- Joined
- Aug 19, 2010
- Messages
- 261
I hope you find the following useful and informative.
This has probably been discussed before, but I recently got to thinking about full flat ground (FFG) blades and how the Edge Pro (EP) puts an edge on them. Now obviously, the EP works great on FFG blades if you want to repair the existing edge: you use the Sharpie method to figure out the existing angle and go from there. If a regrind is called for- especially one at an exact angle- things become a little different. Saber ground blades are simple- you rest the blade on the unground portion, select your angle, and go from there. A FFG blade, however, will not receive the angle indicated by your machine. A FFG blade will rest on the grind meaning the center line will tip slightly downwards causing a lower angle than indicated to be placed on the blade. I put together an image that exaggerates this effect:
A lower angle might not be a bad thing- the knife will cut better- but can you go on knowing you're living a lie?
I contacted Ben about this and he agreed with my reasoning. He also shared a few methods he uses to counteract this problem. Suffice to say his methods are quick and straight forward if you have the tools. I, on the other hand, am rarely satisfied with the easy way so I derived a different method using different tools.
How it works
It's pretty straight forward- if you know the angle the blade was ground at (G) you divide that by two and increase the angle setting by that amount. You will now be sharpening at the desired angle.
Ben's Methods (permission was given to share these)
#1. Use your iPhone
Ben suggested a novel method for those who own an iPhone or similar device and have access to the "Level" app with a digital angle display. Simply lay the knife on a flat surface or table and place the level on the blade. The resulting angle reading is the inclusive Grind Angle. Divide that by 2, add it to the desired angle, and you have the required adjusted angle.
#2. Use a typical grind angle
If all you need is to get close enough, Ben mentioned that most blades you will come across are ground to about 4 degrees. Half of which is 2, which you would add to the pivot angle setting. It's better than nothing, and is sufficient for knives of similar grind.
#3. Knives with saber grinds or a flat in front of the handle
Instead of trying to balance certain knives on the unground portion for the duration of the sharpening session, Ben described how he holds it there only long enough to lay down a partial bevel. Then he simply uses the Sharpie method to locate the new angle, rests the knife on the more stable flat-ground area, and goes to town.
#4. Calculate the grind angle
I spent some time with a calculator, pen and paper and devised a method to calculate the angle using a calipers or a calipers and a good ruler. If you're really *ahem* anal about the angle you sharpen at, use the following method (photoshopped and I've been sitting too long
):
^ That should work...please let me know if it doesn't.
Bonus: CATRA goniometers
While putting this all together I also wondered how one would accurately measure the angle present on a blade. Answer: goniometers! Goniometers measure all kinds of angles, and that includes the edge of knives if you buy the right one. In fact, CATRA apparently sells laser goniometers specifically for this task (and some are affordable!
)
Hobbyist model ($100, +/- 2 degrees)
Portable model (+/- 1 degree)
Bench model (+/- 1/2 degree)
Any feedback is appreciated- hope you enjoyed reading this post.
This has probably been discussed before, but I recently got to thinking about full flat ground (FFG) blades and how the Edge Pro (EP) puts an edge on them. Now obviously, the EP works great on FFG blades if you want to repair the existing edge: you use the Sharpie method to figure out the existing angle and go from there. If a regrind is called for- especially one at an exact angle- things become a little different. Saber ground blades are simple- you rest the blade on the unground portion, select your angle, and go from there. A FFG blade, however, will not receive the angle indicated by your machine. A FFG blade will rest on the grind meaning the center line will tip slightly downwards causing a lower angle than indicated to be placed on the blade. I put together an image that exaggerates this effect:
A lower angle might not be a bad thing- the knife will cut better- but can you go on knowing you're living a lie?
I contacted Ben about this and he agreed with my reasoning. He also shared a few methods he uses to counteract this problem. Suffice to say his methods are quick and straight forward if you have the tools. I, on the other hand, am rarely satisfied with the easy way so I derived a different method using different tools.
How it works
It's pretty straight forward- if you know the angle the blade was ground at (G) you divide that by two and increase the angle setting by that amount. You will now be sharpening at the desired angle.
Ben's Methods (permission was given to share these)
#1. Use your iPhone
Ben suggested a novel method for those who own an iPhone or similar device and have access to the "Level" app with a digital angle display. Simply lay the knife on a flat surface or table and place the level on the blade. The resulting angle reading is the inclusive Grind Angle. Divide that by 2, add it to the desired angle, and you have the required adjusted angle.
#2. Use a typical grind angle
If all you need is to get close enough, Ben mentioned that most blades you will come across are ground to about 4 degrees. Half of which is 2, which you would add to the pivot angle setting. It's better than nothing, and is sufficient for knives of similar grind.
#3. Knives with saber grinds or a flat in front of the handle
Instead of trying to balance certain knives on the unground portion for the duration of the sharpening session, Ben described how he holds it there only long enough to lay down a partial bevel. Then he simply uses the Sharpie method to locate the new angle, rests the knife on the more stable flat-ground area, and goes to town.
#4. Calculate the grind angle
I spent some time with a calculator, pen and paper and devised a method to calculate the angle using a calipers or a calipers and a good ruler. If you're really *ahem* anal about the angle you sharpen at, use the following method (photoshopped and I've been sitting too long
):
^ That should work...please let me know if it doesn't.
Bonus: CATRA goniometers
While putting this all together I also wondered how one would accurately measure the angle present on a blade. Answer: goniometers! Goniometers measure all kinds of angles, and that includes the edge of knives if you buy the right one. In fact, CATRA apparently sells laser goniometers specifically for this task (and some are affordable!
)Hobbyist model ($100, +/- 2 degrees)
Portable model (+/- 1 degree)
Bench model (+/- 1/2 degree)
Any feedback is appreciated- hope you enjoyed reading this post.
