Sunday, February 9, 2014

Dowlels & Tri angles

The seat and back are now glued, and look good. Since I changed the joint from a dovetail to a box joint, I need to add in some support. Well I'm not sure it's a need, but it doesn't hurt. Cassina not only dovetails the back to the seat, but runs dowels in the back as well. I will do the same.

Above is a photo of the Cassina drills drilling between each dovetail area so they can place 1/2 in. dowels that will help support the back piece.

 Above is my ultra amateur and underpowered drill press. I bought it for around $40 at Harbor Freight (a store here in the US that sells tools very cheap!)

The back and seat are clamped in position and the drill depth set and I drill about 1 1/2 in. down.

I glued and hammered the dowels in, and they sit a bit under the surface. I then used a plug cutter to make the dowel caps, glued them in place, and after they had dried I sanded them smooth. Lots of back strength now!

Tri angles

Now that the seat and back have been glued together, the next step is assembling the rest of the pieces. This will consist of joining pieces that have been cut to the 22.5 degree angles, so that when they come together will create a perfect 45 degrees.

At least that's the idea.

In the still from the video clip above, you can see how Cassina has drilled a series of holes in the pieces that will hold the dowels in place and create a strong joint. They've drilled two rows of holes, off set. There's NO way I could drill these holes in each piece and and have them align just right, hiding the dowels on the inside of the joint. I don't have large computer controlled equipment (at least not yet!). So I'm going to do the next best thing.

 The bottom of the seat is pictured above. It's now resting on my table saw, clamped in place, so I can start marking and drilling.

 The first two rows of the piece that seat attaches to have their pilot holes drilled.

 I took the screws and cut them down to the proper length. One sit is slightly longer, to be used along the thicker area of the joint, while the short screws are used on the lower row, closest to the front edge. This serves two purposes; one is to make sure the pieces align parallel along the edge, and not slip around when the glue is applied, and two is to provide pressure as the glue dries. There is no other great way of clamping these pieces in place, since they are at a 45 degree angle.

 First drill through to the seat piece.

So now I've removed the screws, and will put some glue on both surfaces.

 Glued and screwed the first row together

 After the glue is dry, I will remove the screws and install the support wedges. The holes will be drilled again, at 3/8 to fit the dowels later on.

I will screw in the second row of screws. Then it will be time for a nap!

Routing a trough

In the photo above you can see how Cassina has drilled a few holes in the triangle shaped wedge that serves as support for these two angles. In their design the dowels go in to add support and strength to the wedge piece. Mine will have these dowels in the same place, but installed externally. If you look very closely at the picture, you can see a small line that runs along the back side of these wedge pieces. At first I didn't know what it was for, but after doing a test glue up I realized it was a neat idea. What happens is when you put the wedge piece in place with glue, any extra glue has to go somewhere. Most of the time it shoots out the side of a joint, and can be wiped off and sanded away later on. BUT since this joint comes together at such an extreme angle, it would be very difficult to get into that area to wipe or sand any residual glue away. So what Cassina did is to rout a very small trough along the back edge of the wedge. When the glue is put on, and pressure applied to the wedge, the glue would normally shoot out the back. In this case any extra glue goes towards the back, but never makes it past the trough, instead it drips into the through, and never goes further. This is a simple and easy idea, therefore I must copy it!

The first step is to set up a very small straight bit into the router table. Mine is around 1/8 in. (a little over 3mm). I then set a guide on both sides of the table so I know when to stop routing.

Two quick cuts later and they look good.

 Now that the glue has dried in the joint, the next step is to glue in the wedges. I put together a jig that will hold the pieces at 45 degrees so it's easier to work with. I checked to make sure there were no blobs of glue in the joint that would cause trouble with the wedge in place.

I put the wedge in to check the fit, and it's good. BUT it's not perfect.

It's important for the wedge piece to fit nice and snug, at just the right angle. NO gaps! So I removed the wedge, sanded for a while, and checked again. It took a good 45 mins., but now it fits perfectly. There's just a hair of a gap, but once the glue is in and the clamp gets tightened, that gap will disappear.

 I took the wood out, and ran some strips of masking tape, just in case and glue made it out.

I put some glue on the wedge, fit it in place, and clamped it tight. (I put a clamp on the other side a few minutes after I took this picture).

 The fit looks good, no visible gaps!

 I pulled the tape off, and there was no glue spill out! The trough worked!