Category Archives: Cello #1

Cello Week 10 – Setup

Having completed the rather rewarding finishing process I can now set up the instrument ready for stringing.

Fitting the pegs

The first step was to build my own peg shaver as the cheap Chinese one I had bought together with a peg reamer and end-pin reamer was way too small for the pegs I have.

I found a piece of maple off-cut and cut it down to the length of a peg and drilled it slightly larger than the thin end of the peg reamer before reaming out a hole with the thick end matching the thick end of my pegs (about 14mm).  Then I planed away one face until I had a nice parallel slot showing about 5mm wide.  Then I glued another capping piece over the slot and re- reamed the hole.  Finally I fitted the blade from my Chinese shaver together with a very simple fine adjusting mechanism.

The result is shown below.

Finished peg shaver
Finished peg shaver

I also built a very simple jig from 2 pieces of hinged oak to sand a finish onto the pegs.

Jig for sanding the pegs after shaving
Jig for sanding the pegs after shaving

Then I reamed out the pre-drilled holes in the peg box (using a few reverse turns at the end) so that I had a little more than the target 21mm between the edge of the box and the decorative rim of the peg to allow for the wood to compress a bit.

I then set up a simple jig to hold the pegs while I cut them to length and drilled them.  I marked the hole positions a few mm from the centre of the box towards the thicker end of the peg and drilled the holes using a 2mm bit and then chamfered the openings.

Fitting the soundpost

I rough cut a 13mm square sction from a piece of close and straight grained spruce taking care to ensure no runout and then planed it down to an 11mm square section.  Then I carefully planed it down systematically to an octagon and so on till I had a perfect cylinder 11mm diameter.

Actually fitting it could be quite an adventure with the fitting tool and retriever I purchased!

Yes – quite an adventure but eventually got the knack – certainly got my money’s worth from the sound post retriever!  The f-hole was only just wide enough to fit the post through though – must remember to make it a millimetre wider on the next one – took me 2 hrs of frustrated attempts! Phew.

Fitting the nut

I filed down the ebony nut blank to fit the fingerboard profile and also added a 2mm T-extension as some makers have suggested this improves the look and I needed it anyway to get back to the designed dimensions. I tack glued the nut to the end of the fingerboard with a few drops of Titebond.

Nut ended up proud of the fingerboard by 1mm at the A string to about 1.4mm at the C string.

String spacing was set with dividers at 8mm and slots cut with a fine saw and then nut files before lubricating the slots with graphite (pencil lead).

Nut glued onto end of fingerboard
Nut glued onto end of fingerboard
Fitting the saddle

Filed down the ebony saddle blank to match the curve on the bottom of the cello and marked /cut the top with a sharp knife to fit.  Glued in with hot hide glue

Saddle fitted
Saddle fitted
Fitting the bridge

I built myself a simple jig to hold the bridge during fitting:

Close up of the bridge holding jig showing the feet spreader
Close up of the bridge holding jig showing the feet spreader
Jig for holding the bridge during fitting
Jig for holding the bridge during fitting

I used a piece of carbon paper to highlight the area on the feet to remove.

Holding the bridge in position while fitting
Holding the bridge in position while fitting
Feet just about fitted
Feet just about fitted

Then marked the bridge height using a marked up stick on the fingerboard to give 4mm action clearance over fingerboard for the A, up to 6.5mm for the C string and cut the bridge profile on the band saw giving it a few millimetres extra to allow for final adjustments.

Next I used a small plane to get the thickness profile right before hand carving with a sharp knife to get the bridge to target dimensions.  Finally hand sanded to get rid of any tool marks and marked the string positions with dividers (15.8mm string centre to centre) and cut the slots with fine saw and then nut files.  Ordered some parchment to protect the A and D slots.

Stringing up

Finally got to the exciting bit of fitting the strings and seeing what the result of 9 months labour sounds like!

Held the bridge in place with the bridge holding jig I made earlier while I fitted the tailpiece and started stringing it all up with a set of large scale.  Everything seems to work ok – need to do a bit more on the pegs to get a more even grab between the two ends and the bridge needs a bit of tweaking to bring the action down to target and also a coat of linseed oil and the parchment protectors for the A and D strings – but it sounds wonderful!  Very responsive, lovely sweet tone, good depth and well balanced across the strings and right to the top of the fingerboard.  Quite a strong wolf note on F but a 7g eliminator on the G string sorted that out.

Finished at last! 9 months of hard work but sounds wonderfull
Finished at last!
9 months of hard work but sounds wonderful

Will be taking it to our cello-nite on Saturday night to try out on the felli celli!

Cant wait to see how the sound develops as it gets played in.

Finished instrument

I have decided to call her ‘Anna’ – I think she deserves a name after all that work!

Link to all the specifications  for the finished instrument are here.

Link to some better pictures and  recordings made with it by my good friend George Shilling.

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Cello Week 9 – Finishing

Finishing the cello

Finishing Approach

After much reading on the Internet I decided to go for the following approach:

  1. Finish the surface after raising the grain with water
  2. Colour the wood in a UV light box
  3. Deepen the colour by fuming with ammonia
  4. Shellac sealer/ground coats
  5. Coloured oil varnish coat
  6. Artists colour rubbed in with fingers
  7. 3 more coats of coloured oil varnish
  8. Clear oil varnish (2 coats)
  9. Cutting back and polishing

I found an excellent supplier of ready made varnishes and varnish ingredients in Germany at Hammerl and ordered the oil varnish and a few extra ingredients.

UV Lightbox

I then set about designing a UV light box for both giving the white cello an initial suntan and for drying the oil varnish coats.

I settled on a design that I could assemble and disassemble easily for flat storage when not in use.

The base is 1/2″ ply 610mm x 400mm into which I routed some 6mm grooves to take the hardboard sides, front and back. The sides are braced with vertical triangular cross section struts at the edges and onto which are mounting UV fluorescent fittings (4 off 18W 600mm UVA fittings on each side).

The box is 1500mm high and a top piece of similarly grooved 1/2″ ply and with a small USB fan to extract heat/varnish fumes holds it all together.

All the inside surfaces are coated with aluminium foil.

In the UV light box before I put the cover on
In the UV light box before I put the cover on

I lightly glued a piece of scrap on the neck to hold it straight and clean during tanning/varnishing.  Then the cello got a final wipe down with water and a final scraping all over before going into the light box for a week or two depending on how fast it darkens up.

Here is the result after 10 days.

After 2 weeks of tanning
After 2 weeks of tanning

I then tried fuming using household ammonia (only about 9% but seems to work quite well).  Here is the result after 10hrs.

After 10hrs fuming with ammonia
After 10hrs fuming with ammonia

Next I sealed it all with a few coats of a 1lb cut of shellac.

1st coat of shellac sealer
1st coat of shellac sealer
Sealed with shellac ready for 1st coat of varnish
Sealed with shellac ready for 1st coat of varnish

 

 

 

 

 

 

 

 

 

 

 

 

And then the 1st coat of coloured varnish. This is incredibly thin and only a tiny amount was enough for the whole cello.

Just put on the 1st coat of coloured varnish
Just put on the 1st coat of coloured varnish

Then back into the light box to dry.

Once dry (I left it 2 days) I rubbed down with wet 2400 grade micro-mesh and then used a mixture of burnt umber and burnt sienna artist colours rubbed in with my fingers and wiped off with a kitchen towel until the colouring was even.

After rubbing in and then rubbing off some artist oils (Burnt sienna and burnt umber)
After rubbing in and then rubbing off some artist oils (Burnt sienna and burnt umber)

Another 2 coloured coats but still looking too light so had another go smutzing with artists colours.

After rubbing some more artists oils
After rubbing some more artists oils

Next step is a final coloured coat and then 2 clear coats.

After final colour coat
After final colour coat

Next I cut it back with 3200 grade micro-mesh and water and then  pumice and linseed oil on a felt pad. Still left some corduroy grain on the top. Finally polished to a nice matt sheen with rotten-stone and linseed oil.

Then popped off the keeper on the neck before gluing back the fingerboard.

Holding the bridge in position while fitting
Holding the bridge in position while fitting

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Cello week 8 – Assembly

Assembling the box

The big moment has finally arrived and time to glue on the back.

I modified the form so I could dismantle the ends to allow me to keep the form in place while the back was glued on.

Gluing on the back
Gluing on the back
The back glued on - inside view
The back glued on – inside view
The back glued on
The back glued on

 

 

 

 

 

 

 

Before fitting the belly I reamed out the end pin making sure the pin stayed centrally aligned inside the body and leaving 1mm gap between the pin body and the ribs.

Then I fitted steel pins to the belly where it meets the end blocks to make sure everything stayed aligned during gluing.

Heated everything up with my paint stripper air gun and then some weak hide glue and all came together nicely.

Gluing on the belly
Gluing on the belly

One seam had a small gap so popped it and re-glued.

Box al glued up
Box all glued up

Then I used a knife to round the edges and finished off with 400 grit sandpaper.

Edges rounded
Edges rounded

 

 

 

 

 

 

Fitting the neck

I marked the side of the neck where it should meet the top (280mm from the nut) and with an upstand of about 17mm on the bass side and 19mm on the treble side (due to the 1.5 degree cant on the fingerboard).

Then marked the mortice position with a knife and carefully sawed out the sides of the mortice and chiselled out the waste.  When I got close moved to a file and chalk to get a snug fit with the fingerboard centred over the body and projecting a height of 85mm at the bridge position.  This was definitely one of the trickier operations but I kept moving slowly with lots of trial fits and got there in the end.

Here it is assembled before gluing:

Neck joint dry assembled during fitting
Neck joint dry assembled during fitting

And after gluing ready for finishing.

Neck glued on ready for finishing
Neck glued on ready for finishing

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Cello week 7 – The neck

The neck and scroll

Before I did anything I roughly cut out the neck profile to give the wood a few months to settle.

Rough cut the neck to allow the wood to settle
Rough cut the neck to allow the wood to settle

Now with the plates nearly done I levelled the top and squared the sides (they had actually moved appreciably in the intervening 4 months) before cutting the profile more accurately on the bandsaw. I then filed/scraped the outer scroll outline and drilling  the peg holes on the drill press before sawing the scroll sections and then started carving.

Just starting to carve the scroll
Just starting to carve the scroll

After much filing, carving and scraping I got here:

Basic scroll and pegbox carved
Basic scroll and pegbox carved

Next I rough carved the fluting with chisels

Fluting rough cut on the scroll
Fluting rough cut on the scroll
Fluting rough carved
Fluting rough carved

 

 

 

 

 

 

 

Fingerboard

I bought a pre-shaped blank which reduced the amount of shaping required substantially.  First back to the drawing board to get the profile right.  I started with the string profile over the end of the fingerboard with a 20 degree break between strings and string heights over the fingerboard from 4mm (A string) to 6.5mm (C string) as I am going to use Larsen steel strings on this.

Fingerboard length will be 5/6 of string length = 580mm but added a few millimetres for luck.

Then extrapolated to get the bridge profile.

Plans are here: fingerboard profile

1st job was to plane the edges straight and take the twist out of the blank.

Then made a template for the fingerboard profile at the end and started planing away with the jack plane to get a rough shape.  It is quite hard to check for flatness using a straight edge so I just laid it on a flat surface with a light behind and looked underneath for the dark spots.

Once the rough shape was there I used a scraper to fine tune and get the 1/2 string diameter scoop measured with feelers.

Ended up with 8mm sides with a slight scoop on the edges to keep the wall height in the middle.

Fingerboard ready for finishing and gluing to neck
Fingerboard ready for finishing and gluing to neck

After cutting the outline of the neck root ready for fitting to the body I tacked on the fingerboard with a few dabs of weak glue – just hope I will be able to break the joint later!

Gluing the fingerboard to the neck
Gluing the fingerboard to the neck

After fitting to the body I carved and filed the final neck profile and finished off the chamfers on the scroll. Note the chalk on the neck joint from fitting to the body.

Neck nearly ready for gluing to the body
Neck nearly ready for gluing to the body

 

 

 

 

 

 

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Cello week 6 – Plate tuning

Plate tuning

I had to buy a cheap 25W amp and a hefty 8″ driver unit to excite the resonant frequencies in the back and top.

I then used a free app on my Android as a variable frequency sine wave signal source and tea leaves to see the patterns!

There is a lot about plate tuning on the Internet with several systems used. I found two particularly useful articles:

  1. Free Plate tuning, Part Two: Violins by Alan Carruth with an excellent cello example
  2. On Graduating the thickness of violin Plates to achieve tonal repeatability

Here is the mode #5 (bell-mode) on the back.

Back mode 5 @127.5Hz
Back mode 5 @121H

 

 

 

 

 

 

Here is the mode #5 (bell-mode) on the front

Mode 5 on the front @121Hz
Mode 5 on the front @121Hz

and mode #2 (x-mode) on the front

Top mode 2 @ 56.8Hz
Top mode 2 @ 56.8Hz

The back is still a little high compared to the top but I will come back to that once I have cut the f-holes and fitted and tuned the bass bar.

Fitting the bass bar with chalk
Fitting the bass bar with chalk

Having cut the f-holes and glued the bass bar I then re tuned the top to bring the bass bar into balance.

Both Modes #2 and #5 had gone up with the bass bar fitted.

This is how the mode #5 shapes developed as I cut down the bass bar:

Mode #5
Mode #5

I must admit I wasn’t sure at first that this was actually #5 as it looked pretty weird!

Mode #5
Mode #5
Mode #5
Mode #5
Mode #5
Mode #5
Mode #5
Mode #5
Mode #5
Mode #5

 

 

 

 

 

 

And the mode #2 looked like this:

Mode #2
Mode #2

At this stage I had got the mode 5’s on back and front equal at 130Hz and the mode #2s to 60Hz on the front  and 64Hz on the back so a little more to do still.

Final adjustments made.

Mass Mode #1 Mode #2 Mode #5
Back 669g 30Hz 57.6Hz 122Hz

Back mode #2 - final
Back mode #2 – final

Back mode #5 - final
Back mode #5 – final
Belly  490g (without bass bar) 28.4Hz 58.4Hz 120Hz

Belly Mode #2 - final
Belly Mode #2 – final

Belly mode #5 - final
Belly mode #5 – final

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Cello Week 5 – The Top

The Top

Having finally finished the back it is time to move onto the top.

First job was to glue the two book-matched halves together as on the back and then levelling the assembly and marking and cutting out the outline.

The spruce top after glueing the two halves
The spruce top after glueing the two halves

After building two profile templates (one longitudinal and one transversal at the centre line) I power planed down to the rough centreline thickness and started with the thumb plane.  I can’t believe how much easier the spruce is to work compared with the maple on the back. In just a couple of hours the shape is nearly there!

Rough forming the top
Rough forming the top
Top - Nearly there
Top – Nearly there

And then mark and cut the purfling slots before gluing in the purfling and cutting the channels.

Channels marked out with purfling cutter. Corners have to be finished by hand.
Purfling slot marked out with purfling cutter. Corners have to be finished by hand.
Purfling slot cut
Purfling slot cut
Purfling in and channels roughly cut
Purfling in and channels roughly cut

 

 

 

 

 

 

Then shape the inside after drilling some guide holes.

Guide holes drilled to give correct thickness profile
Guide holes drilled to give correct thickness profile
Roughed out
Roughed out

Plate tuning of back and top is next before cutting f holes and fitting bass bar.

F-Holes

The f-holes were marked by pinning the plan to the back of the belly and pricking through with a knife before joining up the marks with a pencil and adjusting the shapes by eye.

Marking out the f-holes on the back of the top
Marking out the f-holes on the back of the top

The holes were then cut with undersized forstener bits and reamed out to the correct size (14mm and 18mm) with my peghole reamer and my endpin reamer.

Holes drilles with a forstner bit and opened out to correct diameter using tapered reamers
Holes drilles with a forstner bit and opened out to correct diameter using tapered reamers

F-holes then roughly cut out with a coping saw.

F-holes roughly sawn out with a coping saw
F-holes roughly sawn out with a coping saw

And then carved to size and matched using a very sharp knife and a scalpel. I undercut the holes so they were bigger on the inside than the outside.

The finished f-holes
The finished f-holes before cutting the vees

Then I cut the vees and glued on the bass bar.

Finished f-holes
Finished f-holes
Bass bar glued in
Bass bar glued in

 

 

 

 

 

 

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Cello Week 4 – The back

The Back

I have 2 beautiful pieces of book matched maple to make up the back.

I started by getting my jack plane (from Axminster) into good working order.  This had never worked particularly  well and after closer inspection I realised why – the blade was slightly bowed and so the burr did not rub off properly.  Well after an hour or so of flattening against my diamond sharpening (stone?) I managed to get it flat and properly sharp and then joy, – producing cigarette paper thin shavings and both halves flat and true in no time.

I used the heat gun to warm everything up, made a new batch of glue and tried a rubbed joint – worked first time and no clamps!

Next was levelling the underside – boy is that maple tough but after about 3 hrs with the jack plane and a few blisters got it done.

Then clamped the ribs to the flat surface to mark out the outline and used a washer to mark the overhang before cutting out on the bandsaw and finishing off with the vertical spindle sander.

Next marked up the thickness of the edge – 5.5mm except for the corners (6mm) and the c-bouts (5mm) before starting all that chiseling! Boy, is that maple hard work!

The maple back – starting to chisel the arch profile after levelling the inner side
Arching

I  built some thin plywood templates to help with the arching profile. There is a great article by Sergei Muratov that gives a good starting point for the arching curves.  I adapted these slightly to give an arch height of 25mm on the back.

I used a power plane to get a rough arch height and then a gouge, small plane, and thumb plane.

Getting closer
Getting closer
Closer still
Closer still
Purfling

Finally finished profiling the outside of the back – this is a long week!  For anyone actually reading this blog you will by now have realised that my weeks are “virtual”  this week started at the beginning of June and now July is nearly over!  This is the result of actually having to “work to live” and in a job that has me trotting round the globe regularly so this virtual week is so far 7 regular weeks long and have still to shape the inside of the back!

Now for the purfling –   I made up the purfling from a 1mm piece of sycamore sandwiched between two 0.5mm pieces of ebonised pear all glued up (hide glue of course) and clamped between 2 cauls.  Then sliced it up on the band saw into 3mm strips and after a bit of cleaning up with a plane all ready to go.

Purfling after slicing up on the bandsaw
Purfling after slicing up on the bandsaw

 

I managed to find a tool for marking the purfling groove on ebay but had to grind the blades down a bit to get them 2mm apart (the width of my purfling) and ground down a very small chisel (I had in my toolbox) to be slightly under 2mm.

Getting ready
Getting ready
Start of cutting a channel
Start of cutting a channel
All purfling channels cut ready for gluing up
All purfling channels cut ready for gluing up

 

 

 

 

 

 

Glued in purfling using a syringe to fill the pre-heated channel with hot hide glue, tap down with a mallet onto kitchen roll to stop it spraying everywhere and clean up with hot damp towel.

1st 2 pieces of purfling glued in
1st 2 pieces of purfling glued in

After gluing all the pieces of bent purfling having taken care to try and get  “bee sting” at the corners I dug out a channel over the purfling with a chisel and then faired the channel into the body with scrapers.

Channels cut and started to fair them in with scrapers
Channels cut and started to fair them in with scrapers
Inside

Now I turn the back over and marked out the desired thickness profile in pencil.

Desired thickness contours marked on inside of back
Desired thickness contours marked on inside of back

I built a simple rounded stop to put under the drillpress and then drilled holes (1mm over-thickness) all over the back to provide a guideline when hogging out. Then using a fearsome wood carving attachment to the angle grinder (from Axminster) which cuts through maple like butter, I rough hogged out the back to the bottom of the previously drilled holes.

After first round of rough hogging out
After first round of rough hogging out

Then it was back to the thumb plane and more blisters to take it down to final thickness prior plate tuning.

Finished hollowing the back
Finished hollowing the back. Note the pencil arrows indicating direction to plane.

 

 

 

 

 

 

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Cello Week 3 – The Ribs

Making the Blocks

Having finished the form the next step is to cut and glue the blocks for the top, bottom and wings.

I cut these from a piece of spruce, cut to length to fit the tapered ribs (120mm at bottom to 116mm at top), flattened the ends and started playing with hide glue for the first time.

Looked at the electrically heated glue pots available for an astronomic price (>£150) and then found a perfect alternative – mini deep fat fryer for £12 from Amazon (thermostatically controlled).  Filled with water – not oil of course – and did a quick experiment to find the setting that gives 135F and then full steam ahead (not literally) with the glue in a jamjar inside the fryer .  Anyway, works an absolute treat and had all 6 blocks glued to the centre layer of the form in no time.

£12 mini fat fryer makes a perfect glue pot
£12 mini fat fryer makes a perfect glue pot
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Form with blocks glued in position

Also  bought a heatgun from Screwfix for £10 for undoing things when I got it wrong and got to try it out immediately!

Next the blocks were marked with the desired profile and carved/filed down to size.

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Corner block profiles marked up
Marking desired profile onto corner and end blocks
Marking desired profile onto corner and end blocks

 

 

 

Corner blocks after shaping
Corner blocks after shaping

Preparing the ribs

I had some nicely figured maple rib blanks that came about 4mm thick so I started by thicknessing to about 2mm on the drum sander before bandsawing to width (with a few mm spare), scraping the outside to give a good smooth finish and then final thicknessing (the inside) on the sander to 1.5mm.

Then I used my bending iron to shape the C bouts after giving them a thorough dampening with a water spray.

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Bent ribs waiting to be assembled

Before gluing up needed to make sure the ribs had thoroughly dried out and shrunk back to their dry size in order to avoid any subsequent cracking.

Gluing the Ribs

This was not quite as easy as it looks – as soon as you put a clamp on they move!  Had to take a few goes at this with several clamps used to hold it in place before squeezing up the pre-shaped cauls.  Also worked much better when both surfaces were pre-sized with glue and pre-heated with a hot air gun.

Gluing up the C bout
Gluing up the C bout
C bout after gluing and trimming
C bout after gluing and trimming

 

 

 

 

 

 

I made up some cauls to hold the ribs against the form to stop things moving around while the ribs were being clamped up.

Gluing up
Gluing up
After trimming the corners
After trimming the corners

After levelling off the ribs I removed the top layer of the form to give room for fitting the linings.

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Getting ready to fit linings

 

 

 

 

 

 

The linings were cut from willow sanded down to 3mm thick and cut into 20mm widths on the bandsaw.  These bent really easily after spraying with water.  Mortices were cut into the corner blocks with a saw and then finished off with a small 2mm chisel and cleaned up with a knife.

Half the linings installed on one side
Half the linings installed on one side

I read on the internet how to make some very simple but effective clamps using rubber bands cut from an old bike wheel inner tube.

Clamping linings using home-made peg clamps
Clamping linings using home-made peg clamps

 

 

 

 

 

 

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