Difficult to sharpen knives

[grepper]

Hey Herman...  I have a pocket knife that I am having difficulty getting sharp.  I've labored away at the thing and no matter what I try it just won't seem to get very sharp.  I've tried coarse wheel, smooth wheel and all in between.  Pressing hard or letting the knife ride on the wheel with almost no pressure doesn't work either.  I've tried thinning the blade with a 15 degree angle and then putting a 20 degree primary bevel on it.  That got it a little sharper, but still not really sharp.

I know Herman has mentioned this before, and now I've seen it on several knives, pocket knives and kitchen knives.  Both new and old knives, I don't think it's an issue that someone used a dry grinder and overheated the knife, or some kind of after production tempering of the blade.

I found the following post about the edge just crumbling away as it's being sharpened.  I can't really tell anything looking at it using a 200X scope, so I don't know if that is happening or not.  http://forum.gon.com/showthread.php?t=729868

The steel on these knives seems pretty hard, but I'm removing metal so I'm doing some-"thing" to it.  Basically just wearing it away. 

The only useful suggestion I've seen is to throw the knife away and get a different knife.

Any metallurgists out there with any ideas?   I'm worry that in my frustrating failure I may start to suffer feelings of inadequacy.

[Herman Trivilino]

You are simply not spending enough time grinding it?  That's the only thing I can think of.  You should be able to monitor your progress with about 40X magnification.  If you are grinding all the way to the edge, you will be able to tell.  If pieces of the edge are breaking off, you will be able to tell.

Try grinding at a more blunt angle and see if you have any luck.

If the steel was softened due to heat treatment it should still take an edge.  If it was hardened you should be able to tell because you either won't be able to grind the steel or chunks of the edge would be breaking off.

[grepper]

Herman, We've talked about this before.  You had mentioned that you had some knives that you just could not get as sharp as others. 

Did you resolve the issue by just grinding longer?

I generally can get a very sharp edge, but occasionally I run into these hard to sharpen blades.

Since you had noticed the same thing, I just wondered if you figured out what was going on.

Mark

[CleanCut]

My eyesight is not what it used to be. What methods are used to monitor progress with grinding? Well positioned light and magnification would be requirements.

[grepper]

Hi CleanCut,

Welcome to the forums!

I've got great lighting and a 20-200X microscope if need be.

I just carefully feel the blade. I can tell when it's getting really sharp. Additionally, it's obvious when a good burr forms.  Also, it hangs on a fingernail, cuts paper etc.  All the standard tests.  It's not hard to tell when sharp is happening.   

The knife I'm talking about I eventually got sharp enough to shave the hair off my arm, but it's still not really super sharp.  A little "hangy" on some paper, especially cross-fiber, even though it's mirror finish due to honing.

Pretty sharp by some standards, but not where I want it.  I still have not figured it out.  Frustrating.

[Ken S]

I would like to share an experience with Cleancut, which might help Mike as well as the forum:

When I first started using my Tormek, my "workshop" was also the garage.  One of several problems was inadequate lighting.  One day I happened to set up my Tormek on my Workmate outside.  I was amazed with the difference really good light made.  The little anglemaster, which I had previously thought was poorly designed, immediately transformed into a useful tool.  Working became pleasant.

Since I moved, I now have a basement shop.  The lighting would appear to be much better (plenty of overhead fluorescent light).   This might be OK for younger eyes.  However, as stated in the Tormek Handbook, good task lighting is required to effectively use the machine. 

So, my advice is to spend some time arranging the light to where you can see really well. 

Ken

[Ken S]

Leonard Lee refers to "tooth" in an edge.  For cutting tomatoes and rope this is desirable.  he recommends a 1000 grit water stone for sharpening kitchen knives. That's about equivalent to the Tormek wheel dressed fine with the burr knocked off by the honing wheel.

For a more polished edge, it may be necessary to go beyond the scope of the Tormek.  An 8000 grit water stone or finer would do this, as would fine diamond paste.

The traditional fingernail test has satisfied my edge testing needs, although the paper test seems promising.  I applaud those of you who use microscopes.  You will push back the sharpness frontier.

My grandchildren are awake....time to close.

Ken

[Herman Trivilino]

Herman, We've talked about this before.  You had mentioned that you had some knives that you just could not get as sharp as others. 

Did you resolve the issue by just grinding longer?

That's hard to say, Mark.  Since I started monitoring my progress with a 40X microscope I've not run into that problem.

Sometimes you just have to grind longer.  It's amazing what you see at 40X magnification.

[Herman Trivilino]

I just carefully feel the blade. I can tell when it's getting really sharp. Additionally, it's obvious when a good burr forms.  Also, it hangs on a fingernail, cuts paper etc.  All the standard tests.  It's not hard to tell when sharp is happening.   

While that's usually the case, I've encountered situations where I could see or feel the burr.  Even with a magnifying glass and good light.  I need the 40X magnifier to see it.

I've no doubt that more experienced sharpeners can see or feel the burr in cases where I cannot.

Another trick is to wipe the blade with an old towel.  The burr will snag the fabric and leave lots of loose threads hanging.  These threads are visible to the naked eye, but are best seen with a magnifying glass.

The cheap magnifying glasses are now made out of plastic but work well.

[mike40]

I have a hard time seeing the burr too. I think the fingernail test, the paper and the pine end grain shaving work ok, but the absence of a candle on the edge seems like the ultimate test to me, although good

magnification is necessary to do this. I have been checking the candle with my magnifier light mounted on my scroll saw, but I think a jeweler's magnifier would work a lot better. When I first  started hand

honing I found that it didn't take much to ruin a nicely sharpened edged with my leather strop before I learned how to use it better. I understand that the burrs shouldn't be wiped away as that can cause tear

out to the edge. I read in the Tormek book or maybe in a Tormek video. Makes sense to me. I have always removed the wire edge with the leather strop, so I was unconsciously doing the right thing apparently,

but in spite of  that, the Tomek produces a better edge the I could do by hand using my diamond plates.