OT - How to join two slabs of cedar?

I bought these two 'live edge' cedar planks...they are going to finish at about 3.5" thick and 75" long. The two edges which will be joined have been jointed so they are flat. I plan to glue the boards together but also want to use some sort of dowel or biscuit...


So I am thinking of using 1" diameter oak dowels. This is to help align the pieces during glue-up and maybe also add some strength. Any better ideas?

Any wood dowels need to be drier than the cedar.

GregSY said:

Any better ideas?

Click to expand...

uuhh maybe post in the woodworking subforum?

Biscuts give more wiggle room. You can even buy the cutter and do it in a vertical mill if you do not own a bisuit cutter. Make sure you reference off the good side.
Any such splines are just for alinement until the glue dries. Any modern glue is stronger then wood so no reinforcement is needed.
Good luck clamping with a live edge. Dry fit and clamp before you glue
Bill D

You could rip it on the table saw and put a plywood spline in.

Like Bill D said, if your edges are properly prepared and your clamping/glue up is good the glue alone will be way stronger than any dowels or biscuits added. This is a long grain - long grain join which mimics the strongest structure naturally present in wood. However like you said, the biscuits will help aligning the glue up and are worth doing. Drilling squared up dowel holes sounds like a pain, biscuits would be easier. IMO the best solution for this job is the Festool Domino, we used it many times for slab joining in the shop I worked at, but it's $$$$.

Maybe you know all this but...I have rarely seen a board that long fresh off the jointer that I would immediately glue up. For a high quality join, I usually true up the edge with a hand plane. A well set up jointer will make this clean-up very quick but I always do at least one pass. First goal of truing up is to square up each edge to at least one side of the table top so clamping cauls will be effective in keeping the whole thing flat during glue-up. cauls on both sides are best but with an irregular slab you could just do one-sided. Kind of a tricky glue-up that you may need to practice a few times and cauls will only be as effective as the reference surface (table top/bottom) is flat. Second goal is to make the edges parallel along their entire length. A very small gap of <1/64" may be permissible in the center of the board if it will close up during clamping. Last goal is to remove chatter and snipe which may be present at the beginning or end of the jointer pass. If you are having real trouble with this a space-filling epoxy or gorilla glue may allow you to take some shortcuts that titebond or similar wood glue would not allow.

Hi Greg:
Most high end woodworkers say a jointed edge makes an inferior glue joint because the jointer knives compress the surface wood fibers and inhibit the glue penetration.
They recommend kissing the jointed edges either with a hard sanding block or with a handplane.

I second the biscuit joint or the plywood spline if you don't want to rely on the glue alone.
Dowels are a pain in the ass; way too hard to align and way too hard to assemble without a lot of swearing and a BFH to help things along.
Back when I was a patternmaker's apprentice we always just glued the joints and relied on toenails at each end of the boards in the waste stock to get the preliminary alignment good enough to pull it in with clamps.
However "pulling it in" did not mean accepting a shitty joint with gaps and squashing the crap out of it to close those gaps.
The patternmaker I worked under was quite the Nazi about having the wood unstressed at the glue line and I'm pretty sure he was right!
Wax paper on the alignment cheeks is your friend so you can get the damned cheeks back off when the glue has dried and you pull off the clamps.

Cheers

Marcus

Edit: Looks like carbonbl beat me to it!!

I definitely prefer biscuits over dowels. Alignment is a lot easier. But with a 3.5" thickness, biscuits are a bit out of their league.

A lot has been said about alignment, but I kind of doubt that you are going to achieve perfect alignment with that thickness and length no matter what method you use. It will take a lot of force to bend a 3.5" thick board into alignment. I am not sure what type of clamp you could use to do this. I would plan on finishing it in a planer after gluing. Or a lot of planning and/or sanding.

Perhaps that plywood spline would be best. I have never used one and have never tried to glue together lumber of these dimensions, but a plywood spline may be the best bet for alignment if it is close to begin with. And a big hammer to beat it together. Or perhaps a shop press. You could put a bevel on one of the saw kerfs for the spline to aid in that process - to guide it in. But the plywood could break under the stress.

If you want to reinforce the glue joint I second the biscuits. Dowels are a real pain in my opinion. Even if you use dowel points and are very careful, just a slight misalignment means you have to remove a lot of wood to feather out the ridge. That is not a problem with biscuits.

EPAIII said:

I definitely prefer biscuits over dowels. Alignment is a lot easier. But with a 3.5" thickness, biscuits are a bit out of their league.

A lot has been said about alignment, but I kind of doubt that you are going to achieve perfect alignment with that thickness and length no matter what method you use. It will take a lot of force to bend a 3.5" thick board into alignment. I am not sure what type of clamp you could use to do this. I would plan on finishing it in a planer after gluing. Or a lot of planning and/or sanding.

Perhaps that plywood spline would be best. I have never used one and have never tried to glue together lumber of these dimensions, but a plywood spline may be the best bet for alignment if it is close to begin with. And a big hammer to beat it together. Or perhaps a shop press. You could put a bevel on one of the saw kerfs for the spline to aid in that process - to guide it in. But the plywood could break under the stress.

Click to expand...

Can't speak for everyone but when I talk about using biscuits for alignment it is for helping to line up the boards vertically during glue up, to minimize the step created on the top/bottom of the panel when two boards are joined. This is more about convenience and being able to speed up clamping during glue-up, which is very helpful if you are working with regular wood glues like titebond which will dry relatively quickly.

I agree that biscuits should not be used to resist force or hold fundamentally different-shaped boards in place. They're not designed for that. IMO even a plywood spline would be iffy if the boards are this thick and not flat. Even if the irregular boards go together around the spline, the hydraulic forces of the wood movement may generate a lot of stress and damage an already "preloaded" joint in a couple weeks/months/years. The way I was taught is that the two boards to be joined should be as flat as possible with edges square before glue-up. Some creative clamping and beating of mallets may be required during the glue up but ideally this is for getting things aligned, not bending boards into place. Then, after glue up, the completed panel should either be put through a jointer and planer or widebelt sander (size permitting) or touched up with a hand plane to make the glued-up panel as flat as required and remove any step at the joint.

Festoon domino is good
Mark

Used to be work like that would get a "rubbed glue job"

Just lean a pair of cauls against the wall, put the fist board against it glue line up. Apply hot hyde glue with a brush to both joint edges. Then "rub" the second board back and forth a bit while lower it onto the first board. Leave the set up leaning together until the glue sets.

TiteBond works that way, no clamping required.

You do have to fit the boards together first.!! ;-)

Thanks. I have a biscuit tool...maybe I'll use it to align the boards after all. I'm all for the strength of glue - my hickory table is all glued with no other means of fastening and it's held together perfectly now for 10 years or so. I can sand the jointed edges a bit....no way am I gonna hand plane them! But this is a pretty rustic table top so the gap need not be flawless. I also plan to have the whole thing sanded in a big belt sander afterwards so the alignment needs to be close but not flawless.

After you successfully join the two slabs, it would make it much more interesting to inlet 3 or 4 butterfly reinforcements in the top surface. Regards, Clark

I made furniture whose end was just about as high as anyone's, and we used biscuits for alignment for edge gluing. But we didn't always use glue on them, because the biscuits will swell from the moisture in the glue, which is why they hold so well. But all that extra glue trapped in the pockets takes a long time to fully dry out, and when it finally does the biscuits and wood over them shrink back to their original thickness. If you haven't waited long enuf before flattening and finishing the surface, you will be able to see the slight depressions, especially with a high gloss finish.

Also, the thinking behind a "spring joint", or slightly hollow joint pulled in, is that it puts the ends of the glue joint in compression, and makes the joint less prone to opening up during the dry season when the ends of the boards dry out thru the end grain more quickly than the rest of the stock.

Lastly, and probably most important for you, is you'll need to make nicely fitted cauls for the "live" edges so they don't get destroyed by the clamps. 3-1/2" thick stock will require some serious clamping force to make a good joint. One way of doing this is to put packing tape over the edges, and then use Bondo on some wood sticks to conform to the edges. Works really well and is fast and cheap, altho stinky.

How wide will your glue-up be? I have a 20" wide planer we can run it through...

Drill several matching full width holes with an auger bit on an extension rod and bolt them together with all thread rods. Recess the nuts into the wood to hide them from the casual observer and as the wood ages and shrinks, periodically tighten the nuts.

Don't bother with biscuits since you indicated you're not really concerned if the alignment isn't perfect. They do not add strength to the glue joint, especially since you're gluing up a large surface area, so alignment is their only purpose, and if alignment isn't a top priority, don't bother. Make sure your glue surfaces are flat and parallel, and make sure you have the best cauls for your clamps on the outside edges. For pretty good alignment put flat cauls with wax paper across the joint and clamp the boards top to bottom. Then clamp the joint closed with clamps across the grain.

richard newman said:

I made furniture whose end was just about as high as anyone's, and we used biscuits for alignment for edge gluing. But we didn't always use glue on them, because the biscuits will swell from the moisture in the glue, which is why they hold so well. But all that extra glue trapped in the pockets takes a long time to fully dry out, and when it finally does the biscuits and wood over them shrink back to their original thickness. If you haven't waited long enuf before flattening and finishing the surface, you will be able to see the slight depressions, especially with a high gloss finish.

Also, the thinking behind a "spring joint", or slightly hollow joint pulled in, is that it puts the ends of the glue joint in compression, and makes the joint less prone to opening up during the dry season when the ends of the boards dry out thru the end grain more quickly than the rest of the stock.

Lastly, and probably most important for you, is you'll need to make nicely fitted cauls for the "live" edges so they don't get destroyed by the clamps. 3-1/2" thick stock will require some serious clamping force to make a good joint. One way of doing this is to put packing tape over the edges, and then use Bondo on some wood sticks to conform to the edges. Works really well and is fast and cheap, altho stinky.

Click to expand...

This is by far the most qualified answer. ^^^^^^^^^^^^^
Follow his suggestions closely.

You might also consider what glue to use. Eastern red cedar is oily.

I have really good success using pocket hole screws. If done right the dowel pins used to cover up the holes can be pleasing to the eye imo.