Knowledge You Can Build On — Est. 1998
Spalted wood cracking
Brian B
Hello all. I am fairly new to turning compared to most and have just got myself a fair amount of spalted beech and rock maple. Previously I have turned thin to final thickness, courtesy of robohippy and his YouTube videos, with good success. This spalted wood, however, has not faired so well. I have turned 4 bowls and all 4 have cracked on me. Is spalted wood better suited to be twice turned? Are there any other tips or tricks to try?
Thanks in advance.
Re: Spalted wood cracking
don stephan
One possible explanation is that not all woods shrink the same. If you can find a copy of Bruce Hoadley's Understanding Wood at a library take a look at it. Absolutely wonderful text on wood, though it took me multiple readings to understand different sections.
Woods shrink more along the growth rings (tangentially) than across them (radially). There is a chart in the above book (and perhaps other places) giving St, Sr, and the ratio Sr/St. Once turned bowls made of woods with a higher ratio move more (warp) as they dry.
Don't have Hoadley's books here at home, but I know beech moves much more with seasonal humidity levels than other woods. Not sure about rock maple.
Initially I dry each once turned bowl in its own paper grocery bag on the concrete floor on grade. If the wood has a significantly higher shrinkage ratio, like beech, I would double bag each bowl to slow the drying and I would probably turn the wall thinner than normal.
After the bowl is completely dry, you can always enhance it by carving a split into a swooping V.
Re: Spalted wood cracking
Lyle Jamieson
My bet is the spalted trees have already dried enough, and cracked. Once the cracks are already in there no method will be successful. Nothing you did wrong. I prefer to turn green to final wall thickness. A lot more fun instead of double turning.
Re: Spalted wood cracking
Dick Coers
Generally, no spalted wood is not more prone to cracking. What wall thickness did you turn to? Consistent wall thickness all around, including bottom? What did you do after turning? My furnace has really be cranking in Central IL. Air is the shop is getting dry, FAST! A picture would help troubleshoot the situation. Lyle made a nice observation. Standing dead trees will form cracks as they stand.
Re: Spalted wood cracking
robo hippy
Well, some woods will just crack. I have found that trees that are standing dead and then harvested tend to crack much more than ones that are green cut. No idea why. I have also found that when turning my green madrone bowls that spring cut trees survive much better than late summer or fall trees. Again, no idea why. Other than that, the pieces may be drying too fast. One method I don't use, but does work, is to wrap the piece in a paper bag, then put that in a sealed plastic bag. Change the paper bag every day. You can reuse the wet one after it dries out. I do too many bowls for that to be practical.
robo hippy
Photo will be Worth 1000 Words Here...
Re: Spalted wood cracking
Mike Brazeau
Beautiful as spalted beech is, I have found beech brutal for cracking when drying.
