For good measure

Ever measure something perfectly Ė more than twice Ė before you cut, but afterward find that the component just doesnít fit? I hate when that happens.

A recent project involved fitting a pewter lid onto a box. The pewter lid came from a source other than my shop, so that meant I had to fit the box to it rather than the other way around. I measured that metal component several times in several locations on the edges, and when I was satisfied I had the dimensions correct I turned to making the box to fit it.

Again, I measured extremely carefully. Repeatedly. I cut the components and did the joinery (mitered corners which would later receive accent splines), followed by a dry fit and careful measuring again to be sure I had the dimensions right. I then assembled it, checked for square while clamping, and all was well. When the glueup was dry I unclamped it and did a quick check of the lid. Didnít fit. It was too snug.

I rechecked my lid measurements and they were fine. I rechecked the boxís interior dimensions, and they were oh-so-close but not quite right. Although Iíd cut everything correctly, the clamping pressure must have been just enough to make the interior dimensions slightly off on the too-small side.

Fortunately, this was an easy fix. I hadnít done the final sanding of the box yet and that helped a bit when I did. And it was fairly easy to shave the edges of that pewter lid to tweak the fit.† The final result was perfect, but still annoying.

Why annoying? Because there have been other times when I purposely erred on the too-large side just a little to account for exactly such an occurrence, and the result was a fit that wasnít as easily fixable because the interior dimensions were just way too large. No amount of sanding or tweaking helps in those cases; you just have to remake the nonfitting portion.

My conclusion? Donít try to anticipate a bad fit. For me, itís better to try to make the measurement perfect. In those cases, one of two things happens: Either it comes out just fine, or if there is a fit issue, itís very slight and almost always on the too-tight side. Which is far easier to tweak.

Till next time,

A.J.

COMMENTS

  1. Stuart Simmons wrote:

    Simple jig. Piece of plywood with a fence down the left side and across the bottom. Fences should form a square corner. Slide a second piece of ply against each open side of the part to be measured.

  2. Jeff Fliss wrote:

    If it where easy everybody would be doing it!

  3. Lonnie C. Major wrote:

    These are my thoughts concerning this problem.
    A. The project in the example involves two completely different types of materials. The lid is a metal, and the box is wood.
    B. Metals have much less expansion properties than those of wood.
    C. If you think the clamping is causing the problem by means of compression, try not tightening your clamps as much as you normally do. It could be that you over tighten them, which will crush the cells of the wood and reduce the dimensions you began with.
    D. If you still have the same problems, try adding a couple of hair thicknesses to your actual measurements when you make the cuts. This is like choosing the more side of the measurement mark.
    E. Another problem you may be having is the sharpness of your marking instrument. I always use a pencil sharpened to an extremely fine point. Believe me when I say, “It helps.”

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