Having just retired I recently started my 3rd cello build. I think this is going to be a real pleasure as I no longer need to burn the candle at both ends to find time for the luthiery.
I started by building a new mold that I can leave in place whlle rough fitting the back and belly to enable the overhang on the edges to be set really accurately. It is designed so that it can be taken out easily after the linings have been fitted.
I cut blocks from willow for the corners and spruce for the ends and glued into the mold before shaping with chisels and files.
Then I scraped the ribs and sanded down to 1.4mm on the drum sander before cutting to size, bending and glueing to the blocks.
Then I could remove the outer parts of the mold to fit the linings which I mitred into the corner blocks.
I had some lovely pieces of book-matched spruce and maple from David Dyke which I cleaned up and carefully planed the edge square and true. This takes a lot of time (for me) to ensure an absolutely perfect fit ready for the rubbed joints. Once dry I then flattened the back surface with the jack plane.
Then I used the rib assembly to mark out the outline on each plate allowing 3mm of overhang (using a pencil and washer) before cutting out on the bandsaw.
Then onto the lengthy process of carving the outside profile of the plates.
Once the plates outer profile had been carved to match the templates I assembled the plates onto the ribs (with the form still in place) and then used a file with a 3mm wood off-cut attached to file the overhangs to an exact 3mm all round and also set the final rib thicknesses (5.2mm on the back and 5.6mm on the belly).
Then I marked the purfling channels set in 5mm from the edge and cut out using a scalpel and a fine chisel.
Next I dismantled the back and front plates from the rib assembly ready to carve out the inside profiles.
To make this quicker I first drilled holes to a depth a few mm shy of the finished thicknesses.
Then a lot of elbow grease with first gouges and then thumb planes to get to the starting profile where I start exciting the plates with a loudspeaker coupled to a variable frequency oscillator.
It turned out that the spruce for top had a very low transversal thickness making it very difficult to maintain the x-mode frequency. I ended up having to fix a patch using some wood from a good stiff guitar top to bolster the transversal stiffness and even after that I had to accept an x-mode frequency more than an octave below the ring mode. This meant trying to keep the back’s ring mode about a semitone higher.
Final tuning was done after cutting the f-holes and fitting the bass bar to the top.
I ended up with the following mode frequencies and plate weights:
|Mode 1||Mode 2 (x-mode)||Mode 5 (ring mode)||Weight|
|Top||26.5Hz||52.6Hz||119Hz (A3 +36cents||488g|
|Back||31.2Hz||63.2Hz||127.5Hz (B3 +55cents)||785g|
Assembling the box
I started by roughly trimming the ends of the blocks before gluing the back on carefully. This was much easier with the rib form still in place.
Then I removed the collapsible rib form, finished shaping the blocks and drilled the pilot hole for the endpin.
Finally I glued on the top plate which fitted pretty well.
The neck & fingerboard
Firstly I planed and scraped the fingerboard blank to size and set the string relief to half the diameter of the strings.
For the neck, I started by squaring up the maple blank and carefully marking the outline in pencil. I had previously made a template from perspex to make this easier – particularly for the scroll where I marked through guide holes with a pin.
Then I used the bandsaw to cut out the outline shape and a handsaw to cut down the neck which I then trued up with rasps and files.
While the scroll was still a square block I drilled the pilot holes for the pegs and then cut the scroll-box cheeks with the bandsaw.
Then I sawed the scroll profile a segment at a time before using gouges and scrapers to reach the finished shape.
Assembling the box
Before shaping the heel I temporarily glued on the fingerboard and fitted the neck joint using chalk and going slowly so that I achieved:
- A fingerboard projection at the bridge of 83mm
- An up-stand of 23mm
- A neck stop of 280mm
This is probably the trickiest bit and absolutely key to playability so worth spending the time to get it right.
Having fitted the neck joint I than shaped the heel and neck with rasps, files and sandpaper before gluing up the neck joint.
Then I trimmed up the heel, cleaned up any surplus glue and sanded down the whole instrument with 600 grade emery paper. Then I wetted the whole instrument to raise the grain and sanded again ready for finishing.
I started by darkening the instrument with a few days in the fume cupboard with a bowl of ammonia and then sealed with a few coats of shellac, rubbed down with 600 grade and then a final shellac coat.
Then I mixed some artist paints (2 parts burnt sienna, 1 part burnt umber and 1 part alizarin crimson) with a few drops of linseed oil and rubbed in evenly with a rag.
Following drying in the UV cabinet the colour was way too light so I repeated the exercise and then gave it its first coat of colour varnish. The back is looking particularly pleasing.
The colour is still a bit on the light side so I gave it another coat of artists colours with more burnt umber and less red and then another coat of varnish.
Then I left it in the UV cabinet for 2 weeks before cutting back, polishing and finishing with a wiped on coat of linseed oil.
Then I re-fitted the fingerboard and finished the neck with a couple of thin coats of linseed oil and burnt sienna artists colours burnished to a good shine.
Then I shaped and fitted the saddle, nut and bridge before stringing up with a set of larsens.
The finished instrument weighs in at 2940g, sounds wonderful
With C/G Spirocores
and looks like this: