Working with wood plasticisers to bend top and back.


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Has anyone here on maestronet experience with softening wood to bend it? 

in principle alkaline solutions seem to function as plasticisers. In some scientific papers I found NaOH and KOH used for bending wood Otherwise ammonia seems to work. I heard as well from a violin maker that some makers in Cremona put their wood into dung or stable manure. 

However, what time is needed and how thick are the plates to make an arch bending possible?

Any input on this is appreciated. 

 

 

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You might want to consider using steam bending instead.  Rockler sells a steam generator kit for bending wood which has gotten good reviews.

Thea various plate mode frequencies (m1, 2, 5 etc.) increase with increasing arch height.  But I expect that the rate of increase would be greater for bent plates than carved ones because the wood grain isn't cut.  So if you want similar mode frequencies the arch height for bent plates doesn't have to be as high which makes the bending easier to do.

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When NaOH (or KOH) are added to wood, it dissolves the lignin, and hemi-celluloses. That's how they make paper. So, it you want to turn your wood into paper pulp, that's the way to do it.

Ammonia will work, but it has to be high pressure, anhydrous ammonia gas, in a pressure tank. If you're set up to work with high pressure ammonia gas, and can deal with the toxic gas released when you open the tank, go for it. Household ammonia solutions won't work.

You can try putting you plates in manure for a month or two, but you might have trouble selling those instruments.

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54 minutes ago, FiddleDoug said:

When NaOH (or KOH) are added to wood, it dissolves the lignin, and hemi-celluloses. That's how they make paper. So, it you want to turn your wood into paper pulp, that's the way to do it.

Ammonia will work, but it has to be high pressure, anhydrous ammonia gas, in a pressure tank. If you're set up to work with high pressure ammonia gas, and can deal with the toxic gas released when you open the tank, go for it. Household ammonia solutions won't work.

You can try putting you plates in manure for a month or two, but you might have trouble selling those instruments.

Doesn't ammonia have the same effect of dissolving lignin as KOH and NaOH? I think so, but I'm not a chemist.

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On January 2, 2021 at 11:05 PM, Marty Kasprzyk said:

So if you want similar mode frequencies the arch height for bent plates doesn't have to be as high which makes the bending easier to do.

I am not looking at tap tones so much any more. I made a fiddle with rather dull and low tap tones which works amazingly well. 

Did you do plate bending?

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On January 2, 2021 at 11:06 PM, FiddleDoug said:

When NaOH (or KOH) are added to wood, it dissolves the lignin, and hemi-celluloses. That's how they make paper. So, it you want to turn your wood into paper pulp, that's the way to do it.

Ammonia will work, but it has to be high pressure, anhydrous ammonia gas, in a pressure tank. If you're set up to work with high pressure ammonia gas, and can deal with the toxic gas released when you open the tank, go for it. Household ammonia solutions won't work.

You can try putting you plates in manure for a month or two, but you might have trouble selling those instruments.

For any alkaline solution much depends to my understanding on the concentration of the solution. I think for making paper pulp it is something really aggressive which of course I wouldn't consider to use.

Then I found a YouTube where someone is bending hardwood sticks which were soaked in ammonia solution. Just for the stink I wouldn't use it anyway. 

I would be very curious to hear one of those 'manure soaked plates violins'. Apparently the bad odors disappear after a while.

But last not least, I am not a chemist, couldn't potash solution work as well?

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On January 3, 2021 at 1:55 AM, JacksonMaberry said:

Helen Michetschlager has a paper on her website describing a method for steam bending plates. Worth a look.

 

I know her procedures. You might remember that I developed from there my own system of bending plates in the super light violin project. Didn't work at that time, because the top wood cracked in rather unexpected directions. But I have to say that this was most likely due to heating with a microwave rather than boiling in a large pot. 

The thing I don't like about Mitchetschlagers method is that you need to glue pieces to for the platforms for top and bottom blocks. Her method seems to be inspired by brescian type of archings which I am currently not interested in. 

 

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On January 3, 2021 at 12:26 AM, Jim Bress said:

Andreas, Check out Evan Smith’s bench. He shows some of his bending process on pg 2 and 3. I didn’t reread it, so not sure how relevant it is to your question. 

 

Again @Evan Smith the great experimenter. 

I had a look and his procedures are very interesting. The problem is that I can't install such big equipment in my shop. But it gives ideas what and how to do the bending without creating cracks.

thanks for forwarding the link, Jim.

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24 minutes ago, Andreas Preuss said:

I am not looking at tap tones so much any more. I made a fiddle with rather dull and low tap tones which works amazingly well. 

Did you do plate bending?

I use flat plates that are about 3.5mm thick for my violas.  The plate halves are glued along their center joint with Gorilla polyurethane glue which is unaffected by moisture or warm temperatures.

The joined plates are clamped in a fixture along their outline edge and screw device is used to bend the plate downward about 5mm at the bridge location.  The plate is then wetted with a paper towel.  A heat lamp is used to heat the plate overnight to dry it.  After the plate is removed from the fixture it has about 3mm permanent arch bend.

 A viola's note pitch range is lower than a violin's so I suspect that a viola's plate's should have frequency low tap tones.  Collin Gough's finite element studies have shown that the various plate mode frequencies increase with increasing arch height which suggests that a shallow arch height might be helpful for making small violas sound more like large ones.

About ten years ago I had made a plot of old violin top plate arch heights vs. the year they were built which included the Stainers, Amati's, Strads, dGs, and I saw a gradual downward trend in arch heights.  I projected this downward slope for another 300 years and concluded that by now the plates of new violins should be close to being flat.

 

 

 

 

 

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The late William Fulton used to do something similar to Michetschlager but heated the wood by immersion in water.  Sadly the full description of the process that used to be in the MIMF seems to be gone, so I can't remind myself of the details.  I don't think he glued in wood for platforms, but I can't swear that he ended up with normal platforms either.

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3 hours ago, Andreas Preuss said:

I know her procedures. You might remember that I developed from there my own system of bending plates in the super light violin project. Didn't work at that time, because the top wood cracked in rather unexpected directions. But I have to say that this was most likely due to heating with a microwave rather than boiling in a large pot. 

The thing I don't like about Mitchetschlagers method is that you need to glue pieces to for the platforms for top and bottom blocks. Her method seems to be inspired by brescian type of archings which I am currently not interested in. 

 

Apologies, Andreas. I do remember this discussion from your previous thread. It all begins to run together a bit. 

What is your interest in recreating (I assume) a Cremonese arching with bent plates? It is hard to imagine how the arching of a carved system can be relevant to a formed system, given the radical differences. 

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2 hours ago, Andres Sender said:

The late William Fulton used to do something similar to Michetschlager but heated the wood by immersion in water.  Sadly the full description of the process that used to be in the MIMF seems to be gone, so I can't remind myself of the details.  I don't think he glued in wood for platforms, but I can't swear that he ended up with normal platforms either.

His method is described in an earlier VSA publication...Vol 11-2

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1 hour ago, JacksonMaberry said:

Apologies, Andreas. I do remember this discussion from your previous thread. It all begins to run together a bit. 

What is your interest in recreating (I assume) a Cremonese arching with bent plates? It is hard to imagine how the arching of a carved system can be relevant to a formed system, given the radical differences. 

I am looking on violin making more and more like wood technology in every single aspect. 

At the same time I am moving away from the idea that the 'Cremonese concept' is the only solution to make a high performance use instrument. 

In those terms I might end up with a completely different arching from Cremonese which works acoustically. And o am not afraid of failure, it just belongs to the creative process.

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11 minutes ago, catnip said:

His method is described in an earlier VSA publication...Vol 11-2

Somehow I remember his wedging method. He left the plates before bending pretty thick, which makes it a bit like working with brute force. I admire though his pioneer spirit trying out something unorthodox.

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4 hours ago, Marty Kasprzyk said:

I use flat plates that are about 3.5mm thick for my violas.  The plate halves are glued along their center joint with Gorilla polyurethane glue which is unaffected by moisture or warm temperatures.

The joined plates are clamped in a fixture along their outline edge and screw device is used to bend the plate downward about 5mm at the bridge location.  The plate is then wetted with a paper towel.  A heat lamp is used to heat the plate overnight to dry it.  After the plate is removed from the fixture it has about 3mm permanent arch bend.

 A viola's note pitch range is lower than a violin's so I suspect that a viola's plate's should have frequency low tap tones.  Collin Gough's finite element studies have shown that the various plate mode frequencies increase with increasing arch height which suggests that a shallow arch height might be helpful for making small violas sound more like large ones.

About ten years ago I had made a plot of old violin top plate arch heights vs. the year they were built which included the Stainers, Amati's, Strads, dGs, and I saw a gradual downward trend in arch heights.  I projected this downward slope for another 300 years and concluded that by now the plates of new violins should be close to being flat.

 

 

 

 

 

But, are you using spruce for the top?

The calculation of the arch height by collecting numbers from different makers from different schools and concluding from there that we would need today go to almost zero is... ??

With the same calculation  the center width of violins would be theoretically probably 130mm or more?

In the end there are infinite number of ideas how to form an arching. Long time I used a partial bent approach 

 

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29 minutes ago, Advocatus Diaboli said:

Andreas, have you tried vacuum forming arches?  

No.

Must be similar to the method making plaster casts using a vacuum cleaner to suck out the air under the clear film protection sheet? 

Must be like putting the flat plates on the negative cast make it air tight and vacuum it into the form, I guess?

I am more interested in the preparation steps, because I suppose you won't use dry wood with the vacuum method.

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