I am making a small pedestal table, and got a hunk of maple, split, planed,
squared, and turned the pedestal, ans put three coats of shellac on it. Now
this wood was pretty much as green as you can get, but I read that stuff
should be turned green. I haven't been doing this for long, and this is the
first large piece I have ever turned. I figured the coats of shellac would
seal it, and keep it from splitting. Was i correct to assume this? anything
else I need to know before I go ahead and put this thing together?
On Tue, 09 Dec 2003 01:19:22 GMT, "Leon"
<[email protected]> wrote:
>
>"js" <[email protected]> wrote in message
>news:t_%[email protected]...
>> ahh aliright. So it will be best to just set it aside, and let it dry. So
>> for future reference, I should actually be turning dry wood.
seasoned wood is harder, very hard in some cases and will be much
slower to work.
On Mon, 08 Dec 2003 13:52:32 GMT, "js"
<[email protected]> wrote:
>True, but doesn't slowing down the rate at which it drys out reduce the risk
>of splitting?
No, because you're dealing with rings.
Drying generates a strain across the board, which leads to shrinkage.
If you dry a board evenly and at moderate speed, it shrinks evenly. If
you dry it rapidly, or unevenly, then it will develop cracks
(typically the honeycomb checking of poor seasoning). This creates a
false impression that "all cracking is caused by poor drying
technique".
If your board is flat and radial-sawn, then this stress causes linear
shrinkage. You get a smaller, flat board. You may notice that radial
shrinkage is less (typically half) the tangential shrinkage.
If your board isn't radial, and it's large relative to the curvature
of the rings within it, then this difference in shrinkage causes the
board to cup.
If the "board" is a ring, containing the centre, then the "ring"
constrains it from cupping. The rings try to shrink more along their
circumference than they do on their radius, so the board is stressed
by circumferential tensions that can't go anywhere. It can't shrink,
as the centre is in the way, and it doesn't shrink so much radially.
If you cut a hoop with a central hole, or if the centre of the log is
soft, then the ring _can_ shrink, by compressing the area of the
centre. In a solid log though, it can only build up a tension.
In any solid disk of more than about 4" diameter, then drying it to
typical "dry" levels generates enough strain to crack it. The strength
of timber varies widely with species, but the strength/stiffness
ratios less so, and so all species show this same problem.
If the disk is off-centre, then some of this compressive stress may be
dissipated instead by warping instead (like the non-radial board). But
any solid section that includes the heart is almost guaranteed to
develop a radial crack.
You _may_ find a dry disk that's uncracked. But there's a huge stress
in there, and any disturbance is likely to cause it to fail
dramatically.
By using PEG-1000 to displace water, you may reduce shrinkage, and
avoid cracking that way. If the disk is thin, then it may warp out of
flat instead. But this radial cracking problem won't just go away, no
matter how carefully you dry it.
--
Die Gotterspammerung - Junkmail of the Gods
On Mon, 08 Dec 2003 12:10:35 GMT, "js"
<[email protected]> wrote:
>I am making a small pedestal table, and got a hunk of maple, split, planed,
>squared, and turned the pedestal, ans put three coats of shellac on it. Now
>this wood was pretty much as green as you can get, but I read that stuff
>should be turned green. I haven't been doing this for long, and this is the
>first large piece I have ever turned. I figured the coats of shellac would
>seal it, and keep it from splitting. Was i correct to assume this? anything
>else I need to know before I go ahead and put this thing together?
>
The trick is not letting it split as it dries. I put my green turnings
in a plastic bag filled with the wood chips to slow the drying
process. Wood can be turned green or dry, and each has its pros and
cons.
True, but doesn't slowing down the rate at which it drys out reduce the risk
of splitting?
As I said, I'm a newbie to it :)
"Andy Dingley" <[email protected]> wrote in message
news:[email protected]...
> On Mon, 08 Dec 2003 12:10:35 GMT, "js"
> <[email protected]> wrote:
>
> >I figured the coats of shellac would
> >seal it, and keep it from splitting. Was i correct to assume this?
>
> No. It _will_ dry out, it'll just take longer to do it. If it's a
> large diameter and still solid, then there's a risk of splitting.
>
> I'd go talk to the woodturning folks over the fence.
>
"js" <[email protected]> wrote in message
news:Am%[email protected]...
> True, but doesn't slowing down the rate at which it drys out reduce the
risk
> of splitting?
>
> As I said, I'm a newbie to it :)
Yes that will reduce the risk of splitting, but keep in mind also that green
wood is not as stable as dried wood. As the green wood does dry, it will
change shape. Many turners like the effect of a perfectly round bowl
changing shape after the green wood dries.
On Mon, 08 Dec 2003 12:10:35 GMT, "js"
<[email protected]> wrote:
>I figured the coats of shellac would
>seal it, and keep it from splitting. Was i correct to assume this?
No. It _will_ dry out, it'll just take longer to do it. If it's a
large diameter and still solid, then there's a risk of splitting.
I'd go talk to the woodturning folks over the fence.
I think a lot of turners like to do the roughing out when the blank is
green, then let it dry before final shaping and finishing....
Bridger
On Mon, 08 Dec 2003 14:35:05 GMT, "js"
<[email protected]> wrote:
>ahh aliright. So it will be best to just set it aside, and let it dry. So
>for future reference, I should actually be turning dry wood.
>
>Thanks again.
>
>"Leon" <[email protected]> wrote in message
>news:CI%[email protected]...
>>
>> "js" <[email protected]> wrote in message
>> news:Am%[email protected]...
>> > True, but doesn't slowing down the rate at which it drys out reduce the
>> risk
>> > of splitting?
>> >
>> > As I said, I'm a newbie to it :)
>>
>> Yes that will reduce the risk of splitting, but keep in mind also that
>green
>> wood is not as stable as dried wood. As the green wood does dry, it will
>> change shape. Many turners like the effect of a perfectly round bowl
>> changing shape after the green wood dries.
>>
>>
>
On Mon, 08 Dec 2003 13:52:32 GMT, "js"
<[email protected]> wrote:
>True, but doesn't slowing down the rate at which it drys out reduce the risk
>of splitting?
>
No. You should consider hollowing the base from below, where it won't
show.
Rodney Myrvaagnes NYC J36 Gjo/a
The sound of a Great Blue Heron's wingbeats going by your head
ahh aliright. So it will be best to just set it aside, and let it dry. So
for future reference, I should actually be turning dry wood.
Thanks again.
"Leon" <[email protected]> wrote in message
news:CI%[email protected]...
>
> "js" <[email protected]> wrote in message
> news:Am%[email protected]...
> > True, but doesn't slowing down the rate at which it drys out reduce the
> risk
> > of splitting?
> >
> > As I said, I'm a newbie to it :)
>
> Yes that will reduce the risk of splitting, but keep in mind also that
green
> wood is not as stable as dried wood. As the green wood does dry, it will
> change shape. Many turners like the effect of a perfectly round bowl
> changing shape after the green wood dries.
>
>
"js" <[email protected]> wrote in message
news:t_%[email protected]...
> ahh aliright. So it will be best to just set it aside, and let it dry. So
> for future reference, I should actually be turning dry wood.
>
Well that is not absolutely true, it is far easier to turn green wood as
it cuts easily. If you need the wood to be stable after turning go with dry
wood. If you want to let nature aid in your artistic impression go with
green.
"Leon" <[email protected]> writes:
> "js" <[email protected]> wrote in message
> news:t_%[email protected]...
>> ahh aliright. So it will be best to just set it aside, and let it dry. So
>> for future reference, I should actually be turning dry wood.
>>
>
>
> Well that is not absolutely true, it is far easier to turn green wood as
> it cuts easily. If you need the wood to be stable after turning go with dry
> wood. If you want to let nature aid in your artistic impression go with
> green.
Isn't it also easier to make large turned objects from green wood,
because after turning the thin walls are flexible enough to survive the
shrinking during drying by warping instead of cracking, while drying a
lage blank without any crack is extremely difficult?
--
Dr. Juergen Hannappel http://lisa2.physik.uni-bonn.de/~hannappe
mailto:[email protected] Phone: +49 228 73 2447 FAX ... 7869
Physikalisches Institut der Uni Bonn Nussallee 12, D-53115 Bonn, Germany
CERN: Phone: +412276 76461 Fax: ..77930 Bat. 892-R-A13 CH-1211 Geneve 23