Question about using magnification to look at your edge

[MT Hanson]

So I have some decent knives and a WorkSharp and I'm trying to solve the edge mystery. I picked up a cheap 60-100x pocket microscope from Radio Shack so I could see what was going on.

So now what? I can see how even the bevels are, which I guess is telling me how consistent my angle/pressure are. I can see how smooth or coarse the scratch pattern is, and if it's the same on both sides (wow; had one that wasn't close). And I can see any micro-chips on my wife's cheap, constant use cooking knives. I guess if I had a burr too small to feel I could see that too.

What I can't see is how sharp the edge actually is. I could be looking at a mirror bevel, perfectly uniform down the length of the blade, but the edge might be 1mm across. The quality of the scope is such that I can only look at the flats; there's not nearly enough light to tilt the blade and look at the actual edge. So what am I looking for? What are the signs, looking at the bevel, that you're "getting there"? Is there a trick or method I'm missing?

 

[Jason B.]

Your missing what I want and that's a SEM, the apex of a well polished edge is easily submicron in size and not much shy of a SEM will view that.

Because of its power your scope will only work well with coarser grits.

 

[HeavyHanded]

I have access at work to a metallurgical microscope that can go to 1600x. I typically use it at 640x because anything finer and I have to focus through a drop of oil. Even at these magnifications, you cannot tell how "nice" the edge is by looking at it. You can tell if it has a burr, or if you've gone all the way to the apex with a grinding step. You can tell if it will cut toothy or refined if it does cut well, but it reveals very little in terms of predicting real performance. At the below magnification, a human hair takes up about half or just a touch more of the viewing area. BTW this edge can shave an arm baby-smooth and dry shave facial hair with just a bit of tug. Done on a DMT 1200 grit and quickly stropped with Flexcut Gold. The debris still visible is from the strop and a bit of metal left from the stone. Focal depth is only a few microns, so very difficult to get a good pic, especially on my workbench and without the piece clamped down.

 

[Obsessed with Edges]

You ABSOLUTELY NEED BRIGHT LIGHT, for starters. Any magnification device (camera lens, binoculars, telescope, microscope) is going to lose a lot of detail in dim light. If necessary, use other lamps nearby to brighten the field of view. The swing-arm style lamps are very handy for this, they can be moved/tilted/rotated as needed to direct the light where you need it. The downside of using a 'pocket microscope' at very high magnification, is you have to keep it very close to the object under inspection. If the built-in illuminator is not very good, this creates more problems than it solves. You might also pick up a standard magnifier in the 10x - 15x range, and use it with external illumination (nearby lamp, or daylight). With better light, you'd do just as well, maybe better, with a lower power magnifier, than you would with high mag under very dim light.

As for what you're trying to see, the light is especially helpful in revealing wire edges, rounded edges, or an edge that hasn't been completely apexed. In each case, the light will be seen reflected in a bright 'thread' along the edge itself. You tilt & rotate the blade under the light, and at certain angles, you'll see that bright thread shining along the edge. If, on the other hand, the edge were perfect, it would be so thin as to not reflect the light. You'd see a reflection from the bevel itself, then as you rotate the blade, that bevel reflection would 'switch off', and the edge would seem to disappear, as it's not reflecting the light.

Any defect along the edge, such as wire edges, burrs, chips or rolled edges will stick out light a sore thumb, IF the light is bright enough. It's steel; it'll GLARE like a mirror in the sun, so anything that doesn't look like a perfect 'V' on the edge is really going to stand out.

The other important thing to do, is to closely examine the edge of a very good/excellent cutter, and correlate what you see under the scope with how the edge is actually performing. Always compare the edge performance to what you see under the scope. If you're slicing paper, for instance, and you notice the edge hangs or grabs the paper at certain points along the edge, use the magnifier to inspect those specific points (in fact, mark the blade near those areas with a Sharpie, so it'll be easier to find them under the scope). Odds are, you'll see a burr, dent or chip there. If the edge is just sliding over the paper without cutting it, look for a rolled edge or a dull/blunt/rounded or overly obtuse (thick) edge.

 

[Sparljo]

What I can't see is how sharp the edge actually is.

Bingo... you need to cut what you are intending to cut and see how it goes.

If you are just playing around trying to get the best polish possible etc, carry on.

 

[unsichtbar]

Any suggestions of brands/model for a cost effective digital microscope lap top setup say 600- 800x ?

 

[HeavyHanded]

The USB desktop ones generally only go to 2-300 and get a magnification boost by displaying larger on a monitor. My shop settled on a metallurgical one with a 5mp camera (wish we'd sprung for the 9megapixel camera). You have to spend a lot of $ to get a good digital microscope (CSI quality) and even then it won't be as strong as a much cheaper optical microscope. We paid about 800.00 for ours and can view opaque materials to 1600x.

 

[MT Hanson]

What I can't see is how sharp the edge actually is.

Bingo... you need to cut what you are intending to cut and see how it goes.

If you are just playing around trying to get the best polish possible etc, carry on.

Well, I know how well it cuts; I've been struggling with improving my edges. I was trying to use the mag as a tool to see what I was doing wrong/right. It is handy for seeing what's getting to the apex and what isn't, but I guess for $12 I shouldn't expect miracles.

Thanks for the responses. I've yet to see a knife tree-top hair if that means what I think it means. I think I'm destined to be happy with shaving or cutting news print. Which is fine for my uses, but when I have some spare time I like to chase unicorns. Can't seem to catch this one.

 

[Obsessed with Edges]

Well, I know how well it cuts; I've been struggling with improving my edges. I was trying to use the mag as a tool to see what I was doing wrong/right. It is handy for seeing what's getting to the apex and what isn't, but I guess for $12 I shouldn't expect miracles.

Thanks for the responses. I've yet to see a knife tree-top hair if that means what I think it means. I think I'm destined to be happy with shaving or cutting news print. Which is fine for my uses, but when I have some spare time I like to chase unicorns. Can't seem to catch this one.

Don't be too discouraged yet. Progress usually comes in steady, but small, increments. You'll get there. I'm generally happy if I can do just a little better each day, as opposed to trying to get it all at once. Just keep looking at your edges and comparing what you see, with how the edge is cutting. That will make a big difference, and you'll get better at recognizing what's going on with your edge (dull/rolled/burrs/dented/chipped/etc.), based on how the edge is performing.

 

[HeavyHanded]

Well, I know how well it cuts; I've been struggling with improving my edges. I was trying to use the mag as a tool to see what I was doing wrong/right. It is handy for seeing what's getting to the apex and what isn't, but I guess for $12 I shouldn't expect miracles.

Thanks for the responses. I've yet to see a knife tree-top hair if that means what I think it means. I think I'm destined to be happy with shaving or cutting news print. Which is fine for my uses, but when I have some spare time I like to chase unicorns. Can't seem to catch this one.

When I use it it means that running a blade along my shin about 1/8 to 1/4" above the skin, the amount of resistance provided by the hair plowing into each other is enough for the blade to cut hairs -not every single hair, but you'll see a bunch come off with each pass. I'll also see little curls of hair being shaved off of individual hairs as it rides along. At this point you're at or very near hair whittling. I suspect you're a lot closer than you think - I've read on straight razor forums of folks getting their razors sharp enough to shave arm hair on a stone, and getting it to pass a hanging hair test with nothing but stropping after that. Of course that's with a 15 degree (approximate) inclusive edge bevel but you get the idea. If you're not stropping, give it a try - by hand, there's no other way to refine an edge to such a degree without some very expensive stones and a lot of skill.

For me its always been 2 steps forward, 1 step back - the more you learn, the more you have to reorder what you know - and it becomes difficult to dream up good batteries of cutting tests. No other way to learn.

 

[David Martin]

Some of those guys really know how to sharpen razors. :thumbup: DM

 

[MT Hanson]

If you're not stropping, give it a try - by hand, there's no other way to refine an edge to such a degree without some very expensive stones and a lot of skill.

I did make a strop out of a $4 piece of tool leather from the craft store. Mounted it on a paddle, let it drink up some neatsfoot for a couple of days, then standard white compound. One of my problems that the magnification exposed was that my angle was too high and I was rounding the edge; a really shallow angle works better, I guess because the leather is fairly soft now and has some give. If I'm not going for mirror edges, is one strop good enough or would I need another one with green compound?

 

[Obsessed with Edges]

...If I'm not going for mirror edges, is one strop good enough or would I need another one with green compound?

If mirror edges aren't a concern, you'd likely do fine with a bare strop. If I were to supplement it with another, I'd probably use a diamond compound instead of the green. The green is very small grit (0.5 micron), and not quite so aggressive as diamond or silicon carbide. It's effect on a relatively coarse edge would likely be minimal, by comparison.