Question about the bowl

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Question about the bowl

Postby Sprot » Mon Jan 12, 2015 10:47 am

Can you help me to identify what I did wrong.

This is a bowl from apple and it got dried over 4 months and thorough oiling with linseed oil. But when a friend, whom I made this, but some water in it it cracked from two places. I made several other bowls out of this wood and not one have had this problem. Was it too dried or not enough oil? Too steep walls? Or just something that sometimes happens?

It was about 20cm in diameter and about 10cm in depth

Sadly I don't have and before picture of this bowl.
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Re: Question about the bowl

Postby woodness sake » Mon Jan 12, 2015 7:38 pm

Making stuff from fruit wood is chancy. Apple is bad; cherry is worse. The stresses that build up in the growing grain structure have to accommodate the differing loads of fruit and leaves as well as intermittent wind loads during the growing season and then nothing while the tree is dormant. Some insight into this might be found by holding an apple at arm's length for a while until you feel the effect on your muscles; 10 or 15 minutes should do it. Also, some splitting may be initiated when a tree is dropped during felling. The weight of the whole tree compressing on a branch can do marvelous damage that will not be apparent until the adjacent material is removed or dried. This is why I don't use fruit wood for anything but spoons and such.
Water in the bowl may have been absorbed unevenly, again because of grain structure. This causes uneven pressure and crushing of the nearby wood cells. As it re-dries, the cells, having lost their elasticity due to curing, do not recover their former shape. Drying is the loss of water content. Curing, or seasoning, changes the cell structure of the wood and makes it rigid.
From what I can see in the photo, you did an excellent job of turning. The wall thickness is even and not too thick or thin. Maybe a little too deep for this particular chunk of wood. Who could know such a thing?
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Re: Question about the bowl

Postby gavin » Thu Jan 15, 2015 8:24 am

Your walls are way too thick. Your dia you say is 20 cm, so it seems your wall thickness is at least 1 cm.

Make the walls thinner.

As a demonstration to us and your self, cut this bowl in half and you will see where the walls are thickest. This will help future bowls' making.

You can feel wall thickness with thumb and forefinger quite well. You can also buy specialist callipers for measuring wall thickness.
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Re: Question about the bowl

Postby Sprot » Fri Jan 16, 2015 10:27 am

As soon as I get the remains I will post the pictures and measurements. Thank you all for help!
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Re: Question about the bowl

Postby woodness sake » Mon Apr 13, 2015 2:28 am

Here are a couple of pictures of a failed bowl turning which was due to felling damage as I described in a previous post. The top picture is of the white oak log piece from which the material came for the bowl shown in the other 2 pictures. Under the small wood chip, at about 4 o'clock, you can see a void left when the wood pulled out as the tree was saw apart. It goes down about 6 inches. The bowl in question came from the area adjacent to this void. I got the bowl turned on the out side just fine. When I started to work on the inside I noticed a crack on the outer surface and when I removed the bowl/mandrel from the lathe I saw that the top of the core was separating about 1/2" down. The material was still quite green and wet so this was not a drying problem. The wood had become damaged and weakened when it impacted the ground during felling and the defect was not made evident until the adjacent wood was removed. Next time, I won't try to get so much out of the log from this area.
note: I no longer have the picture of the log with the grain torn out during felling. This is a substitute showing the condition.
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In this picture, looking in toward the center, you can see how the damage runs right from the outside and through the core. You can also see that the wood is quite dark from being wet.
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In this picture you can see the split has gone right through the bowl. Only the pressure of the centers against the bottom and the end of the mandrel kept the whole thing from flying right off the lathe.
0408151753.jpg
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