So now onto the lap joint for the arm assembly.
Both part K and F have a 3/8 lap joint. Both together make the assembly.
Part K’s lap joint is on the bottom and part F is on the top. That’s an important point to remember.
Before I cut my arm to shape I cut the lap joint. Here’s why.
As I am sitting in the chair the right arm can be cut against the miter slide.
But the left arm, if already cut out must be flipped over to cut the lap joint.
To safely cut the left arm if it’s already cut to shape you would have to some way to support the board.
You can see that you’d have to put a scrap piece between the edge of the arm piece and the miter sled. It would have to be an exactly sized piece so as to keep your work piece from shifting. (You cannot use the cutoff piece from when you cut out the arm shape because it’s missing the material from the saw kerf). It’s also not a good idea because you will have to manage two pieces of wood going through the blade at one time. Not a good idea. I would not suggest doing it.
No matter how you cut the joint you must have some backing support.
I always cut my lap joint before cutting the arm to shape.
I like to cut my part F – the support to width and length before getting to the lap joint.
Cautionary Note: In cutting part F you must remember back to the backrest assembly. We discussed that the backrest assembly has to be the same width as the inside of your chair assembly. Then the length of Part F must equal the width of the back assembly and the width of both laps of part K. So if your back rest is a little more or a little less than the correct 19.5” you must make the correction on the length of your part F.
Regardless of the length part F must be 3.25” wide.
There are several ways to cut a lap joint.
1) Cut by hand
2) Cut on table saw with a regular blade
3) Cut on table saw with a dado blade
4) Using a table saw jig (pretty slick jig!)
5) Cut on a router table
6) Cut with a router using a sled/jig.
Method one is out for me. I’ve done it in the past with some pretty good success, but hand cutting is not in my tool arsenal any longer. So it’s a machine joint for me.
Method 3 – the dado blade is an excellent choice. But I don’t have a dado set up so I’ll skip this method also. It’s a great way to cut the joint – so if you have a dado set go for it.
Let’s first concentrate on cutting the joint on the table saw with a regular blade. You guys who already know the drawback to this method – hang with me, I’ll explain that in a little while.
First off no matter the method you chose to cut your lap joints you need to decide the width of both lap joints. The lap on the arm (part K) is the same width as the support piece (part F).
The width of the lap joint on part F is the same as the width of the arm (part K) AFTER it has been cut out to shape.
You can see that you have two set ups for width, but only one set up for depth to make. It makes sense, in my opinion, then to first set the height of your blade. You’ll need to gather up a few scraps to test your cuts. Make sure the scraps are the same thickness as your work piece materials.
Either set the height with a ruler or a set of set-up blocks. The set up blocks are more accurate and are an inexpensive set of gadgets to have around.
Remember that the top of you saw tooth should just barely hit that 3/8” mark.
I shifted my set up block to other side of the blade to check myself.
Learning Point – if you are using a typical saw blade, your inside and outside teeth are different heights. Keep that in mind when you are setting your height.
Use your fingertip to get the feel of it. You’ll be amazed how your finger can really help you hit the mark. You want to have the blade just at the exact height and you can tell that better with your finger than with your eyes.
Once you feel you’ve got that 3/8” mark set, use two scrap boards to make a test cut. Take a couple of passes on the ends of both boards. Then lay them against each other.
I did pretty good on my first try. Honest – it really was my first try!
Cautionary note – if your set up is not right the first time, it’s either too high or too low – you have to adjust your blade height one-half of the amount you are off. Remember that you are cutting two pieces so half of whatever amount you are off has to come off each piece.
Once you’ve reset your blade height, make another set of test cuts. (I suggest cutting off the first test cuts at the chop saw. This will avoid getting the ends of the boards mixed up—- hum—- is that end the first cut or the second cut—- you get the idea. I’ve done it a lot, so I finally just made myself get in the habit of cutting off the first test cuts.)
Now let me show you the drawback to using this method to cut your lap joints
You see those ridges – those ridges have to go. You’ll either have to use a hand plane to clean up the lap joint or sand it down to be smooth. There’s a small amount of ridge you can live with – but this is too much.
With that said – if I were using a flat topped blade I’d get a better surface. So that’s a choice if you don’t have that slick jig I mentioned above or have a router table or a hand held router. Just remember that you have to account for that ridge when you are doing your set up. It’s hard to get it right – but you can do it.
Now on to how to actually set up the cut on the table saw with just one blade.
First this is a valuable tool to have in your arsenal. It’s a saddle square. You can use it to carry a line from one face of a board to an edge – it works great.
The easiest way to use this square (in my humble opinion) is to place your pencil point on the original line and ease the square over to just touching the pencil tip, then draw your line down the other edge.
Now you can use that second line drawn with the saddle square to set up the exact location of your table saw blade.
THIS POINT IS IMPORTANT
Do not use both your fence and your miter gauge at the same time to make a cut. You’ll very likely end up with a kick back or other sour note.
Use a scrap piece to make a “sub fence” that you will use to butt your work piece against and yet allow you to pass the board through the blade AFTER the board leaves the edge of your scape piece.
Now you can start making your cuts.
The first pass your piece is butted right up against the scrap “sub fence”.
After you pass the blade, pull the work piece to the left of the blade and bring the sled and piece back past the blade.
Next slide your work piece back against the sub fence then move it slightly less than the width of your blade to the left.
Make your next cut and continue along the length of your joint.
Alternatively you can make your cut this way.
This method you hold the piece firmly against the sled, pass it through the blade and WITHOUT moving the board, bring the board and sled back through the blade. I do this all the time with no problems, but if you are just starting out and getting used to the table saw the first way is probably the safest way to go. You must absolutely not allow the board to shift as you bring it back through the blade. If you cannot do that – don’t make the cut this way.
Finally after all those passes this is what you end up with.
You have the ridges to deal with. I honestly don’t like this method except for down and dirty joints to be made in a hurry.
Now onto that 4th method, the slick jig.
This is the jig.
How to set it up and use it accurately is the next installment of my little blog.
As always – any questions or comments are welcome.
-- "Our past judges our present." JFK - 1962; American Heritage Magazine