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jdowning
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[*] posted on 10-22-2014 at 03:20 PM


If there is a direct relationship between sound hole size (area?) and sound board area I am not aware of it but would be interested to learn more.
Where did you say that you read about this on the forum?
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faggiuols
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[*] posted on 10-22-2014 at 11:21 PM


hi David, thanks for your post.
when I find a process difficult I think an easier alternative. is the way my mind works .
as for the neck-block. it seemed me too difficult to make the snap so I chose to do one piece .
the bending of the ribs with the hot iron seem to me difficult and dangerous so I thought I find it easier to do without.
is also a suggestion of a luthier who produce mandolins. He said that when ribs are small you do not need a hot iron. perhaps mandolins have the ribs much smaller and the mode can not be used for oud.
I try, then I say as gone it.
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[*] posted on 10-22-2014 at 11:26 PM


hello Jdowning
maybe I misunderstood .. my English is limited !!!
I do not know how to point your post ..
you wrote:
"It so happens That the total area of the three sound holes is Within 7% of the area of the large sound hole single taken from the oud sound board geometry".

topic - Old Oud - New Project
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[*] posted on 10-23-2014 at 04:24 AM


OK found it!

http://www.mikeouds.com/messageboard/viewthread.php?tid=8488&pa...

This concerns the sound board of a reconstruction of the 14th C 'Urmawi' oud drawing.
I was just making an observation - for the record - that the total area of the three sound holes was within 7% of the alternative single sound hole area based upon the mid 15th C Arnault de Zwolle lute geometry.
I did not draw any conclusions from this observation (or say that the area of the sound holes was within 7% of the total sound board area according to your previous post).

You will find more information about the relationship between sound hole diameter, bowl air volume and bowl geometry etc. here (Helmhotz air resonance)

http://www.mikeouds.com/messageboard/viewthread.php?tid=14874

So far my experimental results in this field of research only apply to single sound hole arrangements. The next step (time permitting) will be to test triple sound hole arrangements - found on surviving old ouds - using an acoustic chamber. The MIT research paper referenced in this topic makes geometrical generalisations about oud and lute triple sound holes that do not seem to correspond to any old lutes or ouds that I have examined to date.

Note also that the Urmawi oud geometry - as drawn - has a two sound hole arrangement that you will not find on any surviving oud that I know about.
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[*] posted on 10-23-2014 at 05:33 AM


thanks so much Jdowning
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[*] posted on 11-7-2014 at 01:03 AM


help !!
Samir ... Jdowning ... Fritz ... I need you!
I cut the ribs of rosewood and I started folding step.
I have let the ribs to the thickness of 3 mm. and I think this is a mistake!
maybe I have to take them to 2.2 / 2.3 mm.?
I have folded the first 4 ribs with about 20 minuts heating in boiling water and I bent with a hot iron with the utmost care, but:
1- the ribs are bent in an uneven manner in the sense that some points, being harder then other, left the portion with transverse deformations!
2 - two of them broke again in the same exact spot ..
I am attaching a few pictures of the tragic work done by me!
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[*] posted on 11-7-2014 at 01:04 AM


this is the bending system ..
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[*] posted on 11-7-2014 at 01:06 AM


the ribs before to bend..

[file]33172[/file]
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[*] posted on 11-7-2014 at 01:14 AM


the ribs at the point of rupture. is the same for both. obviously there is a weak point along the rib. you think it is possible?
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[*] posted on 11-7-2014 at 01:21 AM


see the rib .. is not uniform. I definitely do not bend well, but any advice would be greatly appreciated!
thanks to all



[file]33182[/file]
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[*] posted on 11-7-2014 at 01:23 AM


Now the ribs are so ...
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[*] posted on 11-7-2014 at 03:19 AM


could be a solution?
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[*] posted on 11-7-2014 at 05:07 AM


Your bending iron is too small in diameter and is not hot enough. The small diameter results in line contact with the wood so that the heat is focussed in a narrow line rather than more widely distributed. It also results in high local stress in the wood at the point of contact.

My bending iron is made from 4 inch diameter thick walled copper tubing flattened in a vice to an oval section heated with a small propane torch. See here:

http://www.mikeouds.com/messageboard/viewthread.php?tid=6869&pa...

The bending iron should be heated so that it will almost scorch the wood. Test the temperature with a drop of water which should immediately turn to steam. Then you should have little problem in bending the ribs even when 3mm thick. No need to soak the rib in hot water just a wipe with a damp cloth will do.
Also the crooked grain of your ribs may cause problems in bending (e.g. twisting irregularly to one side).
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[*] posted on 11-7-2014 at 05:30 AM


you can also bend the ribs with the heat gun only, just put it in a vise and point it up.



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[*] posted on 11-7-2014 at 09:00 AM


thank you all.
immediately try to seek a copper pipe of that size.
it seems easier than using only the heat gun.
I will update you.
thanks
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[*] posted on 11-7-2014 at 09:02 AM



Quote:

Also the crooked grain of your ribs may cause problems in bending (e.g. twisting irregularly to one side).

in these cases, how can you do?
Use a press or put in shape like I did is good for something?
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[*] posted on 11-7-2014 at 09:09 AM



Quote:

My bending iron is made from 4 inch diameter thick walled copper tubing flattened in a vice to an oval section heated with a small propane torch

the copper pipe must have a minimum thickness or can also use those of 1 mm. thick?
those of 1 mm. I find them easily!
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[*] posted on 11-7-2014 at 12:51 PM


The pipe must have sufficient heat retaining capacity to maintain the required temperature (as well as being rigid enough not to flex or bend). 1mm wall thickness pipe may not provide the required level of heat control (?) but you could always make a 'heavier' bending iron from two (or three) pipes of 1 mm wall thickness. Just make a longitudinal cut in one pipe and slide it over the other for a reasonably tight fit. The two pipes would be held together when bolted to an iron bracket necessary for supporting the iron and mounting the propane torch. I have not tried it but it should work.
For information I will post some detailed images of my bending iron to show the mounting bracket.

I always use straight (longitudinal) grained wood for ribs but any localised unevenness across the width of a rib can be 'ironed out' by working the rib at an angle to the axis of the bending iron. With a bending iron you can have quite precise control.

My very first bending iron (made way back in 1963) was fabricated from a sheet of 1.5 mm thick copper formed into a 'tunnel' and mounted with screws on to a slab of wood. Heat was provided by an element from a radiant heat electric fire. Not the best arrangement but it did the job. Others have used an aluminium tube with an electrical light bulb as an heating element.
A propane torch can give ample heat and is quickly adjusted to provide the correct temperature.

A heated mold for forming ribs is a method used by some luthiers (guitars and ouds) - best suited for mass production work I imagine.
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[*] posted on 11-8-2014 at 05:29 AM


Here for information are a couple of images of my bending iron should you decide to make one. The overall length of the copper tube is 17 cm (6.5 inches) including the rib fillet bending attachment, wall thickness 3 mm and it is bolted to an iron bracket that in turn is screwed to a wooden block so that the assembly may be held in a vice. The propane cylinder is clamped to a piece of angle iron with a standard cable 'U' clamp so that the flame position may be infinitely adjusted relative to the tube surface allowing a wide control of temperature. It works for me.

Regarding the boiling of ribs prior to bending the only reference I have found to this method is described in 1966 by Irvine Sloane in his book 'Classic Guitar Construction'. I am not sure if this is a method adopted by other guitar makers rather than the traditional hot bending iron (regardless of heat source). Sloane's method involves boiling the ribs until the wood is plastic (for about 1.5 hours) at which point the ribs are removed from the water and rapidly clamped to a mold before plasticity is lost as the wood chills. The ribs are left on the mold to dry for about a week. The success of this method according to Sloane is the use of straight grained, seasoned wood of uniform thickness free of 'figure' (such as flamed maple). The ribs when removed from the mold may be subject to 'spring back' requiring the ribs to be forcibly bent for a few days to correct this fault. Furthermore the boiling process removes natural residues from oily woods such as rosewood. Sloane considers this to be an advantage as it removes the oils that make rosewood otherwise difficult to glue but one has to wonder how boiling might adversely affect the wood structurally and/or acoustically.
So this would appear to be a guitar maker's method that is much more complicated and restrictive, for no good reason, than the traditional hot iron bending.

I have used a boiling water/mold method in conjunction with chemicals in my experiments to successfully form deeply fluted ribs - reported some time ago on this forum. The chemicals modify the structure of the wood (making open cell wood species more dense and harder which might be a good thing acoustically) and temporarily - together with heat from the water - soften the wood so that it is soft and plastic enough to be both deeply fluted in section and curved longitudinally.

[file]33190[/file] [file]33192[/file]
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[*] posted on 11-8-2014 at 12:17 PM


thanks Jdowning
you are very clear. use the lamp seems easier.

now I procure the copper pipe. as soon as I have everything, I try to do it.
remember that you are good with wood and even metal, but I am unable with wood and even metal !!
I see from the photos that the tube is open on both sides, so the flame of propane is not like a blowtorch, but type gas stove!
Thanks, as always, for your valuable advice.
will update you
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[*] posted on 11-8-2014 at 01:01 PM


The pipe is open at both ends.
The flame of the propane torch is more like a blow torch as you can see.
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[*] posted on 11-8-2014 at 01:13 PM


but then put in so that the flame goes on the inner surface of the cylindrical tube? otherwise the heat comes out the other side.
I got it right?
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[*] posted on 11-8-2014 at 01:19 PM


how do you make the temperature of the tube uniform? turn the tube? or heat goes alone in the remaining part of the tube?
maybe it needs to be hot only on the top?
Thanks.
I'd be lost without you!
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[*] posted on 11-8-2014 at 01:49 PM


Quote: Originally posted by faggiuols  
here the block instead of the tail finished.
wood is cedrela also



Hi faggiuols

Cedrela ist a very good wood for the blocks ! Very light in weight, and almost uneffectable by changes of humidity.





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[*] posted on 11-8-2014 at 01:53 PM


Quote: Originally posted by faggiuols  
see the rib .. is not uniform. I definitely do not bend well, but any advice would be greatly appreciated!
thanks to all





Hey

Sometimes its a change of the direction of the grain what creates some probs bending the rib in the right curve. So you have to adapt the stress to the rib on the grain and the abilitư of the wood to be bent. The wood "says" if it will bend more wet or dry, more in a bigger area or in small steps...

It´s a dialog between you and the wood...

Try to understand the reactions of the wood... use different wood as testwoods. Use swap wood to see how it will be bent.

Fritz




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