dry wood cracking issue

[Wes Ramsey]

Last springI cut a sycamore drift log, sealed one end and left the unsealed end sitting directly on my concrete shop floor. I left the chunks long enough that I can cut off the checking. Over the last year the wood has spalted beautifully and I'm trying to work my way through the pile to reclaim that section of my small shop. I screwed the log to a 6" faceplate centered on the heart to get more grain uniformity around the piece. My technique wasn't stellar when I turned the first piece so I did a lot of sanding. Over the next 2 days it developed a large crack from the bottom to about 1/2 way up the side. I figured it had to do with the heat from so much sanding. I just filled it in with coffee grounds and CA and it blends in beautifully with the spalting. This weekend I turned another HF, and thanks to Reed Gray I was able to get a much better finish cut and only spent a few minutes sanding from 100 to 320 grit so I expected it to not crack. Sure enough, the next morning it split from the bottom just like the other one. I also got 3 cracks in the top while I was turning - I think these happened because I turned it to about 3/16" and the dry wood just couldn't handle the vibration.

So I have a few questions I was hoping y'all could help me figure out. As to the crack coming up from the bottom, is there a way to stop that from happening? I always leave the bottom thicker than the rest of the piece, and with the wood being really dry I figure it is easier to relieve pressure by cracking than moving. If that is the case I can just go thinner in the bottom, but is there anything else I can try? And for the vibration cracks at the top, how can I stop that? I thought about taping it or wrapping it in cellophane, but I'm not sure how much that will help. Any ideas?

Here are some pics of the piece I just turned to give you an idea what I'm working with:

http://i156.photobucket.com/albums/t3/wmramse/4E207512-0A29-4B25-99C8-EED65C68192E_zpsw9rdep7m.jpg (http://s156.photobucket.com/user/wmramse/media/4E207512-0A29-4B25-99C8-EED65C68192E_zpsw9rdep7m.jpg.html)
http://i156.photobucket.com/albums/t3/wmramse/704F74F6-A4B5-424F-B640-B52CF20A8D74_zps1ilfzp42.jpg (http://s156.photobucket.com/user/wmramse/media/704F74F6-A4B5-424F-B640-B52CF20A8D74_zps1ilfzp42.jpg.html)
http://i156.photobucket.com/albums/t3/wmramse/DAC86FC8-0E85-4266-B98C-F2D4DA7EAB51_zpszijkx1pp.jpg (http://s156.photobucket.com/user/wmramse/media/DAC86FC8-0E85-4266-B98C-F2D4DA7EAB51_zpszijkx1pp.jpg.html)

[Reed Gray]

Well, in the top picture, There is some discoloration around the 2 cracks on top. They may have been there to begin with. The bottom picture shows that the form is centered on the pith. Almost every log I have ever seen has some cracks coming off the pith. The cracks could have been there before you started, and so tiny that you couldn't see them. If I attempted a piece like this one, I would put some thin CA glue in the bottom, and seal/finish the outside and bottom. Even inside your shop, a piece that size will be very damp in the middle, and some what drier on the outside, so uneven stresses. Perhaps using the stretch film on the outside might have helped. For sure the finish would have slowed it down, especially if you soaked the bottom and pith because that is where the cracks will start. Some times on maple and other lighter colored woods, the plastic can help them mold which isn't pretty.

robo hippy

[Wes Ramsey]

Thanks Reed. The discoloration around the cracks is what is left after erasing the pencil marks I used to help come up with some design ideas. Initially I was thinking about doing a lava/candle wax flow inlaced with copper and had penciled that in. Right now I'm thinking about carving the cracks to be uniform, making 2 more matching cuts and woodburning a star pattern on the top with copper filling the cracks. I don't want to waste the 2 hours I spent making this, but I have tons of wood and don't mind a bit using a piece for practice even if it doesn't come out looking like anything special. As long as I learn something from the experience!

I was thinking of wrapping the piece in plastic just until I finish hollowing. After looking at it so closely for a couple of hours I tend to want to go back and tweak the outside shape a bit before calling it done, so I prefer to finish after hollowing. Is that a bad idea? I usually use Danish oil, but I want to try my hand at a more natural wood look, and I think this wood would look great with a nice lacquer finish. If I do that after parting the piece off will it still help reduce cracking?

The temp in my shop is in the 30s right now, but as soon as it warms up a little I'm gonna some different things on another piece or 2. I just want to study up a little in advance to see if I can keep the cracks to a minimum.

[Reed Gray]

Wait, it is down into the 30's down in Arkansas??? If you apply the Danish oil, that acts as a sealer of sorts, and at least slows things down. You can always turn it off if you want, and add more finish later. I am fairly sure that if you use a Danish oil, that after it cures you can apply a lacquer finish on top of it. Others should chime in here. I really don't do many hollow forms. They interesting to me for exercises in making forms, but never sold well.

robo hippy

[Faust M. Ruggiero]

I had a spalted sycamore log and made several hollow forms. They were all cross grain forms. I always wrap the outside in shrink wrap while I hollow. I also try not to blow too much compressed air into the bowl to chase chips. When finished, I unwrap them and put them in a paper bag a couple weeks. The crack in the not spalted portion of your form is a classic example of radial shrinkage. I'm not sure anything would have prevented it but for sure it was exposed to dry air too long. If you wet sand green wood with foam backed abrasives you will develop less heat and keep the piece moist while sanding. Then you have to let it dry slowly in a bag. Still, no guarantee with the pith as part of the form, especially with sycamore.
It was a nice shape. Get back on the horse and try again.
faust

[robert baccus]

A log of that size will really never dry in a reasonable time. I do vases mostly and double turn. I also keep my wood wet/damp while spalting. Rough cut the outside and immediately wax or film the outside while hollowing. Leave the inside open and put it on the shelf for several months. Double Wax the inside of the lip and base. This actually helps pull the grain together just the opposite of the outside drying fast.

[Wes Ramsey]

Wait, it is down into the 30's down in Arkansas??? If you apply the Danish oil, that acts as a sealer of sorts, and at least slows things down. You can always turn it off if you want, and add more finish later. I am fairly sure that if you use a Danish oil, that after it cures you can apply a lacquer finish on top of it. Others should chime in here. I really don't do many hollow forms. They interesting to me for exercises in making forms, but never sold well.

robo hippy

Reed, It is 11* here right now with an inch of snow and 5" of ice still on the ground from Sunday. Expecting another round tomorrow that's supposed to start with freezing rain. That's the scary stuff! I've got a big red gum leaning just enough that the top could take out my office if it got enough ice buildup on it. I want to turn some of it, but not that bad! I will probably take it out in the spring.


A log of that size will really never dry in a reasonable time. I do vases mostly and double turn. I also keep my wood wet/damp while spalting. Rough cut the outside and immediately wax or film the outside while hollowing. Leave the inside open and put it on the shelf for several months. Double Wax the inside of the lip and base. This actually helps pull the grain together just the opposite of the outside drying fast.

Robert, I don't know how old this log is. We have a cabin just over the border in MO on a creek, and spring rains always bring a fresh batch of driftwood. This one looked pretty solid, but was starting to turn bad in spots so I don't know how old it is. Could have been on the ground for 3-5 years before it was delivered to my gravel bar. But thinking back it did steam a bit when I drilled it out before hollowing so maybe it isn't as dry as I thought. I like the wax idea. I've got some beeswax and mineral spirits I can paint on that should do the trick. I think I'll do 2 of them - one with wax and one with DO and see how they fare.

And thanks, Faust, for the comments!

[Wally Dickerman]

I agree with what's been said about the rim cracks. They were there before you started turning. They radiate from the pith area.

The crack from the bottom? When you turn semi-dry wood you must protect it or it's almost sure to crack. Whenever you stop turning for awhile wrap a plastic bag around the piece. The outside of the piece is drying faster than the inside. As it dries it shrinks a little causing the crack. That is especially true it you've left the bottom area thicker than the sides. A heavy coat of Johnsons Paste wax will protect it very well until you're ready to finish. The wax doesn't penetrate so it's easily removed.

[robert baccus]

When I mentioned wax it was merely slang for end seal. Like wally says any wax will do--I used to make my own by dissolving paraffin in mineral spirits until I discovered endseal. Easier and safer than my home brew.