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Sharpening a negative rake scraper (Read 322 times)
 
Anthony maida
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Sharpening a negative rake scraper
May 29th, 2017 at 7:06pm
 
Hello
           I,am thinking of getting a glen lucas negative rack
           scraper.What is the procedure in sharpening it?
                                                           Thanks Anthony Shocked
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robo_hippy
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Re: Sharpening a negative rake scraper
Reply #1 - May 29th, 2017 at 8:16pm
 
I think Glenn's are sharpened to 33 degrees, which is an unusual angle. If you have any old skew chisels, they will do the exact same thing, and you don't have to pay the price of a 'name' brand tool. If you have any old scrapers, in the 1 inch wide range, and 1/4 to 5/16 thick, they do the exact same thing. Other heavier scrapers will work too.

Most of the time the NRS is sharpened with the same angle on both sides, and range from 25 degrees to 35 or so degrees. Most will have a 1/4 round nose profile, so kind of like half of a round nose scraper if that makes sense. You can sweep across the inside bottom of a bowl and and go through the transition, which is the most difficult part of a bowl to turn. Being the same angle on both sides lets you use them going in either direction. Sharpen the side where you want the burr up first to remove old burr, then flip over and sharpen the other side to raise a new burr. Heavy scrapers will work but you need a 36 grit stone on a high speed grinder, or a heavy duty belt sander to get the angles.

There are some that are sharpened some thing like 25 on the top, and 70 on the bottom. I use these more for the insides of boxes and the insides of vases or more closed forms, and specifically for end grain pieces.

All that being said, I find them more useful on harder woods like black locust, than on softer woods like big leaf maple. I also prefer to shear scrape the inside walls of a bowl rather than use the NRS. A shear cut usually gives a cleaner cut.

This is another video I need to do....

robo hippy
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Jeff Vanden Boogart
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Re: Sharpening a negative rake scraper
Reply #2 - May 29th, 2017 at 9:40pm
 
The big top angles on commercial NRS don't make much sense to me.  Seems like that was decided by the legal department.
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Rick Caron
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Re: Sharpening a negative rake scraper
Reply #3 - May 30th, 2017 at 5:30pm
 
Tried a 70 on the bottom and 20 on the top.  Got use to this     then tried  35 on the bottom and 35 on the top.  Seems to work better.  Just remember what side the burr is on     always up when using.      Grin
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« Last Edit: May 30th, 2017 at 5:33pm by Rick Caron »  
 
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Jeff Vanden Boogart
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Re: Sharpening a negative rake scraper
Reply #4 - May 30th, 2017 at 6:49pm
 
I might give it a try then, Rick.  Just seems like too MUCH negative.
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Anthony maida
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Re: Sharpening a negative rake scraper
Reply #5 - May 30th, 2017 at 9:31pm
 
Thanks guys for you comments

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Ray Stubbs
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Re: Sharpening a negative rake scraper
Reply #6 - May 31st, 2017 at 11:42am
 
This has probably been discussed before, but in order to get the burr, does this come at the bottom of the wheel on the tool or on the top.
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robo_hippy
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Re: Sharpening a negative rake scraper
Reply #7 - May 31st, 2017 at 5:57pm
 
The side that is against the wheel has no burr, and the side that is up and not on the grinding wheel gets the burr. The burrs from a CBN wheel cut way better and last longer than the ones from more standard grinding wheels.

robo hippy
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