Failure/Cracking rate for twice turned bowls? - Woodworking Talk - Woodworkers Forum
 
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post #1 of 8 Old 01-12-2011, 11:16 AM Thread Starter
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Failure/Cracking rate for twice turned bowls?

Over my Christmas vacation I rough turned a bunch of bowls and then put them in brown paper for final drying and a few of them have already got cracks all the way through. Someone suggested instead of the brown paper painting the entire bowl with Anchorseal and turning the walls a bit thinner than I had. I'm disappointed, but not totally crushed.

However I'd like to make sure my expectations are realistic, so assuming I start with logs which are green enough to through water drops while rough turning and then coat them with Anchorseal, what would you use as a percentage for how many bowls you'd expect to survive? Is close to 100% achievable or will there always be a fair amount of bowls which don't make it? Are the bowls which develop a through crack automatically firewood or can they still be safely turned and either repaired or just labeled art (don't hold soup)?

It's a snow day here in CT today so I've got the itch to turn some bowls.
Steve
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post #2 of 8 Old 01-12-2011, 11:56 AM
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if the walls are less than half an inch thick then about %80

i wouldnt advise turning a piece that has a crack running all the way through it, a small catch can separate the cracked piece and it will fly off and possible hit you
its a waste of time to turn a bowl that will break... super glue can fix some breaks but not all.
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post #3 of 8 Old 01-12-2011, 11:58 AM Thread Starter
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Mike, thanks for the info. I heard the guideline was 10% of the diameter, so one of my bowls was 13" in diameter so I left the walls a little over an inch thick and it cracked. Does the 10% rule have a hard maximum width?
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post #4 of 8 Old 01-12-2011, 12:09 PM
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anything over an inch thick when working with green wood is risky, half of the wood i turn is green and it is fun to turn, but is definitely not fun when it splits!
as long as you are careful where you leave the bowl (not a warm house) and the walls are less than an inch thick you can probably get away with it.
have you tried keeping the bowl in a pile of cool, dry wood-shavings? i have not had much experience with this myself but a few things i have put in the shavings bucket have come out fine. generally the bowls i turn are smaller than 8 inches so i dont have much of a problem with walls cracking.
just be careful and dont expose it to much heat too suddenly, it will drain all the water and make it split.
i haven't tried putting a coating on the wood but its worth a try. id like to know if it works, it saves risking the best bits of wood
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post #5 of 8 Old 01-12-2011, 12:15 PM
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Look up boiling green bowls and see what you think. I tried it on one cherry laurel hollow form and it worked quite well for that one. The process is supposed to reduce internal stresses to the point that the incidence of cracking is pretty darn low. Only downside I saw is it will leach out some of the colors in the wood so you might not get what you expect to see occasionally.
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post #6 of 8 Old 01-12-2011, 12:22 PM
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i read that a guy somewhere boiled a rough turned hollow-form and it bleached the colour of the wood and came out lighter than the natural colour, he might have been doing it wrong but i wouldn't risk a big piece of exotic wood.
if you do try boiling the wood test it on a common wood first
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post #7 of 8 Old 01-12-2011, 01:31 PM Thread Starter
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Mike, the bowls were sitting to dry in my basement - not really heated down there, but a comfortable temperature all year round.
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post #8 of 8 Old 01-12-2011, 03:36 PM
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Sprior,
I've had pretty good luck with the rough turned bowls. Are you putting them in a paper grocery bag? I leave the walls about an inch thick and just seal the top edge of the bowl, overlapping onto the inside and outside about a half inch. I put a few handfuls of their shavings in the bag with the bowl, label the bowl and bag with a pencil as to what kind of wood and the date. I haven't had any crack yet. Are you making sure that you cut the pith out of the blank before turning? If you leave the pith in, that part of the bowl on each side will usually crack.
Mike Hawkins
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