Today I finished the purfling on the back. It went pretty smoothly. I first bent the purfling to fit the groove on the back of the cello and then carefully cut the ends to match the purfling on the c-bouts which I had glued on already earlier. For the lower bout I had to make a splice. For the front I had made the splice in the "wrong" direction which I rectified this time. I had much more trouble getting a good spline this way. The photos below show my setup in preparing the purfling. The blowtorch isn't on when I am bending the purfling.

I didn't take photos from the glueup. I used a large injection needle to put the glue in the purfling groove. Keeping the needle in the hot gluepot made sure it stays hot and liquid.

Purfling is a thin laminated strip of wood going round the edge of both the back and the front plates. Its purpose is both decorative and functional. The length wise grain of the purling strengths the edges of the plates.

There is some variation as to when the purfling is done. It seems to be most common to do the purfling after the rough arching so that's what I will also do. Since the purfling is at a constant distance from the finished edge, the ribs (sides) need to have been done at this stage. I have done those, but I will probably describe the process in detail after I have finished the top plate as this is what I am doing at the moment. I hope this little discontinuity won't be confusing. I used the ribs to draw the outline of the cello on the back and the top plates and then removed most of the extra material using a saw and brought the outline to the marked line using a file.

Once the plate has the correct shape, adding the purfling itself can start. ​The first step is to  prepare a flat surface all around the edge of the plate. I first marked the width of the flat surface with a pair of compasses and then flattened the edge using a small plane and a file. As I didn't take many photos when working on the front, the photos below are a mixture from making the back and the front.

After this, the purfling groove is marked with a special pufrling marker. The flat edge helps to do this accurately. I built a purfling marker from a bit maple I had extra from the back, and some nuts and bolts I had available. The blade is from a small knife. First both sides of the purfling are marked lightly with the marker, and then cut carefully deeper using a sharp knife. The width of the groove should of course match the thickness of the purling used. Once the edges have been cut to sufficient depth, the groove can be excavated using a purfling picker. I again made my own from a small chisel I had lying around.

There are a few places which need extra attention. The first are the corners where the purfling from the c-bouts meet the ones from the upper and lower bouts. I made these so that the purfling  in the c-bout stays a constant distance from the edge and purfling from the upper and lower bouts come to meet them. This means that the distance of the purfling from the edge is larger for the upper and lower bouts near the corners.

The second place which needs to be handled differently is at the top of the back plate where the button is. This cannot be marked using the purfling marker. I made a template from the front plate and used that to mark the purfling groove of the back. The photos below also show another little tool I made. It is just a small block of oak with a short piece from the end of a hacksaw screwed in. The oak block makes sure the bit of saw blade stays perpendicular and also that it doesn't cut too deep. With this little helper it was quite easy to make the purfling groove the same depth everywhere. The blade needs to be short so that it can be used also in the tighter parts of the curves. 

Once the groove has been made, the purfling can be bent to follow the shape of the groove. I don't have fancy bending iron so I used an aluminium pipe and a blowtorch to heat it up. The pipe stayed hot quite long so I didn't need to have the blowtorch on while bending. Working this way I could bend the purfling for a couple of grooves before needing to heat the pipe up again. Once the purfling had the correct shape it could be cut to size. I glued in first the purflings in the c-bouts, trimmed them to the level of the plate surface and prepared the end for a nice joint with the purfling from the upper and lower bouts. The purfling wasn't long enough for the lower bout so I had to splice it. I did it widthwise and later read somewhere that one should do it in up/down direction. I think it worked out pretty nicely like this too, and actually the one I made was on the front which will anyways be cut out since the saddle comes where the splice was. I haven't yet done the purfling of the lower bout of the back so I can still make that one correctly.

Some good references:

• ​www.derekroberts.co.uk/making/purfling.htm
• osnesviolins.com/9.Purfling%20&%20Edges.htm
• www.makingtheviolin.com/Marking%20and%20cutting%20the%20purfling%20channel
• www.makingtheviolin.com/Bending%20and%20gluing%20the%20purfling
• www.lumberjocks.com/techyman2/blog/21454
• YouTube: maestroKimon: Making a violin - step 7 - the purfling​
• YouTube: Davide Sora: Arrotondamento dei bordi di fondo e tavola
• YouTube: Davide Sora: Filettatura
• YouTube: David Ireland: Violin: Carving the Top Plate - Part II
• YouTube: David Ireland: Violin: Carving the Bottom Plate - Part II

I opted to do the rough arching using the overhead router method described in Henry Strobel's books. It seemed like an easy way to quickly remove material accurately. I wasn't too concerned about the speed but since I have never built an instrument, I wanted to get it done right. The idea is pretty simple. Using the provided templates and a router, one cuts the back and front to the specified height in the given regions. The trick is to have a pin on the supporting surface which matches the size of the router bit. The templates are then attached to the bottom of the plate and the pin prevents one from pushing the back or front too far. One then progresses from template to template while adjusting the height of the overhead router. I used my drill stand for that since my router fitted nicely on that one.

I started with the largest template (lowest). I attached it to the bottom of the front using double sided tape and small screws. I then gradually lowered the router until the front had the correct thickness for the contour leaving a little the front a little too thick at this stage.  This results in a terraced front which I then smoothed with a gouge. Maybe it is easier to grasp this with some photos.

Because the cello is so large, the back and front are made from two bookmatched pieces. That means that the two pieces come from a single large wedge which is split lengthwise and then opened up like a book. As a result the left and right sides are mirror images of each other. One sees this very clearly on the figured maple back, but not really on the spruce front.

I started taking photos regularly only a little later so for this stage I don't have too much content.

Preparing the spruce front
I first planed roughly the underside of both pieces flat (no photo) and then prepared the edges  for jointing (left). After the glueing was done, I flattened the bottom surface and brought the thickness of the top plate down (right). I had decided to do the rough arching using the overhead router method described in Henry Strobel's Cello Making and I wanted to have a fairly flat top surface for that. One could have left the top as it was.

Preparing the maple back
The back was done in the same way as the front. I first prepared the joint and after glueing, flattened the surfaces. The maple is quite a bit more difficult to work with since it is a lot harder, and it has a lot of figure which makes it tear up more easily. The last picture shows the figure of the maple back nicely.