Sazi
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Bowl crack fix?
Could any maker here please offer advice on fixing a crack on the back of the bowl, between ribs but veering slightly into one rib. The crack is open
a bit - what is the best way to close it and hold it closed? I would appreciate any advice on this matter, thanks, S
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suz_i_dil
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Let's wait for a real luthier opinion, but I don't think you can close it without putting new material into the crack, like wood paste. Then you may
polished and make or ask someone to make a new varnish on the instrument.
But again this is just the opinion of a non luthier forum member.
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Dr. Oud
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you can just rub some good glue (hide, yellow carpenter's, LMI's white instrument glue, some liquid hide (http://www.woodcentral.com/chats/chat_edwards_11108.shtml) * DO NOT USE: white polyvinyl, "crazy" glue or epoxy!. line up the edges and push the
crack together, if the edges don't align you can sometimes apply a little pressure on the high side by tying a strip of rubber (cut from a bike inner
tube) around the oud and positioning a small block over the high side of the crack, with the rubber band over the block - not too much pressure or you
might do more damage; then secure with masking tape wipe off the excess with a damp paper towel or sponge, then dry. Don't use a filler or putty
'cause it's ugly and doesn't bond the edges together. If you can reach inside, reinforce the crack with a strip of parchment paper glued to overlap
the entire crack with the same glue used on the outside. After the glue cures remove the tape and you should be good to go. You can usually clean off
any leftover glue with warm water and a cloth or plastic scrub pad. Often the edges don't exactly line up due to stresses in the bent wood, but no
matter - do not sand the crack to "level" the surface.
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Sazi
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Thanks guys, Richard, that's a great idea with the rubber and the block, just what I need, I think I saw something similar in a construction vid.
Luckily it's not as bad as I was led to believe, long but closes completely and should repair well and invisibly. Ahh, the glue, yes I would never use
anything other than the traditional glue, both for strength and ease of clean-up, and for the benefit of any future repairer. It is really frustrating
to have to deal with bodgy repairs using say, epoxy!
thanks again, S
Now all I have to do is wait for this rain to stop!
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SamirCanada
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hide glue is the best since it will set almost right away and give a really strong bond that actually brings the two surfaces together as it dries.
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jdowning
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I would agree with Richard about use of hide glue for repair of a clean crack in wood that has a surface finish applied - as any surplus glue can be
wiped with a damp cloth without damaging the finish. This also applies to some water soluble synthetic wood working glues (but never white PVA).
However, it must be possible to get the glue into the crack in the first place. If it is a tight hairline crack this might not be possible without
forcing the joint open and perhaps extending the damage. Some luthiers use super glue for this class of repair - 'hot' glue formulated for use on
wood. This stuff 'wicks' into a hairline crack by capilliary action but might dissolve or damage a surface finish around the crack if applied from the
outside of an instrument.
Epoxy glues formulated for use on wood, can have a limited application in instrument making (for new work) where the joint should not have to be taken
apart in future (but not for this class of repair under discussion). However, they require care in application (clean joint surfaces) and may not work
at all well with oily woods. Epoxy and hot glues also require caution in handling.
The discussion link about glues is interesting although it is difficult to separate fact from questionable opinion based on commercial preferences, or
if the questions were fully resolved during the course of discussion. Also the applications under discussion seem to be more related to furniture
rather than instrument making.
The references to alcohol and hide glue do not appear to match historical data where (before the modern age of synthetic glue) the strongest of glues
used for cementing wood, metals and glass was made from a formulation of isinglass and hide glue in alcohol. Both isinglass and hide glues were used
in the past for instrument building and repairs.
Glue made from the swim bladders of fish such as the sturgeon (isinglass) is pure gelatin with a fibrous structure and makes a strong durable glue.
However, isinglass today costs several hundred dollars a kilo to buy (if you can get it) so is not used to make the generally available, relatively
cheap "fish glues". These are made from from ground up fish waste so are not the same thing as isinglass glue. (I recently discussed this in more
detail in "Early Oud Construction Methods?" on the Oud Projects Forum).
One downside of hide glues is that they are a good food for micro organisms so that under favourable circumstances the glue can break down and the
joint disintegrate by bacterial action. In the discussion link above, the recommendation for long term preservation of hide glue joints against
failure, is to protect them with a finish. That is fine for furniture but in an instrument - while the exterior may be finished - the interior is not,
exposing the glue to moisture and other conditions that hide glue does not like.
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Dr. Oud
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While cyanacrylate ("crazy" glue) may be used by some repair tech, I don't like it especially for oud back cracks as it is difficult to undo if the
edges don't align, and they often don't. Hairline cracks, maybe, but most oud back crack open asyymectrically due to the inherent stresses in the bent
ribs. I do use it for inlay repair and filler with matching wood fibers on fingerboards as it cures harder than any other glue except for glass filled
epoxy.
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jdowning
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I rarely use the stuff (crazy glue) for any application - tried once on a 'classical' guitar, some piano action part repairs and for a hairline crack
in cast iron metal work - but it does seem to have a number of practical uses. I am always a bit nervous about sticking my fingers together with
it!
I agree that it is not the way to go with rib repairs where cracks can be 'flexed' a little to get the glue in there. Once a joint is 'contaminated'
with any synthetic glue further repair can become more difficult - if not impossible - than if hide glue was used in the first place.
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carpenter
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<< but in an instrument - while the exterior may be finished - the interior is not, exposing the glue to moisture and other conditions that hide
glue does not like. >>
That said, John - why not? Seems like a (maybe) good idea to me. I've been inside old violins that seem to have some thin, transparent wash of
something on the inside; not recent ones, however. What have you experienced in lutes, &c., and does interior finish, if any, seem to make any
difference? "Subjective," and "no control group" caveats are acceptable.
Possibly there's something about the inside of an instrument being a reflector; a finish inside could make the sound more "bouncy." I sure don't know.
A bunch of the boys were discussing tone, especially sustain and decay as being particular to an instrument. It got deep, but we're most capable of
deep when required.
As usual, nothing was decided with any firmness. I place "interior finish?" before the experts.
And - I've used CA glue on minor repairs, but it's kind of scary - it spreads, and in a hurry, then it's too late. It's not for me, generally. Some
guitar guys seem to love it.
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jdowning
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I am not aware of interior finishes being applied to violins, lutes etc. or if this would be of any benefit acoustically. However, an unfinished
interior might allow an instrument to 'breath' and adjust to any residual stresses over many cycles of temperature/humidity - reaching an optimum
condition over many years. In high temperature/humidity conditions the interiors of my lutes sometimes smell of warm hide glue so I figure that the
glue is slightly softening and the instrument beneficially "stress relieving" (in engineering terminology) on those occasions. Just an unfounded
theory though.
I am not sure if any interior surface 'roughness' would be 'visible' to sound waves by virtue of their speed and frequency - so a 'smoother' finish
might be of no advantage acoustically. However, I don't know but no doubt someone does.
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carpenter
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Many years ago, I was reading through some Violin Society of America articles, and they had evidence of some kind of protein applied to early fiddle
interiors. Egg white? Whiting (don't quite know what that is)? They weren't clear, but it was soaked into the structure of the wood, not on the
surface, with electron microscope photos to prove it.
Anyway, some modern fellow subsequently followed up on it, and claimed acoustical improvements over an unfinished interior (again - "control group?").
I just wondered if it was anything commonly done back when, or just ancient snake oil. I agree with instruments seemingly acclimating over time.
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jdowning
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Getting way off topic here - but this probably refers to salts found within the structure of the wood of 17th C Italian violins possibly because the
logs were floated to their destination and left in sea water for a considerable period of time before being sawn up for instrument use. (soaking in
water or 'ponding' is a method of preserving saw logs from insect infestation and to season the logs).
Recent experimentation to boil instrument woods in salt solutions in an attempt to replicate the early violin 'salted' woods has resulted in claims of
improved acoustical properties by the researchers. This is not a surface finish however.
I have heard of the exterior surfaces of early violins being coated with gesso (filler) prior to varnishing - but not the interior surfaces. I have a
references to this practice so will check it out.
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jdowning
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Jim - this is the reference I had in mind. It is a tutorial by the late David Rubio on applying ground (surface filler) as part of the finishing
process in varnishing the exterior surfaces of violins - based on research involving microscopic examination of early violin fragments. Note that the
interior surfaces of Rubio's violin in the tutorial appear to be left unfinished.
http://rubioviolins.com
I have also found a general discussion paper about the chemical treatment of timber that I wrote about 15 years ago that may be of some interest in
addressing your second question about salt residues found in tone woods. I shall scan this and post it as a new topic on the Forum to avoid further
deviation from the topic of this thread.
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carpenter
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Thanks, John, for the link. I found this interesting:
<< I do not consider that this ground is a part of the varnishing process, more an integral part of the construction. So I treat the components
while still on the mould. This procedure also helps to prevent any distortion which could possibly occur by wetting down a closed instrument or by the
changes to hardness and tensions of individual parts. >>
He's talking fiddles, here, but it might have an oud application. Case-hardening? It's probably New Thread time ...
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jdowning
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Thanks for your comments Jim. I will start the ball rolling with a new thread with some (likely outdated!) information about salted wood and we will
see where it takes us concerning ouds in particular
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