No light reflected, but still not sharp

B

Bo-dacious

Joined
Aug 13, 2016
Messages
408
Hey guys, I just wanted to get your insight on why SOMETIMES when I sharpen my knife to the point that the apex doesn't reflect any light, but the blade is still dull. It sometimes tears paper when I cut it and sometimes it doesn't even cut into it. Are there any other factors involved or is it as simple as "if the apex doesn't reflect light, it's sharp"? I'm pretty sure the apex doesn't reflect light, but does anyone have any tips on that test? This only happens once in a while. Does anybody have any ideas about this? It would be much appreciated as I am very confused.

Thanks guys,

Bo
 
I should note that on other dull knives I'm able to see the light reflected off the apex easily, so it's not like I'm unable to detect it.

Bo
 
Sounds like you have issues in burr removal.
The "sharp" edge might actually be a wire edge/foil burr.
You need to remove it to have a stable edge.
 
I'm sorry for the duplicate post guys the page reloaded and I clicked create thread again. My bad smh.

Bo
 
Bo, forget about reflected light for now. You've got too many dishes in the air at one time.

Sharpen until you have raised a full length burr on one side of the knife, then the opposite side, and then have as delicately as possible removed the burr.

Then you can worry about reflected light, (shining directly down at the edge), showing you where there is remaining burr or other imperfections on the edge.

No disrespect but you need to walk before you can run.
 
Blues: okay that makes sense. But I am able to get a burr just fine and remove that burr. I don't have any problems with that.

Thanks,

Bo
 
In my limited experience, a lingering burr could remain at the edge even when I am super careful in removing it, or think that it is gone.
This happened to me with CPM-SxxV steels.

Running the edge on a burr removal block (cork, hard rubber, wood block, etc) and stropping may help.
I use the blunt_cut's burr folding method.
Hope this helps.
 
As mentioned previously, it's likely a folded burr, albeit very fine. It is possible for a very fine burr to fold and still not be seen by the 'reflected light' observation technique.

I don't rely on visual tests for edge quality or indication of a full apex (like the Sharpie method, which can also be unreliable), but instead focus completely on what the edge is actually doing in cutting tests. The observation that the edge 'sometimes tears paper' and 'sometimes doesn't even cut into it' is classic fine burr behavior. The variability of its behavior is what's indicating the burr is moving & folding. It's more common in softish, sometimes cheaply-produced blades with questionable heat treat and/or heat-damaged edges. I've seen it in a few of my knives, and the fix usually comes down to grinding away the weakened steel near the edge, until the remaining steel behind it starts to exhibit more stability. To do that, I lightly draw the edge vertically over the stone (coarse/medium grit) to scrub the suspect steel away from the apex, then reset the bevels to a full apex and try again. Sometimes, that weak burr-prone steel needs to be scrubbed off a couple or three times, before the edge begins to behave with better stability.

It may still be a good blade that doesn't have heat treat or heat-damaged issues, with just a fine burr that hasn't fully been cleaned up.

My own mantra in sharpening is 'The cutting never lies'. If it's not cutting well (or at all), it can only mean either of two things: (1) it's not fully apexed or (2) there's a burr getting in the way. If it cuts paper repeatedly and easily, it absolutely proves the edge is both apexed and burr-free. That's really the only sharpness test that's proof of success.
 
Last edited:
Depending on your stropping practices, you may have rounded over your apex. It still won't display any visible issue, yet it will no longer slice paper the way it is supposed to.

Agreed about the burr. I usually finish with some gentle high-angle passes on bare leather to make certain I have removed any last bit of burr. Got to be careful here, though, as well, as even bare leather will destroy the maximum sharpness of an apex.

So essentially, I see there being three possible causes for your issue:
1) The edge is not actually successfully apexed
2) You have not successfully removed the entire burr
3) You have rounded over the apex with stropping
 
Blues: okay that makes sense. But I am able to get a burr just fine and remove that burr. I don't have any problems with that.

Thanks,

Bo
 
Ugh now a duplicate reply. Ignore that.

Miso:thank you I will focus on burr removal.

Bean: oh okay, I also use a belt sharpener sometimes which could cause that as well. I just read a post about stropping. It said NOT to use a high angle stroke but either low angle+high pressure or the correct angle + light pressure. Can you guys tell me once and for all the correct way to strop?

Thanks guys,

Bo
 
Bo-dacious said:
Hey guys, I just wanted to get your insight on why SOMETIMES when I sharpen my knife to the point that the apex doesn't reflect any light, but the blade is still dull. It sometimes tears paper when I cut it and sometimes it doesn't even cut into it. Are there any other factors involved or is it as simple as "if the apex doesn't reflect light, it's sharp"? I'm pretty sure the apex doesn't reflect light, but does anyone have any tips on that test? This only happens once in a while. Does anybody have any ideas about this? It would be much appreciated as I am very confused.

Thanks guys,

Bo
Click to expand...
Hi,
Where did you read that the blade is supposed to be sharp when the light stops reflecting from the apex?

When light stops reflecting from apex, its supposed to be close to sharp, as in in within 50 strokes per side, depending on your vision and your grits ,
provided you aren't wobbling very wildly and putting a 40dps microbevel but trying to bevel at 15dps and microbevel at 20

For me if i'm being wobbly but not 1st day extreme wobble, at 600grit , it might be 50 passes per side or more. printer paper thickness of about ~100 micron is easy to see for me, and thats easily within 100-200pps at the wobbliest... a few extra strokes is nothing :)



Cliff Stamp says his personal statistic is about 20 micron thickness of flat on apex is when he stops being able to see a reflection,that is 1/5th or 1/6th printer paper thickness, after which a microbevel (ex +5 degrees) is added in about 5pps on spyderco medium rods (~12 micron) and 5pps on sharpmaker fine stone (~6 micron) , with maybe an extra 2-4pps deburring and 5pps backsharpening strokes


wolfram alpha says 20micron is as a distance ≈ ( 0.1 ≈ 1/10 ) × lower limit for a human eye to discern an object (≈ 2×10^-4 m )
 
Bucket: I picked it up on here somewhere. I remember at least one person saying that it should be at least some what sharp when the edge is apexed. Someone also said you should be able to cut paper after a 220 grit stone if done right. I'm not sure if this is true. What does pps stand for? I don't remember ever reading that. And what is back sharpening? Is that the same as back bevelling?

Thanks bucket,

Bo
 
Obsessed with Edges said:
As mentioned previously, it's likely a folded burr, albeit very fine. It is possible for a very fine burr to fold and still not be seen by the 'reflected light' observation technique.

I don't rely on visual tests for edge quality or indication of a full apex (like the Sharpie method, which can also be unreliable), but instead focus completely on what the edge is actually doing in cutting tests. The observation that the edge 'sometimes tears paper' and 'sometimes doesn't even cut into it' is classic fine burr behavior. The variability of it's behavior is what's indicating the burr is moving & folding. It's more common in softish, sometimes cheaply-produced blades with questionable heat treat and/or heat-damaged edges. I've seen it in a few of my knives, and the fix usually comes down to grinding away the weakened steel near the edge, until the remaining steel behind it starts to exhibit more stability. To do that, I lightly draw the edge vertically over the stone (coarse/medium grit) to scrub the suspect steel away from the apex, then reset the bevels to a full apex and try again. Sometimes, that weak burr-prone steel needs to be scrubbed off a couple or three times, before the edge begins to behave with better stability.

It may still be a good blade that doesn't have heat treat or heat-damaged issues, with just a fine burr that hasn't fully been cleaned up.

My own mantra in sharpening is 'The cutting never lies'. If it's not cutting well (or at all), it can only mean either of two things: (1) it's not fully apexed or (2) there's a burr getting in the way. If it cuts paper repeatedly and easily, it absolutely proves the edge is both apexed and burr-free. That's really the only sharpness test that's proof of success.
Click to expand...

Excellent post. It's pretty much exactly what I experienced this afternoon while playing with a carbon steel Opinel paring knife I purchased years ago from SMKW which was clearly defective but was too cheap for me to be bothered sending back. It looked sharp, felt sharp, no reflected light but the paper told me there was a burr...and I found it. It was a sneaky little bastid too...didn't want to be chased away.
 
Bo-dacious said:
Ugh now a duplicate reply. Ignore that.

Miso:thank you I will focus on burr removal.

Bean: oh okay, I also use a belt sharpener sometimes which could cause that as well. I just read a post about stropping. It said NOT to use a high angle stroke but either low angle+high pressure or the correct angle + light pressure. Can you guys tell me once and for all the correct way to strop?

Thanks guys,

Bo
Click to expand...

Well, stropping is something you'll need to figure out for yourself. JDavis achieves incredible sharpness using an extremely low angle and very light pressure; Outdoors55 uses what looks like light pressure at the same angle as his sharpening and he, too, whittles hair; and I personally use a high angle on a hard strop, then bare leather, and I, too, produce hair whittling edges. So you kind of have to find what works with your personal approach
 
Last edited:
Bo-dacious said:
Bucket: I picked it up on here somewhere. I remember at least one person saying that it should be at least some what sharp when the edge is apexed. Someone also said you should be able to cut paper after a 220 grit stone if done right. I'm not sure if this is true. What does pps stand for? I don't remember ever reading that. And what is back sharpening? Is that the same as back bevelling?

Thanks bucket,

Bo
Click to expand...

Hilarious

pps is passes per side, strokes per side ... as I said above,
to backsharpen is minimize the microbevel created by deburring at a high angle , by doing 5-10 low force edge leading alternating passes per side at the previous angle

a sharpening stone is all the sharpening and deburring equipment needed
 
Bean: good point, I'll try some techniques and figure out what works best.

Bucket: thanks....... I knew What the Ps meant I just didn't know what the first p meant. That's all....

Bo
 
An edge reflecting light indicates flat spots. A clean edge that’s not fully apexed doesn’t necessarily have to reflect light. I wouldn’t use light reflecting off the edge or not as a method of confirming sharpness.
 
Reflected light is an Observational Technique (Secret #4). Reflected light tells you that the edge is wide enough (dull enough) to shine light back at you. When the light begins to disappear, then it is less dull, but it's not necessarily sharp.

That's the problem with the reflected light technique: It is NOT a positive indicator of a fully apexed edge. The BURR (Secret #6) *is* a positive indicator of a single edge bevel being ground all the way to the center.

Cliff Stamp told me that he doesn't have a specific way of getting from "no reflected light" to "sharp". Instead he described it as something that you "get a feel for" after doing it many times. As BucketStove indicated, you might need to do 20 to 100 strokes per side, PAST when you can no longer see light, before the edge is apexed. How will you know? You have to use some other observation to sense sharpness: A cut test, the three finger sticky technique, etc.

To further complicate things, reflected light is not a consistent test. The light source, intensity, and angles involved change the reflection that you see. In some cases, I have seen the reflection disappear completely. Then I have changed my light source or my angle and suddenly the reflection is back!

Reflected light is good for "no burr sharpening" to let you know when you are close. I consider "no burr" sharpening to be a more advanced technique. Not because it's really hard or detailed. More because it requires judgement and/or additional observational skills in order to use it effectively.

Try to build your skill in one area at a time. Learning many techniques can be good and make you more well rounded. Trying to learn many techniques before you gain a competent skill level with a single skill can lead to frustration and mediocre results. Get good at a basic technique and then expand out from there.

Good luck.

Brian.
 
You must log in or register to reply here.
Back
Top