#3 and #4

[Don Noon]

Just starting the next build, this time two at once. I'm not that good about taking tons of great in-process photos, but I'll try to post something here every week or two as I go along.

I haven't settled on the scroll or F-hole design yet, but the body design was done, and I wanted to get into the shop again and make stuff. 2 identical molds are almost done (just need to cut some clamping holes). I'm going to try a collapsable mold this time; I like the idea of being able to glue on a plate while still using the mold to hold the shape.

The wood in the photo is not thermally processed yet, but that will happen soon. This time I'll try to track the change in properties at the billet stage. I'm hopeful that the new equipement and modified processing will give better results than the last one (which I still thought was very good).

Tonally, I'm thinking of aiming for midway between my first two... some of the comfortable tone of my first one, and the power of the second one. That goal may change slightly, when and if I can get input from a good violinist or two.

Hopefully I can get this set done before Darnton's workshop in June.

[Oded Kishony]

I'm going to try a collapsable mold this time; I like the idea of being able to glue on a plate while still using the mold to hold the shape.

Certainly don't need a collapsible form in order to accomplish the above.

~OK

[Don Noon]

OK - a little addition: I want to get all the linings glued on, and then glue on a plate, and then remove the form. I could see gluing on a plate before putting on the linings of the opposite side, but that's not what I want to do. Can a rigid form be taken out from a fully lined garland with one plate also glued on?

Anyway, if it turns out I don't need the collapsability feature, I could just epoxy all the form pieces together . 'Tweren't a big deal to screw on some plates and cut the form up a bit to give it a try.

[catnip]

OK - a little addition: I want to get all the linings glued on, and then glue on a plate, and then remove the form. I could see gluing on a plate before putting on the linings of the opposite side, but that's not what I want to do. Can a rigid form be taken out from a fully lined garland with one plate also glued on?

One thing should be aware of in your collapsible mold design is clamping space so that you can use normal size clamps for the C bouts and at the corners. I know that some makers just clamp the caul to the corner blocks but that might "pop" your corner block off, since it is tricky to clamp to both sides of the block at the same time.

As Oded said you don't need a collapsible mold to do what you want to. You will still have to remove the mold in order to trim and taper your linings cleanly. The advantage on the collapsible mold is that you can remove the garland in order to do preliminary analysis as to weight etc. I try to get the garland with trimmed blocks to about 55 gm. Then you can re-insert the garland back on the mold for safe keep and stability until you are ready to glue the back plate.

I like your idea of building two at a time. Is that local red maple that you are using for your backs?

[DarylG]

Is that local red maple that you are using for your backs?

Looks like Big Leaf.

[Don Noon]

It's big leaf, about 25 years old for sure... that's how long I've had it.

One thing should be aware of in your collapsible mold design is clamping space so that you can use normal size clamps for the C bouts and at the corners. I know that some makers just clamp the caul to the corner blocks but that might "pop" your corner block off, since it is tricky to clamp to both sides of the block at the same time.

I haven't cut the clamp reliefs yet, but there is plenty of space. With the corner blocks jammed in a corner of the form, I'm not too worried about the clamping forces popping the corner block off. The C-bout clamping should be extremely safe, but maybe I'll have to be a little more careful with the other side of the corner block.

[catnip]

I haven't cut the clamp reliefs yet, but there is plenty of space. With the corner blocks jammed in a corner of the form, I'm not too worried about the clamping forces popping the corner block off. The C-bout clamping should be extremely safe, but maybe I'll have to be a little more careful with the other side of the corner block.

Here is a picture of a minimalist form ... just two holes for clamping the C-ribs ... all other sides are clamped using little G-clamps and the blocks themselves. The other little holes are for the classic method of using small dowels and string to tie the cauls to the form which seem to have been replaced the the G-clamp method.

[Don Noon]

The first top set is out of the chamber, and the results are very encouraging. I realize that the wood has 0% moisture content immediately after my processing, and that gradual adsorbtion of moisture from the air will undoubtedly make for less impressive results, but still...

Density decreased ~16%

Modulus decreased ~12%

C increased ~2%

Radiation ratio increased ~20%

Q (inverse damping) increased ~47%

These are quite huge changes in the radiation ratio and damping, especially considering that these are along the grain, and crossgrain changes are usually a lot more significant. I do not have an absolute value for the radiation ratio yet, but if I assume the original RR was 15 (a conservative value for this Simeon Chambers Engelmann), the processed RR would be 18... significantly higher than the maximum 16.7 that Curtin estimated for the Booth Strad in his tap tone article.

The damping is even more radical, originally a "normal" Q of 146, processed Q of 215. It rings forever.

Another couple of things I am pleased with: it doesn't smell like burnt wood, and there is much less surface darkening than the last time.

Again, I'm sure the properties will moderate somewhat as moisture is adsorbed, but I'm also quite sure that it won't completely erase the changes. I look forward to the day when this instrument is completed, so I can see what effect these properties have on the sound. If the properties hold up, the sound should be extremely "something". Loud, for sure, based on high RR and low damping.

[Anders Buen]

The first top set is out of the chamber, and the results are very encouraging. I realize that the wood has 0% moisture content immediately after my processing, and that gradual adsorbtion of moisture from the air will undoubtedly make for less impressive results, but still...

Density decreased ~16%

Modulus decreased ~12%

C increased ~2%

Radiation ratio increased ~20%

Q (inverse damping) increased ~47%

These are quite huge changes in the radiation ratio and damping, especially considering that these are along the grain, and crossgrain changes are usually a lot more significant. I do not have an absolute value for the radiation ratio yet, but if I assume the original RR was 15 (a conservative value for this Simeon Chambers Engelmann), the processed RR would be 18... significantly higher than the maximum 16.7 that Curtin estimated for the Booth Strad in his tap tone article.

The damping is even more radical, originally a "normal" Q of 146, processed Q of 215. It rings forever.

Another couple of things I am pleased with: it doesn't smell like burnt wood, and there is much less surface darkening than the last time.

Again, I'm sure the properties will moderate somewhat as moisture is adsorbed, but I'm also quite sure that it won't completely erase the changes. I look forward to the day when this instrument is completed, so I can see what effect these properties have on the sound. If the properties hold up, the sound should be extremely "something". Loud, for sure, based on high RR and low damping.

What do you think about the possible damping effects of the moisture content? At least I have the impression that in high MC wood the damping is higher, wider resonances and shorter ring in wood blanks. A higher density piece wil contain more water than a low density one. So that would be an opposite effect of your finding that low density give more damping..

Hmm.

[Don Noon]

Anders,

Yes, I agree that higher density wood will likely have more water (per unit volume) than lower density wood. It is not clear, however, that the EMC (Eqilibrium Moisture Content) expressed in percent will be any different. It might also be possible that lower density wood has more space in it to hold more water on a percentage basis, which could lead to higher damping.

While I'm here, I also have some interesting "rustle testing" results on the billet. This is held and close-miked near the center of the billet, while a piece of sandpaper is rubbed across a far edge... a (hopefully) more quantitative way to judge billet response the way Sam Z. reported he judges them.

I recorded the spectrum of this test before and after thermal processing, and took the difference (the two halves of the billet were taken individually):

The sound output is higher almost everywhere, and especially above 1000 Hz. Although the overall level is highly operator-dependent, I have reason to believe that the overall level IS actually much higher in the processed wood, and the levels above 1000 Hz are DEFINITELY stronger. Again, it remains to be seen how much of this change remains as water is adsorbed, but most reports show that processed wood has a much lower EMC than unprocessed wood.

[jezzupe]

Anders,

Yes, I agree that higher density wood will likely have more water (per unit volume) than lower density wood. It is not clear, however, that the EMC (Eqilibrium Moisture Content) expressed in percent will be any different. It might also be possible that lower density wood has more space in it to hold more water on a percentage basis, which could lead to higher damping.

While I'm here, I also have some interesting "rustle testing" results on the billet. This is held and close-miked near the center of the billet, while a piece of sandpaper is rubbed across a far edge... a (hopefully) more quantitative way to judge billet response the way Sam Z. reported he judges them.

I recorded the spectrum of this test before and after thermal processing, and took the difference (the two halves of the billet were taken individually):

The sound output is higher almost everywhere, and especially above 1000 Hz. Although the overall level is highly operator-dependent, I have reason to believe that the overall level IS actually much higher in the processed wood, and the levels above 1000 Hz are DEFINITELY stronger. Again, it remains to be seen how much of this change remains as water is adsorbed, but most reports show that processed wood has a much lower EMC than unprocessed wood.

Well that is what I find as wel related to emc with my "Active microwave" process

[Don Noon]

Just a status update:

One set of spruce and one set of maple are processed. The (processed) spruce looks awfully dark in the photo, but I think it will be nice after carving and varnishing. For the maple I didn't go as hot and as long. It really accentiates the flame, so even if there was no acoustic benefit, I might want to do the processing just for the appearance.

The forms have been opened up for clamp clearance, and the blocks are all attached and rough trimmed.

Not as much progress as I had hoped, but other things have been taking my time this week.

[jezzupe]

Just a status update:

One set of spruce and one set of maple are processed. The (processed) spruce looks awfully dark in the photo, but I think it will be nice after carving and varnishing. For the maple I didn't go as hot and as long. It really accentiates the flame, so even if there was no acoustic benefit, I might want to do the processing just for the appearance.

The forms have been opened up for clamp clearance, and the blocks are all attached and rough trimmed.

Not as much progress as I had hoped, but other things have been taking my time this week.

Wow love the color, when you cut out your plates try posting a shot of the scrap, I'd like to see how deeply the coloration penatrates into the wood.

[Don Noon]

Wow love the color, when you cut out your plates try posting a shot of the scrap, I'd like to see how deeply the coloration penatrates into the wood.

You may have already seen it here. The color is all the way through, I think. There are some extra dark stains on the surface of the spruce, from some condensation in the chamber that dripped down. I fixed that when I did the maple.

[David Tseng]

Don, please excuse me for my ignorance in violin acoustics. What is "radiation ratio"? If Strad's RR is 16.7 and yours, 18, does that mean your wood is over-cooked (Strad wood is about 300 years old and your processed wood would be equivalent to 500 years old)? Who invented this term "radiation ratio"? Is it derived from first principle or, as usual in violin acoustics, some sort of wishywashy correlation parameter? If you could make RR to be 50, would the resulting violin act like an aaser (Acoustic Amplification of Stimulated Emission of Radiation) and the coherent concerto music would project several football field lengths. (Sorry, this is just my imagination induced by the word "RADIATION ratio").

[Michael_Molnar]

Radiation Ratio = the ratio of the speed of sound to the density of the wood.

This is essentially a measure of the stiffness per unit mass.

Here is the Curtin article that explains this.

Stay tuned.

[Don Noon]

"Radiation Ratio" I first heard from Curtin, although I had independently determined that the factor was the most reasonable figure of merit for thin vibrating wood. Mathematically, it is the speed of sound divided by the density. In practical terms, it means that if you have a certain size plate, and you want a certain set of mode frequencies, a higher radiation ratio will allow you to end up with a lighter weight, which translates to less energy needed to vibrate it (ignoring damping, for the moment), and more sound output.

Balsa has and extremely high radiation ratio, and Doug's balsa fiddles do put out a huge amount of sound.

My initial RR of 18 for my cooked wood was at 0% moisture; it has been slowly absorbing moisture, and the RR is declining as expected. It's down to 17 now, I think. I wouldn't worry about having a higher ratio than a Strad, but I'd be really leery of wood that was way lower.

[David Tseng]

Thanks, Michael and Don for explaining the radiation ratio. The idea fits quite well to what I am doing: I select lighter wood and I strengthen the spruce without significantly increasing the density. I don't have a Lucchi meter and am too lazy to make wood strip test, therefore I have no idea what is the value of RR for the wood I use.

[jezzupe]

Thanks for the pics Don, I missed those...

To me its not even a qeustion that proper heat treatment of wood improves its sound qaulities.

Regardless of your veiw on my proceedure of properly microwave cooking wood, this thermal treatment if done right, creates a low heat high humidity envioronment{due to moisture evaporation in the microwave} that in my ears creates a difinitive before and after result.

That does not take any burden off of the builder to exicute a properly balanced instrument, yet may provide a superior raw material to start with. imo

[Don Noon]

Today's pile:

As usual, it doesn't seem like I got much time put into it, but at least some progress managed to happen.

All the wood is now processed. I had hoped I wouldn't have to cook the neck and sides, but they were just too pale compared to the backs. I was worried that the ribs might be too brittle to bend well (turned out that way), so I pre-bent them before processing. They unbent quite a bit in the process, but at least it was partway there. The neck blocks were flat and square a few days ago; they aren't now. At least it's better to warp now than later. I hope they won't be undersize when I get them squared up again.

All the plates are planed and ready for joining (I'm really glad I spent the effort getting the jointer rebuilt!). I'm looking forward to all the gluing this week (I hope).

I also made a whiz-bang C-bout clamping thingie with dual wedgie action so I can get the C-ribs clamped in place really well with one clamp. Yeah I know there are simpler ways to do it, but that's not as cool.

I sliced off a couple of bass bars from the wider top plates, so I was able to get a more accurate reading on the material properties. Looks like the density is .31, radiation ratio a bit over 16. Violins #1 and #2 had RR's of 15 and 15.3 respectively, so I'm looking forward to getting even more power with this set. The density is getting quite low, and will likely want to be a bit thicker in the graduations.

Not in the photo: great stacks of ribs... as long as the bandsaw was set up for the job, I kept cutting.

[Michael_Molnar]

This wood looks nice. Care to share what you did differently?

Mike

[Don Noon]

I now have a good Welch vacuum pump as opposed to the Gast rotary vane previously, so I can get all the air out of the chamber. Surface darkening is now not a problem, which I think was due to some remaining oxygen before.

Second change: more careful in getting closer closer to the "Plato" process... although I do intentionally deviate somewhat from it. I think my modifications helped get rid of the strong "burnt wood" smell, which was rather unpleasant in my last fiddle. These sets have no odor at all.

[JohnCockburn]

Radiation Ratio = the ratio of the speed of sound to the density of the wood.

This is essentially a measure of the stiffness per unit mass.

Here is the Curtin article that explains this.

Stay tuned.

Michael, your link doesn't seem to work. At least not for me.

[Michael_Molnar]

John,

Here is the link

http://www.platetuning.org/Tap_Routine_-_J..._article_06.pdf

For some strange reason, I cannot edit my old posts. Computers are wonderful when they work. Otherwise they are hell.

Mike

[Michael_Molnar]

I discovered that the FULL EDITOR does not work for me. The QUICK EDITOR works, however.

Go figure.