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The "kitchen paper" to which I refer is called generically "Scottex", from the name of the first company to market it here in Italy.

Is a very slightly abrasive absorbent paper made of cellulose fibers that gives a light shine to the wood without scratching the surface.

A coarse cotton or linen cloth do the job in a similar manner, but this paper is a little superior and more cheaper, even if less historically correct......

 

I'm curious to know if someone see some cremonese features in my arching in the video, please do not hesitate......

 

Davide

 

PS the real finished arching is in the video "Scraper working part four" : https://www.youtube.com/watch?v=UrBKKjSNtkE

 

I do!

 

The only thing I'd like to add is that the perfection of your work is surpassing Stradivari. So if you really like to get the "Cremonese" look you have to start be more careless :)

 

Thank you for your videos, I go back to them time after time

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............So if you really like to get the "Cremonese" look you have to start be more careless :)

 

 

Oh yes, I am aware of that and I think about it often, but my instinct is that when I see a mark or a bump I can not ignore it, but I know that I have to work on this aspect to get a perfect "Old Masters" look......if this matter...... :)

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Oh yes, I am aware of that and I think about it often, but my instinct is that when I see a mark or a bump I can not ignore it, but I know that I have to work on this aspect to get a perfect "Old Masters" look......if this matter...... :)

Davide,

 

I think we have entered a new era in violinmaking in which great videos like yours demonstrate how this work is done. I think that, even in violinmaking schools, the students don't get this much exposure watching someone perform.

 

Thanks again.

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Davide,

 

I think we have entered a new era in violinmaking in which great videos like yours demonstrate how this work is done. I think that, even in violinmaking schools, the students don't get this much exposure watching someone perform.

 

Thanks again.

 

Watching at macro shooting I think that I too had never seen the work so closely. Interesting experience. :)

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My father is a retired cabinet maker, as was his father. I spent a lot of years in the shop, working to put myself through school. One of the things that stands out for me to this day is his ability to turn an edge on a scraper that transformed the thing into something incredible. I could never achieve that magic. He'd hold my wrist with burnisher in hand, to show the pressure, the angles... I got so I could turn an edge just fine, but his were something else. For the 15 minutes or so that the scraper held up till it needed to be re-turned it was incredible. To this day I take my sharpened scrapers home to have him turn the edge. It won't last long, but I'll enjoy it while it does.

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My scraper tuning has gotten much better, but I still have days I can't quite get it maxed out. 

 

Well, for one thing, the rod used to turn the edge, must be much harder than the steel used in the scraper.

The turning 'tool' or 'stick' is either a specific rod made for doing that, or else a general tool that is hardened can also be used.

But if the 'turning stick' is the same hardness (or close to) as the scraper, the job becomes difficult, time consuming, or even impossible.

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Well, for one thing, the rod used to turn the edge, must be much harder than the steel used in the scraper.

The turning 'tool' or 'stick' is either a specific rod made for doing that, or else a general tool that is hardened can also be used.

But if the 'turning stick' is the same hardness (or close to) as the scraper, the job becomes difficult, time consuming, or even impossible.

The variables in scrapers are

 

1. steel hardness

2. edge angle.

3.  intended use -- rough scraping or fine

4.  other... ???????

 

Even with the first two, if I am trying to follow MD's instructions on scraper sharpening, if I am not using the steel he uses, the result might be quite different.

 

I imagine that if I were a teacher in a violinmaking school, I would have all the students use the same brand of scraper (same steel). 

 

I fantasize about doing a detailed investigation of scrapers and then making a wonderful video about it. Of course that won't happen, but I bet someone will do it, in the fullness of time.

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On this drawing I notice that on the convex part,  line segment A B is longer than line segment C D .   Where the curve is concave line segment A B is shorter than C D.  So where those two lines are equal length should be the point where convex changes to concave.    I also notice that point two converges with the vertical zero line farther down than the other points.  Since that angle is so small that difference could easily be due to a small error in measuring.   

I'm not a geometer so this observation could be wrong.   

http://screencast.com/t/tiALwYhSu

post-31367-0-34969500-1424621185_thumb.png

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It's been many years since I looked into the mathematics behind the prime arch of the violin belly. IIRC, it was a compound curve assembled from three different curves. Some people may say it is two, but I stick with three. The upper and lower bouts have very different contours. The arch is not symmetrical.

 

Anyone else agree or disagree?

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Davide:

 

very impressive skills.  I love to watch you work.  questions:  how do you smooth the edge of the scraper prior to turning the burr?  do you have different scrapers with different corner radii for various arching edge profiles?  thanks,

 

 

Davide, 

 

Yes thank you for making the videos. I learned much by watching you work. 

 

 

Where is the part of putting the burr in the scraper? It took me years to get that on my own and I still search for better ways to doing it. 

 

Thank you :)

 

I rough the shape of my scrapers on the grinding wheel without overheating the steel (very important) giving them the final shape with a coarse single cut file held perpendicular to the scraper.

Then I sharpen them on a water stone 1200 grit removing all marks of the file and on a 4000 grit removing all marks of 1200 with very few passes on the flat sides of the scraper on 4000 only for remove the burr.

It is important not to overdo the sharpening on the stones to not round off surfaces and preserve the 90° angles of cutting edges.

At this point the scraper is ready for turning the burr with the steel rod, as you see at the start of the video "Scraper working part one" :

https://www.youtube.com/watch?v=58E8nuKuefs

 

and at the start of "part three" :

https://www.youtube.com/watch?v=GpethooO9n8

 

For archings I use only the two scrapers that you see in these videos, the little one with a different radii for each corner and different curve for each side, the bigger one with more simmetrical curves of sides but also with different radii at each corner.

You need radii and shapes that fit well your arching, but of radius smaller than that of the curves to leave in the wood to be able to move within their range without flatten them.

 

Only a clarification :  scrapers freshly sharpened on stones need very very little pressure and angle of the steel rod to turn the burr, the ones you see in the video are already a little used and need a little more "normal" angle and pressure.

The key is to develop the sensitivity in understanding the nuances of these details.

 

Davide

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Thanks, Davide.  I shave with a straight razor (most of the time) so I have waterstones ranging from 225 grit to 20k grit.  Will try this for a couple of new scrapers.  Had always used the knife edge profile, but what you do sounds a lot quicker/easier and obviously works beautifully.

 

For me knife edge profile (single cutting edge) works fine but tends to produce too easily a too protruding burr (difficult to control), good for aggressive rough work but not for finishing.

Surely work better without turning the burr, I frequently use scalpel and knife blade that way but not on archings, and I suspect that the old sword blade scrapers in the Cremona museum were used in this way (I also suspect that they were not from Stradivari but from Ceruti workshop, but that's another story....)

Moreover, the risk of accidentally cut into the wood is very high and makes me a little nervous expecially on soft wood like spruce, but I think if you use very carefully and with great skills can do the job anyway, with slightly different but maybe interesting results on final surface texture.

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Davide ,

I tried out the square edge scrapper last night , and I gotta say ...I loved it ! much less aggressive than the angled scrapper I have been using . I like how one can observe the actual cut much easier , and it's more like erasing the humps and bumps than cutting them down. Thanks ....except now I have to do some grinding and shapping of yet another tool .... fun.

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Davide ,

I tried out the square edge scrapper last night , and I gotta say ...I loved it ! much less aggressive than the angled scrapper I have been using . I like how one can observe the actual cut much easier , and it's more like erasing the humps and bumps than cutting them down. Thanks ....except now I have to do some grinding and shapping of yet another tool .... fun.

 

Scrapers...

 

ahhh - what a treat.

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Scrapers...

 

ahhh - what a treat.

Yes. So I spent some time today measuring scrapers and sharpening.

 

Results:

 

Scrapers:

 

Here are some observations of mine about scrapers as of 2/24/2015. This may change.

 

--  0.32 mm = 0.012 inches -----> This is 1095 steel shimstock HRC ~49

--  0.4 mm = 0.016 inches ------> Scrapers from Int. Violin

--  0.8 mm = 0.032 inches -------> Standard cabinet scrapers, Int. Violin

 

Thickness:

  • It is surprising to me how much stiffer the 0.4 mm scraper feels, over the 0.32 mm scraper.

  • For heavier wood removal, thicker scraper is more effective.

 

Edge angle:

  • The 0.32 mm scraper can be sharpened, held at 90 degrees on diamond stone, then burnished

  • The 0.4 mm scraper works at 45 degee edge angle, also may work at 90 degrees (not tested)

  • The 0.8 mm scraper seems to work with a 45 degree edge angle. Heavy stock removal and for ribs.

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