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Table Top Joinery Challenge
I'm a new member to the forum and thought I would give the forum a try...
I'm building a 6' round table of bubinga. The top is comprised of 8 pie segments, the grain from each segment pointing to the center. I've built each of the segments, glued them a segment at a time until I now have two half-circles (each comprised of 4 segments) that are ready to be joined.
Since my pie angles were not perfect, I've trimed the edge of the half-circles with a spiral trim bit against a aluminum straight edge in order to get a straight joint for glue-up. Unfortunately, I can't seem to make it straight enough! When I butt the two halves together, I've got a small gap (~1/32") at the outer edge. The wood will not bend without signficant pipe clamping pressure due to the changing directions of the grain. Even then, I can insert a piece of paper in the gap the small gap.
I've tried re-trimming the edge, but risk further "blunting" the points of the pie segments. I'm also afraid that applying more clamp pressure will backfire over the long run.
Any suggestions? Biscuit joint with gap filling epoxy? Would that even be viable? Glue block below...
Thanks
I'm building a 6' round table of bubinga. The top is comprised of 8 pie segments, the grain from each segment pointing to the center. I've built each of the segments, glued them a segment at a time until I now have two half-circles (each comprised of 4 segments) that are ready to be joined.
Since my pie angles were not perfect, I've trimed the edge of the half-circles with a spiral trim bit against a aluminum straight edge in order to get a straight joint for glue-up. Unfortunately, I can't seem to make it straight enough! When I butt the two halves together, I've got a small gap (~1/32") at the outer edge. The wood will not bend without signficant pipe clamping pressure due to the changing directions of the grain. Even then, I can insert a piece of paper in the gap the small gap.
I've tried re-trimming the edge, but risk further "blunting" the points of the pie segments. I'm also afraid that applying more clamp pressure will backfire over the long run.
Any suggestions? Biscuit joint with gap filling epoxy? Would that even be viable? Glue block below...
Thanks
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There is a little used kind of tool I can recommend see photo (post #169492, reply #1 of 21)
d_I_white,
Welcome to Knots !
>The wood will not bend<
Ha Ha Ha you noticed that huh ?
Bubinga is just about the strongest wood in the world so yah bending it ( or crushing it ha ha ha ) is not the answer.
>I've tried re-trimming the edge, but risk further "blunting" the points of the pie segments<
What I would do is back track. Don't you hate that ? I do. I have had to cut a bubinga table apart and re-glue ALL of the joints in the top because my gorilla glue was too old and too thick; so I can sympathize.
Back track by continuing to glue it up one wedge at a time, that way you can preserve the points. Forget the gap filling unless you want to look at a gap with goop in it for the life of the table.
Cutting it apart is no big deal just busout the circular saw. You may need to re think the size of the wedges so you don't have to add a little sliver of a wedge at the end.
That last join could require some fancy foot work (chisel ) since you can't get the hand plane in there on all of it. Practice on a bunch of bubinga scrap before the final go is my advice.
Nice table ! I look forward to seeing the finale.
PS: alternatively you could join the halves with the hand plane, blunting the points, then inlay a medallion or some such in the center of the table thus eliminating any points from view.
Happy Holidays !
roc
Give me six hours to chop down a tree and I will spend the first four sharpening the axe. Abraham Lincoln ( 54° shaves )
I think I'll try the Hand (post #169492, reply #2 of 21)
I think I'll try the Hand plane and if necessary, place a "medallion" at the center as you suggest.
I'm not great with a hand plane.
What would you recommend, a #5? Since I have so little to take off, what about a scraper (I have a Stanley #41)
I'm also concerned about keeping the edge square. What's the best technique for doing that? (It seems they used to make a plane with a 90 deree guide on it)
I think I'll try the Hand (post #169492, reply #3 of 21)
I think I'll try the Hand plane and if necessary, place a "medallion" at the center as you suggest.
I'm not great with a hand plane.
What would you recommend, a #5? Since I have so little to take off, what about a scraper (I have a Stanley #41)
I'm also concerned about keeping the edge square. What's the best technique for doing that? (It seems they used to make a plane with a 90 deree guide on it)
. (post #169492, reply #7 of 21)
>I'm not great with a hand plane.<
Well you are great with out a hand plane so just a matter of time.
>What would you recommend, a #5? Since I have so little to take off, what about a scraper (I have a Stanley #41)
I'm also concerned about keeping the edge square. What's the best technique for doing that? (It seems they used to make a plane with a 90 deree guide on it)<
No forget the plane with the 90° guide.
Don't even think of the scraper.
41 is not going to help.
I would use a fairly small plane. With a bit of camber to the blade.
Boy that is going to attract some flames. I mean it though.
That way you can take off the least amount of wood and right where you need to take it off.
It sounds scary but if you balance the halves ( in the orientation I am doing in the photo ), one on top the other, you can see; first if they are in the same plane by putting a straight edge across the two halves. If not plane them so they are. And second look for gaps with a light behind the joint and look for light between the two halves. I even use magnification but I get a little crazy with this woodworking thing.
The mating edges don't have to be square to the face they just have to complement each other. Meaning meet flat with minimal gaps any where ESPECIALLY ON THE PRETTY SIDE. The under side can have a minor razor thin gap for a few inches. No big deal as long as the majority of the length is a great fit up.
Where ever there is a gap , on the pretty side especially, you want to plane all the rest of the joint away to bring the gap (s) closed. Keeping in mind maintaining the face alignment of the two pieces.
Piece of cake right ? Yah . . .
Practice, practice , practice on a bunch of bubinga scrap or . . .
reap the consequences.
You can use a little square as you work on the edge. That will help keep things in the ball park. I definitely would not use the table to learn on. It will be a must to do a couple of practice joints first on scrap.
It isn't that easy to do and even harder to put it all in a post here.
Maybe read up on it in the old FWW articles in FWW on line. Garret Hack and Ian Kirby have good info.
One last thing . . . when jointing bubinga forget about a "sprung" joint. The wood is too stiff. Just shoot for a perfect fit up and go with your best shot.
A perfect joint can be done with a hand plane. Meaning , if the grain is similar, no gap at all and an invisible joint.
Quite satisfying to learn. Not a quick thing to learn or to do though.
PS: probably a good idea to find a long suffering and faithful helper to help stack up and balance the two halves. I don't think it is really possible with the halves parallel with the floor; gravity really helps when they are stacked up vertically. I did the bubinga table in the photo by my self but it is heavy work. Requres a good back and a clear head. Go slow and be safe.
roc
Give me six hours to chop down a tree and I will spend the first four sharpening the axe. Abraham Lincoln ( 54° shaves )
a question (post #169492, reply #4 of 21)
I once planned on doing something like this, but was talked out of it because of concerns about unequal wood movement along the radius. Have you considered this?
Not sure I know what you (post #169492, reply #5 of 21)
Not sure I know what you mean. Are you referring to the design itself? or joining the two halves?
If there's a concern about wood movemet in general, I plan on sealing the entire piece (top and bottom) to keep moisture out.
Often I've seen seasonal (post #169492, reply #11 of 21)
Often I've seen seasonal movement issues explained in terms of using wider boards for a "picture frame" result. Between seasonal expanding and contracting the inside or outside ends of the mitres will open and close. I've attached a picture of a disk from a log with a drying split. Seasonally the crack gets wider or narrower. On a large table the effect will be magnified. Attaching the top to plywood will not counteract the seasonal movement. And sealing/finishing does not prevent moisture movement, only slow it down.
wood movement (post #169492, reply #6 of 21)
Sure will be an interesting experiment. Got a point though ! ! !
Might have to turn this table into a slide apart with a leave or two for larger gatherings.
Hmmmm
roc
Give me six hours to chop down a tree and I will spend the first four sharpening the axe. Abraham Lincoln ( 54° shaves )
Did as you suggested (post #169492, reply #8 of 21)
Did as you suggested yesterday, mated well, glued up now and no gaps. Thanks.
Wasn't previsously worried about expansion until this morning. Turned off the heat in the shop last night and came in this morning to find the table had slightly crowned. (Won't make that mistake again, until I figure out what to do!). I've build coffee, end and sofa tables before of similar design, i.e. hardwood squares pieces, diagonal grains joined together with a border, and have never had a problem. I biscuit join all my joints and seal the entire piece, ususally lacquer.
Would a stable piece of plywood glued and screwed stabilize this? Any other suggestions?
Stable wood (post #169492, reply #9 of 21)
The only truly stable wood is petrified wood. But, it's tough on tools. ;-)
All other wood moves, and will continue to do so based on environment and exposure, particularly differences in exposure. For example, if one leaves a board sitting on a flat surface, only the top side gets exposed to a variation in humidity, so that side absorbs a little moisture, and expands, while the bottom side tries to remain as it was.
Keeping the environment reasonably stable during the build, and being mindful of how parts are stored during the process helps.
I'm pleased that you figured (post #169492, reply #10 of 21)
I'm pleased that you figured out how to join the two halves, but inevitably, the top will self destruct. Natural expansion/contraction will cause failure. Radial designs are normally veneered.
So I'm learning... I glued a (post #169492, reply #12 of 21)
So I'm learning... I glued a 3/4" birch ply substrate to the bottom and sealed it which should completely seal the bottom of the wood from vapor penetration. that leaves the top... I plan on "sealing" the top with a good moisture vapor resistant clear coat. I hope that does it. I guess I'll find out! Thanks for the advice.
Sealed (post #169492, reply #14 of 21)
Nah dude Nah
About the only way to seal out moisture exchange in this is to encase it in thick epoxy all the way around. About anything else is going to breath and exchange with the atmosphere.
The veneer that Sapwood spoke of makes a whole lot of sense.
I hope it goes well for you. I have a couple of stumps here that have not split as they say they should and they were water wet and just cut off the tree when I took possession of them. Thing is they are softer wood. Willow I think the tree guys said. I forget now.
Bubinga that may be a whole different world.
roc
Give me six hours to chop down a tree and I will spend the first four sharpening the axe. Abraham Lincoln ( 54° shaves )
Six foot round table. (post #169492, reply #15 of 21)
Six foot round table. Circumference will be somewhat in excess of 18 feet. What the poster has created is an 18' wide board at the outside perimeter of the top, that tapers to 0" at it's center. I don't know how much that wood of his moves from summer to winter. Let's be conservative and say 1/16" per foot. That's 1 1/8" that will go or come from somewhere. And a lot to ask of biscuits, glue and finish to inhibit moisture change and resist the forces introduced. Maybe if the environment is very-well climate controlled.
It will be interesting. I'd expect a loud BANG! some midwinter's night.
Ray
Or . . . (post #169492, reply #16 of 21)
Or, perhaps a series of pops, like a string of firecrackers going off? ;-)
Bangidy POP, POP, POP (post #169492, reply #17 of 21)
Ha, Ha, Ha
I had to laugh at those images.
>a lot to ask of biscuits [and] glue<
roc
Give me six hours to chop down a tree and I will spend the first four sharpening the axe. Abraham Lincoln ( 54° shaves )
roc, Better the mother in (post #169492, reply #20 of 21)
roc,
Better the mother in law than the toddler in his high chair banging on the top with his little spoon or tippy cup.
Whack, whack, whack- whack, KAPOW!
"oh".... "Did I do that?" .... "I HAVE THE POWER!!!"
ha, ha, ha, aaah, ha, ha, ha, (post #169492, reply #21 of 21)
>"I HAVE THE POWER!!!"<
Use the Shwartz ! And Oh what a shwartz !
roc
Give me six hours to chop down a tree and I will spend the first four sharpening the axe. Abraham Lincoln ( 54° shaves )
What those with negative (post #169492, reply #18 of 21)
What those with negative comments on your proposed construction technique and, it appears, your actual technique are referring to is the likelihood of the segments failing at the joint lines as in the example shown in the attached two images.
The first image shows two squares, of about 12", made up of four triangular pieces of wood-- essentially four bits of wood mitred together. When the two squares were made the wood was 8% MC. I placed one square near a radiator to dry out some more-- the left hand one. I placed the second square in a sheltered outdoor location where rain couldn't get at it-- the right hand one in the image.
When you open the second image you'll see the result of the change in moisture content of these two squares, and what happened to the mitred joints. As you can also see there was only sixteen days between taking the two photographs.
I undertook the exercise to demonstrate this form of construction is likely to fail in normal habitable buildings, and other situations. In your case the long grain of each segment runs radially in your table top, whereas in the pictures I've attached the long grain of each segment is parallel to every outside edge of the made up square. In either arrangement the long term likelihood is that the joints will open up to some extent one way or another as the wood changes moisture content over the seasons, and expands and contracts.
Unfortunately, nearly every wood finish is only water resistant, not waterproof. With, I think, the exception of some epoxy finishes, all wood finishes allow moisture vapour to pass through them in both directions, some more rapidly than others. The wood under the finish will change in size as it changes moisture content in response to seasonal variations in relative humidity (RH). Very few places have unvarying RH: perhaps only some special storage facilities or working environments in museums or medical laboratories, etc might control temperature and RH so that both vary almost immeasurably throughout the year.
If I'd really wanted the look you've created I'd have gone with veneer over a stable substrate, as others have suggested. Slainte.
www.richardjonesfurniture.com
So I'm learning... I glued a (post #169492, reply #13 of 21)
So I'm learning... I glued a 3/4" birch ply substrate to the bottom and sealed it which should completely seal the bottom of the wood from vapor penetration. that leaves the top... I plan on "sealing" the top with a good moisture vapor resistant clear coat. I hope that does it. I guess I'll find out! Thanks for the advice.
Every once in a while, (post #169492, reply #19 of 21)
Every once in a while, there's a piece of wood that doesn't follow the rules. Hopefully you used one of those pieces.