Question: How do you sharpen curved scrapers?

[Luis Martins]

[Darrma]

11 hours ago, Davide Sora said:

 

Done!

 

Wow! Great video. Thanks for posting it Davide 

In your comments you say "Apply the smallest possible pressure" when I have previously (and unsuccessfully)  been using as much pressure as I could reliably apply. Seemingly small, but very important difference, as highlighted by others here.

I've found somewhere I can get a 0.5mm scraper from as well, so I'll try to make a couple in the shapes that you show. Thanks again.

[Davide Sora]

 

In fact, it is not possible to quantify this kind of things effectively because they are based on feelings and it is necessary to develop a specific sensitivity, especially in perceiving when the cutting edge begins to feel under the finger after each pass with the burnisher.

With new scrapers just shaped and sharpened on the stones, that is, with very fresh and sharp corners, only one light pass with the burnisher at a very flat angle might be enough, but after some use and many repeated pass with the burnisher the surfaces will become slightly curved and the edges will be no longer at 90° but at a more open angle, so you will have to increase the angle of your burnisher to allow the cutting edge to be formed. Even higher pressure can be used to try re-flatten the surfaces compressing the steel, but not to turn the cutting edge.

When to much pressure is needed to obtain an efficient cutting edge, probably is time to re-flatten the surface with file and stones, but if your scrapers are of good quality steel this happen not too often, my scrapers can last for a few years before having to completely re-sharpen with files and stones.

 

 

[Darrma]

Hopefully I will develop a feel for these things as I practice and gain more experience.

Am I understanding correctly that the step of flattening the faces of the scraper on the stones is also something that need not be done very regularly? That the most regularly carried out steps will be to lightly top-up and burnish the edge and to fold the edge, as you show in your video?

I confess that at the moment I go through the process of completely flattening the scraper on the stones and completely squaring the edge before I try to re-burnish the tool. I suppose this is making the process far more lengthly than it needs to be.

[Davide Sora]

I use sharpening stones only after the shaping work done with the file to eliminate the file marks and smooth out the surface, not to sharpen in the true sense of the word.

For that, the burnisher is more than enough, because being harder than scrapers steel has a smoothing and polishing effect comparable to that of an extremely fine sharpening stone.

 

In practice, the less time you stay on the stone the better it is, because especially with curved scrapers the sliding motion is very complex and the contact surface is very small, consequently is very difficult to maintain flatness and 90° angles, so you risk more to ruin than to improve the cutting edge of the scraper.

 

[Darrma]

Brilliant. Thank you very, very much for all this information (to everyone who has replied in this thread).

Now I've just got to put it all to practice and get good at it. One thing's for sure: I'll certainly have no excuses now if my scrapers are dull  

[Berl Mendenhall]

One thing we haven't talked about is scraper thickness. I noticed Davide's scrapers are a bit thicker than the main ones I use. I use .4mm mainly, but I also use 2 and 6mm. My 2 is small, about 1 inch long and egg shaped. I like it for purfling channels, no burrs on this one just straight.

[carl1961]

Awesome as always Davide Sora, Thanks for you excellent videos.

[carl1961]

 Thanks Berl Mendenhall, every little detail helps to learn how to better the next violin work.