Gluing up boards


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I'm looking to practice a couple different techniques so that I can learn best how to do it. Basically I'm have 2x4's that I'll plane down and then take 2 12" pieces and 2 8" pieces and try to come out with a 20" x 8" piece. The 3 ways that I want to try are:

*flat glue up

*using dowels for strength

*Dado and rabbet in addition to the glue

My main goal is to try out various methods and maybe even learn something.

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Long grain glue joints are stronger than the wood that surrounds them, so just a flat glue up is as strong as you will need. However, biscuits, splines, finger joinery, and tounge and groove joinery will all assist in alignment, and keep the parts from sliding against eack other as clamping pressure is applied. In my opinion dowels are useless, as they are a mostly end grain glue joint, seasonal movement in the surrounding wood will inevitably pop them loose, and they are difficult to drill matching holes for without a jig.

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I almost always run a tongue and groove joint when gluing up wide panels. But, if it is a 2" or thicker table top I always use one or, some times more, plywood splines as Beechwood suggest. The joint is then actually known as a feather joint. They are also extremely good at strengthening a mitre joint, though I always make a mitred mortice and tenon joint for these, as they are dead easy with a chop saw.

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I have had excellent results without biscuits, dowels or splines.

I made up a set of clamping cauls that I use to hold the panel flat and the edges aligned. The faces of the cauls are coated with packing tape to both repel glue and allow the boards to slide together. The faces of the cauls are slightly bowed so when clamped on the ends, exert pressure across the entire panel. I place a pair of cauls at each end of the glueup and about every 12-15" between. I then use clamps alongside each caul to pull the boards together.

If the boards are reasonable flat and constant thickness I have been able to clean up the joints with a RO sander.

Making the cauls:

I made the cauls out of clear sections of 2x lumber. I start by cutting the 2x4 in half then mill the pieces to about 1 1/2" by 1 3/8. I drill a hole in one piece in the center of the narrow face and countersink it. I then use a screw to connect a second board. As I tighten the screw I place a spacer at each end so the boards are bent as the screw is tightened. Make sure the screw does not come too close to the surface on either end. I then flatten the two boards either on the jointer or table saw. Use a third, unbent board against the fence if using the saw.

Remove the screw and the outside faces are now curved. When clamped at the ends the cauls will bend and the faces will come together nicely. Instead of clamping the ends, I added carriage bolts at each end and use a deep socket in my drill to tighten them.

I was amused to receive an email advertising a hardwood version of these cauls. The ad said they are CNC machined to get the proper curve. I'm sure they are more elegant, but they cost about 30 times what I paid.

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Oy, I had a paragraph written up in response and my thumb hit the back button on the iPad....

The way I did it before I had any fancy machines in the shop was to clamp each set of boards with the edges to be joined up and bottom faces touching. I then used a hand plane to joint the edges and used the cross clamp and caul method mentioned above... My very first attempt at gluing up a panel I used this method and got a perfect panel for a table that is still in use today.

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Now that I'm near a real computer I can add back in a bit of what I had previously written...

A far easier way to make a caul than the one described above is to simply joint the edge of a piece of narrow stock using a hand plane, then start about 6" from the center and work your way to either end. I've found it works best to take two strokes, then move a few inches closer to the end and take another two strokes, move closer to the end and take another two etc. This is much safer than running anything with bolts/screws in it over a spinning blade, and gives you a chance to warm up on your hand plane technique on a throw away piece prior to getting down to the real project.

Another great way to do it if you're not gluing up a bunch of boards at once is to create a spring joint which is essentially a VERY slight hollow in the middle of the jointed edges starting 1/2" to 1" in from either end. You can do this from one or two passes with a hand plane and it will produce a spring joint that when clamped together will keep the ends of the panel nice and tight and avoid the separation that sometimes occurs on the ends of panels. Be careful though and check your progress after each stroke, it is very easy to go too far and create a joint that won't close even with all the clamping pressure you can muster up.

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After doing a straight end-glue of some of the boards, I was very happy with the strength demonstrated. I ended up building a little footstool out of some scrap 2x4's. Some lessons were learned about using the router, about glueing up boards and about choosing wood. At least I got something useful out of what I would consider my first real furniture project.

post-4486-0-46095500-1303665090_thumb.jppost-4486-0-44268000-1303665093_thumb.jp

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Nice, everyone starts somewhere. It took me a while to just jump in and start building, but once I got over the "I don't know enough to build something" phase and entered the "I'll never know how to build anything unless I start building SOMETHING" phase, learning went a lot quicker...

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Nice one! It looks like you laminated your boards running the same way. In the future it's better to glue up your boards the rings of the end grain running one way in one board then the opposite in the next. This reduces the chance of the laminated board cupping as the wood settles. (I hope that makes sense, if not let me know and I will explain it better :) )

To throw another option into the mix I use a tapered comb joint when laminating treads for kite winder stairs.

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For that specific piece I chose the cleaner sides facing up/out. Thanks for the advice though. I appreciate it.

I picked up a biscuit router for $30 off craigslist this week and am playing with that now for jointing boards. Made a picture frame for my wife and biscuited and then glued the mitered edges. We'll see how that turns out once the glue dries.

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... In my opinion dowels are useless, as they are a mostly end grain glue joint ...

Since dowels are round there is as much long grain as there is end grain so to say they're mostly end grain is misleading.

I've used dowels with a jig for panel glue ups and it has worked well. I was using 1 dowel every 8 inches or so. As others have stated, it's more an alignment thing than a strength thing in this usage.

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Since dowels are round there is as much long grain as there is end grain so to say they're mostly end grain is misleading.

What about the hole?

As others have stated, it's more an alignment thing than a strength thing in this usage.

Yes, I stated that.

As far as the suggestion of alternating growth rings, in a perfect world this would be the optimum arrangement, as any cupping would alternate as well. However, asthetics rule. Your decision to put the clean faces up was correct.

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The hole's round too :)

So... the dowel is all long grain except for the tip. If you're edge joining boards the hole you drill in the board is half long grain and half end grain. Sure it would be better if it was all long grain but it's definitely not mostly end grain.

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Based on that then a scarf joint is also an end grain joint. I don't think this is true. It's not a black and white thing where it's either end grain or long grain.

I still think that since the dowel is all long grain and the hole in the board is only partially end grain that it's not a mostly end grain joint.

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Yes, a scarf joint is an end grain joint. It gets it's negligible strength by better resisting twisting forces and by making an increase in overall glue surface, outperforming a plain butt joint. It still benefits from mechanical fasteners or interlocking joinery. Furthermore, a scarf joint isn't cross grain like the type of dowel joint we are discussing.

However, a butt joint is the area in which dowelling is appropriate. In that situation, the dowel is a true long grain to long grain gluing surface, not cross-grain, vastly increasing the gluing area and adding considerable strength to the join. Dry dowels of the compressed variety are the best choice, and unless the stock were to be compromised at least two dowels should be used to resist twisting.

Chip, yes, the real question is "is the joint strong enough?", and in the case of the original posters question, the long edge grain glue joint is plenty strong and does not benefit from doweling.

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