A Question About Compression

In reference to our podcast 360 with 360 WoodWorking, Episode 165 we received the following comment.

Enjoy your podcast. This episode seemed to be focused on a Instagram photo published by Lost Art Press. I happened to see the same picture on their blog website, and Chris explains why the clamps are applied as they are. It’s not wrong after all.

Marty Backe

 

Marty,

We have never mentioned the owner of the pictures we discussed in our podcast because we wanted the take-away to be that you need to personally vet much of the information being asserted on social media (and in other places) because so much of it is based on theory, conjecture, misinterpretation or is purely made up.

The information provided in the blog you referenced is incorrect on so many levels, we thought it prudent to dissect the photo and information provided therein. In order to understand why the information is incorrect, you need to have a rudimentary understanding of the basics of woodworking. What follows is a brief, abbreviated lesson about the nature of wood and how it relates to the assertions made by Chris Schwarz.

Wood is a dense material made up of long fibers bound together by lignin. Because the fibers traverse the material in many directions (but with the vast majority oriented in the same general direction), and are not uniform in thickness and do not necessarily travel the entire length of the tree, wood is neither consistent in structure nor density. Additionally, the bonds between the fibers, and the fibers themselves, vary in strength. This means that, when an attempt to separate the fibers is made, they tend to split where the bonds and/or fibers are weakest (the path of least resistance). The fibers also tend to separate along their length. This is the basic premise upon which the craft of woodworking is based. We introduce tools to the wood that separate the fibers along the path of least resistance in a controlled fashion (or that’s the attempt at any rate). This is basic, first-year apprentice information.

In the case of the two parts Chris is putting together, without considering any other weaknesses inherent to the wood itself, the path of least resistance on either board would be across its thickness. The boards appear to be around 3/4″ to 1″ thick. Can we all agree, given a relatively uniform distribution of fibers throughout the board, that there are fewer fibers stacked up across the thickness than across the width of the board? If that’s the case, and you set a wedge to the end-grain of the wood, oriented across the thickness of the board and drive it in, the tendency for the board is to split in some fashion across its thickness before splitting across its width.

Orienting a clamp as Chris has in his photo provides little support to the fibers being separated by his nail. The clamp is not applied in such a way as to help hold the fibers together as the wedge (or in this case, nail) is driven in. And, speaking of the nail, it appears to be turned in a way that exacerbates the separation of the fibers across the thickness of the boards. Had the nail been turned 90°, the wedging effect would have been reduced. Rosehead nails are tapered – modern ones in only one direction. Had the chosen material been a hardwood, the tendency for the improperly oriented nail to split the board would have increased, regardless of the presence of a clamp or its orientation. But, in this case, we’re not buying the concept that compression is of any help at all. (It’s great for Windsor chair construction, but if you think “compression is your friend,” try it on a set of bloodwood dovetails.)

When you consider the lumber selection, the boards are quartersawn or nearly so. Because of the orientation of the fibers in the quartersawn material, the chances of splitting the boards completely along their length are greatly increased. That’s because there are few, if any, fibers knitted together at an angle to the grain direction of the boards to act as a break to stop a catastrophic split.

As for the nails, toeing them as illustrated can add to the hold of the nails. In this case, however, angling the roseheads creates an additional problem. Rosehead nails were designed to be driven straight into the material thereby leaving the edge of the round, faceted head flush with the material. By angling the nails you’re left with a choice. You either drive the leading edge of the head flush with the surface, leaving the trailing edge exposed to catch fabric, skin or other materials, or you drive the leading edge below the surface of the wood, splitting out some of the surface fibers as illustrated by the first nail in the photo that’s fully driven.

The fact that Chris hasn’t split either the top or bottom board in his photo is most likely due to his pilot hole (which on the top board is actually a clearance hole) being “half or two-thirds the length of the nail” (in addition to the wood being white pine). Plus, the hold of the nail is greatly reduced by such a deep pilot hole. At the end, the clamp did little to prevent the boards from splitting.

— 360 WoodWorking

 

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2 thoughts on “A Question About Compression

  1. Excellent explanation.
    I like Chris Schwarz and I’m sure he is a much more experienced woodworker than I am, but this looked strange to me.
    I am glad you explained why it looked wrong to me and your explanation makes perfect sense.
    Thank you
    Eric

  2. I didn’t expect such a detailed response. Thanks, and it was an interesting and enlightening read.

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