Abrasives and edges

[grepper]

A jig was used, set at a twenty degree angle in order to insure consistency. The edge images are approximately 200X.

I designed version two of the beautiful knife rest that I built for the Tormek, and stuck it on a belt grinder.  I then sharpened using the following abrasive belts.  In order:

150 grit   aluminum oxide
400 grit 3M Trizact "Gator" aluminum oxide
800 grit silicon carbide
1200 grit (9 micron) 3M Microfinishing Film
Smooth side of leather stropping belt using Tormek honing compound

With each abrasive I attempted to get the blade as sharp as possible.

Here's a picture of version 1 prototype beautiful knife guide and version two stuck on the belt grider:

Version 1 beautiful knife guide:



Version 2 knife guide stuck on a belt grinder:





Here is the knife.  It's an Oneida that I subject to all sorts of torture.  So please no complaining about the edge profile.    Note the blue line. This marks the area we will be viewing in all the following images. 




Here's the edge through the succession of abrasives:

150 grit:  This basically destroyed the edge.  I could not get it sharp.  Touching the belt formed an immediate burr on the opposing side. Further attempts just ground away metal.  If lightly honed at this point, it would basically be a saw:



400 grit:  Getting a little sharper.  Barely hangs on nail.  Saws well through paper.  If lightly honed at this point it would be useable for any type of situation where a very toothy, aggressive edge would be useful.



800 grit:  Getting very sharp.  Still a little toothy.  Chop cuts paper pretty well, but somewhat grabby.  Slices paper nicely.  Honed now would be very generally useful.  Nice edge.



1200 grit:  It's very sharp.  Chop cuts paper, hangs well on nail.  A very useable edge.  Still some tooth, but very sharp.  Accidentally bumping against your hand and you will bleed.  The next step is honing.



Honed using Tormek honing compound:  It is extremely, flesh slicing sharp.  When handling this knife it demands the respect due when handling a scapel.  Chop cuts and melts through paper.  Be careful around fingernails.  It is extremely sharp and rather dangerous. 

This is an interesting edge.  The image doesn't due justice to the mirror finish.  It would be great for a cleaver, or probably woodworking tools, or if you wanted to cut non sinuous flesh. .  While very sharp, it suffers limitations in normal use.   I've used knives like this on overly ripe tomatoes with tough skin, and oddly, even though they are razor sharp, they just ride on the surface and smash the tomato.  You need to first break the surface of the skin and then they melt through the tomato like butter.  For an everyday kitchen knife, I'd knock it back down to 800 or 1200 grit to give it just a little bite.



The next version the knife rest I plan to fabricate completely of metal and use a 180 degree articulating ball camera mount head from a tripod for easy, infinitely adjustable rest positioning.

One interesting thing about the knife rest:  It's easier and faster to just do it freehand, and freehanding achieves just as fine of an edge.  A rest is necessary however, at least for me, if the requirement is to match an existing bevel angle.

Hope everybody finds this as interesting as I did 

[Herman Trivilino]

Nice documentation, Mark.  What's the bevel angle?

[grepper]

The block o' wood is cut to 20 degrees.  But as I remember from your jig, there is more to knowing the angle than just the angle of the rest.  Seems like you added in the angel of the blade itself?  You have understood more detail on that than I have, but at any rate, the block o' wood jig/rest/guide thing is chopped at 20 degrees.

[Rob]

very nice work.  What still confuses me is that your tests and also that study Jeff posted completely refute the data supplied by the Canadian article?? You're now back with the traditional Tormek assumption that honing just works and gets you a sharper edge (as long as it's finely and well sharpened in the first place).

He was saying it degraded the steel...it risked giving a multi faceted edge etc.....its becoming like bloomin doctors and cures for things....you don't know who to believe in the end there are so many competing theories!

[grepper]

In the article by Brent Beach, he was sharping to 0.5 micron which is like 60,000 grit.  The Tormek compound, according to Jeff, contains equal amounts of 1,2, and 3 micron abrasives. Most other crayons and compounds are coarser than that.

So, if you start with 0.5 micron in the first place, honing with anything more course is going to degrade the edge.

The thing that makes the Beach article confusing is that it's easy to miss the fact that his edge was so finely sharpened to begin with.

I went from 1200 (15 micron) grit and then honed with the Tormek (8,000 - 14,000 grit) compound, so obviously it further smoothed the edge.

[Rob]

right...so he's only arguing stropping makes an edge worse when the grit size of the paste abrasive is actually larger than that used in the original sharpening?  Cos I must say, I didn't get that....that's kind of obvious right? What I got from it was that the stropping process affects the stability of the steel edge somehow?? 

[grepper]

Well, Rob, I think you summed it up nicely.  You saideth, "so he's only arguing stropping makes an edge worse when the grit size of the paste abrasive is actually larger than that used in the original sharpening?...that's kind of obvious right?"

Looked at from that perspective it does sound rather, umm... duh. LOL.

I guess he was just out to prove that different honing compounds are really not as fine as 3M .05 film film.

Nonetheless, I did come out of it with a better understanding of how micro abrasives and honing compounds effect steel.

[Herman Trivilino]

I think that what's also being said is that honing is not as good as grinding, when you're at that scale of a very small abrasive particle.

So, yes, it would probably be better if you polished the edge on a water stone after sharpening with a Tormek, but the honing with the leather wheel is faster.

Reminds me of the NASA director's incentive to make space travel faster, better, and cheaper.  After he was given his chance to succeed we found out that you can have any two of those three things, but only at the expensive of the third.

So in this case you can get a better edge with a 0.5 micrometer abrasive.  And it'll be cheaper.  But it won't be faster.

[Rob]

Right....I think that's sunk in now....so with respect to the Tormek then, with a regular wheel.  We grind to 1000 grit and get a pretty fine edge.  According to the logic we've just discussed, do we not then jump straight from 1000 grit to a very fine paste grit size?  I forget what grit size wheel equates to what Micron particle size in the paste (Herman documented it recently), but do we not fall directly into Herman's NASA analogy whereby the gap between a 1000 grit graded stone and the paste particle size (in the off the shelf Tormek paste) is too wide? At least wide enough to require a long time to really get a fine edge?

I appreciate this is theoretical because for pretty much everything I do, after 1000 grit and de-burring on the strop, my tools are easily sharp enough for practical purposes. This is for me about really understanding whats happening at the strop because as recorded earlier, try as I do, with the recommended techniques, I still get mixed results with the strop.  It's very tempting (I know) to simply chalk that off to poor technique, but I've been doing it for a long time now, it's not like I'm an unconscious incompetent, quite the contrary, I'm acutely aware of every nuance of the stropping procedure and believe I'm conscious competent.

This thread is very useful in understanding the process at the very edge.  My goal here is to have 100% confidence in the approach being taken so it will consistently yield, predictable results.

Straw poll in the interest of academic research....who here has reached that (apart from Jeff of course)?

Who here, including the veterans, can HONESTLY say that after stropping they are 100% confident the edge is sharper than it was after sharpening every single time, no matter what the tool?

[mike40]

I don't have enough experience with my Tormek to express an opinion about rehoming, but after sharpening my first plane iron to 1,000 grit on the stone wheel. I tried it out a little before honing just so I could see the difference . After honing it had an excellent edge. This is a Stanley/Bailey iron in my S/B #4. I've been using it this morning to smooth some construction fir (Norwegian Spruce) that I'm using to make some new tool holders. I've planed 4meters in length in total  which are now smooth as silk in spite of the hard little knots, all without any chatter. I avoided the one large knot on the 3 boards which was resawn from a 2X4 as it will be eliminated. I am very pleased with how well the edge is standing up. When finished I could not feel any difference in the quality of the cut or the beautiful gossamer shavings I got. I guess I will try honing it when it gets dull to see if that alone will restore the edge, and if so, how long it will last compared to the initial sharpening.

[grepper]

One thing that I got from the Beach article is that I don't like the term "honing". I think it just confuses what sharpening is.

Folks seem to use the term honing when using an abrasive not fixed to a surface as when using a "honing" paste or crayon stick.  Either way, it's just applying a steel cutting abrasive to some sort of surface and sharpening.  But as long as it cuts steel this is still just sharpening, the only difference being that it is using finer abrasive on a soft surface.

As far as I understand it, stropping is different from sharpening.  Stropping uses a surface, such as leather, that is to soft to cut steel and actually further sharpen the edge, but it could still straighten a slightly bent edge, thereby conditioning the edge.  However, just to confuse things, "honing" compound can be applied to a leather strop.   Maybe that should be called stoppening.

As long as steel is being removed with a finer abrasive than was previously used, the bevel should still get smoother and the edge thickness reduced.  In other words, it should become sharper.

It is however fairly easy to dull an edge using the stropping wheel.  Why?  Because if you don't use a jig, it would be very easy to apply the edge being sharpened at a greater angle than the edge was previously sharpened to, thereby rounding the edge.  I suppose that because the leather on the wheel is soft, if you pressed hard enough the leather could actually wrap around the edge, thereby increasing the angle and dulling it, but I find that is probably not as likely.

Maybe "honing"  just means refining a sharpened edge.  But then where does sharpening change to honing?  1000 grit, 2,000 grit or maybe 12,000 grit? 

I think I'll just stick with sharpening and stropping.  Stropping with or without compound.  If using a steel cutting compound, it's still sharpening, but just using a strop as the substrate to hold the compound.

[mike40]

You right right Mark. Stropping is what the leather wheel really does. With respect to the Tormek I have been describing work with the stone wheel as sharpening and honing as work for the leather wheel just for discussion purposes, but in fact the definition of honing is to refine a ground metal surface .Any kind of sharpening beyond rough grinding could be called honing. So I will call the leather wheel work stropping from now on.

[Rob]

Its actually very confusing because throughout this forum the term "honing" is generally accepted to mean stropping with the leather wheel :-)

[jeffs55]

Great pics and very interesting but what has this got to do with the Tormek as it only has two grits plus the honing wheel?

[Rob]

you would need to read through the whole series of threads on stropping and abrasive particle sizes to appreciate the entire debate.