What N0legs did next, How did I do ??

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Sgian Dubh":gdw1fmra said:
Perhaps in a few months you could come back this thread and report on that, ideally with an image or two. Slainte.

Well Richard you were spot on, the top opened on one joint and continued opening until it was 14mm wide.
What I did find odd though was only one out of the eight opened/failed. This was on timber with a 7-9% moisture content and being stored in the lounge, air temp of approx 19-22 degrees.
That top is now going to be "recycled". You live and learn.
I'm planning on another in a week or two. I have decided to go with a solid top, glued up in a different way to the last so I can get this project finished.
I would love a go at veneering a top but I need to do some more learning first, I think MarkII table may be the place to try it out with a top style similar to the failure.
Thanks for the comments.
 
Random Orbital Bob":31wmwsmx said:
From the way you describe the lathe I doubt it has an outboard turning facility because otherwise for a solid wood finish you could have turned it (slowly and carefully of course). My lathe can turn diameters of 30" because the headstock swivels away from the bed. Can you swivel the headstock or turn it outboard?

Hi Bob, you're correct it's a fixed head and I can only turn about 12" max diameter on my lathe at the moment.
When I upgrade, in a year or two, outboard turning is going to be a feature I'll be looking for when I buy, I have a few ideas that require more capacity than I can manage now.
 
n0legs":3542la1k said:
... the top opened on one joint and continued opening until it was 14mm wide.
What I did find odd though was only one out of the eight opened/failed. This was on timber with a 7-9% moisture content and being stored in the lounge, air temp of approx 19-22 degrees.
All that's happened is that as the wood dried in service one joint gave way, and once it had given way it took much of the stress off the other joints meaning they are able to hold together - you sometimes see essentially the same thing in a single radial split in a log that's dried, although this is not always the case as there are often two to five radial splits in such a log or branch. I'm assuming I've got the movement correct in that further shrinkage has occurred. This would be indicated by a triangular shaped opening wider near the circumference than at centre. If the wood had absorbed moisture the wedge shaped opening would be wider at the centre than at the circumference.

Comparing this analysis to the images I put up in my first post you'll notice the wedge shaped splits are the reverse, i.e., further drying lead to the centre of the joins opening more, and moisture gain led to the outer ends of the joint showing a larger gap. I'll leave you to puzzle out why there's an apparent 'discrepancy'. Slainte.
 
Sgian Dubh":11au4f99 said:
I'm assuming I've got the movement correct in that further shrinkage has occurred. This would be indicated by a triangular shaped opening wider near the circumference than at centre.

I'll leave you to puzzle out why there's an apparent 'discrepancy'. Slainte.

Yes that's absolutely correct, it has opened up as you say.

"Figure out the discrepancy" Jeeezzzzzusss Richard I'm learning :lol:
I'm trying to get my head around this wood movement and moisture content stuff let alone come up with a viable answer for it.

I'll give it a shot though.
I know my method of construction was flawed in relation to end grain jointing to side/parallel(???) grain. So the shrinkage and expansion due to the moisture content changes differed vastly at the joints causing them to breakdown. I Think ??????
The air temp in the house being higher increased the moisture content of the timber, Oh hell I don't know I'm just babbling :lol:
 
Raising the temperature of the air would generally reduce the relative humidity (RH), all else being equal, i.e., you warmed the air without adding undue amounts of water vapour through, for example, hanging wet washing, boiling lots of vegetables, etc. Lower RH leads to the wood drying further, although the effect is gradual because wood does not release its bonded moisture easily: nor for that matter does it adsorb additional moisture instantly or especially quickly when it's placed in a more humid atmosphere, although quickly in this case is both a relative and rather vague or unspecific term.

Regarding the shrinkage that occurred in your construction you have to look at the width of the piece of wood drying and shrinking. Let's say that you experience 5% shrinkage across the width - I'm not going to start complicating matters by discussing the difference between radial and tangential shrinkage/expansion of different wood species. Then say that your piece of wood is 10 mm wide and shrinks 5% as it dries. This piece will finish up at 9.5 mm wide. Now take a piece of wood of the same species 100 mm wide that shrinks by 5%, and it ends up 95 mm wide. Now relate that information to the situation you have, i.e., a piece of wood that is essentially a segment of a circle, wide at one end and tapering to 0 or nothing at the other. Next, put enough of those segments together to make a circle (your table top) and extrapolate the end result from that using the information I've just provided.

I haven't even touched on the opposite condition, the expansion of dry wood across the grain as it adsorbs moisture, and nor am I going to complicate matters by discussing such things as the non-linear expansion and contraction rates of wood from Fibre Saturation Point (FSP) to the condition known as oven dry, nor get into hysteresis and other such exotica. Slainte.
 
Thank you Richard, I now have a better understanding of the moisture and movement issues and obviously where I went wrong with the table top. I certainly need to double check my moisture meter readings as I'm now doubting whether it's correct, I fear the wood was still quite "wet".
I'm quite ambitious and I'm really getting into my woodworking. I have plans for future projects that may lead me down this path again, so with this in mind do you have a suggestion of some further reading I should be looking at ?
I already have a few books on woodwork and furniture making but none going into so much detail with regards to moisture and movement etc. Do I need to know more or just get on and make it ?
 
Well, until (and if) I can get my book on timber technology published, probably the easiest to digest source of the sort of information you're after is R Bruce Hoadley's Understanding Wood published by Taunton Press. I think my effort is better and more use to woodworkers, but I'm thoroughly biased and compromised in coming to that conclusion (even though I'm right, ha, ha), and I'm not sure it will be published, but that's not through lack of trying to find a publisher. Slainte.
 
Sgian Dubh":364lg6ym said:
Well, until (and if) I can get my book on timber technology published, probably the easiest to digest source of the sort of information you're after is R Bruce Hoadley's Understanding Wood published by Taunton Press. I think my effort is better and more use to woodworkers, but I'm thoroughly biased and compromised in coming to that conclusion (even though I'm right, ha, ha), and I'm not sure it will be published, but that's not through lack of trying to find a publisher. Slainte.


Will look it up and purchase, thanks.

I did say when you mentioned your book a while back, you publish it and I'll buy it. From the way you described it I reckon it would be a goldmine for someone like me (and many others). Good luck with it, I hope you get it out there.

On a less serious note, many years ago my tutor ( electrical engineering ) told me their was nothing wrong with " Having the arrogance of excellence ". Some of us deserve it :lol:

Again thank you for the explanations.
 

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