Category Archives: Cello #3

Cello build #3

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.

The mold

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.

Inner part of new cello mold
New cello mold bolted up

The ribs

I cut blocks from willow for the corners and spruce for the ends and glued into the mold before shaping with chisels and files.

Blocks glued into mold
Blocks carved to shape

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.

Gluing in the c-bout ribs

Then I could remove the outer parts of the mold to fit the linings which I mitred into the corner blocks.

Top section of mold removed to allow fitting of linings
Linings fitted

The plates

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.

Book-matched back planed flat

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.

Rough shaping of the back with a chisel
Top after starting to rout shelf all round the edge
Back after starting to rout shelf all round the edge

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).

Plates temporarily assembled onto ribs and overhang set ready to do purfling

Then I marked the purfling channels set in 5mm from the edge and cut out using a scalpel and a fine chisel.

Purfling glued in on back plate
Purfling channel cut and faired in to back profile

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.

Back plate drilled to give rough 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.

Gluing on the bass bar

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.

Gluing on the back

Then I removed the collapsible rib form, finished shaping the blocks and drilled the pilot hole for the endpin.

Corner and end blocks shaped and inside cleaned up ready to glue on top plate

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.

Squared up maple neck block marked up ready for cutting on bandsaw

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.

Cleaning up the rough outline of the neck

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.

Cutting the cheeks on the bandsaw

Then I sawed the scroll profile a segment at a time before using gouges and scrapers to reach the finished shape.

Sawing the scroll outline
Scroll nearly done

 

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.

Getting ready to glue on the neck
Neck glued on

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.

Cleaned up and ready to go in the fuming cabinet

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.

After sealing with 2 coats of shellac
After sealing with 2 coats of shellac

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.

After 1st application of artist colours
After 1st application of artist colours

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.

After 1st coat of colour varnish
After 1st coat of colour varnish

 

 

 

 

 

 

 

 

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.

After more artist colour and another coat of varnish
After some more artists colours and 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.

Gluing fingerboard back on cello #3

Then I shaped and fitted the saddle, nut and bridge before stringing up with a set of larsens.

Finished Instrument

The finished instrument weighs in at 2940g, sounds wonderful

With Larsens

With C/G Spirocores

and looks like this:

Cello #3 front view
Cello #3 back view

 

Cello #3 side view
Cello #3 ff holes
Cello #3 peg pox
Cello # 3 scroll