Hapstone angle mystery

3D Anvil

3D Anvil

Joined
Oct 4, 2021
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As I was doing my Venev/CGSW comparison something very odd happened. I was compensating for the very different stone thickness by measuring the angle of the rod on the knife. I followed what I think is the correct procedure of zeroing the angle cube on the clamp arm and then measuring the rod angle with the rod centered on the pivot and the stone in the middle of the blade. Fifteen degrees, bang-on, just as it was with the Venev stones. But when I started using the CGSW stone, I noticed that I was only hitting the front half of the bevel, indicating that the sharpening angle was well off. Measured again. Fifteen degrees, bang-on.

At that point I resorted to the Sharpie trick and finally arrived at an angle of 15.5° to hit the whole bevel, or a full half a degree higher than the angle I was using with the Venev's. What the...?

Just to confirm, I then switched back to a Venev stone, set the angle to 15° with the Angle Cube, and ... it was perfect. This seems impossible, so clearly I'm missing something.

Any ideas?
 
Did you do the sharpie test when you went back to the Venev?
 
How even is your Venev stone in thickness end to end?
 
Less than .1 is good so it isn't that. .1 degrees is about .01" or .25mm where the stone meets the blade, at least on my sharpener.
 
Not 100% sure, but I think what happened is that the CGSW stone wasn't fully seated in the holder. The stone holder can accommodate 4" stones, but since KME-type stones don't have that Edge Pro wedge on either end, they aren't as secure. Thank you for your input in any case.
 
Not sure, I guess it must have been like you said - one end of your stone may have not been seated completely.

Not relevant to this specific mystery, but just a quick note about measuring your angles - don't zero your angle cube on the clamp arm because the clamps can be opened or closed more - depending on the knife grind. Always zero your angle cube on the flat top section of the Hapstone rotating mechanism housing. This is the correct spot for zeroing your angle cube, not the on the clamp itself.

Another tip if I may add - when you swap stones, there is no real need to recalibrate or zero your cube and re-measure 15 degrees all over again. To save a little bit of time, what I do right before swapping stones is to simply zero my cube on top of the stone holder (with the current stone in it and on top of the knife), then I remove the angle cube and stone, replace it with the next stone and place the angle cube on top of the stone holder again. Then I simply adjust my angle until I see zero on the angle cube screen again. This just saves a little time when swapping stones. Of course with this method you're not measuring your actual sharpening angle again, your'e just setting a quick reference to adjust for the different stones. Hope my explanation makes sense? If not, ignore the above... :p
 
777 Edge said:
Not relevant to this specific mystery, but just a quick note about measuring your angles - don't zero your angle cube on the clamp arm because the clamps can be opened or closed more - depending on the knife grind. Always zero your angle cube on the flat top section of the Hapstone rotating mechanism housing. This is the correct spot for zeroing your angle cube, not the on the clamp itself.
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Right, that's what I was doing, but I guess I didn't express it very well.
777 Edge said:
Another tip if I may add - when you swap stones, there is no real need to recalibrate or zero your cube and re-measure 15 degrees all over again. To save a little bit of time, what I do right before swapping stones is to simply zero my cube on top of the stone holder (with the current stone in it and on top of the knife), then I remove the angle cube and stone, replace it with the next stone and place the angle cube on top of the stone holder again. Then I simply adjust my angle until I see zero on the angle cube screen again. This just saves a little time when swapping stones. Of course with this method you're not measuring your actual sharpening angle again, your'e just setting a quick reference to adjust for the different stones. Hope my explanation makes sense? If not, ignore the above... :p
Click to expand...
Great tip! All tips are appreciated.
 
Edit - Wrong trigonometry numbers quoted for edge bevel change vs angle change, thanks for checking D Diemaker ! The fact that I found a 0.7mm change in angle after setting the bevel could possibly also be an experimental set of experimental clamps which could have caused the knife to slip backwards in them while setting the bevel, not sure about this. I'll have to re-run the experiment and see what the real numbers are again.

I thought I may have found what happened to you, 3D Anvil 3D Anvil , but maybe not....


Today I re-profiled a factory bevel on my Spyderco Manix 2 Maxamet knife. As is common, the edge bevels were very inconsistent from the factory. One side was 19 degrees, and the other was 16 degrees as measured with my Gritomatic Goniometer.

I carefully adjusted my angle on my Hapstone R2 to exactly 15 degrees and methodically re-profiled both sides of the knife using my metallic 120 CBN stone. A beast of a stone for a beast of a steel.

I spent about 8-10 minutes with the metallic CBN to get the edge bevel perfect both sides, nicely centered and aligned, both sides the same size and a tiny burr just barely starting to develop.

I measured my freshly re-profiled edge angle again on the same side I first started at, and now it measured 14.7 degrees after my time spent re-profiling. I made sure to zero and check again. The end result was 14.7 degrees after setting the new bevel? I assumed it was due to the steel that was removed after setting the new bevel.

I haven't measured like this for years because when I normally swap stones I don't readjust my angle by zeroing the cube first on the clamp holder and then checking 15 degrees on the stone holder. I always just keep my stone in the stone holder on top of the knife, then zero my angle cube on top of the stone holder before quickly swapping stones and readjusting the angle to get back to this zero reference. (Hope you know what I mean?)

Could something like this have happened to you 3D Anvil 3D Anvil ?

Just a sidenote about zeroing the angle on the Hapstone rotating mechanism - Be aware that you need to place the angle cube right in the center of the small platform when zeroing, because some angle cubes have small feet that could drop off the front or rear of the small platform. This could give you an incorrectly zeroed angle of 0.4-0.5 degrees. (Depending on the size of the feet on the cube.)
 
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777 Edge, I understand what you are saying but the amount of angle change according to my trig is far less than yours. My sharpener has 8" between the stone arm pivot and the knife apex so a .1 degree change equates to .01392" of vertical change at the apex. For 3D Anvil to get a .5 degree change through sharpening @ 15dps he would need to remove .26" from the width of his blade. Full disclosure, to keep it simple I assumed the blade arm to be perpendicular to the pivot support bar so there will be some error at 15 degrees on my sharpener as it is perpendicular at 21 degrees. Still, the error will be pretty minor.

What is the distance between the pivot and typical blade apex on a Hapstone R2? Any idea of what angle the Hapstone stone arm is perpendicular to the pivot support bar?
 
You are 100% correct D Diemaker , I incorrectly calculated the 0.5 degree angular change alone and based it on a fixed distance to the clamp edge of 270mm. This resulted in a distance of 258.291mm from the clamp edge to the pivot for a 15.5 degree sharpening angle, and a distance of 258.36mm for a 15 degree sharpening angle. (That's how I got to the 0.07mm difference)

Interestingly though, I definitely had a 0.3 degree change in angle after a 10 minute bevel setting on my knife today. Could perhaps be what I mentioned above, I was trying out some new experimental clamps for the first time.

Let me delete most of the absolute horse manure I wrote above. Thank you for your recalculation D Diemaker !

My late night rambling red-eye calculation was purely (incorrectly) based on the distance change of side "a".

Here are the numbers for the Hapstone R2 with standard angled clamps, FYI:

Angle between the vertical rod and blade clamp rotating unit = 73 degrees.

Distance from the vertical rod to the tip of the blade clamp (along the same fixed line as the blade clamps) = 270mm

Here are 2 pics of the incorrect assumption I made to get to 0.07mm bevel width change:

Untitled1.jpg
Untitled2.jpg
 
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I'll leave the math to you guys, but what I think happened was that the CGSW stone probably wasn't seated properly in the stone clamp. Problem is, both the Hapstone stone holder and the CGSW stones are trying to accommodate both flat-ended and dovetail systems, but their accommodations don't quite match up, so the CGSW stone mounted in the Hapstone holder tends to get cockeyed.
 
3D Anvil said:
I'll leave the math to you guys, but what I think happened was that the CGSW stone probably wasn't seated properly in the stone clamp. Problem is, both the Hapstone stone holder and the CGSW stones are trying to accommodate both flat-ended and dovetail systems, but their accommodations don't quite match up, so the CGSW stone mounted in the Hapstone holder tends to get cockeyed.
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You're probably right 3D Anvil 3D Anvil , more often the simple answer is the correct one and overthinking it doesn't help. :p
 
3D Anvil said:
I'll leave the math to you guys, but what I think happened was that the CGSW stone probably wasn't seated properly in the stone clamp. Problem is, both the Hapstone stone holder and the CGSW stones are trying to accommodate both flat-ended and dovetail systems, but their accommodations don't quite match up, so the CGSW stone mounted in the Hapstone holder tends to get cockeyed.
Click to expand...
I designed my latest version of stone holders a few weeks back (For KME, Lansky, Work Sharp and more) to specifically work well with the CGSW stones. (And regular dovetail or flat hones also) I love the little cutouts that D Diemaker mills into them, so I thought that they deserve stone holders designed to work with them. Gritomatic will have these in stock soon.

Maybe I can look at designing a set of stone holders for the Hapstone system also if there is a need.
 
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