Advice please: birch blank

[John Shillabeer]

I recently scored a nice looking birch log. By all accounts it had been cut about 6 months and had been stored under a tarp. It was still quite green and unspalted when I cut off the end. As there was no visible pith and the grain was quite attractive, I thought I'd have a go at making a platter; i.e. by mounting a fresh slice off the log end on a faceplate, forming a tenon, chucking it and rough turning to approx final dimensions, sealing with Anchor seal and letting it sit for a while in a cool spot in the shop. It's about 9 1/2 in diameter, 3/4 in thick at the tenon and 1/4 in thick elsewhere. Unfortunately a radial crack formed within a day. Its not very big (yet?) but is large enough to make me wonder if I can rescue the job when the wood is dry.

There us still some of the log remaining and I would like to try again.

Question: what would you experienced turners do differently?

[Harry Robinette]

Your wasting wood end grain is going to crack pretty much ever time. That's why we turn things side grain. As wood drys it shrinks and that action pulls the wood apart causing it ti split.

[Bernie Weishapl]

If you are cutting a slice of the end of the log you will also have the pith in it. It will surely crack unless you do a super glue job on it. Like Harry turn it side grain. Rough it then anchorseal it and let it dry for a few months.

[Rodney Walker]

An end grain slice is going to split pretty much every time. All the wood shrinks at the same rate. The center is smaller so there is less shrinkage as you go out the size of the diameter gets larger so there is more radial shrinkage. Same percentage of shrinkage, just a larger diameter to start with. At a certain point the tension in the wood will exceed the wood's ability to hold together so the wood will split to relieve the tension.
As the others have said, turn your platter side grain. Shrinkage will cause the platter to go oval but it most likely won't split. Bowls are a little different being deeper so more care is needed in drying. If turning green, leave enough material that you can turn it again when it dries.
My long-winded explanation,
Rodney

[Pat Scott]

When you rough out your next side grain platter, your comment "...3/4 in thick at the tenon and 1/4 in thick elsewhere" is going to cause problems as well. Once the blank is dry, 1/4" might not be enough meat to true up. Also having parts of the platter at different thicknesses can lead to cracking as the thinner areas dry out faster than the thick areas. Try and keep the whole platter at the same thickness.

I rough out my plate and platter blanks into 1.5" to 2" discs. Cut them into slabs with the chainsaw, cut them round on the bandsaw, then Anchorseal. If I've done a good job with the chainsaw there is no need to true them up on the lathe. If I do put them on the lathe, I mount the blank between centers and just clean up both sides. I don't cut a tenon or recess, the idea is just to get the blank the same thickness. Then it's off the lathe and anchorsealed.

I used to try and somewhat shape the platter blank. But sometimes the blank warps so much that when it's time to true it up you're really limited by what you can do. By having a solid slab, I have plenty of options for design, shape, etc. The tradeoff is a 2" thick slab might take longer to dry than a thinner piece, but once dry I can do whatever I want with it. Make sure you completely remove the pith.

[Prashun Patel]

"As there was no visible pith..."

There must be. Might not be easy to find, but it has to be there. Slice off a chunk of the log, then cut through the pith to make two "D"s. When you turn each blank, (you can mount it pith side up or down) turn away as much of the pith side as you can stand.

You will also minimize your problems by turning the blank thicker. Rule of thumb is 10% of initial thickness. So, about 1" is what I'd shoot for.

Also FWIW, birch tends to crack a lot on me during drying - even when following all the precautions. I'd consider a DNA soak and then waxing/bagging too.

[John Shillabeer]

Thanks everyone.
I was already aware of the usual approach of working cross grain and was hoping that there might be a "magic bullet" for dealing with what looks to be an exceptionally consistent piece of end grain.
Apparently not.
Thanks again

[Leo Van Der Loo]

There is a product you could use, not guaranteed to be a magic bullet, should work though :)

http://www.leevalley.com/en/Wood/page.aspx?p=20079&cat=1,330,49236&ap=1