Is the 45º clamping thing a myth?—I’d say no
YouTuber Ari Kardasis goes to extremes to find out if clamping pressure really radiates at 45º
May 18, 2023
Yesterday, Hackaday shared this video immediately killing an idea I’ve had for a while. I’ve always wanted to test this, albeit with less techy methods, but I’m glad that Ari Kardasis got to it before me. I love building electronic gizmos, but I don’t have the skills Ari does and as you’ll see in this video, this build required a lot of skill. I was planning to use pressure-sensitive film but was always turned off by the cost of it.
For the record, I’d argue the title (and maybe the message) of this video is misleading. While Ari found that pressure emanates beyond 45º, I don’t think anyone actually believes it stops at 45º. In the same way that the range of human hearing isn’t 2o hZ to 2okHz—nowhere near it actually—that’s just an easy number to remember. I think 45º is easy to visualize, easy to remember, and as you’ll see in the video, close enough to reality that it covers your bets.
This also lands in the “better safe than sorry” and “does it really matter?” territory. Still, it’s cool to see someone test it!
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Comments
While it wouldn't make for a fun video, the distribution of clamping force can be easily estimated using Finite Element Analysis - a standard computational method in engineering. A couple of years ago I asked a friend who had access to an FEA program to do exactly this analysis. Neither of us was surprised that the result confirmed the rule of thumb. The clamping angle is a function of the stiffness of the wood, with stiffer woods providing wider clamping angles. This is easily demonstrated in FEA simulations.
I recall a recent video by Bob Van Dyke where he glued the edges of two long boards (~6') using only one clamp in the middle. Its called a "spring joint". Clearly this case violates the 45-degree rule but is a technique dating to the early history of woodworking. Bob's main concern was that he observed glue squeeze-out along the entire length of the joint - a visual indication of proper stress distribution.
If I think about it, it is unlikely that woodworkers using only modern power equipment will be using the spring joint, as you pretty much need a hand plane to make this approach work. And, I doubt that the original intent of the joint was to save on the use of clamps, but more likely to avoid gaps at the ends of long edge glue-ups arising from sloppy planing technique.
Forgetting the spring-joint for a moment, and assuming you apply your glue properly, squeeze-out is a good indication of proper stress distribution along a joint. If you fail to see squeeze-out in an area, add another clamp! In a normal edge joint (not a spring joint) this process may actually end up looking like you intentionally spaced clamps 45-degrees apart, and could be the source of this "rule of thumb".
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