Bowl Cracks & Tooling Marks

[Brett Bobo]

On several pecan bowls that I rough-turned recently and one that was ready for a finish, cracks developed through the wall of the bowl. Most of the cracks are across from each other and appear to be located at the pith; although, I thought the pith was removed. On the rough-turned bowls, I attempted to turn away the cracks but to no avail--they continued to propogate. What is causing this? What repair options do I have, e.g. epoxy, cyanoacrylate,etc.?

Where do you store your rough-turned bowls for drying? With the Houston weather, the humidity is high, especially this time of year, and I've noticed that the cracks propogate quicker inside the house than in the workshop, which is not conditioned space. Is keeping them outside in the workshop just prolonging the cracking or is keeping them inside drying them out too quickly?

During sanding, I notice the tooling marks or "rings" on the inside of the bowls and particularly at the transition of the bottom to the side walls. Regardless of how much I try to either make a continuous sweep or use a scraper to remove these, they are still noticeable before the finish. What am I doing wrong?

Thanks for the advice,
Brett

[Dennis Ford]

Keeping the blanks in the house is drying them out too fast. The easiest way to crack free drying is SLOW drying. Depending on the species, thickness of rough-out etc, I do one of the following:
1.) wrap with brown paper and store in shop for 2 - 3 months
2.) Seal entire surface with anchor-seal and store in shop for ~ 1 year
3.) Boil the blank and then wrap with brown paper and store for 2 - 3 months (This is an extreme that I rarely go to but it works well)

Some others soak blanks in denatured achohol before drying but unsealed containers of achohol would be a fire hazard in my shop (I sometimes do metal work)

When you are removing the tooling marks, you have to remove more than you realize. Some of the damage is not visible until after sanding.

[David E Keller]

Some bowls crack, so there are no fool proof methods in my hands. I've used the DNA method and the anchorseal method with success in the past. The wall thickness needs to be even and get rid of any sharp edges at the rim. I throw my DNA roughouts into a cabinet after wrapping in newspaper. The anchorsealed blanks go straight into the cabinet after the anchor seal sets up.

As for the rings near the transition from side to bottom... They may be compression marks from the heel of the gouge. If the bevel is too long or the angle too acute(pointy), you may have trouble making the turn without digging the heel into the wood. I find the compression marks to be harder to sand out than simple tooling marks.

When dealing with cracks, there are lots of options. Generally, if the piece is worth saving, I'll fill the cracks with 5 minute epoxy and some kind of coloring agent(coffee, contrasting sawdust, powdered metal, etc). You could carve the areas to make them a feature rather than filling them. Your imagination is the only limitation to what you can do with cracks, but sometimes the best option is to toss the piece in the burn pile and get another chunk of wood.

[John Hart]

My experiences with cracks usually result in abandoning the piece...although David has a valid point in strengthing the wood. The big problem with turning a cracked piece of wood, is that you are exerting forces on that crack...even with light pressure. The wood is flexing. Gotta get it stable.

[Bernie Weishapl]

Brett I leave my bowls at 10% wall thickness which you probably know. I was using the DNA soaking then wrapping with a brown grocery sack. Oh round the rim over so there are no sharp edges. I have found sharp rims cause problems. After attending a demo by Mike Mahoney I have started coating the whole bowl with anchorseal. I put a date and species on before sealing. I have around 45 bowls now drying and not one has cracked so far and some have been drying for several months now. I am trying to get a bunch of bowls roughed so I can have some dry at the same time I am still roughing.

[Brett Bobo]

Bizarre update: The bowl that was ready to be finished, which had substantial cracks (1 1/2" long) on opposite sides of the rim, now leaves no sign of the cracks. Granted, I know wood moves, now especially with bowls, but does it make sense that the cracks would swell and close themselves? After seeing these cracks initially, I left it inside the house figuring it would become firewood as it wasn't worth salvaging. I might expect a similar result if I had left it outside with the high humidity for the bowl to swell. Any ideas or common stories?

[John Hart]

When I was doing my steaming experiments, I used a piece of cracked walnut. When I pulled it out of the steamer, the crack was gone. I couldn't find it. Then, two days later, it was back.

I guess healing isn't permanent with wood. :confused:

[Wayne Spence]

On the piece that the cracks closed up, be careful. The crack is still there and the wood has not grown back together. I am not insulting your intelligence, just making sure. The crack will probably open up in time but even if still closed, turning it, especially the rim, could result in flying wood.

[Thom Sturgill]

One comment on the compression marks - grind the heal off the gouges. Mike Mahoney has a good video on this. Look at CSUSA' s website for the Mahoney
gouges to see what I mean. They have a link to his video too.

You only need a small bevel to guide the cutting, a long bevel leaves pressure marks where the heal crushes the fibers and sometimes does not show until finish is applies or the piece is wet sanded.

[Tim Rinehart]

Bizarre update: The bowl that was ready to be finished, which had substantial cracks (1 1/2" long) on opposite sides of the rim, now leaves no sign of the cracks. Granted, I know wood moves, now especially with bowls, but does it make sense that the cracks would swell and close themselves? After seeing these cracks initially, I left it inside the house figuring it would become firewood as it wasn't worth salvaging. I might expect a similar result if I had left it outside with the high humidity for the bowl to swell. Any ideas or common stories?

Brett,
I've had the same thing happen with a piece of wood that was rough turned, and I almost scrapped it. However, since I throw nothing away for fear it may come in handy "someday"...I had this large, 12" diameter, walnut bowl with anchor seal that cracked while in my dishwasher kiln. It had a couple big cracks on inside, in area of end grain. I suspect that even if you think all cracks are gone by cutting till log shows 'solid wood', that there are still areas which are dryer than others.
Any additional drying just causes a differential crack, as if you had uneven wall thicknesses.

Back to response...
After a couple months, I was looking at that piece of walnut with the cracks , and I could barely see them. My thinking, is that once the rest of the wood drying was complete, the outside effectively shrunk enough to pull the inside crack together. Seems reasonable.

But...that being said, I am skeptical on turning it,though judicious stabilizing with thin CA and light touches of the tools once things get thin could allow me to do it.