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Heat treated bridges


magicfingers
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Any ideas on the treatment of bridges by heating them?? I'm talking cheap bridges like the Auberts 1 star or 3 stars..Anyone ever do this?? How long?? What tempature?? In an oven?? On a hot plate in a skillet??(Maybe throw in some bacon for a BLT) I'm gonna mess around with this idea a little.. Thought maybe some of you guys might have some suggestions...Regards, Lonnie...

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I always use microwave cocking oven in kitchen to heat bridges and bassbar. 1 min. or so, in 600w dial. then they become a little harder and weight down.


I’m wondering what is the idea behind it? If the goal is to loose weight for what reason? A lighter bridge (reduced in mass) may become more harsh and too clear. Remember that a bridge acts like a filter reducing unwanted frequencies. That’s also the reason that a bridge should be tuned and adapted for its instrument where it will be placed on.

The wood cells may be damaged and collapse by such a heat treatment resulting in closed vessels unable to react on waves. Besides that, it sounds a little of what Vuillaume did with his excellent violins: baking to create a certain colour but damaging the good work.

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Lonnie,

if this would be true than the harder the bridge material the better the violin sounds? I'm thinking to place an ebony bridge but never have seen that on a violin (or other string instrument). This may explain that there is an other phenomenon in the game. Somewhere I read that bridges are selected by violinmakers on their 'Eigenfrequency' which means that one drops them on a table from about 30 cm and the one sounding most clear and bright is the one that should be selected. Also a good bridge should have a pitch of about 3 kHz. Maybe that the lowest quality Aubert bridge is so soft that 3kHz is not possible?

Is there anyone who has an explanation for the fact that baked bridges (micro wave) seem to make violins better sound?

Regards,

Frits

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There are other string instruments that have a solid ebony bridge; mandolins and archtop guitars are two that come to mind...I don't think solid ebony would work for violins though, because they would be "too" hard...There is a process for hardening bridges (the higher priced ones) but I'm at a loss as to what the process is..Whether it be a heat process or chemcial process (or both) I don't know; but would like to!!!!Regards, Lonnie...

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As far as I understand it, the main if not only purpose of heat treating a bridge is to remove moisture from it, thereby making it harder or more resonant. Some luthiers do this with sound post wood also and bass bar wood, as has been mentioned.

I never tried it, so I don't know - but couldn't moisture just as easily return to the wood from humidity in the air? Does damage done to the cells by the heat make the wood less receptive to moisture?

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At ambient temperature there will be an equilibrium between the moisture content -which is about 6% - in the wood cells of the bridge and the environment. An equilibrium means that the effective water content remains the same at the same temperature. Suppose that heating the bridge by micro wave removes all the moisture from the inside and exterior of the bridge. After this process is done and the bridge is taken out of the oven a new equilibrium will be set: after a while the same amount (at ambient temperature) of moisture will penetrate into the wood. Unless there is something damaged which prevents the absorption of moisture into the cells. If this is the case than a sealer might also do the job but without damaging the cell structure. Is it therefor that some luthiers give their bridge a coat of linseed oil?

Regards,

Frits

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Quote:

I always use microwave cocking oven in kitchen to heat bridges and bassbar. 1 min. or so, in 600w dial. then they become a little harder and weight down.


I suggest avoiding the temptation of drying a bridge using microwaves. It's destructive to the cells and typically targets the inside center of the bridge first - creating the most damage there where it may not be seen - rather than the entire bridge evenly as may be assumed.

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Hi Tim, I was hoping maybe this would get your attention.. Are you implying that heat treating is a method for harding?? Just don't do it in a microwave oven??? Do you treat the bridges that you make in any way?? Either by heat or a chemcial process??? If it is a trade secret I understand why you would not want to disclose that info..Regards, Lonnie..

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Hello Lonnie,

I heat treat all of my bridges. Even my inexpensive conventional style ones ($5 and under) like this one:

conv_E.jpg

that I make from wood that isn't quite the quality that I'd use for my asymmetric bridges. I use a slow and controlled process - never a microwave. I use chemical treatment on some. I've experimented with many, many, kinds of treatments (heat and chemical) to the wood and then have cut them open, sliced them up, and had a closer look under magnification.

That's all I'm going to say about this for now.

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Okay, one more reply about this.

I treat with heat before they are cut and then bag them up with desiccant until I do the final cutting. Then it's back in the bag with dessicant. They are also shipped bagged in dessicant with the recommendation that they be returned to the dessicant for a while after carving, followed by a coat of something to seal from moisture. Here is a bag of some of the kind of wood used to cut the type of bridge blank shown above.

conv_E_bagged.jpg

and after cutting

conv_E_bagged2.jpg

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Thanks Tim for the tid-bit of info...I'm gonna try my hand at it... I am going to use a hot plate with a heavy piece of steel plate placed on it at a controlled temp. I don't know yet what I will try for a chemical treatment... Any body got any suggestions as to what to use??? Regards, Lonnie....

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Does anybody know if the more expensive (or most expensive) Aubert bridges are also heat treated? And sealed? Maybe this is a 'secret' process normally in use at the suppliers?

In my opinion good quality bridges selected from the best woods don't need to be treated. Just be adapted and tuned to fit for the instrument. That's also what the article in teh Strad (August) by Erik Jansson says.

Thanks,

Frits

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Quote:

Thanks Tim for the tid-bit of info...I'm gonna try my hand at it... I am going to use a hot plate with a heavy piece of steel plate placed on it at a controlled temp.....


You're welcome, good luck, and thanks for being just as considerate as you have been when we've interracted in the past.

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Quote:

There are other string instruments that have a solid ebony bridge; mandolins and archtop guitars are two that come to mind...I don't think solid ebony would work for violins though, because they would be "too" hard......


The fact that mandolins, guitars and that kind of instruments have harder bridges is due to the lower angle between bridge and strings: almost zero. For violins this angle is about 157° (cellos even higher) and the result of this is a much higher vertical pressure on the table of the soundboard: about 55 kg in total for violin. The soundpost helps to withstand this pressure in cooperation with the bass bar and the arching of the table. For instance a banjo or mandolin have flat tables. A higher angle between strings and bridge would damage the soundboard (sometimes a drum). That's the reason why harder bridge material is used in these cases to transfer frequencies easier at a lack of pressure.

Frits

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Heat treated bridges are more dimensionally stable ( read this ), which can be a big deal, especially for cellos, and heating offers one more tonal adjustment option--something that's always handy to have. I don't believe "hardening", as we normally think of it, is a result of this type of heating, unless you convert the bridge to carbon, which I have (accidentally) done. I do mine on a 1/4" plate of aluminum on a hotplate, but a cast-iron skillet would work. Heat until the color changes.

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