Mid-tech edge retention

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rdmalak

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Hi all,

I was wondering if I'm the only having issues with edge retention on a Mid-tech? Before I use the knife it is very sharp to the touch, after every use it's quite dull to the touch. It takes at least a strop or a ceramic rod to bring it back. Then next time I use it I have the same issue. Am I expecting too much from a semi-custom knife of this price? My other gyutos (AS, Blue#2) go through way, way more before trips to the strop.

I appreciate any input on this. Thanks all
 
I have tried both of those methods. No dice. :(

Have you ever sharpened a knife with this steel? I have no experience with it, but it could be that whatever methods you're using are forming a 'micro burr' for want of a better word.

Inspect the edge with some magnification perhaps, see if you can see a non-tactile wire edge.

If not, I'd maybe suggest contacting the maker? That would have been my first suggestion, but maybe you already went that route.
 
what is the knife? "mid-tech" doesn't actually mean anything, particularly. despite that, user error is almost certainly the issue.
 
As others have mentioned, it could be user error and you're not actually removing all of the bur. Some steels / burs are kinda tricky and you really have to hone them down and then run them through soft wood, hard felt, or something with a bit more "grab" then cork.

However,
On some blades made out of tough steel with a chip-resistant temper, I have noticed what seems like a fatigued, not wire, edge. This seems happen to edges that have been maintained for a long time with just rods and strops. So, the steel at the edge has basically just been deformed and realigned time and time again without actually removing any/ much of the steel. It will feel sharp, look fine, and not show any sign of a bur when pulled through cork or examined under magnification, but it will deform back out of alignment very quickly when used. It's just been bent back and forth too many times and needs to be removed.

How many times have you fully sharpened it (taken it though a full progression on the stones)?
Another other thing that can happen with knives that are ground and sharpened too quickly using a high-speed belt or wheel is that the thin metal at the edge heats up too hot and the temper is messed up. This can usually be corrected / improved after a few sharpening and thinning sessions as you remove the damaged steel near the edge and work your way up into what was originally slightly thicker material behind the edge which was not weakened in the same way from the grinding heat.

A third possible cause is that your edge angle is just too acute for the steel and it just can't support it for long.

In the ended it could be any 1 or a combo of these things. But the solution is the same no matter what: give it a good sharpening, not just a stop / hone.
Take it to your coarsest stone and take off a bit more steel than you normally would. Set a nice fresh primary bevel and then work up though your stone progression. Created what you know to be is a clean, fresh edge with no bur, and with a reasonable angle (sometime in the range of 25-30deg as the sum of both sides).

Alternately, if you don't trust your own skill, you could take it to a pro (like Pierre, I dont know anyone else in Canuck-land) and request that they do the sharpening (with waterstones) described above. That way you take yourself out of the equation.
 
First off, yes it is a Rodrigue mid-tech. My fault for not mentioning this already. So this, to me, means the steel is not an issue but I have never had a knife made of this steel before. It should be able to handle a pretty acute angle.

The edge it came with was not great so I brought it to 1000 grit and started again. Brought it up to 4000 only.

I have not used it much due to this issue so it has not been over used on the strop or rod.

I will try and sharpen it again and report back. I was hoping that this knife was going to be as easy to maintain as my other ones but maybe I was incorrect.
 
I actually haven't talked with him about it. Maybe I'll send him a PM.
 
As stated, I have resharpened this knife. This was my progress:

- 1000 until a heavy burr/ once per side
- 1000 until light burr/ 2 times per side, and then some stropping strokes
- 3 draws through wood and cork to knock off the burr
- 4000 was the same
- Same wood/cork de-burr
- 8000 on right face for 5 strokes and 2 stropping strokes on left side
- Both sides on natural stone until could feel good suction
- Wood and cork again

It seems very sharp now. I will report back on how well it holds this new edge.
 
Finishing with the 4000 grit stone may help. Finishing with too fine of a stone on certain steels with some heat treatments will cause them to loose their edge quicker than normal. Mess with it and see if it helps.

Hoss
 
Alright so I used this knife tonight to cut up a bunch of onions and it was most definitely better than before. It still loses it super keen edge quite quickly but is now retaining a much better one than before. Next touch up I will take Devin's advice and not go to too high a grit.

So then my question now, is it normal for CPM154 steel to drop to about 70% sharpness after use? I have never had any experience with this steel before.
 
I sharpened up mine today and noticed that it holds on to a burr/wire edge tenaciously. Also, in my past experience with powdered steels they do loose that super keenness relatively quickly but hold onto a good useable edge for what seems like ages. Jury is still out though on this one as its not my go to knife for heavy production but rather for more detailed work so it doesn't take a beating. Time will tell.
 
That's good to know. Thanks for the info on this type of steel and your feedback about the blades edge holding. I hope you are right. Mine seems to be much better.

How high did you go in your sharpening? 5000?
 
This time around I took it to king 6k. Which is kind of my baseline stone to get a feel for what a steel likes. The last time I took it up to the 10k that Dave used to sell and it kept a good edge for a good bit. I too am still trying to find the sweet spot for this one. I have noticed, given the flexibility of the knife, and probably at the edge as well given its thinness light pressure and patience is a must.
 
I have noticed the same behavior that K-Fed mentioned with PM steels (sg2, CPM154, ZDP189, S30V), all dropping that initial hair-popping edge just as fast (sometimes faster) than good simple carbon, but that "OK" 80% or so edge will last FOREVER.

Getting the most out of steels like these is really a (I think fun) challenge. Like anything, it all comes down to learning the characteristics of the steel, and paying attention to what you do/ how it affects the edge and edge retention.

As I mentioned before, I've found that lowering the overall angle helps as the steel just doesn't seem to support a super acute primary angle. You can also mess around with compound angles where by you lay the first bevel at an angle that is too small for the steel and then go back and put a large angle bevel on the egde of it. I do this on both sides with my SG2 knives and it works well. The angles are not as high as Jon shows that he uses for a 'micro bevel' but they are higher than I would normally sharpen other knives at. This way the fine edge gets a bit more support, but you don't have the higher resistance to cuts like you would normally get if your whole bevel was set at that more obtuse angle.

You also don't necessarily have to "stop" at lower grits; just spend less and less time on the finer grits so that you don't completely remove all of the teeth from the lower grits. A polished toothy is a beautiful oxymoron.
 
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