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70° NRS vs. 70° NRS

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There was a recent thread discussing scraper angles which I was going to bump, but as it is rather long I will just reference it here.
https://aawforum.org/community/index.php?threads/no-battles-please.16601/#post-167475

So here is my question. Suppose that you want to make a 70° negative rake or double bevel scraper. There are several ways to grind the top and bottom bevels to get to 70, here are three examples (top & bottom angles): 10° & 60°; 35° & 35°; 60° & 10°. Each of these grinds will give a 70° included angle, but in the first instance the tip will be directed more toward the top and in the third instance the tip will be directed toward the bottom. In the middle instance the tip will be directed parallel to the tool shaft.

Although the included angle is the same, I am thinking there will be differences in how the 3 options would perform. I have never seen anyone use or advocate option 3 and find it difficult to imagine that it would be that successful a grind. Between options 1 and 2, the middle approach has the advantage of being easier to implement and maintain, and it's reversible. But I wonder if there are any performance advantages or penalties to consider between either of the first two options?
 

Bill Boehme

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What Robert said! I don't think that your #3 would even work or not very well. I also believe that #1 isn't worth the trouble as it's hardly any different that a regular scraper used in the conventional manner with the back of the handle raised slightly.

I prefer a slightly smaller symmetrical included angle (60°).
 

john lucas

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I don't think you will notice a difference. Although I have not tried #3 I don't see how it would be any different if you held the tool level in all 3 cases. The wood only knows the angle not where it is. At least that's my opinion and I will stand by it for at least 3 more seconds.
 

john lucas

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I'm with Tim sort of. My round nose scraper is sharpened down one side quite far. I tried the same grind on both sides and flipping the tool to raise the burr. What happens is it when sharpening one side it hits the grinder. So on that one it still has 2 equal bevels but I went back to cleaning off the old burr with a diamond hone and then raising a new burr with John Jordan's ceramic hone. My flat tool I do have equal grinds on both sides and just flip it for a new burr. I have a really large round nose tool that I decided would simply take too long to get equal grinds on top and bottom so it has a small grind on top and long grind on the bottom.
 

brian horais

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I made my bottom angle the same as my roughing gouge and adjusted the top angle accordingly. You are almost always sharpening the bottom surface (until you run out of top surface), so this way your sharpening can be done with very little additional setup. I keep a sharpening setup in place for my roughing gouge and negative rake scraper (the same setup), that way I sharpen both of them frequently.
 
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I'm with Tim sort of. My round nose scraper is sharpened down one side quite far. I tried the same grind on both sides and flipping the tool to raise the burr. What happens is it when sharpening one side it hits the grinder. So on that one it still has 2 equal bevels but I went back to cleaning off the old burr with a diamond hone and then raising a new burr with John Jordan's ceramic hone. My flat tool I do have equal grinds on both sides and just flip it for a new burr. I have a really large round nose tool that I decided would simply take too long to get equal grinds on top and bottom so it has a small grind on top and long grind on the bottom.

Would a change in your included angle # help with that John?
 
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I think what we need is an 8" grinder with a motor that is only 4" in diameter. Hitting the motor housing on one side is seems to be a limitation for gouges, too.
 
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Well, being 'different', I prefer option 2. I never liked the skew chisel variation of NRS. The edge is too fragile. I prefer a burnished burr for my cutting edge as it is sharper and far more durable. My preferred angles are 60 on the bottom and 25 or so on the top. More blunt than 60 on the bottom makes the burr more difficult to burnish. Any shallower than that and durability goes down. When trying to burnish the skew chisel type, the edge tends to fracture rather than turn. I do use M42 and V10 only for my NRSs. I would suppose with my grind, I could hone down the burnished burr and then sharpen the 60 degree bevel to refresh the edge, but the platform I use makes it simple to move to different angles.

robo hippy
 
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You guys may be right... Yes, more blunt lower angle, more acute top angle... Maybe the coffee hadn't kicked in yet.... Maybe I had one of those flash backs they promised me I would have.....

robo hippy.
 
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