Preparing Scapers


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I use three different thicknesses of blue tempered spring steel shim stock from McMaster-Carr, .01", .015" and .02". For each different shape of scraper, I make one of each thickness. The .02" is a coarse, heavy, meat-eating scraper, particularly good for first passes on maple or removing lots of material. The .015" is an all-purpose, medium scraper, used 90% of the time. The .01" is a fine, finishing scraper, good for the final passes on maple and spruce and producing a perfectly smooth surface. Heres a link to the shim stock I bought: https://www.mcmaster.com/#shim-stock-sheets/=16rdr8y then click on "spring steel." One sheet in each thickness is enough for a lifetime supply of scrapers. 

I first grind a 45º bevel all the way around the edge of the scraper. This bevel angle makes for a very sharp scraper capable of producing a thin burr and leaving a perfectly smooth surface. Then I hone that bevel using 1000, 4000, and 8000 grit water stones, including a few strokes on the flat between grits to remove the burr. Take care to hone all of the grinding marks off and produce a burr around the entire cutting edge with the 1000 grit before moving on to the polishing stones. It can be tricky to hold such a small surface at 45º at first, but it will get easier with practice. Make sure to finish with a stroke or two on the flat side using the finest grit at the very end. 

Finally, I turn the burr with this burnishing rod from Ron Hock: http://www.hocktools.com/products/sb.html I never put a handle on it and it works for me just fine. Use a low, raking light  so that you can see the burr appear as it is being produced. Use your eyes and steady even pressure to turn a small, consistent wire edge all the way around the scraper. An easy mistake to make is to use too much pressure or to go over the same area more than once, which will produce a burr that is hooked too far, making the cutting angle too steep. 

Half the battle in learning to scrape is just getting the things sharpened properly. A beautifully honed, razor sharp scraper that bites greedily into a thumbnail and produces ultra-thin shavings (not dust) will make this a joyful, satisfying task. A dull, improperly tuned scraper will make for a source of endless frustration. 

I'm out of the shop this week, but I will post pictures of the shapes I use when I get back. 

 

Edited by Benjamin DeCorsey
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I bet there is a simple relationship relating the edge angle and the hardness of the steel. Davide Sora uses 90 degrees on what looks like spring steel. But what is the hardness? I have an email in to him about this. Perhaps he will respond here.  The McMaster-Carr spring steel is HRC 48-51.  

 

Please save me from having to do hours of experiments to find the relationship between preferred hardness and edge angle. This stuff must be well know by someone. Now is the time to share what you know. Please.  And thanks in advance, because Maestronet ALWAYS delivers.

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Hi John,  Just a food for thought question because I don't know the answer.  When I'm really working the scraper (not fussy finish work) they build up a lot of heat and the burr last longer and cuts better after I've re-burred it a time or two.  I think this called work or heat hardening (not sure).  Anyway, how does work hardening figure into your thought process?  I'm wondering if you start too hard, then your edge/bur gets work hardened it could get brittle.  

-Jim

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7 hours ago, Jim Bress said:

Hi John,  Just a food for thought question because I don't know the answer.  When I'm really working the scraper (not fussy finish work) they build up a lot of heat and the burr last longer and cuts better after I've re-burred it a time or two.  I think this called work or heat hardening (not sure).  Anyway, how does work hardening figure into your thought process?  I'm wondering if you start too hard, then your edge/bur gets work hardened it could get brittle.  

-Jim

Yes, work hardening complicates things. I don't have an answer. I just watched a Davide Sora video on using scrapers on the scroll. Wow. 

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9 hours ago, violins88 said:

Mike,

 

As I recall, your scrapers are Rockwell 62, with an edge angle of 45 degrees? 

 

John

 

Right. I was afraid to try a burr with such hard steel, but it works with the Stew-Mac burnisher. In fact, your scrapers fit nicely into the burnisher's slot fixing the burr angle.

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My scrapers are almost all made with Eberle branded plates  0.6 mm and 1.0 mm thick , but I have no idea of the characteristics of the steel I bought them many years ago, following the advice of a colleague who said that they were quite good....:)

I found these on the web that should be the same as mine : http://www.howardcore.com/cgi-bin/shopper.cgi?search=action&category=TOOL&template=Templates/HC_SR2.htm&keywords="Scrapers"

Perhaps the steel is like this, but I'm not sure : http://www.eberle-augsburg.de/en/strip-steel/strip-steel/spring-steel/

I think that an excessively hard steel is not good for scrapers, on Dictum catalog they indicate 50 to 54 RC

Almost all my scrapers are 0.6 mm thick, except the big and squared one for ribs and the one with angled bevel that are 1.0 mm thick and the two oval and the semicircular that I bought as is and are 0.5 mm thick, not sure on the brand.

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58ca79bd0f536_RasieraEberle.jpg.8fba82c1697a3e0370436e4e413a7f89.jpg

 

 

 

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I find it most difficult to make my scrapers great when I need them to be at their best, because then I want to do work and not sharpen scrapers. Quite often I find myself in the situation when I'm impatient and pushing hard with a dull scraper instead of fixing the problem.

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I picked up a junk store  3/8 tungsten carbide drill bit just because it was there and was cheap and it is so cool.

One day I tried it for a burnisher on the ol scrapers,,,,,,

It is the best, bar none,,and I have a number of burnishers,,

The grain of the carbide is like micro mesh to the scrapers, and it remains flawlessly perfect.

One test drive of one of these babies and you would be hooked for life,,(pun intended)

 

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