With most of the turning done I turned my attention to figuring out how to attach the foot to the main body and the main body to the bowl. Those two connections are identified with the red arrows. The bowl to body connection will require a spacer to center the bowl in the opening while the bottom connection between the body and the foot just set against each other.
Three different methods were tried in different test pieces made from scraps. The first uses a simple screw run up from the foot into the body or from the inside of the bowl down through a spacer into the body. There are two problems with this method. Without a flat spot at the joint (red arrow) I could not get the connection tight enough to prevent the pieces from rocking back and forth with the small single point of contact between the two parts. The bottom photo shows the minimum size of the flat spot highlighted in red required for stability and is just not acceptable for the piece.
The second method is to use a threaded piece of ¼” steel. Holes are then drilled in each piece and threaded with a bottoming tap. Assembly is done by screwing the two pieces onto the rod. This worked better than the screw but there was a couple of problems. First, there is a limit to how tight the pieces can be screwed down without stripping the threads in the wood and second was that though the assembly was stiffer it still wasn’t as rigid as I wanted so this is out.
In the third method ½” diameter holes are drilled in each piece. A ½” diameter oak dowel is then inserted and glued in place resulting in a rigid connection with no flex. I think this works because in both the screw and threaded rod samples the connection’s rigidity is a function of how tightly the two pieces are held together at a single point of contact where the two curved surfaces meet. That’s why when I added a small flat on each of the pieces in the first example the joint became more rigid as the size of the flat increased. When the ½” oak dowel is used the size of the point of contact became irrelevant since when the foot, dowel and body are glued together the dowel has to bend for any deflection to occur. At least that’s my theory.
With a method of joining the pieces together the next step is to locate the holes and that is not a simple task on these curved pieces. First to locate is the hole’s center inside of the body. The side-to-side center is found by putting a square on the centerline of the opening and transferring that to the blue tape. 
To find the front to back center the piece is laid on its face then an adjustable square is used to measure the overall width. Half that dimension locates the front to back center and the intersection (red arrow) with the side-to-side pencil line is where the hole will be drilled. 
Now that I have a center point where the dowel hole will be drilled, I need to mark it in line with the center line of the body’s arc. That requires the setup shown in the top photo. A backer board gets clamped to the drill press fence then the piece’s body gets clamped to the board. An electronic level (red arrow) is set on a steel rule and used to level the beveled ends of the body. That way I know the hole will be drilled square with the body’s center line. The center finder is run down toward the body which gets adjusted by moving the fence forward or backward and the backer board side to side until the center finder lines up with the center point on the blue tape as shown in the bottom photo.
Swapping out the center finder for the ½” Forstner bit and drilling the hole is next. The tape is my depth gauge. The bottom photo shows a nice clean cut through the blue tape. It took maybe 30 seconds to actually drill the hole and probably at least an hour coming up with a way to locate the hole and setting up the drill press to make the hole then double checking to see if everything was accurate. 
Drilling the outside hole in the body is next. Accurately locating this hole proved to be much more difficult that the inside hole. Mostly because the outside hole is further from the center both vertically and horizontally. The two photos below show the Rube Goldberg assembly of parts used to locate the center point of the hole.
1. Like the inside hole a ruler is used to locate the center point.
2. Next a combination square is clamped down so its right-side face is on the ruler’s center line.
3. A small 90-degree triangle is used to set the combination square at 90 degrees to the ruler.
4. The small machinist square gets clamped to the combination square so its inside face aligns with the center line of the body and is parallel to the base of the combination square.
5. Last an electronic angle gauge is attached to the machinist square using its built-in magnets. When it reads 90 degrees the combination square is plumb so the square’s blade is aligned with the body’s center line.
When everything is plumb and square, I can make a line at the top of the body that gives me the side-to-side center line for the hole. Sorry for the long-winded explanation but there’s a lot of moving pieces to accurately locate this line.
The body then gets clamped and aligned in the drill press just like when the inside holes were drilled. Last is to set the front back so the drill bit is centered on the crown of the body. That’s all been done in the top left photo. The other two photos are of the drilled hole which looks symmetrical from both front and side views which is a very good thing.
To verify that the holes are really square, plumb and true an oak dowel is inserted the into the hole to see if it is vertical from both front and side views which they were and that’s a huge relief since fixing an out of alignment hole is not something I want to try and do.
Next Up – Drilling Base Holes, Fitting Dowels & Making End Cap Blanks
No comments:
Post a Comment