This is what is called a bird mouth joint. Used originally to make masts and spars on ships. I marked the joints with a pencil on the piece on the left so you could see them. You could cut them on a table saw but I bought router bits for 8 and 12 sided from Magnate, http://www.magnate.net/ , and run them on the Delta router/shaper. The interlocking joint is much stronger and a lot easier to clamp up. One side of the stave has the bird mouth and the other is cut at 90 degrees.
Above are two staves glued up. I glue up in twos and then glue up the two sets of twos into half column. Then the two halves are glued together. This will be an 8" column and with a larger column of this size each stave needs a .5" by .5" clamping block about .5" from the edge. Short blocks can break off as there can be considerable clamping pressure needed if there is wood movement. Also see http://users2.ev1.net/~fshagan/bm.htm for a more detailed write up.
NOTE. I agree with Mike that the all at once method is better way to go if two people are involved. I haven't worked out a method that lets me consistently get everything assembled by my self before the glue starts to dry. Art Ransom
On another note, when putting columns together I use a bird mouth joint. If you have a shaper you can use a router bit to accomplish the bird mouth. I don't have a shaper so I use a table saw. Once I have the size figured out, I start to truing up the boards and cutting the 45º cuts to form the bird mouth. Here there are 2 schools of thought to getting these put together. I use an all at once method. Just remember the project outcome depends on the preparation. Don't skip or skimp on it or you will pay for it in the end. You will notice there is a saw cut I make to collect glue and any dust that could cause a seam spread. Note. the gap at the corner is very important to get tight glue joint on both surfaces. Art Ransom This was a job of 4 columns and there was zero wood filler used! OK I'm bragging.
I start by placing all 8 lengths bird mouth up and start running the glue to them. For this job I suggest Elmer's Pro-bond Interior carpenter glue. It is thicker that Titebond and will stay put. I spread it around with a stiff brush then lay them flat. I will then put a piece of duct tape on the bottom edge to use as a roll-up guide to keep them in order until I can clamp them. If you look at the picture you will see the tape, layout and the first four rolled up. Roll the other side to the same point and then with one motion close the gap and flip the duct tape tail over the seam and this will keep you round.
The next thing I do is wrap the first end with stretch wrap. You can get this at u-haul stores or box companies. I have used the stretch wrap to clamp the columns and not used the straps but it takes about 30 wraps stretched pretty tight to get a good squeeze. In this application I used plain ratchet straps, the el-cheepos, to put the squeeze on. The stretch tape acts as a barrier to keep the clamps out of the glue. You can see the tape, wrap and clamp with a double wrap for even pressure. I have it all glued with 5 clamps and holding nicely as you can see in the first and last pictures.
Here are the 4 columns , 2- 6' smooth 8"diameter and 2- 8' roped 8" diameter one left hand and one right hand. These were a 4 start with a 2.5 rope bit.
Mike cheats because has someone to help him. I run a one man shop and am short that extra pair of hands that makes glue up MUCH easier! After reviewing Mike's method I came up with the idea of the metal bases to hold the bottom three pieces in place. They are just 6" pieces welded at 90 degrees and the welded to the base at 45 degrees.
Here are the first five pieces in place with temporary braces to hold them in place while I put the last three pieces in. After all pieces are in place I use the old rope and stick method to hold every thing together while I put the first band clamp on. I start in the center and work toward the ends. After you get the first band clamp in place check the joints for fit. I have adopted Mike's idea of using ratchet tie downs and shrink wrap and it works great.
The support bases work great to hold the staves as I glue them up. Since I use a shaper to do the joint there is not the void at the corner that Mike gets using the saw. To get the void I use a hand plane on the edge of the stave that mates to the joint. I take off about 1/16" off the edge.
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