Gouge size question

[MikeC]

I just acquired a gouge and stamped on the handle is 5/13 I thought that meant that the curvature is that of a circle 13mm in diameter.  But it seems to fit more of a 18mm circle.  Am I misunderstanding the markings or is it marked wrong?  

[Michael_Molnar]

The 13 should mean it is 13 mm wide. The 5 is a curvature . I printed a circle template and measure all my gouges against that. Then I stamp that radius on the handle.

[MikeC]

Thanks,   I was just now googling and found that.  So the 5 indicates the amount of curvature and the 13 is the width.    I'm working on the channel fluting and wasn't happy with the selection of gouges that I have.  

[Michael_Molnar]

Here is a photo of my gouge set showing the radius stamped at the end.

[MikeC]

I have some swiss made gouges like that but they only have a number stamped on the blade, nothing on the handle.   I could measure the width but not sure how to determine the sweep.  Not that the numbers matter that much I just use whichever seems best for the task.   When I ordered this one I didn't understand the numbers so it's a little shallower than I expected.  I'll find some use for it though.  

[Wood Butcher]

47 minutes ago, MikeC said:

Thanks,   I was just now googling and found that.  So the 5 indicates the amount of curvature and the 13 is the width.    I'm working on the channel fluting and wasn't happy with the selection of gouges that I have.  

A number 5 is a bit too flat for the fluting, although personal taste can vary.

[MikeC]

agreed. When this one arrived I thought that's too flat.  The one I already had is a little too deep.  I have a few others as well but none quite what I was wanting for this.   I was watching Davide Sora's videos and he was using a #6 / 13  for the outer bouts.  

[Davide Sora]

15 hours ago, MikeC said:

agreed. When this one arrived I thought that's too flat.  The one I already had is a little too deep.  I have a few others as well but none quite what I was wanting for this.   I was watching Davide Sora's videos and he was using a #6 / 13  for the outer bouts.  

Hi Mike,

thanks for watching my videos.

For the channel in upper and lower bouts I use a n6, 13.7 mm wide and 13 mm radius for the back, and a n7, 14.5 mm wide and 11 mm radius for the belly. The width is not mandatory (I used the ones I had) as long as it is wider than the width of the channel. The extreme accuracy of the radius is also not critical, close enough is fine as long as it's not too flat. In the most recent video I made for the top plate channel (second link below), it is shown more clearly what the gouge measurements refer to.

https://youtu.be/5O5wpNYJstk?t=139

https://youtu.be/Kb_Cs7ym-5k?t=61

To measure the radius I use two systems: draw the circle and overlap the gouge (less accurate but that's okay), or imprint the gouge profile on wood and overlap the circle drawn on transparent plastic (more accurate if you like).

 

[MikeC]

Hi Davide thank you for your reply.  I don't have the plastic guide so I have to draw a circle on paper to judge the curve of my gouges.  I'll use the gouge that I have.  It may be a little bit flat but it's close being a no.5  13  

I've watched all your videos more than once!     

[Lafont]

Dear Davide,

Why do you use different radii for back and belly? Style/Aesthetic? Or functional decision? Also do you use different radii for strad and del gesu model?

Thank you very much, also for recent yt videos!

Christian 

[MikeC]

I was wondering about that also.  Why different for back and belly? 

[Michael_Molnar]

6 minutes ago, MikeC said:

I was wondering about that also.  Why different for back and belly? 

The two plates have different “architectures” or arch structures.

[avandesande]

2 minutes ago, Michael_Molnar said:

The two plates have different “architectures” or arch structures.

What would be the trend to match the arching?

[Davide Sora]

As Michael Molnar rightly says, different “architectures”. The arch of the top rises more suddenly than the back, so I prefer to keep a narrower channel radius. Of course, the inside of the channel will then be modified and a little enlarged to blend it with the arch, using a narrower radius is mainly a precaution not to get too deep inside from the start.

For Guarneri I use the same narrower radius gouge for the top and the back, but in this case to avoid having a too flat curve towards the outside, even if it is not my intention to copy the very narrow and deep channel seen on Del Gesù especially in the corners, I don't like it and acoustically it has no influence.

[MikeC]

Looking at CT scans there doesn't appear to be all that much difference.  If you overlay a scan of the top long arch and back long arch the difference is barely the thickness of the plates.  There is some difference in the area of the end blocks mostly.    I don't have my overlay picture available but here are some scans from Strad 3D.    

 

[Davide Sora]

1 hour ago, MikeC said:

Looking at CT scans there doesn't appear to be all that much difference.  If you overlay a scan of the top long arch and back long arch the difference is barely the thickness of the plates.  There is some difference in the area of the end blocks mostly.    I don't have my overlay picture available but here are some scans from Strad 3D.   

In fact it is rather difficult to understand how the original channel was before theblending with the arch, and even more so with the edges so worn. There is practically no trace of the original channel even in my violins, after finishing with the scraper. What I do is dictated by how the situation evolves starting from a channel with a narrower or wider radius to arrive at the finished archings I like, it is a personal thing based on how we proceed with subsequent work.

[Lafont]

Thank you

[Michael_Molnar]

23 hours ago, avandesande said:

What would be the trend to match the arching?

Davide offers good explanations. 

[David Burgess]

On 11/7/2020 at 10:01 AM, Michael_Molnar said:

The two plates have different “architectures” or arch structures.

I suspect that much of this in historical instruments is due to the early days of plaster molds. At one time, it was more common to remove plaster to correct irregularities, than add it, resulting in progressively fuller top archings. Adding plaster successfully is still rather difficult and time consuming, but now, there is much more emphasis on correcting the archings as much as possible, (including pulling down the high spots), prior to making the plaster cast. That's probably what is being done in the thread with a photo of Raphael Carrabba's restoration of the Strad cello.

 

[plasterercaster]

1 hour ago, David Burgess said:

I suspect that much of this in historical instruments is due to the early use of plaster molds. At one time, it was more common to remove plaster to correct irregularities, than add it, resulting in progressively fuller top archings. Adding plaster successfully is still rather difficult and time consuming, but now, there is much more emphasis on correcting the archings as much as possible, (including pulling down the high spots), prior to making the plaster cast. That's probably what is being done in the thread with a photo of Raphael Carrabba's restoration of the Strad cello.

 

 

One can see a difference in the arching shapes between front and back on many historical instruments which have never been anywhere near a plaster mold. Sacconi mentions "the specific functions of the back and of the belly, for which they are given different curvatures". 

 

[David Burgess]

2 hours ago, plasterercaster said:

One can see a difference in the arching shapes between front and back on many historical instruments which have never been anywhere near a plaster mold.

How do you know they have never been anywhere near a plaster mold? Much major work has either never been documented, or the documentation was never released to the public, including some work I have done. Many owners don't want anyone else to know about major work which has been done to their instruments.

You also need to consider the typical distortions from string tension. These can usually be figured out pretty well by using "thought experiments" if one is handy at that sort of thing, but one can also do an accelerated test by making precise templates of a violin top, putting the instrument under string tension, and exposing it to high humidity. Cycling repeatedly between high and medium humidity will make the distortion happen even faster, as will increased string tension or higher temperatures.

[MikeC]

David B.  When I look at back and belly plates,  not that I've seen any old Cremona up close in person,  but anyway they look remarkably similar.  I think the difference in shape could be due to string pressure rather than a difference in design.  What's your opinion?  

One thing I would like to do and probably on this build is make them as identical as I can and see what happens to the belly over some time.  See if it turns out looking like the usual flatter in the center and bulging slightly towards the end blocks.  

[plasterercaster]

1 hour ago, David Burgess said:

How do you know they have never been anywhere near a plaster mold? Much major work has either never been documented, or the documentation was never released to the public, including some work I have done. Many owners don't want anyone else to know about major work which has been done to their instruments.

You also need to consider the typical distortions from string tension. These can usually be figured out pretty well by using "thought experiments" if one is handy at that sort of thing, but one can also do an accelerated test by making precise templates of a violin top, putting the instrument under string tension, and exposing it to high humidity. Cycling repeatedly between high and medium humidity will make the distortion happen even faster, as will increased string tension or higher temperatures.

I have also done lots of major restoration work, and am well versed in client confidentiality.  

To change the arching of a front of average thickness by pressing it in a cast is actually quite difficult and a time consuming process. Getting it to stay in that that shape and not revert back to how it was before is also a challenge.

Yes, if there are lots of cracks and patches etc and the violin has been thinned out it's easier to change the shape, but still these changes in shape tend to be local to the area being worked on, not the arching as a whole. 

I was referring to historical instruments in good condition with few or no repairs and healthy thicknesses (there are still plenty around) that still display differences in arching shape between front and back. Why would they have been in a mold? Or rather why would they have been in mold long enough to change to whole arching, and for the arching to then stay in that changed shape?

I agree that string tension and humidity would play a part in changing the shape of the arching, but again many examples exist without heavy tension distortion.

[David Burgess]

13 hours ago, plasterercaster said:

1. To change the arching of a front of average thickness by pressing it in a cast is actually quite difficult and a time consuming process. Getting it to stay in that that shape and not revert back to how it was before is also a challenge.

2. I was referring to historical instruments in good condition with few or no repairs and healthy thicknesses (there are still plenty around) that still display differences in arching shape between front and back. Why would they have been in a mold?

1. Tops (even when they are very thick) can be bent quite a bit.

https://helenviolinmaker.com/wp-content/uploads/2017/04/Dartington-talk-transcript-with-pics.pdf

https://www.talkbass.com/threads/fulton-violin-plate-bending.281323/

2. To correct distortion due to sustained string load, combined with conditions of high humidity, temperature, or both. The ability to climate-control interior spaces is a relatively recent thing, and a lot of instrument owners still don't pay much attention to it, or make much of an effort. That's the main reason I've been trying to better educate people about this for several decades now. If relative humidity isn't allowed to go above 60%, distortion is greatly reduced.

[Wood Butcher]

2 minutes ago, David Burgess said:

1. Tops (even when they are very thick) can be bent quite a bit.

https://helenviolinmaker.com/wp-content/uploads/2017/04/Dartington-talk-transcript-with-pics.pdf

https://www.talkbass.com/threads/fulton-violin-plate-bending.281323/

2. To correct distortion due to sustained string load, combined with conditions of high humidity/temperature. The ability to climate-control interior spaces is a relatively recent thing, and a lot of instrument owners still don't pay much attention to it, or make much of an effort. That's the main reason I've been trying to better educate people about this for several decades now. If relative humidity isn't allowed to go above 60%, distortion is greatly reduced.

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