Zebrano woes

[MikeBDC]

Hi, I hope you are all well.

I bought some Zebrano to use as a frame for a large mirror. Unfortunately, I couldn't get 1" timber so I went for 2" with the intention of deep cutting it.

Even as we were putting it through the rip saw, we could feel it tightening on the blade. Wedges helped to get it through but as soon as it had been cut it bowed massively (and we're talking about a bow of around 15cm over a 2.4mtr length) :shock:

If I have any jobs where I need to board out a lighthouse, I'll bear this timber in mind. Has anyone else experienced this?

Regards,
Mike-with-some-expensive-firewood

 

[Boatfixer]

I have some 8x2 slabs of mahogany which came out of an old bank where they had been used for door linings on the lifts. It is lovely looking wood but as soon as a saw blade goes near it you can watch it wonder off in all directions..

 

[Sgian Dubh]

Even as we were putting it through the rip saw, we could feel it tightening on the blade. Wedges helped to get it through but as soon as it had been cut it bowed massively (and we're talking about a bow of around 15cm over a 2.4mtr length). Has anyone else experienced this? Mike-with-some-expensive-firewood

This happens from time to time and is stress release. The stress may have been there in the growing tree, or it may have been induced through a poorly controlled kilning procedure resulting, in this case, in what I think you're describing as the quite rare reverse case-hardening rather than the more common case-hardening.

You may find this link to a short article on my website about timber drying faults a useful introduction, which may prompt you to undertake further study on the subject. Slainte.

 

[Bluekingfisher]

Even as we were putting it through the rip saw, we could feel it tightening on the blade. Wedges helped to get it through but as soon as it had been cut it bowed massively (and we're talking about a bow of around 15cm over a 2.4mtr length). Has anyone else experienced this? Mike-with-some-expensive-firewood

This happens from time to time and is stress release. The stress may have been there in the growing tree, or it may have been induced through a poorly controlled kilning procedure resulting, in this case, in what I think you're describing as the quite rare reverse case-hardening rather than the more common case-hardening.

You may find this link to a short article on my website about timber drying faults a useful introduction, which may prompt you to undertake further study on the subject. Slainte.

Very interesting and informative piece of written work Richard.

Thanks for sharing.

 

[Baldhead]

Even as we were putting it through the rip saw, we could feel it tightening on the blade. Wedges helped to get it through but as soon as it had been cut it bowed massively (and we're talking about a bow of around 15cm over a 2.4mtr length). Has anyone else experienced this? Mike-with-some-expensive-firewood

This happens from time to time and is stress release. The stress may have been there in the growing tree, or it may have been induced through a poorly controlled kilning procedure resulting, in this case, in what I think you're describing as the quite rare reverse case-hardening rather than the more common case-hardening.

You may find this link to a short article on my website about timber drying faults a useful introduction, which may prompt you to undertake further study on the subject. Slainte.

Very interesting and informative piece of written work Richard.

Thanks for sharing.

+1 thanks for sharing that Richard.
If you carry out a 'fork test' as described and you find the timber in question is suffering from stress is there anything you can do to minimise any further stress movement?

Baldhead

 

[MikeBDC]

This happens from time to time and is stress release. The stress may have been there in the growing tree, or it may have been induced through a poorly controlled kilning procedure resulting, in this case, in what I think you're describing as the quite rare reverse case-hardening rather than the more common case-hardening.

You may find this link to a short article on my website about timber drying faults a useful introduction, which may prompt you to undertake further study on the subject. Slainte.

Very interesting article and a nice website - thank you for the link.

We have clamped the planks in the reverse direction of the curl and utilised spacer blocks to try to induce a "counter-bow". From what I have read, I don't hold out much hope of straightening them but anything's worth a go.

Does anyone have other remedies we can try?

 

[n0legs]

Well I'm probably going to get called a dull begger for this, but ..........
Could you steam warped and bowed timber to straighten it ?
If steaming allows enough suppleness to bend, could you steam then clamp straight.
I'm interested as I have a lovely piece of oak with a bend. It's approx 15mm thick, 210 wide and about a metre long. It would be really a useful piece without the bend. So far I've weighted it down flat but the bend still exists.

 

[Sgian Dubh]

If you carry out a 'fork test' as described and you find the timber in question is suffering from stress is there anything you can do to minimise any further stress movement? Baldhead

Yes, sometimes. There are techniques using steam in a controlled manner to plasticise the lignin and take the stresses out. They're not always successful, especially in a home cobbled effort lacking specialised facilities, but I am aware of success stories reported by amateurs and small professional workshops. I think this also answers n0legs's question.

I think MikeBDC's pessimism about the attempted cure for his bowed zebrano is well founded. Dry over-bending is highly unlikely to take out the stresses that have been built into the wood, that got there either through natural growth characteristics, or man-made in the kilning. Slainte.

Edit to add further information.

... is there anything you can do to minimise any further stress movement? Baldhead

Yes. Don't deep rip for a start. So a second strategy is to use the piece for something else where a finished size close to the existing thickness is required. For example, true up a 1" rough sawn board to 16 - 22 mm and try to take roughly equal amounts from both faces thus keeping the stress approximately centred. It doesn't always work, but success is pretty common.

Lastly, the reality is that a case-hardened board, strictly speaking, is 'not fit for purpose'. Returning it for replacement is an option. Some yards or timber merchants may argue the fitness for purpose stance, but they can't argue with the fork or prong test which proves incontrovertibly that there is stress in the board, although it doesn't prove absolutely that the stress is either case-hardening or reverse case-hardening, just that it's stressed, which may be natural, not man-made which is always the case in wood that is case-hardened or reverse case-hardened . Additional observations may strongly suggest case-hardening/ reverse case-hardening is the cause of the stress, e.g., surface checking, honeycombing, collapse, etc.

 

[Steve Maskery]

If I were you, I'd make the frame out of something nice and stable, then edge it with, say 3mm solid zebrano, then veneer over with zeb veneer. It will look the same. You could even cut your own veneers if you have a bandsaw with a well-set-up coarse blade. I should add that I have never veneered with zebrano, so this is supposition rather than the voice of experience!

 

[RogerS]

Zebrano veneers just fine, Steve.

Re the wood wandering after cutting. I've long given up trying to be parsimonious with exotics and ripping down a thick piece to try and squeeze out two thinner pieces. In my experience it is not worth it. Just get the closest timber to your finished size you can get and then thickness it down equally from both sides.

 

[n0legs]

Zebrano veneers just fine, Steve.


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Roger I've got to say, that looks stunning =D>

 

[RogerS]

Zebrano veneers just fine, Steve.


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Roger I've got to say, that looks stunning =D>

That's very kind of you to say so. Here's a (small) photo of the complete clock

 

[n0legs]

Oh wow !!! =D>
That is gorgeous. Absolutely love the workings on show.
Cracking job you did there =D>