With the longitudinal arching guide done, I could start with the rough arching. This time I will try to do it with hand tools. Mainly to avoid the noise and dust generated by power tools. Last time I used the overhead router method. It worked fine and got me pretty close but it was also a lot of work.

First I marked the edge thickness of 5.5 mm. Then I took my no. 5 scrub plane and started planing. At first it seemed like an impossibly big task, but It all goes actually pretty fast. The back is lot thicker than it needs to be, so I have a lot of material to remove. Sometimes I think a small electric jointer plane would be great to have. At the moment there is simply no space for that.

I can now start shaping the outside of the back. The order of operations seems to vary a lot from maker to maker. Some now establish the edge thickness and do the purfling before starting on the arching, others start with the arching and do the purfling in the end. In any case I thought now would be a good time to make at least the long arching guide for the back. Last time I had done it from thin plywood. This time I will try thin aluminium sheet (0.8 mm). Mainly to be certain it keeps its shape.

I added locating pins for the back this morning. They should be about 15 mm from the edge. So I measured the distance from the edge of the button to the ribs and added 10 mm accounting for the width of the edge. I drilled the whole with the nail I am also going to use as the pin. The diameter is just under 2 mm. The pins were added to both ends of the back. Now I can remove the back from ribs and easily put it back on its place.

With the outline drawn I could then saw to the line. I made this frame saw a while back so that I would be prepared for this. It was hard work but the saw was great. The blade is a thin Turbo-Cut 400. I stayed quite far from the line just to be sure.

Time to mark the outline. I mark both the outline of the ribs, and the edge of the back which should be offset by 4 mm for a 4/4 cello. With the scale of this 3/4 cello (I am scaling all linear dimensions by 91.4 %) that comes to 3.6 mm. Luckily I have a washer of exactly the right dimension. In addition to those I also added enough wood for the button. Do not forget to do that!

With the ribs done it is time to continue with the plates. I had already glued the two halves of  both plates together so I could start flattening them out. I started with the back. It was already pretty close I just needed to remove some glue from the joint and come chipping left from my rough flattening earlier. There's some nice figure in the back.

Many luthiers seem to carry the same operations in parallel to both the front and the back. I don't know yet how I will do this. Somehow doing one first and then the next seems logical to me. Maybe since I rarely work for more than an hour a day.

I glued the back together today. That went really well and I almost didn't put any clamps this time, almost. I should try that out some time with wood that I am not building an instrument from.

Next up is to prepare the joints for glueing. The hide glue used in instrument making does't fill any gaps so it is very important to get the two pieces to be jointed to match very well. This is done by lighting the boards from one side and looking for any gaps. I had already jointed the boards before taking any photos so I simulated the effect by inserting a 0.05 mm feeler gauge between the boards at one end. The light is more or less in the center of the back lengthwise so the gap between the boards on the centre photo is roughly half of that. Once the feeler gauge is taken away there is only very little light coming between the two halves of the back.

The same that I've done with the front needs to be done with the back. The grain already runs almost parallel to the joint so I don't need to fix that. But I did make them match on both sides so that one is the mirror of the other. The figured hard maple of back is quite a bit more difficult to work with than the soft spruce of the front. Having a sharp blade on the plane is a must.