Davide Sora

Titanium neck heel reinforcement

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3 hours ago, David Burgess said:

I do, although I think the value in doing so isn't nearly as clear as it is for cellos.

 

ya, but you really don't need a roller cam, anti pump up lifters and roller rockers, but it nice to know they are there! ;)

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4 hours ago, David Burgess said:

I do, although I think the value in doing so isn't nearly as clear as it is for cellos.

Fair answer.  If you don’t mind me ask, What size dowels do you use for violin and viola?

Thanks,

Jim

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11 hours ago, jezzupe said:

I know you are 100% right, but that does not mean my way is not stronger and less prone to adverse distortion.

Generally the saying goes something like; if 100 people were in a room and only 1 of them thought the sky was blue most times during the day and all the others thought it was plaid, the truth is the sky is blue and the truth is the truth, so regardless of what the others think, they are wrong.

Usually that's where the statement ends,  "the truth is the truth" , but what it doesn't go on to say is if your stuck in a room with a 99 idiots who think the sky is plaid, it's plaid, because the real truth is the stupid low iq mob wins every time  and it doesn't matter what you think even if you're right :lol:

If you were really bright, you'd hide your plywood under a seamless veneer and keep it a trade secret.  Same for your politics.  :P

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2 hours ago, Violadamore said:

If you were really bright, you'd hide your plywood under a seamless veneer and keep it a trade secret.  Same for your politics.  :P

Well that's what the Krylon's for silly , it helps keep the titanium from rusting too :rolleyes: Hey I can;t control what all my idiot "friends" on facebook think :lol:

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Hi, everyone. I have read this with interest. I don't mean to steer the topic away from cellos but the Stewmac copy mentioned tonal benefits in guitar and bass necks. I wonder if any one here has tried titanium in a fretted instrument neck and has noticed a tonal improvement beyond increased stability?

Thanks,

Pete

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At NAMM last week I saw Riversong guitars, with adjustable necks.  How cool is that?  An adjustable rod that ends in the guitar soundhole.  With a special tool, you can change the fingerboard height, to vary the action.  I want to see this on a violin!! :-o) :D :P

http://www.riversongguitars.com/

See their through neck design herre: http://www.riversongguitars.com/guitars/

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On my last cello I put 1/2" carbon fiber through the heel front to back, and carbon fiber the length of the neck, no dropping at all, feels solid.

How ever I now believe that the Burgess Doweling Method is probably superior in the ease of installation, and it's ability to do the job it was intended to preform. As I found the CF to be psycho-tramatic to install. I thought that I had overcome the tendency to severely over think everything and pursue the most difficult way of annoying myself, however I now see that relapse is not only possible but most likely probable.

Evan slipping

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On 2/1/2018 at 10:38 AM, David Burgess said:

Here's an exaggerated drawing which didn't make it into the article, illustrating the sort of bending in the heel associated with the neck projection dropping (dotted line represents a straigtedge).

Bent%20neck.jpg

I guess the heel distortion contributes more than the neck/fb combination.

I can see that it can happen if you use relatively fresh wood, but if you use well seasoned wood, shouldn't it be quite stable?

KYC

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On 2/1/2018 at 6:38 PM, David Burgess said:

Here's an exaggerated drawing which didn't make it into the article, illustrating the sort of bending in the heel associated with the neck projection dropping (dotted line represents a straightedge).

Bent%20neck.jpg

Hi David - I've been mulling over your drawing and wonder if the distortion that you show didn't occur after you loosened the neck from the neck-block.

 

The compressive strength of maple perpendicular to the grain is around 750 psi. (applicable to the neck where it is glued into the neck-block) *

The tensile strength of maple perpendicular to the grain is around 652 psi. (applicable to the neck where it is furthest from the neck-block) *

The compressive strength of spruce parallel to the grain is around 4 500 psi. (applicable to the neck-block) **

The tensile strength of maple parallel to the grain is around 13 000 psi (applicable to the reinforcing dowel) *

* (corrected 2018 feb 11) ref https://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr190/chapter_05.pdf

** (corrected 2018 feb 11) http://www.woodbin.com/ref/wood-strength-table/

If one looks at the part of the neck that is under compression and the area of the glued joint in a parallel grained end-block, there is almost zero chance of the neck wood compressing or bowing anywhere on that side. Maybe a bit on that piece above the body - but there, the x-section of the neck is at its maximum and the unsupported length is measure in a few mm.

On the "open" side of the neck (furthest from the neck-block) the story is different. The tensile strength is 7 * (corrected 2018 feb 11) times less than the compressive strength i.e. the movement will be 7x (corrected 2018 feb 11) as much for the same area. However the shape of the X-section means that the area under most tension is tending towards zero i.e. the stresses are at their highest just under the varnish. This is where the wood will stretch - allowing the f/b to rotate towards the belly. The stresses here are perilously close to failure - hence the number of broken cello necks - and so it is likely that the stress exceeds the "yield point" of the wood.This is confirmed by the fact that the fingerboard doesn't return to the as-built position after we remove the string tension. Remove the neck from the body and the stresses trapped under the varnish attempt to relax by bending the end-block face concave.

My calcs, led me to insert a 16mm dia.maple dowel down the neck to improve the properties of the wood under tension by something like 200 times. The glue area kept the stresses in the structural epoxy low enough that there should be no possibility of glue-creep occurring.

cheers edi

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3 hours ago, chungviolins said:

I can see that it can happen if you use relatively fresh wood, but if you use well seasoned wood, shouldn't it be quite stable?

No. Certainly wet wood will bend more, but dried or seasoned wood (which has attained a state of retaining moisture according to the ambient humidity level), also has some plastic qualities, and will deform under sustained load.

Generally speaking, the higher the moisture content of the wood, the more it will deform. That's why I recommend that people with instruments they highly value for one reason or another, keep them in environments  not exceeding 60% relative humidity.

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Good evening MN,

This thread arrived at a useful time for me, since I was just setting the neck on the cello I'm trying to build.  It inspired me to reinforce my neck heel with a spline.  I thought I'd add my two cents now because David Burgess suggested that cutting the spline on a table saw is dangerous (which it is), and because I don't remember reading any recommendation for a wedged spline.  I was keen to find something that would glue very tightly.  At this time of year, with chair dowels loosening all over the house, I thought dowels might not be what I want.  And I don't trust my skills to fit a plain rectangular spline.  A wedge-shaped spline seemed to be the answer.  The photos should be self-explanatory.  I glued my nearly-finished neck on the center line of a wedge-shaped piece of 2x4, cut at an angle (about 4 degrees) so that the throat of the neck would be parallel with the table of the saw.  It gave me a nice, wide stable base for pushing through the saw.  I used hide glue, of course, so it wouldn't interfere with gluing to the neck block later on.  I set my blade at a 2 degree angle, and was (very) careful to set it low enough to leave at least a quarter inch of wood above the cut.  I tried to set the fence so that the top of the blade was just a little to one side of center.  I ran the neck through twice, once for each side.  It's worth practicing on scrap.  You want an A shaped cut, not a Y.  For the sake of my fingers, I used a push stick and a feather board (as seen in the photo).  I've also rigged my saw with a kick plate (as you can see in the last photo)--I REALLY don't like taking my hands or sticks off my work until the saw is done spinning.  A bonus with the kick plate is that I can turn off the saw while I'm still in the cut, so the blade has nearly stopped by the time I'm through my workpiece.  The spline was easy to cut on the band saw and shape with a plane.  The wedge shape makes it practical to get a very tight fit--just like fitting tuning pegs.  The photos shouldn't need much more explanation. IMG_1900.thumb.JPG.381fdd0c319dff32dc3c708e499101e9.JPG

IMG_1903.thumb.JPG.afcace1e43f0aa7f664336d96739d88e.JPG

IMG_1919.thumb.JPG.6637c6dfb8dd8a5096036b18341b1d40.JPGIMG_1920.thumb.JPG.992c70afc9b47ce536c62b0fa246fcd4.JPGIMG_1921.thumb.JPG.8e78d08f1b0aef3f55176e1fb2a3b737.JPGIMG_1922.thumb.JPG.7cf83c48c61a49b7a977b6dbaeaf0ea3.JPG

 

Edited by Mark Landeryou
Didn't mean to include the picture I just deleted.

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21 hours ago, Mark Landeryou said:

- snip-

IMG_1903.thumb.JPG.afcace1e43f0aa7f664336d96739d88e.JPG

 

Hi Mark -  Unfortunately a spline there does nothing for the neck.

If one imagines that that pencil line in the pic above is the Neutral Axis (where there is no stress). That part of the spline from the NA towards the end-block is doing almost nothing. Because the neck is glued to the end-block, the compressive load is transferred into end-block. That end-block has ~ 5x the area of the maple under compression and 5x the resistance to deformation. This means that there will be precious little movement at the front of the neck.

Make a dummy spruce end-block and dry fit it to the neck and look at the assembly and imagine loading it under compression.

On the peg-box side of the NA you introduced a slot into an area that is under stress - not a good idea.  Wood doesn't handle tension perpendicular to the grain well.

(Read my post above - I have corrected a huge boo-boo - I cringe to admitting to not checking the units (kPa) before typing them and calling them psi! - an ~ 7x error. Definitely getting old )

I repair broken cello necks by drilling and inserting a 16mm dowel - doing my best to come as close as 3mm to the varnish. Somewhere in the archives you may find what I wrote then.

cheers edi

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Mark, I fear that the void you left there is actually making the heel more vulnerable. The goal is to insert the dowel (or whatever material you choose) as close to surface as possible so it stops the stretching of the weak side. Your neck has hollow right there. I would suggest drilling right through the hole and insert dowel. Or if you have tapered reamer to fit the hole (perhaps guitar bridge pin reamer) I would just ream it and insert long tapered pin. Even if you stop cm or so from heel it will be better than empty space.

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Back to the topic... what about bamboo for the inserts? It has been used for backing bows (archery) because of its tensile strength.

I can imagine packing hemp cords soaked with hide glue into the gap that Mark has (before inserting the wedge) making it as strong as hell. Many possibilities....

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On 2/3/2018 at 3:58 PM, edi malinaric said:

Hi David - I've been mulling over your drawing and wonder if the distortion that you show didn't occur after you loosened the neck from the neck-block....

...If one looks at the part of the neck that is under compression and the area of the glued joint in a parallel grained end-block, there is almost zero chance of the neck wood compressing or bowing anywhere on that side. Maybe a bit on that piece above the body - but there, the x-section of the neck is at its maximum and the unsupported length is measure in a few mm.

 

The portion of the neck heel above the mortise  (the overstand) can be quite large on a cello, with most players preferring at least 22 mm, and I've seen as much as 30 on wide model cellos. I think that's where most of the compression takes place, on the unsupported portion. I tried to loosely illustrate this on the exaggerated drawing, putting most of the bend in the upper 1/3rd.

What one will sometimes find though is that the bending forces on the neck (perhaps combined with some side forces or minor bumps at the scroll end) have  loosened it from the mortise, part way down, allowing compression, curvature and bending even on the portion of the neck within the mortise.

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1 hour ago, David Burgess said:

The portion of the neck heel above the mortise  (the overstand) can be quite large on a cello, with most players preferring at least 22 mm, and I've seen as much as 30 on wide model cellos. I think that's where most of the compression takes place, on the unsupported portion. I tried to loosely illustrate this on the exaggerated drawing, putting most of the bend in the upper 1/3rd.

What one will sometimes find though is that the bending forces on the neck (perhaps combined with some side forces or minor bumps at the scroll end) have  loosened it from the mortise, part way down, allowing compression, curvature and bending even on the portion of the neck within the mortise.

Hi David - good call - how often does one come across a half-failed joint in a cello neck?

Years back I measured X-sections of my cello's heel and calculated the expected deflections on the compression and tension sides. During a couple of house moves these notes went AWOL - or more likely they are just lying in some unpacked box waiting to see the light of day once more (fish moths permitting!)

I have a heat dis-assembled cello waiting for its time on the bench. Guess it's time to revisit those calcs.

regards edi

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2 hours ago, David Burgess said:

The portion of the neck heel above the mortise  (the overstand) can be quite large on a cello, with most players preferring at least 22 mm, and I've seen as much as 30 on wide model cellos. I think that's where most of the compression takes place, on the unsupported portion. I tried to loosely illustrate this on the exaggerated drawing, putting most of the bend in the upper 1/3rd.

What one will sometimes find though is that the bending forces on the neck (perhaps combined with some side forces or minor bumps at the scroll end) have  loosened it from the mortise, part way down, allowing compression, curvature and bending even on the portion of the neck within the mortise.

Hi David,

Do you ever see the top plate bending inward just south of the upper block?

This might  add a little to the fingerboard tipping downward.  

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30 minutes ago, Marty Kasprzyk said:

Hi David,

Do you ever see the top plate bending inward just south of the upper block?

This might  add a little to the fingerboard tipping downward.  

Yes, and the neck reinforcement won't do anything for that. On new instruments, I try to put a little less re-curve in that area, and leave it a little stouter, knowing that this can happen.

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Perhaps if there is any hidden non wood in an instrument it might be a good idea to put an extra label in the treble f hole alerting future repairers that there was metal lurking in the neck heel.

DLB

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On 2/3/2018 at 12:29 AM, Pete Moss said:

Hi, everyone. I have read this with interest. I don't mean to steer the topic away from cellos but the Stewmac copy mentioned tonal benefits in guitar and bass necks. I wonder if any one here has tried titanium in a fretted instrument neck and has noticed a tonal improvement beyond increased stability?

Thanks,

Pete

There should be no tonal difference. 

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3 hours ago, Dwight Brown said:

Perhaps if there is any hidden non wood in an instrument it might be a good idea to put an extra label in the treble f hole alerting future repairers that there was metal lurking in the neck heel.

DLB

Perhaps if there was some kind of discreet label at the neck butt under the FB indicating some kind of hard insert.

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