Finishing green wood?

[jl]

Yesterday I went for a walk in the woods and brought back a white birch sapling for practicing on the lathe. I have a General Maxi-Lathe, which I bought before Christmas. While the shavings were flying over my head I wondered how to finish green wood?

I know one can make roughly shaped blanks from green wood, let them dry and give the final shape and finish a few months later.

But what about when the piece is given its final shape green, let to dry and twist. It can not be returned to the lathe. When is the piece sanded. When is the finish applied and what type?

When it comes to wood turning I am just as green as the wood I had on the lathe yesterday. Some days I seem to be doing the right thing, the next day everything goes wrong and I feel very frustrated.

I'ld appreciate your help.

[kwgeorge]

The main reason for twice turning is wood is because it is green. The normal rule of thumb for wood drying is that it takes 1 year of drying time for 1” thick wood. So for 2” thick wood it would take two years to dry and so on. The wood may never fully dry as it will only achieve equilibrium moister content with its surrounding humidity. And since that changes wood moves. Most people see 12% and lower as a good working level. Of course then you have to worry about the piece having this level throughout the whole piece but that is another conversation all together.

Wood that you turn wet will warp and possibly crack. The amount that the wood warps has a lot to do with the species of the wood. I have had some wood warp only slightly and I have had others warp very badly. Normally you would want to first turn the wood in a rough shape of what you want it to look like in the end. You would make the wall thickness relative to the size of your object. The bigger the object the more wall thickness you will need to help deter warping. A good rule on that is if the piece is 8 inches around you will need a ¾” wall thickness. Smaller object can have a smaller wall thickness and larger pieces will need more. You will also want to apply some type of sealer to the end grain are of the wood that you are drying. End grain will lose moister much faster than other areas so you will have more warping. Applying the end grain sealer makes the end grain dry slower and avoids quite a bit of warp.

There are a lot of magic formulas and such that people have come up with in a quest to dry the wood or stabilize it so they can turn it to finish shape right away. Bottom line is, trees contain moister, that moister is going to eventually evaporate, the cell walls will collapse and the wood will warp. So then it becomes a mater of controlling that.

[Jim Boyd]

I've turned green wood and finished it as I would dry wood. They always warp some and sometimes more. I found the thinner it was turned the less cracks I got.

[jl]

kwgeorge:

I understand the purpose of rough turning the blanks. Thank you for the precision about wall thickness in relation to diameter. It won't be long before I use this information and make some blanks, since I have an unlimited supply of green wood and logs left behind after harvest.

I have seen on the internet (don't remember were) a bowl that was turned green to completion and left to dry and twist. It was made from round wood (white birch) and turned end grain. I suspect its shape allowed its rim to twist into a wave rather than crack. It was a very interesting shape.

Jim:

I was turning a mushroom just for fun and practice, when I wondered about how and when to finish it. I'll try to apply the finish right away on the next one and see how it turns out. Not surprisingly the one I turned on Sunday already shows signs of cracks. I'm just experiementing!

Thank you to both for your replies.