Tuesday, May 13, 2014

Knotty problems-working with knots in wood

Hi Everyone,
Well, it's been raining a lot here but the good news is that everything is green and flowers are beginning to blossom. Sounds like good bowl turning weather to me!

I have a quantity of western red cedar in the wood shop that I need to turn into bowls this spring and I turned one this morning:

A common thing to see in wood, especially softwoods like cedar and pine, are knots. Knots and the surrounding wood are lovely and you can see the amazing detail in this photo and the one below it:

Knots can cause problems: they can loosen and drop out of a turned piece leaving a big hole. Since the pith of the tree is present in a knot, it can crack radially. And cracking can cause the entire knot to crack into to several pieces and basically ruin a turned piece.

I do love to turn bowls out of solid pine and cedar logs but knots are always going to be a problem in those species so I do several things to deal with this:

1. Inspect the log section carefully and make sure there are no loose knots. If I find that I set the wood aside. I will turn a log if the knots are well integrated into the surround wood.

2. Once the blank is stable and balanced, I turn up the speed and make sure my turning chisels are really sharp. This results in a nice, smooth surface across the knot.

3. Do the entire turn in one session,

4. When I'm done cutting and finishing the bowl I treat it with Pentacryl, a wood stabilizer. I apply a very liberal coat of Pentacryl daily for about 4 days and when that's finished, I place the bowl in a large, heavy grocery bag and let it sit for about a month. This will stabilize the knot and all of the rest of the wood and make it very stable. I've had minor cracking by doing this but never major cracking and I've never lost a bowl. Knock on wood.

Always inspect your logs carefully before turning them and reject or trim away problem areas. You can't avoid problems 100% of the time, but you can avoid most turning difficulties with knots.


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