Sign in to follow this  
HonestEngineer

Angles between corners and belly/back plates

Recommended Posts

The engineer and mathematician in me likes every last miniscule detail to be tied down rigorously. As I get close to assembling the ribs on my viola I find myself asking the following question:

The surfaces of the back and belly plates as they glue onto the ribs won't be parallel to each other (the ribs will be 40mm tall at tailgut end and 37mm at the neck end). So should the corners be perpendicular to the back plate, perpendicular to the belly plate, half way in between or even slightly closer to perpendicular with one plate than the other? My logical mind keeps telling me the differences are going to be so miniscule as to be perhaps irrelevant. But some instinct tells me that getting this wrong might harm the aesthetics (or worse still the tone) of the instrument.

Any thoughts would be greatly appreciated.

 

 

Share this post


Link to post
Share on other sites

I mean this in the most helpful way possible, but you are over thinking it.  I would say living up to your name!  :-).  I am fond of overthinking myself.  You just want it to be great and I get that.  My rib corners are perpendicular to the back.  All of my rib surfaces are perpendicular to the back.  I believe that a difference in tone between any of your scenarios is nonexistent.

Share this post


Link to post
Share on other sites
2 hours ago, HonestEngineer said:

The engineer and mathematician in me likes every last miniscule detail to be tied down rigorously. As I get close to assembling the ribs on my viola I find myself asking the following question:

The surfaces of the back and belly plates as they glue onto the ribs won't be parallel to each other (the ribs will be 40mm tall at tailgut end and 37mm at the neck end). So should the corners be perpendicular to the back plate, perpendicular to the belly plate, half way in between or even slightly closer to perpendicular with one plate than the other? My logical mind keeps telling me the differences are going to be so miniscule as to be perhaps irrelevant. But some instinct tells me that getting this wrong might harm the aesthetics (or worse still the tone) of the instrument.

Any thoughts would be greatly appreciated.

 

 

The whole thing is floppy. A injunear might like perpendicular right angles but violins are actually made with wrong angles.

Share this post


Link to post
Share on other sites
4 hours ago, Thomas Coleman said:

I mean this in the most helpful way possible, but you are over thinking it.  I would say living up to your name!  :-).  I am fond of overthinking myself.  You just want it to be great and I get that.  My rib corners are perpendicular to the back.  All of my rib surfaces are perpendicular to the back.  I believe that a difference in tone between any of your scenarios is nonexistent.

!

Share this post


Link to post
Share on other sites

The whole thing goes kaput after string tension and humidity start to twist and gyrate the corpus like a drunken belly dancer.

I try to make the angles perpendicular to the back, and let fate have it's way after that. 

The taper usually occurs as a nice linear slope from end to end. Or from the upper corner block, diving into the top block at a slightly more aggressive angle. 

Share this post


Link to post
Share on other sites
12 hours ago, HonestEngineer said:

The engineer and mathematician in me likes every last miniscule detail to be tied down rigorously. As I get close to assembling the ribs on my viola I find myself asking the following question:

The surfaces of the back and belly plates as they glue onto the ribs won't be parallel to each other (the ribs will be 40mm tall at tailgut end and 37mm at the neck end). So should the corners be perpendicular to the back plate, perpendicular to the belly plate, half way in between or even slightly closer to perpendicular with one plate than the other? My logical mind keeps telling me the differences are going to be so miniscule as to be perhaps irrelevant. But some instinct tells me that getting this wrong might harm the aesthetics (or worse still the tone) of the instrument.

Any thoughts would be greatly appreciated.

 

 

If you view this questioin from the point of view of antique violins, which have after all survived for hundreds of years, and in particlar contemplate those antique violins where the ribs were built on the back without useing any form, you will dicover that the end grain face of the blocks (should there be any) that were inserted afterwards, do not even remotely fit  to the back. Rather they were generally sloped up towards the corners some 20°. This might horrify your engineer soul, but should one ask oneself what function a corner block has at all, I think that one would conclude that the block's function is only to hold the upper/lower rib to the middle rib, as a sort of glue block,  no more, no less and that an airtight fit to the back does not have any particular utility. Seen like that, you may conclude that you might be tendentially fighting with windmills.

Share this post


Link to post
Share on other sites
35 minutes ago, Delabo said:

What is the purpose of the slope ?

Visual appeal ?

Just to make fitting easy and quick, no need to fit perfectly, most the corner blockless violins I see are perfectly fine , if you think about it a top or back at 3mm or less might have less glue surface per inch than a pinched corner. 

Share this post


Link to post
Share on other sites
1 hour ago, Delabo said:

What is the purpose of the slope ?

Visual appeal ?

I was describing observed fact, not advocating anything. As I said, the blocks (when used), were conceived as a sort of “Glue Block” https://encyclopedia2.thefreedictionary.com/Glue+block to hold the ribs together, and not as a means of enlarging the rib cage/back glueing area, which is ample already. If you have ever fitted a brand new block into rib corners, you will know that it is awkward to piggle out any rest-glue and dirt, right into the deepest far corner, and it will be much easier & quiker to cut the block at an angle, so everything looks like it is shipshape and fits when looking through the f hole, even if there is no end of “glue room” where you can't see it (until you have to take the back off) behind.

Share this post


Link to post
Share on other sites
15 hours ago, HonestEngineer said:

The engineer and mathematician in me likes every last miniscule detail to be tied down rigorously. As I get close to assembling the ribs on my viola I find myself asking the following question:

The surfaces of the back and belly plates as they glue onto the ribs won't be parallel to each other (the ribs will be 40mm tall at tailgut end and 37mm at the neck end). So should the corners be perpendicular to the back plate, perpendicular to the belly plate, half way in between or even slightly closer to perpendicular with one plate than the other? My logical mind keeps telling me the differences are going to be so miniscule as to be perhaps irrelevant. But some instinct tells me that getting this wrong might harm the aesthetics (or worse still the tone) of the instrument.

Any thoughts would be greatly appreciated.

In the classic Cremonese ribs system (which is what I use too) the back and the top plates are quite parallel from bottom block up to the upper corners, so the blocks and rib's mitres are 90° with both top and back.

Slant is concentrated in the upper bout reaching about 2 mm at the top block.

I have personally interpreted this inclination as 1.5 mm on the top and 0.5 mm on the back starting immediately after the upper rib's mitres, leaving all the C bout area parallel.

Maybe this could satisfy your "engineering" need for perfect 90° angles.:)

Visual aesthetic is also improved and in my opinion it also serves to avoid  the sinking of the top plate, but this is another very controversial and discussed story.....

Share this post


Link to post
Share on other sites
3 hours ago, Davide Sora said:
 

In the classic Cremonese ribs system (which is what I use too) the back and the top plates are quite parallel from bottom block up to the upper corners, so the blocks and rib's mitres are 90° with both top and back.

Slant is concentrated in the upper bout reaching about 2 mm at the top block.

 

I have personally interpreted this inclination as 1.5 mm on the top and 0.5 mm on the back starting immediately after the upper rib's mitres, leaving all the C bout area parallel.

 
Maybe this could satisfy your "engineering" need for perfect 90° angles.:)

Visual aesthetic is also improved and in my opinion it also serves to avoid  the sinking of the top plate, but this is another very controversial and discussed story.....

Fascinating.

Previous to reading this explanation I thought there was a slope on Cremonese instruments from top block to bottom block, but it sounds like you are saying any slope is only above the C bout neck end, unless I have misunderstood.

On a completely unrelated point, I have watched your superb videos, and noticed that you make the bottom rib in two parts (albeit matched very perfectly). Is this just your personal preference, or do we see this on some Cremonese instruments ?

Share this post


Link to post
Share on other sites
5 hours ago, Delabo said:

Fascinating.

Previous to reading this explanation I thought there was a slope on Cremonese instruments from top block to bottom block, but it sounds like you are saying any slope is only above the C bout neck end, unless I have misunderstood.

On a completely unrelated point, I have watched your superb videos, and noticed that you make the bottom rib in two parts (albeit matched very perfectly). Is this just your personal preference, or do we see this on some Cremonese instruments ?

 

 

You understood correctly, the inclination is confined to the upper bout and the rest is all the same height.

If I have a batch of ribs long enough I always make one piece lower and  upper ribs : better resistance to block splitting and no joint neededB)

But it's not always easy to find a good quality 45 cm long piece for a one piece lower ribs so often you need to use two pieces.

Cremonese violin were almost always made this way (one piece ribs), this is mainly due to the baroque construction where the neck was nailed and a one piece upper rib guaranteed the resistance necessary to reduce the risk that the block would split during this delicate operation.

Today it's rare to see this feature on old violin because the modernized neck is morticed cutting into the block and the lower rib is often cut to adapt the ribs width to the shrinking of the plates, but if you look at the maple flames you will notice that the inclination is always in the same direction along the rib.

Share this post


Link to post
Share on other sites

Thanks all - an interesting discussion. I think that allows me to be comfortable with doing what my instincts were telling me to do... make ribs and blocks perpendicular to the back and deal with the taper on the belly side of the ribs/blocks.

I'm intrigued by the idea of concentrating the taper in the upper bout. Does that not put a spring in the belly such that the joint between the upper bout ribs and the belly wants to spring open?

Share this post


Link to post
Share on other sites

David,
I'd like to know how exactly the sinking of the front is prevented by tapering the front upper bouts.....if you can compare it to springing a bass bar ?
Although the upper bout taper is obviously Cremonese, I use a full body taper so the front plate can fit onto the ribs flat without bending.  
Seems to make better mechanical sense to me, might be wrong of course. 

Share this post


Link to post
Share on other sites
23 hours ago, Davide Sora said:

Visual aesthetic is also improved and in my opinion it also serves to avoid  the sinking of the top plate, but this is another very controversial and discussed story.....

 

4 hours ago, ~ Ben Conover said:

David,
I'd like to know how exactly the sinking of the front is prevented by tapering the front upper bouts.....if you can compare it to springing a bass bar ?
Although the upper bout taper is obviously Cremonese, I use a full body taper so the front plate can fit onto the ribs flat without bending.  
Seems to make better mechanical sense to me, might be wrong of course. 

 

I probably had to express myself better : I should have said "helps to prevent the sinking of the top avoiding that its plane (gluing surface) becomes concave".

 

I think  that the "cremonese style" ribs slant allow that the inevitable bowing of the soundbox caused by strings tension would result in a concave gluing  surface of the ribs (top side) that as a consequence it also forces the top plane (gluing surface) to sag in the wrong direction.

This does not completely avoid the deformation of the top which is very complex and due to various factors, but I think that it helps to keep it within certain limits.
 

These are just my illations (in the end our work is driven by illations....) but I did not notice any contraindications in doing this, while when I was doing the "straight" taper as you do I always had the impression of a slight negative bending, but maybe this has just an aesthetical value.

Would you explain why you think the "straight" taper make better mechanical sense?

 
I am always interested in hearing different points of view from mine, my working principles are not set in stone.....:)
 

 

Share this post


Link to post
Share on other sites

I used a two piece mold for construction a few years ago and I notice my front corners are not straight up and down anymore though I made them perpendicular when new.  These were non tapered ribs and blocks and all I used was a higher tailblock sloping gently downwards to a slightly lower neckblock.   Doesn't seem to hurt playability or sound any to my knowledge.   Probably just weak wood.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this  

  • Recently Browsing   0 members

    No registered users viewing this page.