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Buttresses and CF Reinforcement
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=14532		 Page 1 of 2
Author:  Steve Walden [ Thu Nov 15, 2007 4:14 am ]
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I have been mulling over the design for a bolted neck to body/cantilevered finger board.  I have a question for those who use a CF rod, either round or rectangular cross section, in how you fasten them to the neck block and the waist block.  The rod from the NB/FB (top) to the back/waist is in compression and that connection is easy to configure.  My question arises when you use another rod from the bottom of the neck block to the waist attachment.  Since it is in tension how do you attch the ends?  If simply set into a rabbet or recess and epoxied, I would think it would not be a strong enough attachment.


Please pardon the crude Paint scketch.


Thanks,
Author:  Rick Turner [ Thu Nov 15, 2007 4:51 am ]
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First of all, put the pivot right up at the top of the body under the fingerboard.   Why a pivot at the buttress?   Buttress in tension? See the photo in the end block thread of how I top the center seam reinforcement with CF.   Glued in it's plenty strong enough, and what we do is to carry it out to the ends of the back; it's let into the end blocks.   Believe me, this all works just fine, and it's massively strong.
Author:  Dave White [ Thu Nov 15, 2007 4:55 am ]
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[QUOTE=WaldenWorx]   If simply set into a rabbet or recess and epoxied, I would think it would not be a strong enough attachment.[/QUOTE]

Steve,

Why not? I use two parallel cf rods, one at the top and one at the bottom (rather than the top one going to the bottom at the waist as in your diagram). I (maybe wrongly) view the top rods as transferring the string pull on the neck block into the strong side rim assembly (under compression) and the bottom rods in tension as resisting the straightening of the back arch over time - a sort of "drip, drip drip erosion" sort of pressure. I rout channels for the rods in the neck block and in the side support braces. The rods are cut to fit tightly and are slotted in from the top and bottom in these channels and set in with epoxy. I then glue in wood fillers into the remaining channel spaces. The side waist brace supports are inlet into the linings at the top and bottom and glued to the rims with hot-hide glue. I've posted this pic before so apologies:

Author:  Dave White [ Thu Nov 15, 2007 5:09 am ]
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Rick,

I've posted this in the block grain direction post but will ask it here as well.

The picture of your butrees brace set up is really neat. I'll have to have a go with the cf capped backstrip sometime soon. Presumably you have to have the back in it's final lengthwise arch before you glue on the cf strip? And then put on the back braces with notches to bridge the back strip? I don't build in a sanded dish (as I don't do spherical surfaces) so would have to work out how to handle this.
Author:  Steve Walden [ Thu Nov 15, 2007 5:16 am ]
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Rick - Thanks for the quick answer.  I understand what you posted before about the back joint reinforcement.  I see what you mean about the back being in tension and the resultant of the CF over the back strip. 


My question now deals with the picture that appeared in that same thread that showed four rods from the NB to the waist.  The picture showed them parallel to each other.  A pair just under the top and a pair just above the back.


I can see the angled pair or a pair as pictured from NB to waist just under the top being beneficial, but not the pair close to the back.  If memory serves, was it Dave White's picture?  I just don't see that back pair as useful if the reinforced backstrip is used.


Thanks,


 
Author:  Dave White [ Thu Nov 15, 2007 5:23 am ]
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Steve,

Live posting is fun isn't it I don't (currently) use a cf capped centre seam so the back pair of cf braces do serve a purpose for me.
Author:  Rick Turner [ Thu Nov 15, 2007 5:28 am ]
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I don't do them parallel; I splay them to get that nice triangle effect for stability.   I'm not trying to get any tension effect out of the flying buttresses; they're strictly compression members. I suppose one could put a couple of strips of CF directly on the back and splay them out from the neck block to the waist brace, too, but this is getting to the place where enough is enough.   This whole system is so much stronger than a conventional guitar that it's just ridiculous.   I was able to stand on the center of the back of the H. Kaiser guitar without doing any damage whatsoever, and that was before I CF topped the back strip.
Author:  Steve Walden [ Thu Nov 15, 2007 5:49 am ]
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Dave - Thanks - we were typing at the same time and I took a break to get lunch!  No offense, but I was questioning the need for the second set of rods close to the back.  If they are in tension, as I suspect, the ends need to be anchored in the wood effectively.  How do you anchor them?


As in the other thread Rick mentioned, the back is being stretched.  His CF on the backstrip counters that, even with a dished back.  It would be even more effective with a flat back.


Rick, for neck reset and string height issues if the neck rotates up I suppose it doesn't matter where the fulcrum is.  To me, the greatest moment is the fulcrum point at the heelcap.  Not having seen as many instruments as you, does the heel tend to move away from the body or does it push into the body as the guitar is stressed over time?


I wish I had better graphics capabilities to illustrate what I am writing......  Thanks in advance for the help!  I have an engineering background and want to understand the mechanics of stress on a guitar before I build.  Although, I am not as anal as some, I hope.
Author:  Dave White [ Thu Nov 15, 2007 5:55 am ]
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Steve,

No worries. I described in my post above how I anchor them. Routed channels, tight fit of the cf rods, epoxy on the cf rods, wooden filler strips glued in channel voids. The bottom rods are to counter the flattening of the back arch - Rick uses the cf centre strip cap for this. What is it about thois that you don't think works?
Author:  Rick Turner [ Thu Nov 15, 2007 6:01 am ]
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On the Howe Orme instruments, the pivot is at the heel cap. They, by the way, are over 100 years old and they work and sound amazing.

I put the pivot up just under the fingerboard at the top of the outside of the neck block area so as to have the least effect on the intonation as the neck angle is adjusted. I pivot off of two bolt heads; the bolts are threaded into inserts in the heel face.   This allows over all intonation adjustment as well as yaw adjustment for string alignment. This gives you full parametric adjustment of the neck angles and global intonation, and assembling the guitars and setting the neck correctly is amazingly easy. It goes to that lazy part of me that wants setup to be simple.   In production, I think this may be the fastest way to put on a neck and have complete control over all the necessary parameters including action adjustment..no need to ever mess with saddle height.

I'll get some photos of the whole arrangement soon and post them.   
Author:  Steve Walden [ Thu Nov 15, 2007 6:31 am ]
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Dave - You are fast on the draw with the keyboard!  My only question is the ends of the rod attachment.  By your description in the last post: "Routed channels, tight fit of the cf rods, epoxy on the cf rods, wooden filler strips glued in channel voids." ..  I can see that you have anchored them strongly.  I was visuallizing only a pocket that the rod was epoxied into.


I suppose, as compared to Rick's method, that your method may be overkill.  Compression is easy to handle with the materials we use.  Especially the rods you have under the top or Turner's angled to the back are good in compression.  Tension, it seems to me, is a different animal.  If you look at the tension force vectors in the body caused by string tension, keeping the countermeasure in plane with these vectors works best.  The Turner backstrip cf does this. 


Anyway, this discussion is giving me ideas!  Now, I just have to get my shop enclosed and airconditioned....  Rel Hum was 95% yesterday morning.


Cheers,
Author:  Steve Walden [ Thu Nov 15, 2007 6:38 am ]
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Rick - I eagerly anticipate the posting of your photos! 


I see now that you were talking of a hard pivot that you use to move your neck around.  I was speaking only of an imaginary pivot to calculate moments.....


Again, Thanks! 
Author:  Dave White [ Thu Nov 15, 2007 6:44 am ]
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[QUOTE=WaldenWorx] I suppose, as compared to Rick's method, that your method may be overkill.  Compression is easy to handle with the materials we use.  Especially the rods you have under the top or Turner's angled to the back are good in compression.  Tension, it seems to me, is a different animal.  If you look at the tension force vectors in the body caused by string tension, keeping the countermeasure in plane with these vectors works best. [/QUOTE]

Steve,

I don't mind overkill for a few dollars and very little extra weight My bottom cf rods are in the same plane as the back, just like Ricks cf cap, just not actually on the back.

Anyway, happy thinking!!
Author:  Steve Walden [ Thu Nov 15, 2007 6:58 am ]
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Dave - "Anyway, happy thinking!!"  That is right!!  Its all theory until I start cutting and carving wood (and CF).


At least you have the finished products!  My wood is stored in an interior closet and the only resemblance to GLOs are the white crayon markings on the backs outlining the body! 


I'll be posting pictures of my shop coming together and then my GLOs that I hope sound a tenth as good as yours.
Author:  Sam Price [ Thu Nov 15, 2007 7:28 am ]
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BRILLIANT timing.....I am excited by this design, the thought that the upper bout is potentially freed for tone rather than strength.

This build technique including the adjustable neck is something I am trying very hard to emulate and complete- it *does* take time to process in the old grey matter, measuring thrice cutting once is incredibly important here- all credit goes to those who have designed this and made the information available to rookies like myself; Rick Turner, Dave White, Doolin...
Author:  Rick Turner [ Thu Nov 15, 2007 7:46 am ]
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Sam, once you get past the conceptual differences, this way to build is actually much easier. You also have a ton of freedom to either let the upper bout work or if you prefer, you can lock it up solid.   This also makes experimentation much easier...Don't like the top? Cut it off and make another.
Author:  Sam Price [ Thu Nov 15, 2007 8:10 am ]
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[QUOTE=Rick Turner] Sam, once you get past the conceptual differences, this way to build is actually much easier. You also have a ton of freedom to either let the upper bout work or if you prefer, you can lock it up solid.   This also makes experimentation much easier...Don't like the top? Cut it off and make another.[/QUOTE]

I love it!!
Author:  Steve Walden [ Thu Nov 15, 2007 9:03 am ]
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Me too.  That is another reason I am impressed with the Taylor NT system.  The neck can be removed, reshimmed and reinstalled in about 5 minutes.  But, if I understand it correctly, with Rick's system the neck angle and height can be adjusted without removing strings and neck.  To me, that is the ultimate system.


Rick, does this fulcrum/joint affect sustain and tone?  And, if so, how?
Author:  Sam Price [ Thu Nov 15, 2007 9:12 am ]
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[QUOTE=Sam Price] all credit goes to those who have designed this and made the information available to rookies like myself; Rick Turner, Dave White, Doolin...[/QUOTE]

argh!

My kingdom for an edit button!!! - hopefully this blether should read that: I'm the rookie, the other names in this sentence are the experts I'm learning from....

or am I being too paranoid?
Author:  Rick Turner [ Thu Nov 15, 2007 9:28 am ]
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It's hard to say how the neck joint affects tone because of all the other factors going on. What I can say is that these guitars have tremendous punch and the harmonic sustain is terrific. These guitars certainly do not suffer from how the neck is attached in any way I can hear, and I actually believe that the tonal texture is more complex because of there being more active top area.    

I want to make a more or less conventionally shaped and braced dreadnought...but with less bracing in the upper bout...to compare. Rosewood/Adirondack/scalloped braces in classic Martin style below the waist, and my thing up top with the cantilevered neck.   I want to see if I can make a real "banjo killer".   

With this neck system, action height adjustments take about 15 seconds...and that's if you're fumbling with the Allen wrenches.   It's all done from the outside with two Allen screws...one to adjust, and one to lock the adjustment. You can do the tweak while the guitar is in playing position.   You could even do it between songs while performing if you needed to for some crazy reason like playing slide.
Author:  JohnAbercrombie [ Thu Nov 15, 2007 10:06 am ]
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Rick-
I think I recall you mentioning that you use a trussrod with a steel reinforcement in the heel for these adjustable necks?
Do you think an adjustable neck without steel in the heel would work? (ie, did you try that and decide it needed the steel reinforcement?)

Thanks.

John

Author:  Howard Klepper [ Thu Nov 15, 2007 11:14 am ]
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"Flying buttress" sounds cool (and Gothic), but technically, those rods are struts. A buttress reinforces a wall against lateral forces. A strut is a frame member that is resisting a compressive load. I've been tempted to call them flying buttresses myself, but the left side of my brain won't let me.
Author:  Rick Turner [ Thu Nov 15, 2007 11:25 am ]
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Beg to differ..."Flying buttresses" resist the lateral force imposed on the top of a wall by the roof wanting to spread due to the interior not having any cross beam chords.   The beauty of the gothic cathedrals was the absence of roof trusses, and the weight of the roof pushed against the top of the walls. Without the lateral support of the flying buttresses, the whole shebang collapses.

In the guitar, that lateral thrust is from the neck pressing on the neck block and end of the guitar up there just under the fingerboard. The collapsing force is inward rather than outward, but the vector of the flying buttress support is exactly the same...diagonal to the actual thrust...as with a church, though the thrust on the church walls is also via a diagonal force vector from the roof wanting to collapse outward.

I think they could be called either quite accurately, but the word "strut" is already used by some in reference to guitar bracing...as in "strut shaving", etc. Now that may be an incorrect usage, but I've heard guitar braces called struts for at least 40 years.
Author:  Rick Turner [ Thu Nov 15, 2007 11:31 am ]
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I terminate my truss rod in a 3/8" x (about) 3 1/2" steel dowel rod that goes through the heel.   The top flat rod of the double truss rod is welded to the round steel rod.   We mill a slot to index the flat bar and then tap a hole through for the adjustable rod.    The steel dowel rod then has two additional holes in it, one through hole for the tilt adjustment bolt and a threaded hole for the locking screw.

I don't trust the end grain in the heel to hold the tension of neck adjustment, and one of my Howe Ormes has suffered from a heel crack.   They have a small nickel silver dowel in some of them, but it's not enough to have prevented cracking.

So yes, I do think the heel needs reinforcement, besides which the rod is perfect for the additional tasks of being the bearing for the adjustment bold and being tapped for the locking screw.

I do recognize that future repairs will be difficult...I hate to imagine replacing a stripped truss rod, for instance...
Author:  Kent Chasson [ Thu Nov 15, 2007 11:37 am ]
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Does anyone go the next logical step and "strut" to the butt?  Two more rods from the waist (at the back) to the tail block (at the top).


The top of the tail block is under quite a bit of tension from the string pull.  Seems like you could effect the other half of the neck reset issue...top bellying.  It would also give the rods from the heel something to push against and you could get by with a smaller block at the waist.


You wouldn't be far from being able to brace based solely on sound and not structure.
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