Dull Blade that won't take an edge

E

ericnpeterson

Joined
Nov 18, 2013
Messages
209
Hey group,
Any suggestions for a blade that suddenly is just impossible to get an edge with?
I've got a Case Yellow Trapper that now I just can't get to sharpen anymore.
All my other knives I can get a razor edge with.
The Trapper use to get a really good edge, now, I can sit for hours and it won't even cut paper.
I'm using a Smith Diamond stone to sharpen, and like I said, no problems at all with my others.
Suggestions please?
Thanks!
-E
 
Your trappers temper( heat treat) could be messed up maybe you could try to send it to case is it cv or ss is my other question
 
How are you sharpening? I've gotten pretty decent with freehand, but if I get tired, frustrated, in a rush, I can put different degrees of bevels on that edge and it gets impossible to sharpen...... or seems that way.

It's a whole lot of work reprofiling or correcting an edge. I generally stick it in a DMT aligner to correct as it's much faster/easier.

I would take a good look at the edge with a handheld lighted microscope. Awesome for figuring stuff out with an edge. Look for a wire edge too!
 
If it's been sharpened enough, the edge may be up in a "fatter" part of the blade and it needs reprofiled.
 
Use the sharpy trick.
Mark the very edge of the blade on both sides and give it a few swipes on the stone. The sharpy ink will tell you where you are making contact with the stone. There is a good chance you are hitting the shoulder and not the very edge of the knife. I've done this countless times. If that's the case than just raise your angle just enough to start removing the ink on the very end.
Sharpys are a very important part of my sharpening equipment.

It is early, so if my post doesn't make sense just google "sharpy trick for sharpening". Good luck, I know how frustrating this can be.
 
ericnpeterson said:
Hey group,
Any suggestions for a blade that suddenly is just impossible to get an edge with?
I've got a Case Yellow Trapper that now I just can't get to sharpen anymore.
All my other knives I can get a razor edge with.
The Trapper use to get a really good edge, now, I can sit for hours and it won't even cut paper.
I'm using a Smith Diamond stone to sharpen, and like I said, no problems at all with my others.
Suggestions please?
Thanks!
-E
Click to expand...

This is NOT a heat treat defect, if it previously took & kept a sharp edge (which proves the factory's HT was good). This is, of course, assuming it hasn't been subjected to overheating in the interim, such as grinding on a powered wheel/belt.

More than likely, the steel behind the edge is getting a bit too thick after repeated sharpenings, if it hasn't yet been reprofiled (i.e. thinning the primary grind above the edge). I have an older (1988) Case trapper in CV & yellow delrin that initially behaved similarly (on the clip blade), and it took a few repeated attempts at thinning the steel behind the edge to get it back to razor sharp. Since then, it's been cutting like a laser. On Case '54 pattern trappers in general, I've noticed this same tendency fairly often, mostly with the spey blades. Seems like they could do a little better by thinning the factory grind a bit, on the Trapper.


David
 
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It's a SS Trapper.
I'm free-hand sharpening... but I think I've gotten pretty good at it, like I say I keep all my others sharp.
Mostly only a few swipes and it's sharp.
And it used to get very sharp, never had an issue before until recently.
The Spey blade has never been an issue, I get that edge dangerously sharp.
I think you're right about re-profiling... a machine needs too do that?
How do I go about re-profiling?
 
ericnpeterson said:
It's a SS Trapper.
I'm free-hand sharpening... but I think I've gotten pretty good at it, like I say I keep all my others sharp.
Mostly only a few swipes and it's sharp.
And it used to get very sharp, never had an issue before until recently.
The Spey blade has never been an issue, I get that edge dangerously sharp.
I think you're right about re-profiling... a machine needs too do that?
How do I go about re-profiling?
Click to expand...

I've done it by using a low-angle scrubbing motion, grinding down the shoulders of the edge bevels, on my diamond hones (usually); a Coarse or Fine DMT is what I use for it. It could also be done on other stones, like a SiC stone or aluminum oxide stone of the hardware store variety. Case's SS and CV blades all grind quite easily on such stones and others; I've even done this on an SS Case trapper on a piece of natural siltstone (very fine sandstone) picked up from the ground and used like a waterstone. Since you're already working with a Smith's diamond hone, that should work for it. You might consider using the stone wet, with water or dish soap + water, to keep it from clogging while grinding. Some stainless steels like Case's SS can be kind of 'gummy' and will clog a hone pretty fast when doing heavier grinding. I'd recommend the same for the SiC/AlOx stones, for the same reason.


David
 
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If he has moved up into the thicker part of the blade, wouldn't his sharpening show (using the Sharpie trick) that he is now removing metal away from the edge? I don't care how thick a piece of metal is, it seems to me that you should be able to apex it.
 
postoak said:
If he has moved up into the thicker part of the blade, wouldn't his sharpening show (using the Sharpie trick) that he is now removing metal away from the edge? I don't care how thick a piece of metal is, it seems to me that you should be able to apex it.
Click to expand...

Ability to apex isn't in question; I'm sure it will be apexed so long as technique is good, and he's indicated he can get all his other knives sharp (therefore good technique probably isn't in question either). The assumption is that the steel behind the apex is becoming thicker as repeated sharpenings have moved the edge further up into the thicker portion of the primary grind. If he's been resharpening each time at the same angle as always, but with the steel behind becoming thicker each time, the cutting ability of the edge will degrade as the edge is moved up. There comes a point where even if the edge is cleanly apexed, the thickness of the steel behind it will predominantly determine how the edge cuts, and the crispness of the apex itself won't be able to make up for that. That's the reason for the recommendation to thin the primary grind (reprofile), to get the thickness of the new edge back to where it'll perform as expected. Speaking hypothetically, if he's been sharpening to 40° inclusive, that'll do OK if the primary grind behind it is relatively thin. But 40° inclusive, at just a little bit thicker primary behind it, will degrade rapidly in cutting ability, even to a point where the edge can seem 'dull' with a crisp apex on it; especially if the usual standard for 'sharp' is doing things like slicing paper or shaving/hair-popping, which sometimes goes away entirely if the apex isn't absolutely perfect.


David
 
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If I'm not mistaken, the stock thickness of that blade is going to be thin even after being worked back a bit. If the edge angle is increasing with repeated sharpenings that might account for the loss in performance. HT being bad is not likely as t used to hold an edge and now doesn't - the opposite of a burned factory edge.
 
The OP, Eric, says the blade won't cut paper. If an edge won't cut printer paper, I don't think it's been apexed. The two edge bevels have not been ground until they meet in the middle. Even a very thick edge should be able to cut paper if it's apexed.

I would use the reflected light technique to see if the edge is dull enough to reflect. If it is, then it needs more work to apex it. It either needs more work at a low angle, or less work at a higher angle.

Brian.
 
Another idea:

If he's been at it 'for hours' (per the original posting), it may be worth checking to make sure the diamond hone isn't already clogged up. I used to run into issues like this with my Lansky diamond hones on softish stainless; some diamond hones seem to be much more prone to clogging than others. If the hone is clogged up, it'll stop cutting and do nothing but blunt the edge instead. Just something to check into, to be sure...

Give the hone a good scrubbing with an old toothbrush and perhaps some Comet/Ajax powdered cleanser & water. Then try again.


David
 
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I could, and have, put a sharp edge on a plastic putty knife or a strip of mild steel fabrication material.

Get a seriously coarse stone and get that roundy edge offathar.
 
Yeah, I've been cleaning the hone, used water... mineral oil when sharpening, sometimes I use just water.
Even using the coarse side has not helped this knife... now it's like a butter knife.
I'm thinking of just taking it to Ace hardware... they sell Case knives there and do sharpening... maybe a machine grind
will reprofile the bevel for me?
 
ericnpeterson said:
... I'm thinking of just taking it to Ace hardware... they sell Case knives there and do sharpening... maybe a machine grind will reprofile the bevel for me?
Click to expand...
Hi,
Why do that?
You've sharpened before and have other razor sharp knives you can use,
so you can take your time with this one,
and figure out what is going on,
its only one of two things,


not likely, but you're wobbling too much, so angle is different with each stroke
or you keep forgetting what the angle is, so every fifty or one hundred strokes you switch to a different angle
you keep lowering the angle, so each time its taking forever, and then you lower the angle again...
you don't have to "rebevel" all at once from 20 degrees per side down to 10, start with 20 degrees or 19 degrees


I've done all these things, you just have to look at what you're doing, figure out which thing you're doing wrong, then don't do it anymore :D

Try this, grab two or three magazines and make yourself a rebeveling jig, put one magazine on edge of table, and then use the other two for your wooden block, one magazine for raising a burr (lower angle), two magazines for cutting the burr off (double angle), raising the burr takes the most time, if its taking more than 5 minutes increase the angle (move closer to edge of table)
Simple sharpening jig - stefanwolf88
How to Sharpen a Knife with Paul Sellers
PaulSellersKnifeSharpeningSystem.png
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ericnpeterson said:
Yeah, I've been cleaning the hone, used water... mineral oil when sharpening, sometimes I use just water.
Even using the coarse side has not helped this knife... now it's like a butter knife.
I'm thinking of just taking it to Ace hardware... they sell Case knives there and do sharpening... maybe a machine grind
will reprofile the bevel for me?
Click to expand...

How coarse is the diamond hone?

Also, if you do visit ACE Hardware, you might consider picking up one of the SiC stones they carry. If there's an issue with the diamond hone you're using now, trying an alternative stone could be worthwhile, and a SiC stone works well with Case's blades anyway. I'd personally not give anybody my knife for sharpening, without first knowing for sure they'll do a good job (especially if they're using powered sharpening equipment). See if they can show you what they use for sharpening and how they go about it, first.


David
 
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