Well I’m back from being sick and spent some time in the shop last night working on the arm assemblies. I worked on the lap joints and the basic shaping tonight. The next step will be to do the finish shaping, the angle for the back support and the assembly itself.
First I want to show you that some of the wood I picked despite trying to get the best stuff did have a few problems, but they can generally be worked around. This piece has a check, but by moving the template around on the board I was able to use the board while avoiding the check.
The armrest assembly is joined by using a lap joint. I’m going to be making the joint a little differently than I have in the past. But let me tell you a little about lap joints first and then how I’ve done it in the past before I go into how I’m going to do it this time.
A half lap joint is a very basic joint, but it can be a very strong joint to connect two pieces of stock if done properly and in the right situations. The joint makes an intersection of sorts of the two pieces of wood. This intersection can be at the end of a board, in the middle or anywhere in between. I’ve seen half lap joints that are angled in different pieces, but generally speaking the joint is made by putting two boards together at a right angle.
Generally the two boards you want to join are of the same thickness (not necessarily the same width). Each board must have one half of its thickness removed – this makes it so the joint does not add any thickness to the project’s completed joint. You want the joint to look pretty close to seamless. I’m sure there are exceptions to this rule, but for the most part, you want the joint to be seamless. I’ve not done a half lap on anything less than a 3/4 board and would think that any thing thinner may be hard to work with and still keep the strength of the board in tact after having removed half of it to make this joint. I suppose though that if you make the joint and secure it quickly then the chance of breaking would be negated since you are adding the second board that’s been cut to the first. But, again, I’ve not done a board less than 3/4”.
Two definitions are in order:
The shoulder of the joint is the portion cut across the face of the board with the board lying flat on the table saw.
The cheek of the joint is the portion cut across the face with the board standing upright in the tenon jig.
This joint can be cut several ways, on the table saw, with or without a dado set, on the router table, on a radial arm saw, the band saw or can be hand cut. I’m not going to post this part, but I did try to make a set of these using only hand tools. They came out – ok – but not perfect enough to give to the church for the auction. So I’ve reverted back to the power tools to get this job done. I’ll have to wait to perfect my hand tool skills for another project.
Ok in the past I’ve used a table saw, the router table, a hand held router and the bandsaw to make the lap joints. The bandsaw is pretty self explanatory as you simply cut the joint like you are resawing a board and then cut out the shape of the arm and you are on your way.
When I used a hand held router I made a platform/jig to hold the boards and ran my plunge router back and forth over the material until I had reached my half way point. I generally had already cut the arm to shape so there was not a lot of material to cut out with this method. It’s important to have a good guide fence to run the router against so that you do not go past your cut mark.
With the router table it’s a bit more tricky. You cannot cut the arm’s shape before you route because you will be using your miter gauge to slide the board across the cutter. If you cut the shapes out first then you have nothing to ride against your miter gauge. You could make a sled to put the material on and then having had it cut to shape would not be a problem. You do not want to try to run the board through the router freehand. There is not enough width to this particular board to do that safely. In addition, you may be able to get the joint cut in one pass (thickness wise) but it may take two passes depending on the size of your router and the quality of your bit.
On a table saw there are three ways to cut the joint. With a single blade, with a dado set and with a tenon jig.
With a single blade or a dado set you must not cut the arm to its shape for the same reason you could not do so on the router table. You will not have a surface to bear on the miter gauge. With these two methods you must set up a stop block on your fence at the furthest point that you want your joint to be. This block should be set in front of the blade. Again do not attempt to run the board over the blade without using your miter gauge. It’s extremely dangerous and it’s not worth the risk.
After the block and distance are set, it’s just a matter of running your board over the blade the number of times it takes to cut the whole cheek. The downside to this is that both a single blade and a dado set often leaves ridges that must be either sanded down, planed down or chiseled away. But that’s not enough to keep from using this method – it’s just one down side. One last thought on this – put some sandpaper on the face of your miter gauge to give it some “grab” so the material will not shift as you are moving it.
Ok – now on to the way that I’m going to do this job this time around. I’m going to use the tenon jig method. It’s got it’s down side and I’ll explain that as I go.
The first thing is to determine what the measurement for the material you want to remove is. Since I’m using 3/4 material, my half measurement is 3/8. Therefore, I want to set my blade height to just a smidge below 3/8. I don’t want it right at 3/8 as this is will give just a little bit of sanding to do and I can use the sand dust and a touch of glue to fill in the joint lines. Ok – now to test your blade height is a very simple procedure. Use a piece of scrap (the same thickness as your work piece) and using your miter gauge run the board over the blade. Now flip the board over, position it so it will be in line with the first cut, and run the board back through the blade. You should have just a very small sliver of material holding the cut end to the rest of the board.
You can see in the picture that my sliver is very small. (It actually looks larger in the picture than it really is.) If your sliver is to large, then simply raise the blade a tiny bit and retry the cut. Remember that when you raise the blade even a tiny bit – you are doubling the height of the cut because you will be flipping your board over to cut both sides. Having achieved this I’m ready to set up to do my shoulder cuts.
My first piece to cut will be the back support. You need to decide which side you want as the top/bottom and which edge you want toward the chair or facing out from the chair. The side that you want as the top is the side that you cut the lap on. The edge will come at another point but just need to make sure which is which for now.
I don’t measure anything that I don’t have to. Therefore, I use my arm pattern to mark the section that needs to be cut out.
I then set a stop block on the saw’s fence just in front of the blade and move the fence so that the blade will cut just in front of my marked line. In other words, the outside of the blade will be cutting on the fence side of the mark.
Once that is set up I run the piece over the blade. The next step is to make a second cut at the other end of the board on the same face side. Remember this is one-half of the lap joint so you do not cut both faces of the board.
Next is to cut the shoulder for the arm itself. It is a different distance than the back support so move your fence accordingly. It’s important at this stage to make sure you have marked your boards as to which side to cut the lap on. The arms have their lap joint cut on the bottom of the board. Also, because you have not cut out the shape at this point you need to make sure which side to cut on each board. The reason for this is, in my instance, that I have one board that has a check in it that I want to avoid. I need to make sure that I cut the boards so that when I cut out the final shape this check will be avoided.
Also remember that because you have not cut out the shape yet, you will be making a shoulder cut across the entire width of the board. There is only one cut on the arm boards. Remember this is the second half of the lap joint so you do not cut both faces of the board.
Next on to the tenon jig to cut the cheeks. I use a high-faced home made tenon jig so that I can stand these long pieces up on end and have plenty of support. You should not try to cut the cheeks using only the standard fence, that would be much to dangerous.
The first piece of business is to set the piece in the jig and make sure it is square to the table. Next move the fence/jig towards the blade until your blade is set the required distance. I use a square and draw a line on the piece straight down from the shoulder cut to give me a more accurate setting.
The back support piece has a much smaller cheek than does the armrest itself. If your cheek is small enough you can run your blade to just over the edge of the shoulder cut. This is how high you must cut in order to release the waste from your work piece. However, I very seldom ever make a cut like this in one pass. Some would but I prefer to sneak up on it. So I make a pass about a third of the way through, then raise the blade another third and so on until the waste is released.
The cheek for the armrest is another story. My blade does not go up as high as necessary to but this cheek all the way through. Therefore, I need another solution. What I ended up doing was cutting as much as I could on the table saw then I used a hand saw to cut that last little bit. Worked great.
After all the lap joints are cut check to make sure they fit.
Next is to actually shape the parts by cutting on the bandsaw. Make sure that you will end up with a left and right arm. They are mirror images of one another. Also make sure that the lap is on the bottom of the arm before you cut the shape.
I rough cut my arms on the bandsaw keeping pretty close to the line then I put the two arms together and either sand down to the line or use my new microplane to clean them up. I prefer the microplane.
So after all of this – this is what your arm should look like. This picture was taken before the final shaping – but you get the idea.
Next will be cutting the bevel on the back piece where the backrest will sit. This is the tricky part and I am going to try something new on this also. That’s another day though.
Hope you enjoyed this edition. As always, any comments appreciated.
-- "Our past judges our present." JFK - 1962; American Heritage Magazine