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 Post subject: Re: Starting a new edge?
PostPosted: Tue Feb 25, 2014 2:48 pm 

Joined: Fri Feb 14, 2014 4:23 pm
Posts: 7
bgentry wrote:Cliff says 20 microns wide


To clarify, I should be more careful to note that exact statistic is mine, in general it depends on the visual acuity of the person, for me when an apex hits 20 microns I have trouble seeing it under light at all, even with careful inspection. I determined this by measuring the apex widths at various points; when I could see them clearly, when they became difficult to see, when I could only see them under careful rotation and when I could not see them at all. For me 20 microns is the point at which it hits the latter fairly consistency, however if you have exceptional visual acuity (mine is average) you could likely see it smaller. For most people they will stop seeing the edge at a far higher apex thickness because you have to turn the edge carefully to get it to reflect the light as otherwise it just scatters it. But it is trivial to learn how to do properly as it is just rotating the knife side/side and then up/down to see if it catches the light.

bgentry wrote:Once I've eliminated the reflection and want to polish the edge bevels, how do I know when to stop?


Brian, there are two direct ways and an indirect way :

-visual, magnification
-physical, cutting

The indirect way is experience because in a short period of time if you pay attention (and count) you will quickly realize how long it takes to reset the edge when you change abrasives. You can also develop a feel for the stone because a fine stone cutting into a coarse finish feels different than working on an edge which matches its grit pattern.

The thing to realize in general is that (coarse rule) it is better to go a little further than to not go enough. If you leave a coarse scratch in an edge and don't remove it in an intermediate grit it takes much more work at the finishing grit to remove it than if you over stressed the edge slightly and increased the burr size.

All I would suggest is that in the beginning you go a little further than you have concluded is necessary, keep track of honing times, and gradually try to zero in on the minimal grinding each time you sharpen. For me this keeps the challenge there and keeps it from getting boring, set goals and try to achieve them to keep it fun and rewarding as well as practical.


ken123 wrote:
You are using a ~ 10x difference in grit here and would be better served with a 1k stone.



It isn't better for reasons I have noted which defines how it is being evaluated, yes you can define a different criteria and you can do that with any evaluation.

Image

This is the edge off of a 121REX/70 HRC knife with the 700X Bester, honed with the above methods at ~150X linear magnification (the angular magnification is listed over 400X). This apex is formed with minimal burr and the scratch pattern is far finer than would be produced off of the Bester with standard saturated/wash sharpening. I can produce the same edge off of the 240X SPS-II or practically any stone if desired. Again you have made this clear this isn't of interest to you, knowing how is of interest to some. It is in fact one of the most talked about subjects I have since I started doing wide abrasive/methods on stones and describing the results : http://www.cliffstamp.com/knives/forum/ ... 265,page=1 and people have started doing the same type of work with their stones to expand their range.

As of late I have been experimenting with minimal sharpening time, mainly as I get knives from friends often who volunteer in soup kitchens and the like. With very short sharpening times (1-2 minutes per blade) using an intermediate stone can actually slow the sharpening down more so than speeding it up as the time in actually getting out a 1000 k stone, using it to reset the edge, flushing the stone and putting it away is actually more than the time to hone to dry on the 240X, even when not including maintenance on the 1K stone. Hence as of late I have been experimenting with wider and wider gap ranges to see at what point the time actually increases. As the gap increases there has to be more time spent honing to dry and at some point this would over come the time saving. Again, this might not be of interest to you as well, but being able to reduce sharpening time and minimize equipment is of interest to some. For me it has both academic interests and practical ones as I rarely carry full sets of stones with me, but I sharpen a lot when I am outside of my direct workplace.

ken123 wrote:You're mentioning edge thicknesses of 20 micron (without supporting data) and go on to say magnification isn't needed. I really don't see where the 20 micron 'data' is relevant.


I noted magnification isn't needed if you destress the edge first as you use the reflected light line to judge the apex, the 20 micron apex thickness is my visual acuity limit which I have measured.

ken123 wrote:You are describing deviation from a theoretical norm, not measurement bias.


Not a theoretical norm, the physical ideal or true value. Biased data has been shifted from the population and the sample isn't representative. An apex which is biased is not representative of the ideal value in the same manner. Biased is used to describe both the effect (source) and the result (shift).

ken123 wrote:If the damaged steel had been removed, the burr would be far more uniform. Saying it was 'under' is confusing at best.


Yes there was damaged steel left on the edge, I noted that in the original post. My point was that side/side sharpening without removing that burr can cause it to keep forming as the edge will be pushed to one side and then then other and this bending keeps putting stress right under that burr. Cutting it off eliminates it with the least amount of passes on the stone (usually just 1-2 passes) and minimizes sharpening time and material removal.

ken123 wrote: ... as opposed to simply saying removing damaged or fatigued metal.


There are terms which are more technically correct, you could say destrain the edge as you are removing the effect (strain) not the cause (stress). However people commonly use stress in that manner as the effect so it is easily understood when I say destress the edge. It is so easily understood that it is starting now to spead across YT and I have not seen anyone yet not understand what people are talking about when they say destress an edge, though again an engineer would likely pause at the use of stress to refer to the result not the source, but again that is lay usage.

I have at times eliminated lay usage but it removes the descriptions away from a large portion of the audience and the amount of questions I get goes up in those cases which isn't productive. The terminology I use fights that middle ground between trying to inform and not be misleading while also making it accessible to people without the desire to invest in technical training. Obviously if you speak to a different audience then a different set of terminology is likely to be more optimal.

ken123 wrote:... it is not a demonstration of clogging the stone to do so.


The stone is spot loaded in the initial shaping and then refined in the exact same area, it is used very dry to accelerate the spot loading, there are also other techniques used such as ultra-light, cross hatching, and so on. In order to get the kind of edge noted off of the Bester in the above picture it would be necessary to focus more on the same techniques. This was a video done on request to illustrate the ability of very coarse stones to produce fine cutting edges. The exact stone is not relevant at all, as noted I have another video doing the same thing with a brick. The reason I concentrated on the heel was that was the part which had the most dulling, you can see at several points where I stop to check the edge for reflection of light, not all parts of the blade required the same work.


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