Reply by Doss

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Posted on Is 89 degrees square

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779 posts in 2263 days

#1 posted 03-23-2012 04:53 PM

We have rules in engineering about tolerances… how accurate can you afford?

Yes tolerances due stack, but not if you make adjustments as you go along.

To put it in perspective, let’s build a square frame (like a picture frame) using 10’ long by 1/16” wide strips of wood (just helping with a visualization of lines).

First piece of wood down. Measure 90°. Put second piece down. Measure 90° again. Put third piece down.

This time though, we get sloppy and lay the piece at 89.75° relative to inside angles. The result? Instead of closing your perfect square, you are now roughly 1/2” (0.5235971141695884”) from perpendicular to the inside of the square. At 89° the gap grows to a little over 2” from perpendicular.

The question is, is 89.75 or 89° close enough for you and can you make the adjustment?

Yes, this is not a compounding problem where the slightly off angle will definitely bite you when building a square, but it helps in visualizing an error in measurement and how significant it can be. I’d say if you build things with long straight runs, long sides that need to appear square to each other, or need really tight miters, then I’d try to get as accurate a measuring device as possible.

This does not stop you from making a mistake when cutting or attaching though or even as the wood moves due to changing conditions.

-- "Well, at least we can still use it as firewood... maybe." - Doss

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