Recommendation? Grinding a convex edge

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Way-Barney

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Jun 4, 2023
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Good evening guys,

What is the best way to grind a convex profile?

Edge up or edge down, if both are ok are there disadvantages/advantages for each?
 
I flat grind most of the way first, down to 0.03" or 0.04" at the edge depending.
I put two layers of tape where I don't want to remove material (ricasso, high up the bevel etc).
I use 120 grit, with lots of tension, but on a slack unsupported spot above my flat platen, where the belt is running horizontal. I stand to the side and have the edge away from the incoming belt. Equivalent to edge down. You need to be careful how you hold and move the blade. Further away from the platen is less firm. Drawing it close to your platen will be firmer and steeper. You can easily create a very thin edge and overheat. You need to be especially careful getting the angles you want near the tip.
 
Richard338 said:
I flat grind most of the way first, down to 0.03" or 0.04" at the edge depending.
I put two layers of tape where I don't want to remove material (ricasso, high up the bevel etc).
I use 120 grit, with lots of tension, but on a slack unsupported spot above my flat platen, where the belt is running horizontal. I stand to the side and have the edge away from the incoming belt. Equivalent to edge down. You need to be careful how you hold and move the blade. Further away from the platen is less firm. Drawing it close to your platen will be firmer and steeper. You can easily create a very thin edge and overheat. You need to be especially careful getting the angles you want near the tip.
Click to expand...
Hi Richard,
I have made a small adjustable tool rest to position the blade exactly in that area, by my calculations it will be possible to use either edge up or edge down and position the rest at any distance above or below the platen. Weo makes a good point about seeing the center line, but I thought it would be removing such a small amount of the material that it should be easy to guesstimate.

Hello Gilbert,
What would be your suggestions for each?

Thank you for the replies Gents, your advice is appreciated.
 
Way-Barney said:
Hi Richard,
I have made a small adjustable tool rest to position the blade exactly in that area, by my calculations it will be possible to use either edge up or edge down and position the rest at any distance above or below the platen. Weo makes a good point about seeing the center line, but I thought it would be removing such a small amount of the material that it should be easy to guesstimate.

Hello Gilbert,
What would be your suggestions for each?

Thank you for the replies Gents, your advice is appreciated.
Click to expand...
I can't imagine going edge up on a slack belt to a vanishing edge. I scribe a center, and two outer lines where I stop the flat grind. That's all edge up. For the convex it's edge away and check frequently what is happening.
 
I grind with the edge facing me, that way I can also see the shadow between the apex of the edge and the belt- which allows me to fine tune the convex geometry using flat planes that I smooth out later
 
I sometimes grind convex edge up, but the belt in reverse, going away from me. I use a VERY slow speed, fresh belts and often wet the belt. I also use soft platens (Felt, leather), which tend to help, too on very thin kitchen or fillet knives.
 
For a Bowie knife or similar I would use a slack belt edge down or slack portion of the rotary platen. For a thin knife sometimes leather backing edge up ,but usually on the rotary platen edge up unless on the slack portion.
 
Taz said:
I sometimes grind convex edge up, but the belt in reverse, going away from me. I use a VERY slow speed, fresh belts and often wet the belt. I also use soft platens (Felt, leather), which tend to help, too on very thin kitchen or fillet knives.
Click to expand...
Taz just described my method of grinding the edge - run in reverse with edge up so I can see what's going on. Either with slack belt with platen dropped back out of way (or removed), or grinding on a soft platen (leather, felt, etc). This is all after grinding a flat grind so edge is .020" or so, then the convex grind. For thin kitchen blades the edge will be down around .010" before moving to convex grind.
 
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