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global confusion

rmarisco Nov 16, 2013 04:14 PM

so… i started reading knife threads and now realize that the reason we don't often choose the global knife we own is that we have undoubtedly ruined the edge. i had no idea it was made with a slight convex turn on the edge. (it was a gift.) in fact, i found a global company-produced video on youtube that showed Tsuchida-san ("Mr. Global") sharpening blades - again, no mention of the slight curve in the global edge. https://www.youtube.com/watch?v=te1KI...

Now i'm wondering - can i get that edge back if i use the global-made sharpener? (http://www.surlatable.com/product/PRO...
)i see people warning against ruining the edge, but i have not found any tips on how to return it to the correct edge on these knives after they are badly sharpened, which seems to be too easy to do! surely that is what this little 3 section sharpener does? or is it just another convenient way to mash up the edge on the global?

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  1. rmarisco RE: rmarisco Nov 16, 2013 07:14 PM

    seriously?? no chowhounds weighing in?? am i to understand by your silence that, in fact, global is a not worth the effort??

    9 Replies
    1. re: rmarisco
      TeRReT RE: rmarisco Nov 16, 2013 07:15 PM

      you posted only 3 hours ago, most people aren't sitting here with nothing to do, like me, just be patient and people will reply

      1. re: TeRReT
        rmarisco RE: TeRReT Nov 16, 2013 07:21 PM

        ok while i agree it is saturday night and any self respecting chowhound should be out sampling some chic new restaurant in an up-and-coming neighborhood somewhere… i thought there would be some blade head in america who was around to care about my sad plight! (cue the violins)

      2. re: rmarisco
        Chemicalkinetics RE: rmarisco Nov 16, 2013 07:46 PM

        Come on. It was only 3 hours. You do know some of us have other important tasks -- like playing video games. :) Just teasing you.

        As you have said, Global knives have a slight convex edge. Therefore, typical sharpening techniques will convert this convex edge to an straight edge (V-edge) or double bevel according to this picture.

        http://www.egullet.com/imgs/egci/shar...

        < we own is that we have undoubtedly ruined the edge>

        How do you know that? Any reason why you think that?

        I would not say "changing from convex edge to straight edge" is ruining the edge -- if that is what you meant.

        <how to return it to the correct edge on these knives>

        This is the thing. I am not sure if you want to return it back to a convex edge (assuming this is your definition of a correct edge). A convex edge is good, but I think you are better off to work with a straight edge for now. It takes more skill to maintain a convex edge.

        You may think you have "ruined" the edge because the knife is not sharp. Here is a challenge for convex edge. It takes a while to convert a convex edge to a straight edge. During your first time sharpening, you will be hitting the side of the blade instead of the edge. So your initial effort is effectively thinning the blade.

        1. re: Chemicalkinetics
          Chemicalkinetics RE: Chemicalkinetics Nov 17, 2013 06:50 AM

          11 hours of silent. What does this mean? :D

          1. re: Chemicalkinetics
            TeRReT RE: Chemicalkinetics Nov 17, 2013 07:13 AM

            You are getting old and can't play video games for 12 hours anymore?

            1. re: TeRReT
              Chemicalkinetics RE: TeRReT Nov 17, 2013 08:11 AM

              :D
              Both!

              1. re: TeRReT
                Chemicalkinetics RE: TeRReT Nov 17, 2013 09:40 PM

                More than 24 hours now. :)

                1. re: Chemicalkinetics
                  rmarisco RE: Chemicalkinetics Nov 18, 2013 08:27 AM

                  it means i was out of town….

                  also, i know the edge must be ruined: i've been sharpening that knife for years without knowledge of the special convex edge. NO ONE TOLD ME!!! i had no idea i was supposed to research this knife before using it.. i just want to do the right thing by the knife: if i'm not worried about the convex or the straight edge, i'm just gonna keep sharpening it like normal. BUT if i've somehow ruined the poor thing i need to try to fix it i think! so would that little global-made sharpener be of any value??

                  1. re: rmarisco
                    Chemicalkinetics RE: rmarisco Nov 18, 2013 08:50 AM

                    <it means i was out of town….>

                    I thought it means that you want to toss the knife away.

                    <i know the edge must be ruined: i've been sharpening that knife for years without knowledge of the special convex edge. >

                    Good, then you must have already converted the knife from a convex edge to a straight V edge. Good. Just keep doing it.

                    <BUT if i've somehow ruined the poor thing i need to try to fix it i think! >

                    As long as your knife is sharp and cutting.... I think you are fine.

                    <so would that little global-made sharpener be of any value??>

                    Just my guess: it has value, but not in the value of keeping a convex edge. I think it is just like any other wheel knife sharpener, like the MinoSharpners:

                    http://www.minosharp.jp/

        2. TeRReT RE: rmarisco Nov 16, 2013 07:20 PM

          How do you sharpen the knife presently? Did you ruin it by sharpening it?

          You probably have two choices, you can either try to reprofile the edge and the the convex edge back, or you can just go ahead and reprofile it completely and put a flat or beveled edge on it.

          Either way you might want to have it professionally done to get it back to a proper edge if it is in fact ruined, and then maintain it after that.

          1. Sid Post RE: rmarisco Nov 17, 2013 11:19 AM

            You have a couple of options, you can sharpen with 20 degree bevels or take it to someone who has has a belt sander that can put slack in the belt for the final 'polish'.

            A convex edge can be approximated at home 'free hand' with good waterstones if you have a steady and consistent hand. You have to be pretty picky and really pay attention to subtle details to tell the difference in a proper bevel sharpening versus a convex 'rounded' bevel edge. I personally find the convex bevel edge useful on field knives but, more trouble then it is worth for kitchen knives. If I had a belt sander, I would use convex bevel edges though.

            12 Replies
            1. re: Sid Post
              rmarisco RE: Sid Post Nov 18, 2013 08:31 AM

              can you please explain the value on field knives vs. kitchen knives? i'm still learning here...

              1. re: rmarisco
                j
                JavaBean RE: rmarisco Nov 19, 2013 07:38 AM

                In a nutshell, convex bevel edges have leave more metal behind the edge, and are stronger than V-grind. They are more commonly used on axes, outdoor knives, and meat cleavers...knives that see hard impacts.

                Some kitchen knives like your global have them. You can maintain the convex edge by sharpening them with sandpaper & a mouse pad or regrind a V-edge.

                1. re: JavaBean
                  Eiron RE: JavaBean Nov 19, 2013 08:53 AM

                  Hey, JavaBean, PM me when you get the chance.

                  1. re: Eiron
                    j
                    JavaBean RE: Eiron Nov 19, 2013 12:07 PM

                    PM'd. What's happening?

                    1. re: JavaBean
                      Eiron RE: JavaBean Nov 19, 2013 12:11 PM

                      Testing! :-)

                      1. re: Eiron
                        j
                        JavaBean RE: Eiron Nov 19, 2013 12:19 PM

                        What are you testing?

                        1. re: JavaBean
                          Eiron RE: JavaBean Nov 19, 2013 12:32 PM

                          No PM. :-(

                          Are you using the eddress I've got on my profile page?

                          1. re: Eiron
                            j
                            JavaBean RE: Eiron Nov 19, 2013 12:35 PM

                            i thought i did, i'll resend.

                            1. re: JavaBean
                              j
                              JavaBean RE: JavaBean Nov 19, 2013 12:39 PM

                              Fire two...did you get it?

                              1. re: JavaBean
                                Eiron RE: JavaBean Nov 19, 2013 01:12 PM

                                Nope.

                                I listed it so that you can copy/paste.
                                Leave off the "http:\\" :-)

                                1. re: Eiron
                                  j
                                  JavaBean RE: Eiron Nov 19, 2013 01:17 PM

                                  Three times a charm?

                                  1. re: JavaBean
                                    Eiron RE: JavaBean Nov 19, 2013 01:22 PM

                                    Oops! They all ended up caught in my spam filter...

                                    (Funny, nothing else ever gets caught there!)

            2. Eiron RE: rmarisco Nov 18, 2013 08:52 AM

              Okay, here's my addition to the thread. :-)

              "... the reason we don't often choose the global knife we own is that we have undoubtedly ruined the edge ..."
              What do you mean by "ruined the edge," & how do you know? How long have you had this knife, when was it last sharpened, who (typically) does the sharpening, & what method is used top sharpen it? Oh, just out of curiosity, which knife is it? Their chef knife?

              The Minosharp does not say that it returns a convex edge to the blade, & I'm not sure you could do an acceptable job of this with a pull-thru sharpener anyway.

              I've sharpened Globals by hand using water stones & returned them to better-than-factory sharpness. It's not difficult if you're already practiced at hand sharpening. Belt sharpening is an easier & quicker method, but it's also easier to mess things up (true with ANY form of powered sharpening).

              We can try to help once we get a bit more info from you.

              14 Replies
              1. re: Eiron
                rmarisco RE: Eiron Nov 18, 2013 09:22 AM

                i guess we've had the knife 13 years - it's a millennium 2000 global knife. (who knew it had been so long? time flies when you're sharpening knives..) so it's pretty unlikely that convex edge is still around…

                i sharpen all my knives the same - no japanese knives except the global - only henkels and whustof (and one chicago cutlery which is incredibly old and ridiculously perfect for my hand). i use the whetstone as my father taught me: he butchered meat for many years in his restaurant, and his father was a butcher, so i'm hoping that i've retained the knowledge passed through the generations. well, that and watching all kinds of videos on youtube to confirm i'm doing it correctly!

                maybe i just need to change the angle to get that global in better shape. i think that's an easy place to start..

                1. re: rmarisco
                  Eiron RE: rmarisco Nov 18, 2013 10:07 AM

                  Ah, yes, if you've been sharpening the Global to the same angle as your Henckels, Wusthof & Chicago, then you're not getting the full potential out of the Global. The edge shouldn't be worse than the others, but it probably won't be any better.

                  Yes, the easiest place to start is by simply lowering the sharpening angle to Global's 15°-16° (per side). The "rule of thumb" for initial angle is to stack two quarters on the whet stone & lay the spine of the knife on top of them. (Of course, this will vary depending on how tall your blade is. You didn't say which blade you have. I believe the M2k line was produced in all shapes & sizes, yes?) If you've been using a 22°-23° angle for each side (correct for your other knives), then it may take a little work to get back to Global's angles. A coarse stone will get the initial angle set more quickly.

                  1. re: Eiron
                    c
                    Cynic2701 RE: Eiron Nov 18, 2013 10:33 AM

                    In my experience, those angles are guidelines for what manufacturers expect their knives to have to endure: users that aren't as careful as they probably should be, that lack sharpening skills, that may improperly store their knives, and that may be using their knife on glass/ceramic/stone/metal cutting boards.

                    Interestingly, Global themselves have done statistically validated tests that show that skilled waterstone sharpeners can improve the edge on knives by thousands of percent increase in edge retention:

                    http://www.global-knife.com/catra/ind...

                    The angles that you mention (i.e. 22°-23°) are incredibly obtuse--even axes and wood working knives are sharpened to 20° and I've taken whittling knives to 17.5° just fine.

                    Admittedly, it is very difficult to provide a blanket statement for edge angles as the variables can be extremely wide--there are differences in steel, heat treatment, hardness, toughness, and expected use. This is furthermore compounded by people recommending that one should raise the spine of the blade by "X" distance in order to achieve "Y" angle: the hypotenuse of such a triangle is determined by the distance from the edge to the spine, and therefore is a variable factor that should be taken into account. In essence, a very tall blade that is raised off the stone by 1 inch will be sharpened at a different angle than a very short blade that is raised off the stone by 1 inch.

                    If I may offer a suggestion - based upon my estimation that your Global is their "mystery stainless steel" hardened to 56-58 HRC - then perhaps an angle between 30° - 35° inclusive (i.e. 15° - 17.5° per side) and taken to approximately 3000 - 4000 JIS grit would be suitable. Personally, when I sharpen my own knives, I take the angles down by one degree each time I sharpen until I reach an edge that begins to fail by either chipping or rolling. Once that angle has been found, I widen the edge by a degree or two and try to remember that for next time. This way, one will discover and use the most optimal edge geometry that is possible for the knife.

                    1. re: Cynic2701
                      c
                      Cynic2701 RE: Cynic2701 Nov 18, 2013 10:48 AM

                      And now that I'm thinking about it, I'd hazard a guess that the edge might actually be stable at 25° - 30° inclusive (i.e. 12.5° - 15° per side) which would provide enormous increases in cutting ability.

                      You would want to be a bit more careful with a sub-30° inclusive edge, but I would think it might be ok. I have a Blue #1 nakiri that I've taken to 12° - 14° (i.e. 6° - 7° per side) that does just fine. Once again, though, there is a difference in hardness, toughness, and expected use which equates to a very large increase in cutting ability.

                      1. re: Cynic2701
                        Eiron RE: Cynic2701 Nov 18, 2013 11:00 AM

                        Hi Cynic2701,

                        I agree.

                        A couple of things to remember:
                        1) As you said, "it is very difficult to provide a blanket statement for edge angles." I was trying to provide generalized guidance, not specifics. At this stage in the knife's life (& user's experience), I believe this approach is best. Well, at least for what I can tell from these very short forum exchanges.
                        2) I don't get the feeling from rmarisco's posts that s/he has the sharpening eqpt you list, or the interest to spend multiple iterations of minute angle changes to reach the desired sharpness goal. (I could be wrong; it's just my feeling.) Nor do I feel a method such as the one you follow is necessary in order for the OP to see a marked improvement in performance.

                        Basically, I was trying to say, "Just sharpen the thing to a lower angle for now. It should improve the performance. Here's a rough guide for angles." If rmarisco then comes back & wants more detailed info, your response would be a good place to go. :-)

                        1. re: Eiron
                          c
                          Cynic2701 RE: Eiron Nov 18, 2013 11:08 AM

                          Hi Eiron,

                          Thanks for your input. I didn't mean to single you out in particular; you were just the first person in the thread that I replied to.

                          As a self-proclaimed knife enthusiast and sharpening geek, I can work myself into a tizzy on the subject of knives :)

                          1. re: Cynic2701
                            Eiron RE: Cynic2701 Nov 18, 2013 11:13 AM

                            No worries. You're in good company around here. ;-)

                            1. re: Eiron
                              Chemicalkinetics RE: Eiron Nov 18, 2013 11:37 AM

                              I think you two are way ahead of rmarisco's questions. I am sure rmarisco currently just want a knife that is properly sharpened. Having a 17° edge angle vs a 20° edge angle may not mean a lot at this stage.

                              The big question really is: Have he/she ruined the Global knives?

                              1. re: Chemicalkinetics
                                c
                                Cynic2701 RE: Chemicalkinetics Nov 18, 2013 11:58 AM

                                I'd guess it depends on what was done to "ruin" the knife. Is the profile still ok? When you put the edge on a flat surface, are they any parts where light peeks through? If you run the knife between your fingers right above the edge (don't cut yourself! be careful) does it feel "wavy" or inconsistent?

                                Really the only thing you could do to "ruin" a knife is grind too much of it away (ending up with a fillet knife from a chef knife) or heating it up to tempering temperatures for an hour or more (e.g. leaving it in an oven at 400+ degrees for a few hours--which I've actually seen before, sadly). A knife sharpener using powered wheels and with poor skills could over-grind an area on the knife causing holes to appear in the edge later.

                                It's hard to say without physically having the knife in my hands.

                                1. re: Chemicalkinetics
                                  cowboyardee RE: Chemicalkinetics Nov 18, 2013 02:42 PM

                                  rmarisco hasn't really explained what he/she means by 'ruined' knives. As you know, if the knife is sharp and cuts well, then it's not ruined regardless of whether the edge is no longer convex.

                                  My guess would be that rmarisco may have inadvertently sharpened at such an obtuse angle that the knife no longer cuts well. In this case, we're likely talking about a significantly more than even 22 degrees per side (which as you know is common for German knives). This can happen if you sharpen a convex edge in such a way that you are bringing up a burr right away - if you raise the angle while sharpening the knife to get around the convexity. In this case, bringing the angle down should fix the problem.

                                  Of course its possible that rmarisco is just worried that the knife is no longer convex and that he/she has been doing it 'wrong.' If the knife is sharp and cuts well, then there's no problem.

                                  1. re: cowboyardee
                                    Chemicalkinetics RE: cowboyardee Nov 18, 2013 03:17 PM

                                    <This can happen if you sharpen a convex edge in such a way that you are bringing up a burr right away>

                                    Good point.

                                    <Of course its possible that rmarisco is just worried that the knife is no longer convex and that he/she has been doing it 'wrong.'>

                                    I am leaning toward this, but you are right. We don't know.

                                    1. re: Chemicalkinetics
                                      rmarisco RE: Chemicalkinetics Nov 18, 2013 06:11 PM

                                      y'all are killin' me here! now i know what it feels like to be a member of congress i think…

                                      i just wanted to know IF i should attempt to get the convex edge back on my old global! The global currently has an edge the same as my other knives - all sharpened to a euro. style angle since that is the way i was taught by my father. i don't have a tape measure, protractor, or any other gear: i have ears, hands, and a good whetstone. i didn't even know the global was a japanese knife until a few days ago!! my knives have mostly been gifts from the family, so i just assumed the global was european style like the others: never even crossed my mind that it might be japanese!

                                      so, i was asking if i needed to get that convex edge back for optimum use, and if i did need to get that convex edge back, would the minosharp tool be the best way to do it??

                                      i now see that my best solution is to forget the convex question and just change my angle and sharpen it to a japanese angle.

                                      and, thanks all for trying to not assign gender around this question - girls can be blade brains too! i might just sharpen that global tonight, between football and quilting (HA!)

                                      1. re: rmarisco
                                        cowboyardee RE: rmarisco Nov 18, 2013 07:16 PM

                                        You shouldn't worry about making the edge convex again. Just sharpen it well, however you know how. If you feel the knife isn't cutting as well as you'd like after sharpening, try lowering the angle on the edge.

                                        Convex edges are *slightly* more resistant to chipping and folding than flat edges set at a similar angle. This is why it might be preferred in a 'field knife' that will be used to hack wood, cut rope and cardboard, dig holes, and other heavy tasks. For a kitchen knife, the difference is so minimal that it's not worth worrying about. Other Japanese knives use flat edge bevels and perform just as well or better than Globals.

                                        The main issue with Globals and their convex edges centers around the first couple times you sharpen them. If you use a flat stone or other method of creating flat bevels, you wind up either raising the edge angle in order to sharpen the cutting edge itself, or else you have to grind away for a while to flatten the bevels before you're sharpening the actual cutting edge. In your case, the bevels are already flat from years of sharpening, so your only concern is whether your knife is cutting well. If it isn't, lower the edge angles, and maybe thin the 'shoulders' of the edge a bit if necessary.

                                        1. re: cowboyardee
                                          Chemicalkinetics RE: cowboyardee Nov 18, 2013 07:47 PM

                                          <so your only concern is whether your knife is cutting well.>

                                          Agree.

                  2. hambone RE: rmarisco Nov 18, 2013 12:36 PM

                    I gave a Global I got as a gift to a friend.

                    I find the knife to light and small for my big mitts.

                    2 Replies
                    1. re: hambone
                      rmarisco RE: hambone Nov 18, 2013 06:17 PM

                      interesting..because that is pretty much my husband's argument as well. i like it because it is all one piece and i find it well balanced. once i get it sharpened properly i am hoping to get it back into the knife rotation more frequently.

                      1. re: rmarisco
                        hambone RE: rmarisco Nov 19, 2013 12:02 PM

                        I won't knock the edge. Knife was as sharp as any I've ever owned/used (except ceramic.)

                        The friend I gave it to loves it.

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