Thread: Saving some cupped Redgum?

Cheers everyone. Sadly no moisture meter but I'll take a pic and put it up this afternoon when I've manoeuvred it into a reasonable location. The more I read the more I wonder if it's worth trying to save - I could wait 12 months and then spend hours thicknessing and sanding it, building a frame and legs for it, oiling it and then finding someone to buy the thing only to find it cracks the next change of season. I only paid $100 for it so I'm not too worried about just cutting it up for small projects but still, as I'm sure everyone will agree when they see the pic it would make a hell of a table top.

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Originally Posted by truckjohn

I have a piece of jet black gaboon ebony thats like a barometer. It was close to 20 years old when I got it 10 years ago - and its still moving and shifting all over the place every season. In dry weather - its dead flat. In humid weather - the last 8" on one end takes an ugly kink that's really severe. The wood is beautiful and black and unstable as water.

You resisted using it in something for 10 years? Mmmm, it would be wonderful for detailing and marquetry boxes!

Putty, I've had a bit of a think about this. I rather like the idea of using a circular saw to make cuts in the back to relieve the stress. Fill and glue the cuts with the equivalent of stringing. It could be made to look quite trendy. Also, it will be on the bottom, so unseen.

I saw this video when it was first released and it was rather a clever and litteral solution to a problem. It certainly let's you keep the mass of the top.

Making a good skirted base to attach it down to will go towards keeping it behaved.

If it doesn't move more than ~2mm across its width over 12 months, when it is sealed it should not move more than this, and is very likely to move much less.
There are table designs using, for example Z-clips, to hold the top on is able to cope with some movement.
Of course to remove the cup you will still have to follow the advice posted by others.

If it is dry and sitting in the same location for 12 months then it s also unlikely to crack further and I encourage you to stick with it.

Originally Posted by woodPixel

You resisted using it in something for 10 years? Mmmm, it would be wonderful for detailing and marquetry boxes!

Putty, I've had a bit of a think about this. I rather like the idea of using a circular saw to make cuts in the back to relieve the stress. Fill and glue the cuts with the equivalent of stringing. It could be made to look quite trendy. Also, it will be on the bottom, so unseen.

I saw this video when it was first released and it was rather a clever and litteral solution to a problem. It certainly let's you keep the mass of the top.

Making a good skirted base to attach it down to will go towards keeping it behaved.

I just measured it up again - it's 50mm, not 70mm thick, my bad. Given that thickness how deep would you recommend I make the relief cuts? And what is this 'stringing' you speak of...?

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I haven't rewatched the video yet, but I'd imagine he's discussed it.... But I'd think you might need to cut the full width to a depth of about half way.

Its probably quite a guess. As you make the cuts, you'll see the slab flatten down as the stress is relieved. So cuts may be deeper than others and some might not go completely from one side to the other (if you wish to preserve a natural edge....but will this crack??). I suppose this is the art of the process.

I don't think you'll ever get it to go magically 100% flat with this method, but I do think you'll get pretty close. The final flattening exercise should be fairly straight forward.

With the stringing, it is simply a strip of wood that is the thickness of the kerf and a bit taller. After it is glued in, plane it back to a hair over the slab. Flatten them all at the end.

As you cut, add the stringing so if you overlap the cuts, you'll neatly cut through the last insert. Much easier than trying to put a jigsaw puzzle at the end. Maybe slower, but then again it will give time for the slab to release its tension in its own time.

Again, I think it's an art, so it will take time to ensure you both GUESS the best place to cut and also make it look good....

Time for some pictures Putty!


Edit: I misremembered the video. After rewatching it, I think his use of the "nakajima" butterfly's is absolutely awful. My thought was along the method of how I do stringing in marquetry, but on a collosal scale. After each cut is made, insert the strip of beading each time. If you do this with a saw, I'd use a track. One could also use a router with a 1/4" bit. If you made them gentle curves (using a pre made fence/track) you could make it more serene and artistic.

As a note, I know this as its exactly this technique I did for a few commissions on outdoor BBQ tables. I used a router to follow gigantic stylised drawings of kookaburras, kingfishers, goannas and trees. Each table had one each, but covering most of the table. After each cut I glued in the strip. The tables were gum and the strips were a very dark red gum. It was extraordinarily effective. The lady who commissioned them actually wept when she collected them.

Originally Posted by woodPixel

I haven't rewatched the video yet, but I'd imagine he's discussed it.... But I'd think you might need to cut the full width to a depth of about half way.

Its probably quite a guess. As you make the cuts, you'll see the slab flatten down as the stress is relieved. So cuts may be deeper than others and some might not go completely from one side to the other (if you wish to preserve a natural edge....but will this crack??). I suppose this is the art of the process.

I don't think you'll ever get it to go magically 100% flat with this method, but I do think you'll get pretty close. The final flattening exercise should be fairly straight forward.

With the stringing, it is simply a strip of wood that is the thickness of the kerf and a bit taller. After it is glued in, plane it back to a hair over the slab. Flatten them all at the end.

As you cut, add the stringing so if you overlap the cuts, you'll neatly cut through the last insert. Much easier than trying to put a jigsaw puzzle at the end. Maybe slower, but then again it will give time for the slab to release its tension in its own time.

Again, I think it's an art, so it will take time to ensure you both GUESS the best place to cut and also make it look good....

Time for some pictures Putty!

Not much to look at in its weathered, beaten up current form, but it gives you an idea what I have to work with.

I've made some relief cuts in the 'low' side and I'm just going to leave it out for a few weeks/months and see how it comes out. I'm not going to be devastated if it doesn't work out because in all reality I will make a lot more money from it with a lot less stress (no pun intended) in small pieces as carvings and things like this than I will from the whole slab in one piece.

Don't get me wrong I'm not in this for the money, but in the same breath as a small startup with all the costs of setting up a workshop, even buying second hand wherever I can, I'm running at a big loss and at some point turning a profit will be a necessity.

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Originally Posted by woodPixel

I haven't rewatched the video yet, but I'd imagine he's discussed it.... But I'd think you might need to cut the full width to a depth of about half way.

He said the depth of the cut should be 3/4 of the thickness. For red gum I would say it has to be more than that.

Edit: I misremembered the video. After rewatching it, I think his use of the "nakajima" butterfly's is absolutely awful. My thought was along the method of how I do stringing in marquetry, but on a collosal scale. After each cut is made, insert the strip of beading each time. If you do this with a saw, I'd use a track. One could also use a router with a 1/4" bit. If you made them gentle curves (using a pre made fence/track) you could make it more serene and artistic.

I agree I'd use a track saw and I would also make the strips to be inserted from the same slab if possible. I also don't know if it is all that necessary to make those slots with the router. I presume the idea here is to stablise the slab from further movement, any ideas?

I notice the OP has slits on the concave side of the slab. but stresses are only relieved if the cut is made from the convex side and as you drive the strips into the slit, you open up the slit and flatten the slab.

Originally Posted by justonething

He said the depth of the cut should be 3/4 of the thickness. For red gum I would say it has been to be more than that.




I agree I'd use a track saw and I would also make the strips to be inserted from the same slab if possible. I also don't know if it is all that necessary to make those slots with the router. I presume the idea here is to stablise the slab from further movement, any ideas?

I notice the OP has slits on the concave side of the slab. but stresses are only relieved if the cut is made from the convex side and as you drive the strips into the slit, you open up the slit and flatten the slab.

Yeah my bad - that will teach me to do important things when I'm distracted. Not to worry, I'll chop it up next weekend when I get home and make knick knacks out of it. It was probably a little ambitious for my first table top anyway.

Thanks everyone for their advice.

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I think you would be taking a risk of the unknown if you think it is flat, make a table and sell it. It then goes to a different environment and re-cups.

I'm actually building something in River Red Gum (Eucalyptus camaldulensis) right now, so I feel your pain. The stuff curls like a Pringle. I dressed some 27mm stock down to 20mm and within 24 hours it was borderline unusable it had cupped so much. the only reason I was able to use it was because I was using dovetail joints, which would pull it into alignment.

I know many would disagree, but I would go as far as to say the Red Gum isn't really appropriate for table tops or similar application where it's left in large pieces. It's just too dynamic. I'm willing to bet that if you flattened it out to 40mm, it would just cup again following all that stress relief.

I've been told that water and sunlight fix, but I think that's just a temporary solution. It's almost assuredly going to continue to move.

Nonetheless, good luck. Hopefully it works out.

Cheers,
Luke