Dining Table - Joint for top question?

[Elill]

Hi all,

I am about to embark on a new dining table project. It'll be about 1800 round ~30mm thick (working on this) and hopefully made of wedges per the diagram below. There will be more wedges than shown, but you get the idea.

Regarding the joint for these. I was planning on running a 6mm slot cutter along each wedge and using strips of hardwood ply (50mm wide). I wont go all the way to the edge, but I've done a cross section that hopefully explains it. If the timber is thick enough I'll do two slots/floating tenons.

Will this be an adequate enough joint? any tips/suggestions?

Its going to be made from spotted gum slab (which I already have). I plan on making two halves and then joining them together. My method for "jointing" is to cut the wedges approximately to size and then but them up against each other and run my festool track saw over the join (this works really well, oh and I don't own a jointer...)

This will be quite an ambitious project for me, so any help would be appreciated.

Cheers,
Peter

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[Trav]

I think your joinery sounds fine - 1 slot would be enough. Depending on what glue you are using, it is usually stronger than the timber itself. The spline helps with alignment and giving an increased surface area. Getting the thin points to meet perfectly will be a challenge - what about a hexagonal hub for the pieces to radiate from? I'd also cut the timber long then do the final outside shaping once it is all glued together.

The key questions I'd be asking myself is how to manage wood movement and grain direction, especially when cutting from a slab. Make sure the timber is well seasoned otherwise it will invariably split. My guess is that most tables like this are actually veneered, not solid timber, because of the movement issues. But others are more expert than I.

The other question is how to fit the base/legs to the top, again keeping in mind the need for the timber to expand and contract.

Trav

[rod1949]

:whs:

[Timless Timber]

If your worried about movement of the timber potentially pushing joint/s apart, you COULD try secret draw screw joints.

This has the effect of being 'an internal sash cramp' for the life of the piece (The joint always remains under tension).

Downside is, it can't later be re - sawn without hitting steel... :no: :o

Just to add confusion (My PC drawing skills suck).

http://i9.photobucket.com/albums/a70/troutylow/DrawScrewJointKeyway_zps21dd779c.jpg

So I use a drill bit the same dia as the head of the woodscrew for making the head of the keyway and a straight cut router bit in a laminex trimmer, with fence to cut the keyway to take the shaft of the shrew thats screwed into the mating piece of wood. I grind & make a chisel edge on a matching Sydney Cook Woodscrew and add a washer big enough to bridge the routed keyway slot - and set the cutter depth into a battery drill chuck...so it sits in the bottom of the drilled hole at head of the keyway - then push it along as it spins so it cuts the keyway slot to take the head of the screw in its mating piece of timber.

You obviously set you screws in the mating piece of wood - back the length of the keyway so that when clamped together - you "tap" the mating piece along until the screw shank and head travel along to the end of the key way.

I do this dry fit first with each joint, so I know they will all go together and tap up with the wooden mallet into position,

Then I tap apart in the opposite direction - unclamp and tighten the mating screw a half turn so when it goes back together with glue & cramps (not overtight - the wood has to be able to slide along when tapped with the mallet) it will pull the joint up tight - once it pulls up THEN put the pressure on the sash cramps until glue is set (I use 72 hour Araldite epoxy resin)!

The steel screws remain hidden in the joint for the life of the piece of furniture and because they go in a fraction shorter due to the extra half turn....before final assembly, they work like in internal cramp mechanism - to keep the joint under tension. As long as the movement (shrinkage expansion) in the timber is less than the cramping tension of the screws inside the joint - the joints should never open.

Typically for table top boards jointing, I would use the old 3 inch Sydney Cooke screws.

Finding Sydney Cook 3 inch wood screws today?... good luck with that, I stocked up with a couple boxes before they ceased manufacture.... but those ran out years ago. :(

I guess you could substitute another brand, just not the ones from China made from case hardened plasticine steel that bend when you breath on them! :rolleyes:

If you set the joints out properly you obviously do each step to every keyway, before moving on to the next step... (Drill Holes for keyway end, route slots, cut head relief, fix screws into mating pieces - test fit & tap up, undo and tighten screws half a turn, glue up and put together under cramps until dry).

Thats MY way of doing it, others may have easier quicker or even better ways.

[CMB]

If using the tongue method, consider having the grain running across the tongue. By orientating the grain perpendicular to the pieces being jointed you will achieve greater joint strength. Will also add a nice detail to the edges of the table if the joint is to be left visible.

Craig.

[Elill]

Many thanks for the replies.

The screw method looks interesting. Something to investigate, I like the idea.

Regarding glue, I was just going to use Titebond 3, which is my standard go to stuff. Thoughts? should I use some type of epoxy?

The idea with the grain was to have it in line with the centre of the table, i.e. I'd be getting say a 900 x 300 slab, measuring in 150 at one end (the middle) and cutting across the grain the the opposing corner. So all the gain meets in the middle. The idea was to use the same slab on opposite sides of the table so that the colour/grain variations go around.

I had also planned on "flipping" the grain for each wedge glued side by side. I am not sure the technical term for this, but in my books it shows the grain "going up" "grain going down" and so forth for "regular" joining of boards. Assuming I don't have any quarter sawn stuff

[Timless Timber]

should I use some type of epoxy?

:2tsup: :2tsup: :2tsup:

[Elill]

Riteo, whats the best?

The other idea I had was using Hoffmann (http://www.hoffmann-usa.com/)(plastic) dovetails on the underside of the table. I could cover it in a little timber inlay. I'd not go the whole way through.

[Timless Timber]

When buying epoxy resins in bulk, it's not cheap!

I liked using Epiglass (Epiglue).

Epiglass HT9000 Epoxy Resin System | International (http://www.yachtpaint.com/aus/diy/products/epiglass/search.aspx)

Also

Megapoxy

Mega Poxy (http://megapoxy.com/)

But heck, standard Araldite 72 hour from Bunnings works just as well.

They are all stronger than the parent timber your joining.

As for the Plastic dovetails? (Versus steel screw)? - you need to ask? :wink:

[Elill]

Cool, thanks.

Think of the clamping area though with dovetails v screws. The Dovetail has a much larger surface area of applied force v a screw.

Brass pocket screws easier? those draw screws look like a real PITA

[Timless Timber]

Once you grind your screw as a cutter - you have it for subsequent use so that time consuming step is eliminated - for subsequent joints.

Yes larger surface area on the plastic.... but less pressure required to break the plastic than the screw.

You want it to stay together, or be quick to make? - if speed & effort is a concern, then butt join off the saw with epoxy. :)

All your methods will work... its how long do you want it to last?

I don't bother making anything unless its made for a min 200 years +.... but that's just my philosophy - it ain't worth making unless designed and built for 3 or 4 generations use.... anything less than that and it should have been left growing as a tree (its a carbon sequestration thing / global cooling and all).

Others mileage may vary of course.

[Elill]

I was reading Joyce last night and he has a section on the secret screw technique. I understand it better now, something to think about. Its a more eloquent options compared to say connecting bolts which would need "caps" to be made to hide. But then in saying that I cold use Zipbolts which would provide some mechanical clamping to the joint (again a bugger to hide)

I am quite concerned about movement...but then I am sort of wedded to the concept so am thinking "what the hell just do it".

Joyce does say that in timber > 25mm to use two floating tenons (I knew there was a reason for suggesting that)

[Elill]

Is this the right stuff?

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