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Geoff-UK

cello rib taper

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I'm just starting a cello - my mould is a three piece, spacers to full depth.

At present its going to be parallel - prob to just under the Servais dimensions of max rib height 127.5mm - since my model is the Servais, but reduced to 29 1/2" belly.

Anyone have any tips on the relation between arching height/ total body height and overall length in cellos ?

Since I've shortened the body length - should I reduce the rib/arching accordingly or keep it similar ?

On the three violins I've done I've always tapered the inside mould on the top plate by 2mm - from the upper blocks ( I've read all the various posts on the pros and cons of this tapering in violins )

The Servais apparently tapers 2.5 - 3mm from the upper blocks.

With cellos, do people generally taper the top rib face, or back ?

How - in measuring old instruments, can one be certain that any reduction was taken off the top or back rib face. For instance - the info I have on the Servais just says rib height for top block, uppers etc - it does not infer the belly side or the back side was reduced. I would have thought the ribs would have just bent themselves toward this stiffest plate - ie the back ?

My instict - If I did it off the top of my head, would be to taper in the back from the upper corners - let the rib garland adjust themselves to the back plate when glued on and - once off the mould, flat off the belly ribs as a true plane surface and mark my top plate from them directly - and not spring the bass bar.

Anyone see any problems with that approach.

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quote:


Originally posted by:
Geoff-UK
My instict - If I

did it off the top of my head, would be to taper in the back from

the upper corners - let the rib garland adjust themselves to the

back plate when glued on and - once off the mould, flat off the

belly ribs as a true plane surface and mark my top plate from them

directly - and not spring the bass bar. Anyone see any problems

with that approach.

How much do you plan on removing from the back upper corners?

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Consensus of opinion seems to be that the Cremonese made the taper on the top surface, perhaps to counteract bending forces on the body when strung up.

It might make more sense to me though that the taper is an artifact of nailing in the neck before attaching the back. The surface of the block/neck where it's glued to the back would have needed to be planed flush after the neck was attached, and maybe planed even more to get the gluing surface at the correct angle after tweaking things to make final corrections to neck projection.

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quote:


Originally posted by:
David Burgess
The surface of

the block/neck where it's glued to the back would have needed to be

planed flush after the neck was attached, and maybe planed even

more to get the gluing surface at the correct angle after tweaking

things to make final corrections to neck projection.

If the block/neck needs planing, then would we end-up in some cases

with both the top of the ribs planed, and the bottom/backside of

the ribs planed as well?

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to answer your question - New Newbie - I had wondered about that. The mesurements I have for the Servais give rib height the same at bottom, lower and upper corners - with 2.5mm reduction to top block.

But just where on the upper corners - as in, at the bitter end, or at he start or end of the block position. Would have thought it essentially would go from the corner point of the block.

With the violins I usually end up flattening off the edge on a sheet of glass lined up with emery cloth or the like - so really the upper corners probably get chamfered off a bit in the process. I'm not sure that will work with a cello due to it bulk.

I tend to see some sense in what David said - we often, I think, presume things were intentional, when actually they were just the end result of some other process.

I didn't know whether there was an issue with cellos, regards this - that was in any way different to violins/violas in general. Maybe I do the front then, same as the violins ? ... ponders !

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I agree, the tapering might be a result of the planing of the gluing surface for the button and neck block... But the Cremonese probably were also aware of the nice visual effect, or what do you think?

I made my first cello with parallel ribs, and it really looked as if the upper ribs were far taller than the lower ones, although they were exactly the same...

I have been thinking that to taper the ribs on the top side makes some sense if you belong to the people who fit their bass bars with a "spring". IF the edges of your table were all in a plane before your started fitting, they would have a slight banana shape WITH the bar and to glue the table to the ribs you'd might pull down the table a bit in the centre (depending on exactly how the bar was made). In that case the tapered part, (from the upper corner blocks) makes all the allowance the slightly bent table needs to be glued on without (much of) that deformation.

On old instruments, the table is usually tension free in the shape it has when glued to the ribs. If you put that table on a bass bar frame, you might end up with a table with some trouble when it is glued back on the ribs, because they are almost never flat... a new table on the other hand often has to be pulled down at the ends in order... hmm, maybe I should start a bass-bar thread instead of hijacking this one? In any case the tapering-question is an interesting subject, I will give it some more thought.

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quote:


Originally posted by: magnus nedregard

snip

I made my first cello with parallel ribs, and it really looked as if the upper ribs were far taller than the lower ones, although they were exactly the same...

snip

Thats a useful comment - something I had not really thought about. I don't like things that 'look wrong' - I know the bass bar thing is a whole different issue - but delving through the past posts on that I came to similar conclusions. I've not fitted enough to really be confident about springing them in - not that I've really tried it, maybe give it a go with the violin I'm on now.

I see standard measurements for cellos quoting as much as 6mm difference top to bottom - so with that amount I would go with doing the back and the belly 3mm each. Maybe , as you say, it needs it visually.

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quote:


Originally posted by:
magnus nedregard
I made my

first cello with parallel ribs, and it really looked as if the

upper ribs were far taller than the lower ones, although they were

exactly the same...

This makes sense.  This might be why there is some confusion

about the whole process.

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I knew about tapering in violins, but never thought to check on my old cello. But there it is. A drop of nearly 7mm, all in the upper bout. And all the tapering was done on the top.

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Yes, I think a drop of about 6-7 mm is not too much, I've done even more but then I think it might be a good idea to "distribute" the difference a bit; perhaps a slight reduction from the lower block to the upper corners and then a faster drop from there to the top block. Or, as an alternative, taper only from the upper corners, but distributed on the top and the back? I think otherwise the table might bend too much...

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Hi,

Sorry, I am a little late on this topic, but it's still an

unanswered question I think.  There is still a lot of

interrogations. Why tapered ?  With or without

tension on the tables, With or without tension on the bass bar,

Tapered on the back or on the table ?  etc...

It's hard for me to say what's the best solution or

explanation because we don't have enough or

serious theories of this making technique (Acoustical,

Structural or Esthetic benefits ?).  I agree with David

and Magnus, that it might be the result of something else (planning

of the neck, correction of the surface for the table), but I also

think that it's not the only explanation.

When I am thinking about that subject, I am always thinking about

the basses and the viols.  They are tapered on the back !

 It's really apparent ! It might be possible that

the classical makers made the same thing on violins and cellos to

give some tension to the back for acoustical reasons or also

esthetic reasons...  

When you put a table with a bass bar without spring or tension on

the gluing surface, it might be possible to close the instrument

depending on the amount of spring on the back.  If there is a

lot of tension or spring on the back, you might have to taper the

sides on the table side also to close the instrument.  If you

have a tension or spring on the bass bar, you don't have any choice

I think.  You have to taper the gluing surface of the sides on

the table side also.  I don't think that it's good to force a

banana shaped table with a lot of spring on a flat surface.

There is another interrogation I think.  How to taper the

sides ?  A flat surface between the upper block and the

corners or maybe a slightly rounded surface ? 

It would be nice to get more information from bass and viol

makers...

Richard

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