Teaching Tension & Compression

I recently had a student that found it difficult to fully grasp the concept of tension and compression wood. This student understood that if a piece of timber was only held at one end, then the compression wood was underneath, and that's where the first cut would be made; but when it was balanced at either end, they just couldn't see it. What I needed was a way to help this student understand where the cut should be made - this gained particular significance as I'd been told that they had failed a previous attempt at CS30 on demonstrating knowledge of tension and compression! Find out my solution after the jump...

After we had been down the woodyard, practicing the crosscutting, I have to admit that I thought we'd got it sussed. But we hadn't - my fault really and now I needed to come up with something that would help this student. Walking back, I was running various ideas through my head when I had a moment of inspiration.

I needed something quick, simple and easy to understand. Perhaps something this student could take away with them to practice with.

The result can be seen in the picture at the top of this post - click on it to get it full size (A4). Here's how it works...

  • Cut out around the edge of the rectangles, and then fold in half as it shows.

  • After folding it, glue it together just to hold the halves in place.

  • The elliptical pads represent where the wood is held up - so if you place the single pad touching on a table, or whatever, with the other end free, you'll see that the free end sags down (because there's nothing holding it up). Holding it this way, you can also see that the letter 'T' (tension) is uppermost and the number '2' (second cut) is showing. This tells you that the compression wood, which you would cut into first, is on the underside of the timber.

  • Now turn the paper over and balance the two pads at either end across your hands. You can now see that the letter 'C' (compression) is on top, and the number '1' (first cut) is showing. This tells you that the first cut to make is the compression wood on top.

It's easier to do, than to explain ;-)

Anyway, if it's of use to anyone, then please feel free to download it and give it a go. If you're a trainer, then feel free to use it. As for my student? They passed with flying colours.

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