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jdowning
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Nailed Necks
Earlier this year I became curious about why early European luthiers - violin, guitar and lute makers - attached the necks of their instruments, not
only with glue, but with forged iron nails driven through the neck block. I was also curious to find out if this practice - historically - applied to
ouds (the oud, supposedly, being the direct ancestor of the European lute).
So far no evidence has come to light confirming nails being used for this purpose by oud makers. Instead - at least as far as the earliest surviving
(19th C) ouds are concerned - necks are joined to the neck block with glue and a dovetail or a simpler dowel joint. The question is does the dovetail
extension or dowel provide extra strength to the neck joint or is it just a device to ensure correct alignment of the joint when being glued - or a
bit of both?
The same question applies to the nailed joint of the Western luthiers.
So, some brief trials were undertaken to test the relative strength of a glued/nailed joint - during the hot, humid conditions of this past summer.
The results may be of some interest to the oud makers of this forum.
Here are a couple of images of an early 17th C lute neck block showing a large headed iron nail driven though the neck block and a similar image for a
Baroque guitar - again with a single nail driven through the neck block. Images kindly provided by luthiers Daniel Sinier and Françoise de Ridder
http://sinierderidder.free.fr
Violin makers such as Antonio Stradivarius (17th C) used three or four nails (dependent upon the size of the instrument) to attach the neck.
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jdowning
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Here are another two examples of nails used by the early lute makers,
The first is a sketch made from an X-ray image of a late
16th C lute by Michielle Harton - showing a single iron nail driven through the neck block into the neck. Note the irregularity of the blacksmith
forged nail.
The second image shows a lute by Hans Frei (mid 16th C) that has been modified later in life (17th C) from its original 6 courses to 10 courses
requiring a wider neck. Here the luthier - believing perhaps - that if one nail reinforced the strength of the neck joint then three nails would be
even better!
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jdowning
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Luthier Marcos Kaiser Mori has kindly provided some more examples of nailed neck joints in lutes.
http://www.marcoskaiser.com
The first shows a single nail in the neck block of a lute by Wendelin Tieffenbrücker, dated 1606, that has later been converted to a chitarrone by
the addition of an extended neck.
The second image shows multiple nails used in a Theorboed lute (again an extended neck) by Martin Kaiser, 1609, instrument #E 24, Musée de la
Musique, Paris. Three nails are used in the neck block and two nails to attach the extended neck.
Again the luthier appears to have faith in the power of the nail!
Note the irregularity of the hand made forged iron nails.
More to follow.
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jdowning
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To judge from surviving instruments (19th C and later) oud neck joints are generally made perpendicular to the plane of the fingerboard whereas those
of the early lute (at least beyond the Medieval period) slope at an acute angle. The reason is that lutes from the late 16th C had up to 10 courses of
strings requiring a wider neck than the 5 or 6 course oud. In order to maintain a practical depth to the neck (D) at the neck joint the neck joint was
cut at an appropriate angle to give the required fingerboard width at the neck joint.
Such a sloping neck joint presents difficulties when it comes to gluing the neck to the neck block as the neck will slide relative to the neck block
as a clamping force is applied unless some means is taken to prevent this movement.
Although the situation in gluing a perpendicular joint is potentially less of a problem, the use of a sliding dovetail neck joint is often found on
old ouds. One obvious advantage is that the neck may be fitted and adjusted as a 'dry run' prior to final gluing - always a good thing with glued
joints.
Although the sliding dovetail joint would have been a practical solution to gluing a sloping lute neck joint - it was not used, as far as I am aware,
by lute makers of the 16th and 17th C.
In Germany, the lute making tradition was revived in the mid 19th C, by popular nationalistic demand, in the form of guitar-lutes, instruments,
however, that had no relationship to the lightly built lutes of the 16th and 17th C being just guitars that were lute shaped. By the mid 20th C - with
a developing interest in rediscovering the huge surviving repertoire of lute music of the 16th and 17th C - heavily built instruments were being
produced that were more authentic looking but were still designed essentially for use by classical guitarists. These instruments persisted into the
early 1970's until authentic copies of original lutes started to become available.
'Die Guitar un Ihr Bau' by Franz Jahnel was published in 1963 and represents the modern state of knowledge, as it then was, about the construction of
fretted instruments such as the guitar, mandoline, lute etc.
It is interesting to note that the detailed information presented about the lute shows a neck joint with sliding dovetail (see attached image)
although the author does state that this type of joint is only one possibility. He also states that Medieval lutes had neck joints with a tenon
(although no lutes of that period survive to confirm this - one way or another).
So was Franz Jahnel passing on some unwritten traditional information about lute neck joints of the 16th and 17th C? Unlikely, alas, as his scale
drawing claiming to represent an early lute appears, by its design, to be nothing more than one of those heavily built, non authentic, instruments of
1960's vintage.
More to follow.
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jdowning
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A modern method of gluing the neck of a lute to the neck block is to use a round headed wood screw to pull the glued joint together - acting as a
clamping force until the glue has cured. Usually the screw is left in place after the glue has cured.
This method can be used for both slow setting synthetic glues or for traditional hot hide glues if the joint is first partially assembled, the glue
run into the joint and the screw immediately tightened with a power operated driver.
A problem with modern wood screws is that that the unthreaded shank of the screw is smaller in diameter than the outside diameter of the threaded
portion (not the case with the old fashioned cut thread screws where the unthreaded shank is the same diameter as the threaded portion).
This means that a clearance hole must first be drilled through the neck block to allow the threaded portion of the screw to pass unhindered. This in
turn means that the neck must be restrained with a guide block - temporarily fixed to the neck block - to prevent the neck sliding or rotating
relative to the neck block when being clamped in place by the wood screw.
Nevertheless, this arrangement like the sliding dovetail joint of the oud allows adjustments to be made to the neck assembly before being finally
glued in place.
The question now is - how can a nail (or nails) be used to replace the function of a wood screw for this type of joint? What might have been the step
by step procedure used by the ancient luthiers - perhaps not as straightforward as it might at first appear?
Only one way to find out!
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jdowning
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The first step in this trial is to make the nail - or 'spike'. The blacksmith made nails of earlier times were hand forged by heating a strip of iron
to bright red temperature - until soft - and then hammering the nail to the required shape on an anvil. The flat head of the nail was made by first
'upsetting' the end of the nail to form a 'bulge'. The nail was then placed in a 'heading' tool (after again heating to red heat) and the flat head
then formed by hammering - like a rivet.
For convenience I have started with commercially available 'square' cut nails that were once standard (until about as late as the 1950's) until the
now familiar round wire nails became generally available.
The head of the nail was heated with a propane torch and then formed in the heading tool. This is an original blacksmith's forged heading tool, picked
up at auction, but a less fancy version can be easily made by drilling an appropriate diameter hole in a thick bar of steel.
The tapered cut nails of the 19th C were not pointed. The blunt end reduced tendency to split the wood.
The finished nail will now be tested in a trial neck/neck block assembly with vertical joint - as found on ouds and pre 16th C lutes.
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jdowning
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The test neck/neck block assembly was made from pine/cedar with a vertical neck joint. The neck block was first drilled with a small diameter pilot
hole to guide the nail perpendicular to the neck joint. The neck was not pre-drilled and the test was undertaken 'dry' without using glue
With the assembly positioned in correct alignment and with the neck held in a vice the nail was then hammered through the neck block and into the
neck. The nail cut an oblong section hole in the neck block and did not split the neck. However, due to non uniformity of the nail and its tendency
to follow grain direction in the neck - the neck joint was found to be slightly out of alignment across the joint face when the nail was fully driven
home. This was corrected by withdrawing the neck slightly and applying force on the nail to bend it (the iron of the nail is quite soft) to bring the
joint faces to a perfect fit. While it would then be possible to withdraw the neck again to allow glue to be applied to the joint before hammering the
nail finally in place to complete the assembly, I doubt if this is the procedure that was followed by the ancient lute makers.
The nails used on the surviving lutes - to judge from the x-ray images - were thinner in section than the test nail and so more easily self bent when
being driven into place. Also a preferred neck material was Lime wood (veneered with hardwood) - relatively soft and light with little pronounced
grain that might cause a nail to wander out of alignment.
My guess, on the basis of this limited test. is that the old lute makers first drilled a pilot hole in the neck block. Then with the neck held in a
vice and the assembly held in correct alignment, the nail was driven through the neck block into the neck for a short distance - just to register the
nail position relative to the neck. The neck was then withdrawn, glue applied to the neck joint and the nail finally driven home to complete the
assembly.
If a single nail failed to bring the joint faces together in perfect alignment then additional nails may have been used to correct the situation.
The primary purpose of the nail with its large diameter head is, therefore, to quickly apply a clamping force and at the same time keep the joint
assembly in correct alignment. A secondary benefit is that, once in place, the nail will prevent joint movement and possible separation when the hide
glue is subject to humidity cycling over time.
A second trial using a thinner 'square' section forged nail was undertaken this past summer to test the relative survival rate of a plain,
un-reinforced, vertical neck joint made with hide glue to one reinforced with a nail - a destructive test, both joints being subject, under load, to
extreme conditions of temperature and relative humidity.
More to follow.
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jdowning
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For the second trial a thinner nail was prepared - again by reforging the head of a cut nail (for convenience). I use old style cut nails still made
for authentic historical carpentry work by the Tremont nail company.
This time around a Rosehead Clinch nail 3 inches (75 mm) long was used the head being heated with a propane torch and the head increased in diameter
by forging in the heading tool.
The finished nail is much thinner in section than version #1 so should allow easier seating of the joint faces when driven through the neck block.
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Aymara
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Thanks J. for this very informative thread.
What I personally miss in most todays ouds and maybe lutes too, is the use of truss rods to make the neck adjustable. I find this important,
especially when we keep in mind that both instruments are played world wide under very different climatic conditions. Even different string tensions
and changing humidity over the seasons, demand truss rods in my opinion.
Sorry, truss rods are a bit off topic here, but I think they are the last historical development after nailed and screwed necks, don't you think
so?
BTW, have truss rods ever been used in modern lutes? Do you know anything about that?
Greetings from Germany
Chris
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jdowning
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Thanks for your observations Chris.
This study concerning nailed neck joints came about partly as a result of some thoughts expressed during the topic recently posted by bulerias1981 on
page 2 of the 'Oud Maintenance Forum' - "Metal Parts in Oud (screws, nails) and the Workings of a Screw".
Comments included the function of truss rods in ouds and fretted instruments such as guitars. Richard Hankey (Dr Oud) explained that the purpose of a
truss rod was to adjust the curvature of a neck as an aid to providing optimum string 'action' along the length of a fingerboard - but not as a means
to reset a neck that had 'pulled up' under string tension over time. The latter problem requires removal and resetting of the neck in the case of an
oud.
Nailed (or screwed) neck joints on the other hand are not intended to allow for any adjustment of a neck - they just remain in place and provide some
additional reinforcement to the neck joint under conditions of fluctuating temperature and relative humidity - conditions that over time can cause the
hide glue in the joints to partially soften and give way under stress. Indeed a nailed neck joint is a bit of a nuisance if the neck must eventually
be removed for repair (not so with a screw that can be removed at any time).
So I do not see nailed or screwed neck joints being in any way historically connected to the modern invention of the truss rod.
On the other hand - although truss rods can be found and are accepted as a good idea in some modern oud designs - the objective among the lute
fraternity these days (it has not always been so) is to copy surviving instruments as closely as possible without trying to improve on traditional
design. So I am not aware of truss rods being used on modern made lutes.
As with the oud, a low string action along the length of the fingerboard of a lute is desirable and this can be achieved historically by using tied on
frets that graduate from thick (at the nut end) to thin at neck joint end. Another method is to shape the fingerboard into a slight longitudinal curve
to achieve the same objective and/or by planing the fingerboard lower on the treble side than the bass side (at the nut end).
Providing additional thickness of the fingerboard at the nut end is also a way of allowing for future neck/fingerboard adjustments - not requiring
removal of the neck - but by planing back the fingerboard. There is, of course, a limit to this dependent upon how badly the neck has pulled up over
time.
The results of the second trial comparing the survival of a plain glued butt joint to a nailed glued butt joint under load and subject to extremes of
temperature and relative humidity are to be reported next.
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Aymara
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Hi again J.
Shure, but the truss rod gives more stability ... the neck itself can't bend as much, but mainly at the neck joint.
It might be interesting to know, if layered necks (three pieces) give more stability regarding bending. I bet, the wood choice made for the layers
will play a major role?
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The latter problem requires removal and resetting of the neck in the case of an oud.
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Yes, and not only in the case of an oud.
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Indeed a nailed neck joint is a bit of a nuisance if the neck must eventually be removed for repair (not so with a screw that can be removed at any
time).
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Yes, the screw has a clear advantage.
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... copy surviving instruments as closely as possible without trying to improve on traditional design.
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I would have expected it being similar to oud, where we have the traditionalists on the one hand and people willing to improve and further develop the
instrument on the other hand.
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The results of the second trial comparing the survival of a plain glued butt joint to a nailed glued butt joint under load and subject to extremes of
temperature and relative humidity are to be reported next.
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Fine, I'm staying tuned 
Greetings from Germany
Chris
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jdowning
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The test rig for the second trial was a straightforward affair with two simplified 'necks' of pine (cut from the same piece of wood) glued side by
side to a pine 'neck block'. The 'necks' were glued to the block with high bloom strength (fast setting, high strength) hot hide glue in an inverted
position - one being also nailed in place.
Prior to gluing the joints the end grain of the 'necks' was sealed as is usual practice. This is to prevent loss of joint strength due to the glue
being absorbed into the end grain. My method for sealing end grain is to coat the joint surface with hot glue and then to immediately scorch the glue
with a hot iron to form a brittle surface crust of glue. The crust is removed by scraping, filing or sanding, the joint verified again for precise
fit, and then glued.
To obtain maximum joint strength the two joint faces must be brought into intimate contact with adequate clamping pressure - maintained until the glue
has fully cured. Clamping pressure is provided by the nail the case of the nailed joint. However, for the other joint no external clamps were used the
joint surfaces being held firmly together with strong hand pressure for a couple of minutes until the glue had gelled and then left undisturbed to
fully cure for 24 hours.
For the nailed joint a pilot hole was first drilled through the 'neck block' and the nail driven part way into the 'neck' with the assembly held in
correct alignment. The 'dry' joint was then separated, hot glue applied and the nail driven fully into the neck - the prepared nail hole providing
correct registration of the joint and preventing the joint sliding out of alignment. The thinner section, more flexible nail allowed the joint to seat
perfectly (unlike the nail in test #1).
The block was then bolted to a wall, under cover, in an exterior building and each 'neck' was loaded with a 1.5 Kilogram weight placed at a distance
of 20 cm from the joint and the rig exposed to the fluctuating temperatures and relative humidity of a Canadian Summer (hot and humid!)
As this test was intended to be an accelerated, destructive test of the joints, the loading of the joints was intentionally designed to be
significantly more severe than would be experienced in an oud (or lute).
More on that next.
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Aymara
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Isn't the string tension on an oud / lute neck much higher?
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More on that next.
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Interesting.
Greetings from Germany
Chris
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jdowning
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The attached simplified sketch compares the forces acting on a neck joint on an oud (or lute) with vertical neck joint and a lute with sloping neck
joint. For this example string tension is taken as 40 Kilograms with a neck length of 20 cm and string height above the neck joint of 3 mm.
The string force can be resolved into two components at the nut one acting parallel to the fingerboard (FC) and the other vertical to the fingerboard
(FB). The latter force, acting at a distance of
20 cm from the neck joint creates a bending moment on the neck joint tending to separate the joint at point B. However, due to the low angle of the
strings relative to the finger board surface the force FB is quite small - about 0.5 Kg - giving a bending moment of about 10 kg.cm.
(Force FB is also equivalent to the shearing force FC acting on the joint surfaces tending to cause the joint to slide apart).
The predominant component force FC acting in a direction normal to the joint surfaces is just a bit less than the string tension and is a compression
force tending to clamp the joint surfaces together.
In the case of the sloping neck joint of the lute the compression force FC of about 40 Kg acting parallel to the surface of the fingerboard is
resolved into two component forces - a compression force of about 36 Kg (Fc) acting normal to the joint surfaces and a shear force of about 18 Kg (Fs)
acting parallel to the joint faces.
For the second trial (which simulates the vertical neck joint case) the suspended load of 1.5 Kg (FB) is, therefore, 3X greater than the calculated
load produced by a total string tension load of 40 Kg. Furthermore the tests joints, in addition to the resultant bending moment (30 kg.cm)
experience a shear force of 1.5 Kg - all without the benefit of any sustained clamping force - except for that applied by the nail in the case of the
nailed joint.
So the loading conditions on the glued joints are more severe than would be experienced by an oud or lute under string tension - so quite rapid
failure of the joints under conditions of fluctuating high ambient conditions of temperature and relative humidity might be expected? And which joint
will be first to fail?
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Aymara
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Thanks for the detailed explanation.
I think, the nail makes not much difference. To make a difference, it would need to be much longer. Maybe half the length of the neck?
Or am I wrong?
Greetings from Germany
Chris
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jdowning
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What would be the advantage of a much longer nail when the primary purpose of a nail is to register and provide a clamping force to the neck joint at
the gluing stage and then reinforce the neck joint against shear/ tensile failure when the glue temporarily weakens under adverse temperature/
relative humidity conditions?
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Aymara
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It might give more stability against bending through the string tension, which seems to be more noticable near the neck joint than in the upper
half.
Or am I wrong?
Greetings from Germany
Chris
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jdowning
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The #2 test rig was first set up in my granary loft where there is free air flow (good for seasoning wood) and daily temperatures were elevated. In
order to keep Relative Humidity as high as possible (low to high 70's) the rig was covered with a plastic sheet to form a tent and a bowl of water
placed underneath.
As no failure or impending failure of the joints was in evidence after several days, the rig was later moved to my barn (this time without the tent
and water bowl) where temperatures were cooler and RH relatively higher (but still within the upper 70's range).
After a total of 27 days (August 02 to August 28), with still no sign of joint failure, a plastic tent was again placed over the rig with a pan of
boiling water underneath for a period of two hours each day during the afternoon in an attempt to raise the RH to above 80% (an RH of 82 % was the
highest achieved by this method). In order to further promote joint failure the suspended load on each 'neck' was increased to 2.75 Kg.
On September 02 the un-nailed joint was found to have failed overnight with no sign of failure of the nailed joint.
So although the nailed joint 'wins the contest' - as anticipated - what I found surprising was that the un-nailed joint survived for so long without
failing during the period when ambient conditions ranged from 37% to 100% and temperatures ranging from 12°C to 25°.
The attached chart summarises the daily temperature and RH fluctuations taken from the Weather Bureau hourly records for August and September.
Typically the lowest temperatures and highest RH occurred each day during the early hours of the morning reaching a minimum value around mid day when
temperatures were at a maximum.
The attached image shows the failed joint and it can be seen that there is a significant area where failure had occurred in the glue film (no wood
fibres in evidence). The joint face measures 50 mm wide by 25 mm deep.
The nailed joint was forcibly broken by hand and - apart from a small area lacking wood fibres - it can be seen that the wood of the joint failed
before the glue (i.e. the glue was stronger than the wood).
It might be concluded from this single test that the nailed joint was inherently stronger because of the more effective, greater clamping force
applied by the nail when the joint was first glued together. A likely secondary benefit of the nail was that it helped to stabilise the joint and
prevent separation under fluctuating conditions of temperature and RH.
It should be noted that the critical condition of RH is 84% where hide glue loses about 33% of its strength. However this condition is only achieved
in a joint if the glue and surrounding wood is saturated at a stable 84%. This condition is unlikely to occur under the short term excursions of RH as
experienced by the joints under test. So this is good to know!
The next test will be to determine the practical methodology for nailing a lute neck joint with sloping faces. Will the nail alone provide correct
registration of the joint when fully driven home or will temporary guide blocks be required as in the case of a screwed joint of this type?
More to follow
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jdowning
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Chris wonders if a long nail (at least half the length of the neck) would give more stability to a neck against bending - perhaps thinking that a long
iron nail would be the equivalent of some kind of truss rod (for which there is no evidence historically)?
It might be concluded from these trials that the purpose of the nail is primarily to register the neck to the neck block and provide adequate clamping
pressure when the joint is being assembled (necessary for optimum strength of the glued joint). As the nail must remain in place it then has a
secondary function in preventing future separation of the joint - either through the bending forces or shear forces - under circumstances where the
glue becomes temporarily weakened.
After all the function of a nail in a more general application is to hold two pieces of wood together (with or without glue) - for example to assemble
the frame of a house, fix wooden siding to the frame, fix floor boards to joists etc.
Note that the nails used by the early luthiers do not extend far into the neck - they are just long enough to provide the necessary clamping force
through friction. Iron nails of this type are also relatively soft and thin and so easily permanently bent beyond their elastic limit so can not
contribute much if anything to the overall stiffness of the neck against bending under string tension - even if they could be driven into place.
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jdowning
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Other historical examples of nailed neck joints can be found in early violins where the neck is butt joined to the ribs (not constructed in the
Spanish way where the ribs are glued into slots cut into an integral neck/neck block).
It is of interest to note that the early luthiers might construct both plucked and bowed instruments - so a lute maker would also make viols or
violins. It is perhaps no surprise then that some techniques were applied by the luthiers to both types of instrument.
Roger Hargrave is a master violin maker with extensive first hand experience in the examination and measurement of some of the most famous of the
surviving instruments of the violin family by makers such as Stradivarius and Guaneri del Gesù. Fortunately for the world of instrument makers, he is
willing to share his extensive experience in a series of articles about the violins that he has examined, their characteristics, materials and methods
of construction etc. - all written in a clear, easy to read manner. These articles are freely available - in English or German - at:
http://www.roger-hargrave.de
Click on the 'Library' button
Having briefly looked at the content of the articles it did not take long to find a reference to nailed neck joints in the article about the work of
Guaneri del Gesù working in the early 18th C Italy.
The neck joint of a violin by Andrea Guaneri was shaped to fit the upper curve of the ribs with a gouge and so was not perfection in its fit - yet it
did the job.
Stradivarius used from three to five nails dependent upon the size of instrument (violin or cello). Del Gesù used five on a violin but as Roger
Hargrave proposes two of these may may have first been driven into the neck and with their heads clipped off prevented the neck from moving relative
to the neck block when pilot holes were being drilled for three other nails.
The attached image by Hargrave shows a plan view of the nails driven through the neck joint. In his article about Stainer violins there is also an
X-ray image showing the position of a nail in the neck block of a violin.
The third image shows the tips of three nails visible in the heel of the neck of the 'Harrison' violin by Stradivarius, 1693 in the Rawlins Gallery,
National Music Musem.
Another twist to this tale is the article "The Case for Casein" where Roger Hargrave suggests that casein glue (a slow setting strong waterproof glue
made from cheese and lime) might have been used by some luthiers instead of hide glue. Although known since ancient times a modern version of casein
glue was - until recently - used for wooden airframe structures the most famous example being the De Haviland 'Mosquito' aircraft of World War 2
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jdowning
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.... and here is another X-Ray image of three nails in the neck joint of a Guaneri viola - no other information is available at present to identify
the source of the image.
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jdowning
Oud Junkie
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Registered: 8-2-2006
Location: Ontario, Canada
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The purpose of the third and final test is to determine the best method for nailing a sloping neck joint typical of a lute. The reason for sloping a
lute neck joint is to achieve a wider fingerboard at the neck joint (in order to accommodate a greater number of courses) without increasing the depth
of the neck. The slope chosen for the test is about 20° from the vertical giving a width of 60 mm for a depth of 25 mm (for a vertical oud style
joint the width would be 50 mm for a depth of 25mm).
The 'neck block' for the test rig was cut from cedar and drilled with a pilot hole to guide the nail. The 'neck' was made from so called American
Yellow Poplar (which is not a Poplar species at all but Magnolia, a very large, beautiful tree from the Southern States). It is a softer wood with
less pronounced grain than Pine. I did not have any Limewood which would have been the most historically correct choice.
The 'neck joint' was left with a sawn finish as this was just a quick 'rough and ready' trial.
The nail used in Test #2 was modified by filing into a more uniform square section with a pointed tip - to simulate original nails seen in the
previously posted X-Ray images. The modified nail was then heated to red heat with a propane torch and allowed to slowly cool to ensure that the nail
was fully softened (annealed).
The first step was to hammer the nail through the neck block until the point just protruded. The neck was then held correctly positioned and aligned
with the neck block and the nail hammered into the neck for a short distance in order to register the neck with the neck block. The joint was then
pulled apart leaving the nail protruding. (This is the point in the procedure where hot hide glue would be applied to the joint faces. With the glue
applied the joint would then be reassembled with the protruding nail providing correct register).
With the test joint reassembled the nail was fully hammered into place. The joint did not appear to move out of alignment and appeared to be correctly
seated but - unfortunately - the neck split and so it was difficult to fully assess the outcome. Well seasoned Magnolia wood may be more prone to
splitting than anticipated.
The test will, therefore, be repeated this time again using White Pine for the neck. The nail will also be shortened by about 20 mm (3/4 inch) as it
is likely that the excessive length contributed to the splitting. From this experience the length of the nail should be about 2X the maximum thickness
of the neck block.
Also the joint faces will be finished smooth to ensure that the rough sawn faces of this test did not contribute to the joint faces not sliding as the
nail was driven home.
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jdowning
Oud Junkie
Posts: 3485
Registered: 8-2-2006
Location: Ontario, Canada
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For the repeated test #3 a new neck block/neck assembly has been made up - this time with a neck joint slope of 30° to the vertical, both joint faces
finished smooth and with the nail shortened to 57 mm in length (2X the maximum thickness of the neck block).
With a maximum depth of the neck of 25 mm the sloping joint gives a maximum width at the neck joint of 85 mm.
The procedure for nailing was as previously reported. With the nail driven fully through the neck block and into the neck the neck joint faces were
perfectly seated but the neck had moved upwards relative to the neck block by about 2 mm.
Splitting the neck to reveal the nail shows that when being driven into the neck the nail had bent downwards relative to the top surface of the
neck.
This suggests that a pilot hole must first be drilled for the full length of the nail as a guide to prevent the nail bending.
To drill the pilot hole in correct alignment, the pilot hole in the neck block will be drilled first. The neck and and neck block will then be
temporarily glued together in the correct position with a spot of hot hide glue applied to the joint face. The pilot hole will then be completed (once
the glue has set) using the pilot hole in the neck block to guide the drill bit into the neck. The joint will then be broken apart and prepared for
reassembly, gluing and nailing.
This procedure will be tested next.
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jdowning
Oud Junkie
Posts: 3485
Registered: 8-2-2006
Location: Ontario, Canada
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Drilling a full depth pilot hole did not prevent relative movement of the joint faces as the nail was hammered in place - if anything it made matters
a bit worse with the joint being displaced by about 3 mm or so (but with the joint faces gain brought into perfect contact)
After the test, the neck was again cut open along the axis of the nail to reveal the position of the nail. It can be seen that as the point of the
nail entered the pilot hole in the neck it made contact first with the top of the pilot hole - the wedging action of the point then initially pushing
the neck upwards (point A). After the nail had entered about half way into the neck the nail then began to run straight again.
Had the wood grain run vertically in the neck (as it normally would) then it is likely that tendency of the nail to wander would have been minimised -
largely unaffected by the difference in hardness between the early and latewood cells.
To conclude, the best results might be obtained by:
1) Using a wood with little or no pronounced grain such as Limewood for the neck (veneered on the outside with Ebony or other harder wood).
2) Drill a pilot hole in the neck block only - not in the neck.
3) The point of the square nail should be flattened to minimise chance of splitting the wood of the neck.
Although not tried in this test, a guide block temporarily glued to the neck block - to prevent relative movement of the neck joint faces as the nail
is being driven into place - would likely be beneficial as it is in the case of a screwed joint).
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Aymara
Oud Junkie
Posts: 1162
Registered: 10-14-2009
Location: Germany / Ruhr Region
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Thanks again J.,
very interesting information, especially the comparison with violins.
One question: Do you think pilot holes where historically used? Any evidence available?
I'm just curious.
Greetings from Germany
Chris
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