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 ARCHIVED TOPIC: Does a Center Strip add strength?


Please note this is an archived topic, so it is locked and unable to be replied to. You may, however, start a new topic and refer to this topic with a link: http://www.banjohangout.org/archive/350575

Quickstep192 - Posted - 01/26/2019:  10:28:27


I'm fixing to make a neck of mahogany with a maple center strip. The outer mahogany pieces will have the grain mirror imaged and the center maple strip will have the grain running perpendicular to the fretboard. (See attached pic)

Does the center strip really add strength? I mean it's still all wood right?

I'm mostly adding it to act as a guide when shaping the neck, but wondering if it adds enough strength to eliminate the need for a truss rod.

Thoughts?



 

boarstud - Posted - 01/26/2019:  10:42:32


I have a hand-made banjo neck like what your describing, except the woods are reversed (maple neck with a perpendicular mahogany strip down the middle) and no truss rod. It is a 1986 creation and has held up well, but Randy Wood just steamed it back to shape. Personally, I would want the finest truss rod installed for insurance from this problem.

stelldeergibber - Posted - 01/26/2019:  11:24:43


Don't forget that a truss rod does not simply add strength, it adds adjustability. The maple strip you show has a grain orientation which is described as quarter sawn, which does provide strength, and just having a strip in the center allows the now two pieces of mahogany to be oriented mirror-style, as you say, which discourages warping. I'd never skip a truss rod, though.

pickin_fool - Posted - 01/26/2019:  17:46:26


a strip of wood can either add strength or lessen what strength is already there..it will, in all likelihood help prevent warping and/or twisting..



if i was going to build a neck myself tho i would use 5 or 7 pieces..just fot appearances sake

Zachary Hoyt - Posted - 01/26/2019:  18:02:39


My first banjo neck was made in 2005 from 3 3/4" thick pieces of maple, with no truss rod, and a piece of mahogany for the fretboard. It was very primitive(ugly) but it was playable and I played it for 5 years with steel strings. If you're using synthetic strings I would think that you don't need anything to strengthen or adjust the neck, but for steel strings I would feel safer with a truss rod or a fixed bar to keep the neck straight, but that's just my preference. If you think about the much smaller cross section of a violin neck with four steel strings on it and no stripe or extra support that would seem to indicate that you might be fine, but I don't know.
Zach

Dan Drabek - Posted - 01/26/2019:  18:47:32


Mahogany is more stable than maple, so if anything, the mahogany neck would be helping the maple lamination to keep from warping.
Truss rods do not strengthen a neck, or stabilize it. They do make it adjustable.
Splitting the neck and book matching the grain on the other hand, does help stabilize the neck as the tendency to move is counteracted by the opposing grain.

DD

The Old Timer - Posted - 01/26/2019:  18:51:32


I've always heard it was just to prevent warping/twisting.

rcc56 - Posted - 01/26/2019:  18:53:06


"Does a maple center strip add strength?" In my opinion, yes, if it is well seasoned hard maple and is glued with hot hide glue.  If you use another glue, the joint will be subject to "creep."  Hide hide glue does not creep, Titebond and most of the rest do.



Many 5 string banjos were made before WWII with hardwood center strips. Many have held up very well, and others not.



I have seen quite a few wartime Martin guitars with ebony center strips that are straight as an arrow.



Necks warp for a variety of reason-- inadequately seasoned wood, exposure to heat above 100 degrees Fahrenheit, long term storage tuned up to pitch or above pitch with too-heavy strings, etc.



It could be argued that installing an old single rod Gibson style truss rod actually decreases wood strength, and puts the burden on the rod instead. I have seen many old Gibson instruments that have reached the maximum adjustment point on the rod, and can't be tightened further.



I know of many 100+ year old banjos with 3 piece necks that are doing just fine. Also some with one piece mahogany or cherry necks. A lot of it depends on how well the instrument is cared for, and how heavily it is strung.



That's my 10 cents worth.


Edited by - rcc56 on 01/26/2019 18:54:59

darwinyarwin - Posted - 01/26/2019:  19:08:20


The center strip has always been a standard way to strengthen necks and to prevent warping, twisting, etc. (Well, not "always"; but since the 30's anyway.) It was the major way to reinforce necks before truss rods became common. Think about the word "lamination" and why it's usually considered a good thing. The theory was - and still is - that forces acting on the neck in one direction would be resisted by hardwood centers and grains oriented to support each part of the neck. It makes for a stronger, more stable neck. It used to be a selling point on higher end banjos. Now everybody mistakenly thinks the strip is just for show.


Edited by - darwinyarwin on 01/26/2019 19:10:36

banjobart - Posted - 01/26/2019:  20:23:24


Reinforcing strips do not work on banjos. The problem twice as often as not is a back bow, not a forward bow caused by string tension as with guitars. The string tension on a banjo is minimal compared to guitars.The string tension or reinforcing strip (wood, steel or carbon fiber) will not overcome the force of the neck wood if it wants to move. A banjo should have a two-way steel truss rod to correct a bow in either direction, up or down.



Never glue a fingerboard on a neck until it has seasoned for at least a month after rough profiling to shape with the bandsaw.



The neck wood and fingerboard should be stored in the same room and conditions for a month before gluing.



Never leave a banjo shut in the car parked in the sun for hours to overheat. That also warps a neck.



I have learned these lessons the hard way with a lifetime verbal (unwritten) warranty.



I have made and warrantied 5,000 necks.



My first banjo (over 40 years old) is here with no truss rod and the neck is straight edge straight. But I would not make necks and sell them to the public without a two-way truss rod. My first banjo has never been outdoors or left the house in a car and has lived in climate controlled environment.


Edited by - banjobart on 01/26/2019 20:33:40

Ken LeVan - Posted - 01/27/2019:  05:11:41


Everything Bart says is true.  I haven't made 5,000 necks by any means - not even close, but I have been making them for 50 years, (also with an unwritten unconditional warranty) and the only ones that have ever failed were two twisted longnecks made before 2-way truss rods were available.



Nowadays I use epoxy to glue the fingerboards on to necks.



During my banjo making and industrial design career, I watched Martin stubbornly go through three or four failed attempts to make mahogany necks without adjustable reinforcement, and they finally "caved". Players who can afford Martins are much less tolerant of bowed necks than in the past and expect to be able to adust them to a fair-thee-well.



I only very rarely make one-piece necks, and always make them 2-piece with opposing grain some center strip, which I don't consider to be reinforcement as much as a decorative touch and I use it as a guide while ripping the dado for the truss rod.



The only neck I have ever made without reinforcement was a kid's short A-scale, which nonetheless had a carbon fiber strip - minimal reinforcement, I guess, but not adjustable.



There are some very skilled people on this forum who have very carefully engineered their own no-truss-rod solutions to neck reinforcement with tempered steel and aluminum and they may share their experiences on this thread - trust me, what they do is more complicated than installing a $10 truss rod in a dado.



apropos of the OP, here's a picture of a 6-string banjo neck I recently made from Honduras mahogany with a laminated center strip. It also has a two-way truss rod.



IanBoone - Posted - 01/27/2019:  09:22:01


This is all super interesting!!! I’m just starting to dip my foot into some woodworking, and the whole process is still mind blowing of how different peices of wood can look and feel so unified. I doubt I’ll be making banjo necks anytime soon, but all this is inspiring to see nonetheless!

Also Ken LeVan, did my last emails get through to you? I’m sure you’re busy, but I just wanted to make sure they didn’t go to spam or something

Ken LeVan - Posted - 01/27/2019:  12:14:25


quote:

Originally posted by IanBoone

This is all super interesting!!! I’m just starting to dip my foot into some woodworking, and the whole process is still mind blowing of how different peices of wood can look and feel so unified. I doubt I’ll be making banjo necks anytime soon, but all this is inspiring to see nonetheless!



Also Ken LeVan, did my last emails get through to you? I’m sure you’re busy, but I just wanted to make sure they didn’t go to spam or something






Thanks for writing Ian, I DID lose a bunch of emails and I had been looking for something from you.  My email has gone weird and I have been spending a lot of time with tech support and struggling to retrieve lost things.  Please resend.



Ken

mikehalloran - Posted - 01/27/2019:  13:04:06


What Ken and Bart say.



I have a hundred+ year old Gibson mandolin with a mahogany/ebony/mahogany neck and ebony fretboard. The mahogany on the treble side has bowed while the other side did not. The ebony center strip, likewise, is nice and straight. If this instrument was subjected to excess heat, I wouldn’t know — not in the 23 years I’ve owned it but the 79 years prior?



I have a Kay bass with a similar twist under the treble side of the fingerboard only. The one-piece maple neck isn’t that beefy. I showed it to a well known local bass tech who suggested inlaying ebony in the neck. When I pointed out that the ebony fingerboard was nearly an inch thick over the warp, he conceded that might not be the ideal solution.



A single truss rod will not prevent the warp that either the above instruments exhibit.



Although ODE was well known for using multi-laminated necks to eliminate potential warping, their cheapest Grade 0 necks were one-piece mahogany. My Grade 0 long neck banjo neck is as nice as you could want 55 years later and I’ve never pulled it to adjust the truss rod. Nowadays, a one-piece mahogany neck would cost a premium and laminations are often done to conserve expensive lumber.



Wood will do what it’s going to do. Laminations alone will not prevent this.


Edited by - mikehalloran on 01/27/2019 13:07:48

IanBoone - Posted - 01/27/2019:  13:21:29


quote:

Originally posted by Ken LeVan

quote:

Originally posted by IanBoone

This is all super interesting!!! I’m just starting to dip my foot into some woodworking, and the whole process is still mind blowing of how different peices of wood can look and feel so unified. I doubt I’ll be making banjo necks anytime soon, but all this is inspiring to see nonetheless!



Also Ken LeVan, did my last emails get through to you? I’m sure you’re busy, but I just wanted to make sure they didn’t go to spam or something






Thanks for writing Ian, I DID lose a bunch of emails and I had been looking for something from you.  My email has gone weird and I have been spending a lot of time with tech support and struggling to retrieve lost things.  Please resend.



Ken






Oh so glad I asked!!! Just re-sent, let me know if you don’t get it. Sorry you have to deal with a bunch of tech support stuff, that’s the worst!! 



Sorry to comendeer the thread! Back to wood!

Dan Drabek - Posted - 01/27/2019:  16:00:20


quote:

Originally posted by mikehalloran

What Ken and Bart say.



I have a hundred+ year old Gibson mandolin with a mahogany/ebony/mahogany neck and ebony fretboard. The mahogany on the treble side has bowed while the other side did not. The ebony center strip, likewise, is nice and straight. If this instrument was subjected to excess heat, I wouldn’t know — not in the 23 years I’ve owned it but the 79 years prior?



I have a Kay bass with a similar twist under the treble side of the fingerboard only. The one-piece maple neck isn’t that beefy. I showed it to a well known local bass tech who suggested inlaying ebony in the neck. When I pointed out that the ebony fingerboard was nearly an inch thick over the warp, he conceded that might not be the ideal solution.



A single truss rod will not prevent the warp that either the above instruments exhibit.



Although ODE was well known for using multi-laminated necks to eliminate potential warping, their cheapest Grade 0 necks were one-piece mahogany. My Grade 0 long neck banjo neck is as nice as you could want 55 years later and I’ve never pulled it to adjust the truss rod. Nowadays, a one-piece mahogany neck would cost a premium and laminations are often done to conserve expensive lumber.



Wood will do what it’s going to do. Laminations alone will not prevent this.






Good to see you back on the forum Mike. 



I agree with the others that a neck will go where it wants regardless of laminations, but I think it helps. The more laminations, the more help it provides. Look at the laminated gunstocks by bench rest shooters. They are if anything, more fixated on wood movement than are luthiers. 



I also believe that a properly inlaid steel, aluminum or carbon reinforcement bar will stop wood from moving. If they don't, it's because they aren't big enough. The bigger the bar, and the thinner the neck, the more resistant they will be to warpage in any direction. Build a neck out of carbon fiber and cover it with wood veneer and show me how the wood will overpower the reinforcement. It's all relative. 



Jose Ramirez pioneered use of a 1/4" lamination of ebony in their classical guitar necks many decades ago, and they still build them the same way. Of course, ebony is more warp resistant than the maple that was suggested by the OP. And classical guitar necks are a lot fatter than banjo necks. But their string tension is still greater than that of a banjo. I don't know of any high-end classical guitar builder who uses adjustable truss rods in their guitars. And they have stood the test of time.



Of course, as Ken noted, Martin was dragged kicking and screaming into the truss rod camp. But to tell the truth, I don't know if it was the result of excessive repair work, or simply another marketing decision, since as Ken also noted, the truss rod arrangement has become expected and part of the identity of modern stringed instruments. And if I ever attempted to build banjos for sale in the thousands, you can bet I would install two way truss rods, whether needed or not. 



DD

mikehalloran - Posted - 01/27/2019:  21:19:08


>I don't know of any high-end classical guitar builder who uses adjustable truss rods in their guitars.<



It’s quite common these days, actually. Kenny Hill over in Ben Lomond is one of many who uses them on high end classical guitars. hillguitar.com/showroom/guitar...rres.html 



The adoption of the truss rod adjustable through the sound hole allows them to hide it, of course. Even one of my Martin classicals from the late 1990s had it. My earlier Martin classicals have ebony reinforcement—still have two.



Martin’s first truss rod necks had a P suffix for Low Profile. That didn’t last very long and soon the P became the standard neck and all became so equipped. 

steen - Posted - 01/28/2019:  00:51:08


In the old days necks could be straightened in a "heat box". Is that method still in use? Steen

OldPappy - Posted - 01/28/2019:  05:45:43


Heat is still used to straighten a neck, but it is seldom a long term fix as the wood will usually warp again.

When building a neck careful selection of wood is critical. Almost all of the stock currently in my shop has seasoned for decades, the boards I selected for necks were planed two years ago and allowed to sit in the bins. When I pick out boards for a neck I look at the grain orientation and I carefully look at whether the boards are true. Any which have developed any movement will not be used for necks.

I understand why others insist on adjustable truss rods, but I build fairly thin necks and do not want to cut a dado deep enough for one because it hollows the neck from end to end. The transition area from shaft to peghead is already the weakest point in the neck and cutting that channel weakens it even more. That said, I may someday change my mind about this after I have built thousands of necks, but I doubt I will live long enough for that.

I almost never build a one piece neck, and when I want that look I laminate two pieces cut from the same board with the grain cross oriented.

I use 3/8" carbon fiber reinforcement bars, and I have found that all CF bars are not equal. Those from LMII are stiffer than some I have gotten elsewhere. The bar goes through the weak transition area.

jwold - Posted - 01/28/2019:  17:18:05


quote:

Originally posted by banjobart

Reinforcing strips do not work on banjos. The problem twice as often as not is a back bow, not a forward bow caused by string tension as with guitars. The string tension on a banjo is minimal compared to guitars.The string tension or reinforcing strip (wood, steel or carbon fiber) will not overcome the force of the neck wood if it wants to move. A banjo should have a two-way steel truss rod to correct a bow in either direction, up or down.



Never glue a fingerboard on a neck until it has seasoned for at least a month after rough profiling to shape with the bandsaw.



The neck wood and fingerboard should be stored in the same room and conditions for a month before gluing.



Never leave a banjo shut in the car parked in the sun for hours to overheat. That also warps a neck.



I have learned these lessons the hard way with a lifetime verbal (unwritten) warranty.



I have made and warrantied 5,000 necks.



My first banjo (over 40 years old) is here with no truss rod and the neck is straight edge straight. But I would not make necks and sell them to the public without a two-way truss rod. My first banjo has never been outdoors or left the house in a car and has lived in climate controlled environment.






Kind of overly protective of your first born, eh?  That banjo has led a sheltered life...  ;^)

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