the case from the top/bottom and left/right. I consider this a “trick” and not a “technique” because I don’t recall seeing it in any woodworking books that I have read.

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Here are the 2 sides and the middle divider right before I clamped them together. They are arranged in the same order as they will be in the finished case (L=left, R=Right).

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Here I have clamped the boards together (note the QuickGrips) and fixed them 2 different ways on my workbench. I held them in the Moxon style vise for planing the end grain and the leg vise plus sliding deadman for long grain. I usually plane the end grain first, working toward the back of the case. This way splitting out of the grain (spelching) will likely be removed by planing long grain, but if it is not removed at least it will not show.

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Here I am working with the dresser bottom and sub-top. Those 2 were pretty heavy and required some creative clamping, which the Roubo bench was happy to provide.

It is critical to note that once I clamp the boards together and work the first edge I do not remove the clamps until I finished all four edges! Well, I never remove all the clamps. To get the constructs in and out of the vises I had to temporarily remove one or two of them at a time but I always left at least 2 clamps otherwise the boards could shift and my precious precision would have been lost!

Really, I admit this is not for everyone. These clamped case sides get pretty heavy and if you can get a square line in the right place it is unnecessary; however, if you can handle the weight this makes it pretty easy to make boards exactly the same size. Once you have that it is easier to make a “square” case. Next step – joinery. Finally.

Bob Jones

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