Help - ratio of wood to remove to stop splitting

[badgeringtim]

Again im throwing myself on the sword of those more knowledgeable than myself.
Having spend the best part of the day hollowing a large bowl with an adze from a relatively large ash log, i want to make sure it doesnt split (like the last one).
To do this i know i need to remove some of the small growth rings from the center of the log, which is now the 'top' of the bowl. I know that the more i remove the less chance there is of splitting - but the more i remove the shallower the bowl and more hard work i will be undoing!

I wondered if there was a rule of thumb - perhapse a ratio to work this out

The log was a good 45 cm thick, so the bowl total height is around 20 cm - having removed a little from the 'top' and the base and with more hollowing to do (if my hand operates tomorrow, what with the blisters and all!) with a chisel to make the walls at most 1/2 " thick.

Any ideas would be good - currenty i have removed about 2-3 cm which i know probably is not enought but i really did have to stop, the ridges in the adze handle im sure are good to make it less slippy but make me realise my hands arent as tough as they once were!

Thanks all, if it works ill get some pics up.

 

[bhofmann]

I would take about an inch either side of the pith from a log 45cm in diameter.

But I'm sorry to say there is no hard and fast rule, or at least I don't know of it. Splitting is caused when the shrinkage of the vessels (maybe not the correct term) cannot take place without some not being split from their neighbouring vessels. More often than not, bowls split because their walls are too thick. The thinner you make the walls, the more likely it is that the wood will be able to move and bend to allow the vessels to stay together as they shrink.

Again, some woods are more prone to split than others.

 

[mr dazzler]

One thing I have found when making thinggs from green wood stock, is dont be a tight wad, meaning dont try and get too big a component from too small a blank. I used to try to get big ladles from 3 inch poles, it just doesnt work....Same with chair spindles. They are only about 5/8 - 3/4 inch diameter finished, but you need inch square blanks to make them
I'd agree remove an inch or so from you log halves. Ideally before you did the adze hollowing work (think of all the effort wasted otherwise...) Its also a good opportunity to flatten the surface and get a good face side. I find this helps in setting out the dimensions etc. The other thing is let the wood dry gradually. If an open bowl type form is forced its more likely to crack. Spindles and legs are simple round cylinders basically and almost never check or crack if force dried, but a bowl probably will seeing as it is able to release water and dry out from 2 sides. Try putting the bowl in a porous sack with chain saw chippings.
Good luck with it, hope it works out. Dont forget topost pictures

 

[badgeringtim]

Yeah i knew realy that i should have taken more off the face, going to be a painfull day today, never got a blister from axe work, but something about the adze had given me a beaute! might have to try to saw the front face. sigh....
Will head out in a mo and see what can be done!
Thanks for the comments gents - i have saved some of the shave horse shavings from the base to keep in the sack with it to make it dry as slow as poss.
I think the tight wad was comment above is probably bob on!

 

[robin wood]

All good advice. I reckon if you are 1" clear of the pith you should be OK. I always axe away the centre first before starting hollowing, this gives you the finished flat surface of the top of the bowl and allows you to lay out where you want the hollow to be. As said above don't be tight, better a smaller but perfect bowl than a big cracked one. And as above carve as thin as you can, max 1/2" at the thickest points but 1/4" better.

 

[badgeringtim]

Thanks robin - im sure you have said something very similar in response to a previous adzing question.
Well - im not down to 1/2" yet - quite but close and have had to call it a rest for the day.
Just have to hope having it in boot of my car in a black bag with lots of the damp chips from it, will keep it ok until i have another bit of time. by the time the middle is smoothed out with a gouge and the base flattened with the draw knife will be much thinner. I do have pic of it so far on my phone but how to get that here... maybe wait until its in better shape. Now to try sharpening curved things like gouges and adzes!!

cheers all.