Silky Oak cupping?

[waveink]

OK, I thought I did it right - but today as I am faced with four shallow bowls, obviously I was wrong!

I started with some Northern Silky - it was 200mm wide and about 40 mm thick, but cupped. Moisture content was about 12%, had been sitting in the workshop for about a year. I crosscut the four sides to a bread box, then flattened one side with hand planes. I didn't get back to the boards for a couple of days - all good. When I got back to them the flattened side was still flat. The sides of the box were to be 20mm thick, and since I lost a lot in flattening some of them (they were about 32mm at the thinnest part), I wasn't going to be able to re-saw and get two out of each piece. Hence I took them down to about 23mm on the bandsaw, hoping I may be able to use the thinner sections for veneering at a later date, and again left them for a day. Next day I ran them through the planer to get down to 21mm with the band sawn side up, then flipped them and took 1mm off the hand planed side. Set them on the bench ready for dovetails, was called away and didn't get back for three days - today - and now all four of the boards are cupped at least 3mm!

Two questions: 1. Obviously, what could I have done to avoid this and 2. is there a rescue at this point other than re-flattening and ending up with 12mm boards?

Scratching my head ...

pete

[Christos]

By what you describe I would have done the same thing take them down and let them sit for a little while.

There is only one thing that I see that might have caused an issue and that would have been re sawing on the bandsaw the 32mm to 23mm as this I think might now have exposed the central part of the timber for one side. Possibly giving a different moisture content.

I do recall suggestion on how to fix on this forum, might be worth while doing a search.

[waveink]

Thanks Christos,

I was beginning to wonder if I would get any response - I kind of figured that 77 views and no comments meant that no one had any different ideas. I'll see what I can do to re-flatten. I have taken the worst one and sprayed water on the inside of the cup and clamped it to by workbench - see if I can re-dress the drying? I'll let you know if I have any luck.

pete

[pmcgee]

It might be drastic, but one idea I have read is to cut a cupped board in two or three along the length.

Each piece will then be much less curved and can be flattened and rejoined without losing too much depth.

Cheers,
Paul

[waveink]

It might be drastic, but one idea I have read is to cut a cupped board in two or three along the length.

Each piece will then be much less curved and can be flattened and rejoined without losing too much depth.

Cheers,
Paul

Hmmm, you're right, pretty drastic. I have just sprayed the cupped side with water and have clamped them to my workbench with a small piece of timber under the middle of the cup. I plan on tightening a little at a time and seeing if that works before I start ripping strips.

[Christos]

Do keep us posted as I would be interested to see what the results are with the resolution.

[DJ’s Timber]

Set them on the bench ready for dovetails, was called away and didn't get back for three days - today - and now all four of the boards are cupped at least 3mm!

Two questions: 1. Obviously, what could I have done to avoid this

When you say you left it on the bench, did you have some racking sticks between the bench and board or was the board directly on the bench? The timber needs to be able to breathe on both sides equally, otherwise the exposed side absorbs more moisture causing it to swell which results in cupped board , stacking boards with racking sticks in between will go along way to minimising cupping.

[waveink]

When you say you left it on the bench, did you have some racking sticks between the bench and board or was the board directly on the bench? The timber needs to be able to breathe on both sides equally, otherwise the exposed side absorbs more moisture causing it to swell which results in cupped board , stacking boards with racking sticks in between will go along way to minimising cupping.

Hi DJ,

I did leave them on the bench without stacking sticks because I thought I was coming right back to them - but then a small emergency happened and it ended up being 3 days! Interestingly though, the reverse happened. The side that was exposed dried faster, making the underside expand and the cupping went upwards.

pete

[waveink]

Do keep us posted as I would be interested to see what the results are with the resolution.

Hey Christos,

I seem to have sorted the problem eventually. Took experimenting with a couple of different set ups, but the most effective is illustrated in the photos below. Three small block strategically placed with the board in the vise, then spray water on the inside of the cup and gently tighten the vise. Over the course of about four hours, I tightened and sprayed about three more times, only about 1/20th of a turn on the vice handle each time. Then let the board was dry and it was basically flat - flat enough that I could plane out the difference and not lose more than .5mm on the thickness.

Good solution - but hopefully I won't have to do it again!

pete

IMG_0574.jpgIMG_0575.jpgIMG_0576.jpg

[Christos]

Thanks for the update. I hate loosing good wood.