Green roughed bowls cracking

[Ken Glass]

Hey Gang,
I have a question I am sure someone can answer. I have been roughing end grain Walnut vessels, some 9-15 " tall by 6-8" wide from green Walnut. It seems as if it goes well until they come out of the DNA and get wrapped until they stop losing weight for 4-5 days. Somewhere in the process of drying they seems to crack, and not little cracks, big honking cracks that ruin most of them. I have tried double wrapping them in brown paper, and even adding some chips from the rough turning to slow them from drying too fast. They are drying in my basement shop, which is fairly dry in the winter. Now the question: Can I coat or soak the rough turning with Tung oil or Antique oil to slow the drying process or will it stop the process? Other green rough turned bowls ( other than Walnut) have dried in two-three weeks and have been fine to finish turn without cracking or warping. Is there something about Walnut or is it because they are end grain turned? Inquiring minds want to know.

[Tom Bucanan]

If you want to be be really careful, coat them in Anchorseal or some other wax emusion

[David Walser]

Ken,

You say these are end grain vessels. Are you leaving the pith? If so, I'm not sure you can dry the walnut without there being cracks. The reason is, on average, wood shrinks more along the circumference than it does along the diameter. (IIRC, the average is 10% greater shrinkage along the circumference than along the diameter. That varies with species and other factors.) That is, assume that you have a log section that has a diameter of 10" and a circumference of 31.4" (Diameter x Pi = Circumference). If you marked two points at the edge of the log section 5" apart (and 5 inches from the center of the log), you would find that, as the wood dries, those two points moved more towards each other than they moved towards the center of the log. How can the wood shrink more in one direction than another? It can't -- without cracking.

However, if you split the log lengthwise, each half or quarter of the log can shrink without much risk of splitting.

HTH

[Ken Glass]

David,
I have hollowed the pith out of the turning when I roughed it. Most of what is left, is neither sapwood or pith. It is mostly heartwood.

[Gary Max]

Is your DNA worn out---it only last so long and it stops doing its job????

[Ken Glass]

Gary,
Good question. The DNA is been added to, but 3/4 of it is only a few months old with a gallon being added last week.

[M Toupin]

David,
I have hollowed the pith out of the turning when I roughed it. Most of what is left, is neither sapwood or pith. It is mostly heartwood.

Unless you have a hollow tube left, you still have a base with the pith which is creating your problems. Cut your blanks from a quartered log which will leave you a end grain blank with no pith. Granted, you're going to have to start with a bigger log, but you should have much better luck.

Mike

[David Christopher]

Is your DNA worn out---it only last so long and it stops doing its job????


How do you ware out DNA ( serious question )

[Dale Miner]

I've turned several end grain walnut pieces, somewhere around 8 or 9 inch dia by 7 to 10 deep, with the pith centered. Lost the first couple, and had pretty good success with the rest by coating the pith and surrounding area with CA, and once that dried, coating the rest of the bottom with anchorseal, and double bagging. I do not do the DNA thing. Since the pith is centered, the rough outs can have thinner walls and not run the risk of going to far out of round to clean up on the second turning. I still leave the bottoms around 5/8 to 7/8 inch thick in an attempt to slow the drying of the bottom.

Another suggestion, drying the rough outs in the house during the winter months seems to extract a toll on the pieces. The heated indoors drys the wood to fast. Leaving the rough outs in an unheated garage or shed for several weeks seems to improve the sucess rate. Also, the cooler temps seems to help the sapwood maintain the white color (if you are leaving sapwood).

Later,
Dale M

[Steve Kubien]

How do you ware out DNA ( serious question )

As I understand things, the alcohol displaces some of the water in the wood. As alcohol moves in, water moves out. Take the wood out and the water stays in the solution, thereby making it a weaker solution than what you started with. Use the solution enough times and more and more water goes in while alcohol goes out. Get too much water and the wood requires a longer soak and the solution loses its effectiveness. I am not chemist and I do not play one t.v. but that's my understanding.

Cheers,
Steve

[Don Eddard]

As I understand things, the alcohol displaces some of the water in the wood. As alcohol moves in, water moves out. Take the wood out and the water stays in the solution, thereby making it a weaker solution than what you started with. Use the solution enough times and more and more water goes in while alcohol goes out. Get too much water and the wood requires a longer soak and the solution loses its effectiveness. I am not chemist and I do not play one t.v. but that's my understanding.

Cheers,
Steve
In my experience, I've had to replenish the DNA in the bucket due to evaporation long before it stops being effective for drying.

Ken, considering that yours is only a few months old, with a fresh gallon mixed in, I think it's safe to say yours is still plenty potent. I think the pith at the bottom of your vessel, coupled with the fast, dry winter heat, is causing your cracking problem.

[Bernie Weishapl]

I have did several end grain vase with the pith centered. I soak and saturate the pith with CA. I let it dry and then I generally turn my end grain which are mainly vases to final thickness and soak with antique oil. Only had one crack around the neck once.

[Bill Bolen]

Most of my vase forms have the pith turned away. I do the same a Bernie with the bit remaining on the bottom. I've only lost one to big cracks. The smaller ones I fill with saw dust and ca, sand and finish...Bill...

[Jeff Nicol]

Ken, With the end grain turnings of any wood it is more subject to checking and cracking than non endgrain work. There are many types fo wood that dry faster and crack more readily. Walnut, hickory, cherry, aspen and many others tend to check within a very short time of the end grain being exposed to the air. As has been said already the very best way is to use a green wood sealer (Anchorseal or equivilant) to slow the drying as soon as you are done with the roughing process. I have never done the DNA method as I have lots of roughed out pieces waiting to be finished and a lot of thicker slabs that are air drying waiting to be needed to use for a project. So if you are in a hurry to get an end grain piece finished from wet to dry, you most always will get a crack. I used to be very impatient when I started turning and I lost many to cracks and terrrible warping, but now I force myself to wait. It really is painful to see all the work put into a beautiful turning to see it come out of the bag as firewood.

Good luck,

Jeff

[Reed Gray]

Walnut has always been an easy wood for me to dry. Turning it endgrain isn't some thing that I have tried except for boxes. Generally cracks happen for 2 reasons. One is the wood is drying too fast, and can't adjust to the stresses fast enough. The other is that there are cracks in the wood that you don't see, and they get a lot bigger, never smaller. I don't do the DNA soak. With my thin turned bowls (green, to 1/4 to 1/2 inch, then dried and warped, then sanded and finished), it did nothing that could be seen or measured. I do wrap the outsides of the bowl. A couple of layers of newspaper, and secure it to the rim with a couple of wraps of the plastic film (6 inch roll, about 1 inch hanging over the rim, and wrapped with some tension) that is used to keep boxes on a pallet. Remove the paper that is on the inside of the bowl. This has done wonders for drying even the most difficult of woods (Pacific Madrone specifically). I can turn them thicker than normal, and they still don't crack. I have even just wrapped the rim, and gotten the same results.

Are your bowls cracking from the rim down, or from the bottom up? Your garage, and your climate are pretty dry this time of year, that could be part of the problem. Rounding over the rim edges and base edges can help as well.

robo hippy

[Ken Glass]

Thanks for all the replies. I have used a portion of several of the replies. I have coated the bottom with Anchorsol and double wrapped the turning. I may check it in a few days and then coat it with Antique oil to retard the drying time even further. I will let everyone know the results. I do think my shop is very dry this time of the year and I may even move the turning to the garage if the present method does not prove better results.

[Dana Berenson]

The only time I've had this problem is when I only left the bowl in the DNA for 24 hours. (esp. with larger bowls) - Try soaking it for several days and see if that helps.