Trouble with segmented Platter

Just recently I’ve been making some segmented platters out of Jarrah wood with the last one having 2mm stripes of Blackbutt between each jarrah segment. They are about 580mm in diameter. All the timber is furniture grade and are just under 290mm long by 89mm wide and 38mm thick. Each segment has been cut so the grain runs down the length. The glue used is Dorus Express, it took about 3 to 4 days to assembly each one and the timber has been in my workshop for out 3 months, so it’s dry and should be acclimatised. After about 2 days after they are turned they start to cup, sides lifting. Trying to flatten them by pressure on the bottom and they crack open, the gape is larger on the out side. So it would appear the timber shrinks after glueing up.
Has anyone had this problem before and if so how to get around it?
I was going to add some photos but have not worked out how at the moment.

A photo will be helpful in working out the problem.
Jim

Never seen dorus express. A quick google tells me its a fast setting PVA glue. Which means it is water based yes? So would have wet the wood again. :pi: Surmising from your description it is segmented like a cake slice. Shrinking happens more across the grain than the length of the grain, hence the wider crack at the rim. To keep this shape together you have to have absolutely no humidity change. Ain't gonna happen. So a design change perhaps needed.

Here's the pics of the platters, (below).
(I got 'out of round' to email them to me.)

Quote:

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Originally Posted by out of round

HI I’ve attached the photos that I was going to attach to question. One is from the first one I made which was just Jarrah the other is from the one which is Jarrah and backbut, the third shows the cross section.
Once they have split they go back to flat.

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Attachment 303080 Attachment 303081 Attachment 303082

Shame, they were looking really good.

That is a shame, it looked nice. However, radial joints like that will very often fail. The glue you have used is water based which means that the timber will swell by absorbing the moisture in the glue. As the timber dries out it will shrink causing the joints to fail. Obviously the greatest shrinkage will be on the perimeter. One possibility, is to use a glue not water based, some thing like epoxy.
Another alternative that may work, is to glue up with your water based glue, in say four sections and let sit for a while to dry out again, then glue two sections together and wait some more . Then glue the two halves together. You will most likely have to adjust the joints as you go.
Even so all those radial joints may cause you some heart aches.
Good luck..
Jim

I bought this book by Malcolm Tibbetts: The Art of Segmented Wood Turning: A Step-By-Step Guide: Malcolm Tibbetts: 9780941936866: Amazon.com: Books

It is an exceptional book in every regard. I cannot recommend it highly enough.

Great gobs of the book talk about grain, expansion, gluing methods, timber, weather, drying, moisture readings, etc.

If you are doing one or two bowls you may be wasting your time, but if you are doing a bunch then it's a Must Have.

In the book, he warns specifically of this type of glue up. The forces acting on the glue are unreal. He also suggests titebond 1 or 2 mostly. There are a few exotics, but these, I think it said, are used 90% of the time.

Segmented looks like great fun, but I think it can also lead to a lot of pain and "learning experiences"

"...both beautiful and constantly alive and moving...So different from lifeless steel or unchanging plastic, it is the movement in timber, its sheer unpredictability, that provides the challenge, the fascination that, allied to its beauty, must make wood the most exciting and wonderful material with which to design and work." (Aidan, 1989).


I like to keep this thought with me always when working with wood and especially with laminations or segmentations.

All things are possible with wood, however the sucessful craftsman have a very good understanding of the properties of wood, its movement, how it is likely to move as it is prepared, during the making process and after completion, even seasonally well after completion. They work with the wood not against it. PowderPost is one of those very successful craftsman in <st1:stockticker>IMO</st1:stockticker> and has a wealth of knowledge with FNQ timbers in this regard.

The reasons you are having difficulty with keeping these “pie slice” segmentations together in Jarrah is that jarrah is well known to be a difficult timber to deal with in this sort of application.

It has relatively high wood movement compared to other timbers but of more interest is that its tangential movement is 6.5% - 8.0%, where as its radial movement is 4.0% - 5.0% - almost twice!

If you study the grain in the platter “pie slices” you will see how the grain alignment combined with the changes in moisture over time (short or long term) will stress the glue joints. Look at all aspects of the grain orientation and how the grain alignment varies compared to where the finished platter is moving, cracking warping.

The trick is to understand this movement and to limit it, or more correctly limit the damage that will occur through seasonal natural cycles of the timber taking up and then loosing moisture.

The calculated “unit tangential movement” for jarrah is 0.3 so for a 600mm circumference platter and a 3% change in moisture content the movement is 0.30 x 3% x 600 = 5.4 mm for a 1500mm circumference platter it will be approx 13.5mm at the outer rim in a tangential direction, which is about what has happened as you have experienced.


http://www.finlayson.com.au/download..._in_timber.pdf explains some of the above. Figure 2 holds the key. If you wish to pursue these segmented platters using only quartersawn boards may help somewhat but will not overcome the issue.

Jarrah

Thank you everyone for your many suggestions. One of the first books I bought was "The Art of Segmented Wood Turning" by Malcolm Tibbetts when I started segment woodwork. I have made quite a few segmented bowls and vases without any problems. But this is the first time I had tried to make a platter this way. I'm going to have another go, but this time the gluing up will be over a few days and the Platter will be made up in quarters and left for a week before the final glueing and I'll see what happens.https://www.woodworkforums.com/images/icons/icon11.png
Thank again