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Jim Bress

Neck (length) reinforcement

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As requested in the recent thread "Carbon Fiber Rods in Neck: Best Practices?" I saved my burning questions for a new thread after searching MN and GOOGLE including going to the dark side and reading guitar forums. :ph34r:

From my readings, it appears that reinforcing the neck (e.g. with CF) is to create a more stable neck.  Very little has been said on the affect of tone or playability.  I know that really good makers are using CF reinforcements along the FB gluing surface.  The stability reasons are all from guitar forums.  My question is why. Stability? Increased sustain, volume, or other acoustic reasons?  For stability, is neck warpage a typical problem for violins, violas, or celli?  Or is it mitigating a potential problem if the instrument finds itself in a high humidity environment?  Considering the lifespan of an instrument, it does seem prudent to prepare for the future.

Based on the answers, I am thinking about a little experiment with different reinforcement material using my #1 as the guinea pig if there are potential tonal benefits.  That's what first violins are for right? ;)  

Thoughts anyone?

Thanks,

Jim

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I don't think that laminating in any material with very different long term shrinkage properties and short term temperature and moisture

expansion coefficients from wood will enhance the long term  stability of the violin.

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38 minutes ago, donbarzino said:

I don't think that laminating in any material with very different long term shrinkage properties and short term temperature and moisture

expansion coefficients from wood will enhance the long term  stability of the violin.

It works for guitars. Why would violins be any different?

You're already laminating two different woods together.

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3 minutes ago, Nick Allen said:

It works for guitars. Why would violins be any different?

You're already laminating two different woods together.

Glued in reinforcement has been used for only a few decades in guitars.

Metal truss rods have been around a bit longer but they are usually free floating in their channel not laminated.

I believe all woods share more similarities than any wood does with graphite fiber and even then there are some

long term problems with the long term shrinkage differential between maple necks and ebony fingerboards.

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Structurally, a neck reinforcement on a cello could reduce warping and seasonal fluctuation, assuming the changes come from the handle of the neck and not the glue joint into the mortise and top.

Tonally, there could be some improvement if the rod were to reduce weight while maintaining structural integrity. I would imagine that the harder and denser the wood, the more of a difference the rod would make.

A friend of mine made a banjo some years back and installed a carbon fiber rod after finding that the neck was starting to twist. It solved the issue but improved the tone of the instrument as well. 

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1 hour ago, Jim Bress said:

From my readings, it appears that reinforcing the neck (e.g. with CF) is to create a more stable neck.  Very little has been said on the affect of tone or playability. 

I use a piece of bloodwood instead of cf.  My reason was even though I have 65 sg. neck wood the grain would orient towards being flatsawn instead of being quartered.  Not really knowing or asking what violins makers were taught I figured I'd just route a channel for a bloodwood strip.  And I was assuming that there would be some tone enhancement by doing so also.  I think there is but does it matter any for violins?  Don't know.

If there is good quartered wood to use for a neck, coupled with decent fingerboard ebony,  then I'd think there wouldn't be any need for reinforcement inside.  You could install a cf reinforcement piece along with the vertical piece into the heel - then one would realy know if it's going to be a neck block, a weak button area on the back plate or an overly thin weak area around the belly and neck block area - it sure won't be the neck causing a problem with projection later down the road. 

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Jim, 

the guitar seems to be a completely different animal. Heavy necks seem not to support plucked sound. So guitar makers invented all sort of laminations to form a lighter composite material to solve the problem. 

In violin making we don't need this. The only consideration seems to prevent warping which might result in that the pitch lowers. (Much more for cellos than violins anyway)

Just from experience I noticed that necks are more stable if both the maple neck and the fingerboard have a light hollow scoop and are therefore glued with some tension together. But I have no real explanation why this should be structurally more stable because this pinch of tension shouldn't change too much. Or, maybe moisture changes which are the cause for all warping, can't act on a tensioned neck as much as on a a neck without internal tension. Just a guess.

For cellos it is more crucial because the root of the neck can warp causing the fingerboard to drop towards the top. I think @David Burgess is glueing a feather lengthwise into the neck root to prevent this. 

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A good friend of mine who makes very fine instruments gave the differing rates of shrinkage and expansion as why he did not want to use CF pins or CF neck reinforcements. I suggested that necks are grafted and if the reinforcement and the wood eventually tore each other apart, then a neck graft was a simple enough remedy. He agreed that the neck was fungible, but that he still would not use CF pins and rods. I have found them to be quite excellent when it comes to keeping necks from dropping, putting a pin in the heel, but don't think that violins need neck stiffeners. If it flexes, replace the fingerboard.

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10 hours ago, A432 said:

Wouldn't sealing the endgrain of the neck & head block minimize this ?

I am not building cellos so I can't answer this question. On violins sizing the end grain seems to be sufficient.

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Thanks everyone for your input.  A bit of overlap in the discussion so I picked a few quotes even though more than one contributor offered same or similar thoughts.

21 hours ago, The Violin Beautiful said:

Structurally, a neck reinforcement on a cello could reduce warping and seasonal fluctuation, assuming the changes come from the handle of the neck and not the glue joint into the mortise and top.

Tonally, there could be some improvement if the rod were to reduce weight while maintaining structural integrity. I would imagine that the harder and denser the wood, the more of a difference the rod would make.

A friend of mine made a banjo some years back and installed a carbon fiber rod after finding that the neck was starting to twist. It solved the issue but improved the tone of the instrument as well. 

Because I have respected makers that are Friends of mine that will not make any instrument without carbon fiber insert it makes me wonder whether I am falling short of best practices.  However, Cello neck is my main concern.  I also see titanium reinforcement bars for sale.  I expect if they have tonal effects, the effects of the two materials would be different.  May in a good way, maybe not.  I do not know how often violin, viola, or celli necks warp.  In other words, whether or not a problem actually exists. 

13 hours ago, Andreas Preuss said:

Jim, 

the guitar seems to be a completely different animal. Heavy necks seem not to support plucked sound. So guitar makers invented all sort of laminations to form a lighter composite material to solve the problem. 

In violin making we don't need this. The only consideration seems to prevent warping which might result in that the pitch lowers. (Much more for cellos than violins anyway)

Just from experience I noticed that necks are more stable if both the maple neck and the fingerboard have a light hollow scoop and are therefore glued with some tension together. But I have no real explanation why this should be structurally more stable because this pinch of tension shouldn't change too much. Or, maybe moisture changes which are the cause for all warping, can't act on a tensioned neck as much as on a a neck without internal tension. Just a guess.

For cellos it is more crucial because the root of the neck can warp causing the fingerboard to drop towards the top. I think @David Burgess is glueing a feather lengthwise into the neck root to prevent this. 

For cello root necks I will definitely pin the neck root.  At this point I don't know if that practice will migrate to viola and violin making.  As I get more comfortable with the procedure it's more likely that I will.

11 hours ago, duane88 said:

A good friend of mine who makes very fine instruments gave the differing rates of shrinkage and expansion as why he did not want to use CF pins or CF neck reinforcements. I suggested that necks are grafted and if the reinforcement and the wood eventually tore each other apart, then a neck graft was a simple enough remedy. He agreed that the neck was fungible, but that he still would not use CF pins and rods. I have found them to be quite excellent when it comes to keeping necks from dropping, putting a pin in the heel, but don't think that violins need neck stiffeners. If it flexes, replace the fingerboard.

One of my thoughts was to reinforce the fingerboard.  If results are the same it could keep future restorers from cursing my name. :)

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52 minutes ago, Jim Bress said:

- snip -  .

One of my thoughts was to reinforce the fingerboard.  If results are the same it could keep future restorers from cursing my name. :)
 

Hi Jim -  you are absolutely correct.

I've just been making some hen scratchings on a clipboard - looking at the properties of ebony and maple, the areas under compression and tension, their distances from the strings and OUCH (shudder, shame, blush and cringe) - the movement due to compression is greater than that due to the tension.

Insert the c/f stiffener into the f/b - I suggest a  3mm deep x12mm wide c/f bar (route 5mm deep and cover with 3mm ebony veneer and plane it flush.) This will reduce the movement due to compression to 1/3 of what it was.

There is very little to be gained by inserting it into the neck just under the fingerboard - you are too close to the Neutral Axis of the neck to gain full benefit of the c/f.

Of course placing a 3mm widex8mm deep bar within 3mm of the bottom of the neck would do no harm.

My apologies to all.

cheers edi

 

 

 

 

 

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Totally agree with Mr Malinaric - positioning of reinforcement bar on a violin is right where the natural bending moment is centered so there will be little benefit.  The ebony fingerboard, on the other hand, is well positioned to absorb a lot of compression load and move the bending moment center deep within the neck, which is exactly what you want.

Of course that is an engineering view and should be dismissed out of hand - or so I have been advised.  As a craftsman I would simply note that my 100yr+ instruments with original necks have no obvious warping, twisting or disfigurement.  Don't fix what ain't broke.

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2 hours ago, Shunyata said:

Totally agree with Mr Malinaric - positioning of reinforcement bar on a violin is right where the natural bending moment is centered so there will be little benefit.  The ebony fingerboard, on the other hand, is well positioned to absorb a lot of compression load and move the bending moment center deep within the neck, which is exactly what you want.

Of course that is an engineering view and should be dismissed out of hand - or so I have been advised.  As a craftsman I would simply note that my 100yr+ instruments with original necks have no obvious warping, twisting or disfigurement.  Don't fix what ain't broke.

 

Hi Shunyata - what's this Mr Malinaric?

I sign off as Edi (I was named after two previous Uncles both Eduards - abbreviation Edo. The diminutive of Eduard in Croatian is Edica - that I abbreviated to Edi. This was necessary because my Uncle and I ended up in the same firm of consulting engineers. Just thought someone might want to know)  :-)

All I know is that soon after being strung up, the fingerboard drops slightly towards the belly. Brian, the luthier who was kind enough to show me the ropes, anticipates the drop by setting the f/b a mm or so higher than he wants. He inserted a c/f bar and - halleluja - a far smaller settling.

As for "Don't fix what ain't broke" - what's wrong with better?

Just down the road there's a 2.0 litre Bugatti Type 35. A true classic of motoring history. 

It looks OK - but hell -  my 2.0 litre Subaru Outback diesel  has 2 more gears, can seat 3 more people, has 4 wheel drive, is 5 times more economical (I look to refuel when the trip odo reads 830 km), has huge luggage space, goes faster, is more powerful, more comfortable, much quieter and completely waterproof - not to mention having heating and cooling to suit.

Shall I talk about driving a convertible E-type Jaguar from Windhoek to Cape Town - a distance of 1470 km.

Sounds fun - except it had been rolled, and there was no windscreen at all - just a clean line from front to back.

Did I mention that it was in winter?

Winter anorak over jersey, woolen shirt, thermal underwear, gloves under skiing mitts. Neck scarf, my rally crash helmet and goggles - and I froze. Wind chill is for real -  especially on a 13,5 hour trip. (Couldn't drive faster - 120 kph and above, the wind pressure against my head caused the neck muscles to cramp.)

Believe me better is nice.

cheers edi

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No offense intended with the honorific, Edi. 

I am virtually certain the neck on a violin drops due to flexure in the body, not bending of the neck.  You can convince yourself by putting a neck in a vice and hanging a 15lb weight on it, which is about the maximum bending moment you will ever generate with very high tension strings.  You won't see any discernible deflection, especially with the fingerboard on.

On the other hand, have at it if you enjoy the fitting work.  You probably aren't hurting anything.

 

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A carbon fiber bar in the neck lessens damping.  They have been used for a very long time without issues due to shrinkage, and the tonal changes are exactly as you would expect.

CARBON FIBER PINS ARE ALWAYS A BAD IDEA!

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3 hours ago, Jerry Pasewicz said:

 

CARBON FIBER PINS ARE ALWAYS A BAD IDEA!

Oh my! Do you mean the "pins" inserted into the heel? Would you care to expand on this? Thanks!

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2 hours ago, arglebargle said:

Oh my! Do you mean the "pins" inserted into the heel? Would you care to expand on this? Thanks!

Nope, I mean “carbon fiber” pins inserted in the heal.  Wood expands and contracts.  If you put pins in that do not expand and contract (carbon damn fiber as opposed to wood), the hole around the pin will eventually become misshapen and loose. Carbon fiber is an inappropriate material for this application.  I am a little sensitive about the inappropriate use of carbon fiber having been the one who has had to deal with the aftermath of such failed strokes of genius. 

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3 hours ago, Jerry Pasewicz said:

Nope, I mean “carbon fiber” pins inserted in the heal.  Wood expands and contracts.  If you put pins in that do not expand and contract (carbon damn fiber as opposed to wood), the hole around the pin will eventually become misshapen and loose. Carbon fiber is an inappropriate material for this application.  I am a little sensitive about the inappropriate use of carbon fiber having been the one who has had to deal with the aftermath of such failed strokes of genius. 

Got it. I assume you are not a fan of the one piece inserts that are set in both the neck and heel.

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20 minutes ago, arglebargle said:

Got it. I assume you are not a fan of the one piece inserts that are set in both the neck and heel.

I am not familiar with them, so I could not say.  Can you point me to a picture, or website?

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4 hours ago, Jerry Pasewicz said:

Nope, I mean “carbon fiber” pins inserted in the heal.  Wood expands and contracts.  If you put pins in that do not expand and contract (carbon damn fiber as opposed to wood), the hole around the pin will eventually become misshapen and loose. Carbon fiber is an inappropriate material for this application.  I am a little sensitive about the inappropriate use of carbon fiber having been the one who has had to deal with the aftermath of such failed strokes of genius. 

I have been using the Peg Ringer cf rings on the the bottom block around the endpin hole. Do you think this is a bad idea?

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1 hour ago, lpr5184 said:

I have been using the Peg Ringer cf rings on the the bottom block around the endpin hole. Do you think this is a bad idea?

I do not think it is a bad idea, however, having worked in the trade for many years, I cannot say that broken lower blocks are really an issue.  I understand they are advertised as a preventative for lower blocks, but I think it is a solution in search of a problem.  That said, I can certainly endorse the rings as a preventative for pegbox cracks, and many makers have been using the system for a long time successfully for this purpose. 

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1 hour ago, Jerry Pasewicz said:

I do not think it is a bad idea, however, having worked in the trade for many years, I cannot say that broken lower blocks are really an issue.  I understand they are advertised as a preventative for lower blocks, but I think it is a solution in search of a problem.  That said, I can certainly endorse the rings as a preventative for pegbox cracks, and many makers have been using the system for a long time successfully for this purpose. 

Thanks Jerry

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As a double bass luthier, I've installed carbon fiber reinforcments on bass necks a number of times. It has the predictable improvements to playability where you see reduced scoop under string tension. It always seems to add more pizzicato sustain, stronger articulation, and more midrange to the sound. Basses tend to have a more "energetic" sound after installation, but may also Seem a  bit brighter. Particularly on bass, the neck is far too thin for the tension it's holding so anything you can do to make it stronger is a good thing.

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