Regrinding Victorinox knife

[Jan]

As I have already mentioned I measured the edge angle of my quite new 6" long Victorinox knife (6.8003.15) with my laser goniometer and got circa 20°. I was wondering about it and asked Victorinox for possible explanation but received only a formal answer. 

So I decided to reground the knife to an edge angle of 30°. I tried to do it with utmost care. I set the angle using kenjig concept to avoid blade tappering. Because the knife was flexible I mounted it into the Long knife jig. Because the spine thickness was only 1.4 mm I used a 0.55 mm thick shim to symmetrize the blade position in the knife jig (Wootz recommendation).

I have reground the knife away from the edge (Steve recommendation) for longer exit burr. The SG stone graded fine was not able to remove the steel in reasonable time so I regraded it coarse, removed the steel and graded it fine again.

I have decided for jigged honing on the lather wheel to avoid edge rounding. To minimize the knife handle colliding with the grindstone I used a Wootz-type adapter to elevate the bar of the USB.

At the end I measured bevel angles with my laser goniometer again. The results are following:
bevel angle on the right site = 14.5°,
bevel angle on the left site = 15.5°.

I would be happier with 15° for both sides but the 0.5° is an accuracy level and even more the edge angle is 30°. 

That's the story of how I was regrinding my new Victorinox knife. 

Jan

[Janne]

Hello.
Is the spine thickness 1,4 mm parallell or does it get thinner closer to the edge?
I think that using a shim to keep the knife centered to the shaft of the jig you have to compensate for eventual unparallellity.
One of my cooking knifes is about 3 mm thick at the top and about 1 mm at where the grinding area begins with a height of about 45 mm.
For me if the knife jig has an ofset ( 1,5 mm?) I would take in consideration if the blade of the knife is parallell or coned ( from top to edge). This fact mean that there is different needs of shim to get both the top and the edge centered to the shaft of the jig.
Just a humble question, is the coned shape your problem, since you seem very exact and thorrough in your description?  14,5 and 15,5 instead of 15 and 15 due to a parallell compensation with shim for the top and to less shim for the edge?
Position the knife in the jig, with shim. Try to measure the edge compared to the shaft of the jig if you get the edge centered.
Regards Janne

[Jan]

Janne (Grinder of Sweden),

my Victorinox knife does not have parallel sides, it tappers towards the edge, the angle of the blade is about 3°. This is accommodated by the jaws of the knife jig.  If the blade tappers strongly towards the edge you may need a pair of shims to guarantee good grip of the knife jig jaws.

The Tormek knife jig works perfectly for knife blades thickness of 2.5 mm with some tolerance. The offset is 1.25 mm. If the knife is thinner than 2.5 mm you can compensate it using a shim. For details read the topic Long Knife Jig asymmetry problem started by Wootz http://forum.tormek.com/index.php?topic=2577.0

My sentence "I would be happier with 15° for both sides ..." was a joke. Sorry for confusing you.  In fact I am satisfied with the result.

Jan

[wootz]

Hi Janne,
All you questions have been explained here for the SVM-45 knife jig: http://forum.tormek.com/index.php?topic=2962.0

As to your suggestion:

Position the knife in the jig, with shim. Try to measure the edge compared to the shaft of the jig if you get the edge centered.

- though it would be good to have some sort of practical verification of shim calculations before the actual grind, I found it practically awkward to use laser goniometer on a knife clamped in a jig.
But you know, as I am typing this, it came to me that AngleCube relative reading on both sides of the blade mounted in the jig and set on the stone in the grinding position, should be able to tell how adequate the shim is (the AngleCube accuracy is 0.2 degree). Am going to try it today-tomorrow.


Jan, thank you so much for your post on using the Long Knife Jig with shims; I've never had a chance to practically verify this.

UPDATE: Alas, AngleCube cannot be used for this purpose.

[Jan]

Having now the possibility to measure the bevel angle of each side with the laser goniometer, I am also paying more attention to symmetrical montage of the blade into the knife jig, especially in the case of the flat-sided V grind. 

The other thing I am trying to resolve is a correct burr forming procedure. The handbook recommendation is to grind the first side until a burr forms and then turn the knife jig upside down and grind the other side. Because on the other side the burr often appears immediately we are in a great temptation to stop the grinding before we obtain fully symmetrical edge. In some cases this asymmetry is not visible with naked eye.

Therefore I now turn the knife jig upside down after each 5 to 6 passes, what helps me to keep the edge symmetrical. 

Jan

[Ken S]

Jan,

You raise a very valid issue about when and how often to switch grinding sides with a knife. I started staying on one side until the burr appeared. In my case, the assymetry was very visible. I changed technique. This is a problem in progress for me. I have not ruled out operator error. I have no better than average inate manual ability (based on a test in my college psychology class in 1970). This is both a blessing and a curse. I believe it helps me when working with beginners, although, it would be nice to be the gifted one at times.

Wootz,

I am continuing to develop correct thickness shims ground to a very acute bevel and sized to be stand in targets for knives. The flat targets would present a more usable flat surface for the Anglemaster.

Interesting subject.

Ken

[wootz]

...
The other thing I am trying to resolve is correct burr forming procedure. The handbook recommendation is to grind the first side until a burr forms and then turn the knife jig upside down and grind the other side. Because on the other side the burr often appears immediately we are in a great temptation to stop the grinding before we obtain fully symmetrical edge. In some cases this asymmetry is not visible with naked eye.

Therefore I now turn the knife jig upside down after each 5 to 6 passes, what helps me to keep the edge symmetrical. 

Jan

Initially I was also caught by this misguidance, getting asymmetric bevel due to one side overgrinding, but this changed after I saw Steve Bottoroff saying in his video to flip over with each pass.
Grinding on the coarse stone (#220) I flip the blade after each pass, and on fine (#1000) after every 2-4 passes, till the burr forms. Only with the finest SJ (#4000) I polish one side to my satisfaction before flipping over to the other.

[Jan]

Wootz,

thank you very much for your confirmation that frequent switching of grinding sides is the correct way how to avoid asymmetrical bevel. 

Thanks also for sharing the number of passes you use for different stones. It is important guidance for me. 

My problem with the metallic shims is that they do not hold on the blade when it is mounted into the jig. I have tried to magnetise the shims but many loose the magnetisation too quickly. Now I am thinking about some adhesive. Do you have some recipe for this? 

Jan

[Jan]

Jan,

You raise a very valid issue about when and how often to switch grinding sides with a knife. I started staying on one side until the burr appeared. In my case, the assymetry was very visible. I changed technique. This is a problem in progress for me.

Yes, Ken, the burr forming procedure is a key issue for every knife sharpener. 

The handbook procedure may work well when we are sharpening a knife and remove only very limited amount of steel. But when we are re-shaping the knife and remove much steel the risk to ground an asymmetric bevel is high. 

Even more the volume of removed steel is significantly larger for the handbook procedure (A) than for frequent switching of grinding sides (B). When the handbook procedure removes more steel it also consumes more grindstone. 

Those two reasons fully justify Steve's approach mentioned by Wootz.

Jan

[WolfY]

I agree with Steve's recommendations about frequent side change when sharpening a knife.
At first pass with dull knife I do 2 passes ( 1 pass= start from tip and end at tip).

But I do not use chims. I start with the Jig zeroed in length and knife handle on right side. When flipping I make 1~2 turns to shorten the TTL length of protrusion. Depends on knife width. It compensates for the angle difference. I'm not concerned if it is not 100% same angle but look at the bevels to see if they look symmetrical. The eye is sensitive enough to give satisfying result.
Of cause it's not science work and it is not necessary. Using 1~2 turns is enough for most knifes. Just experience can tell how much in every particular knife. For help use the WM-200. A tool I frequently use.
Most important with this technique is to remember how many turns and to turn back after every knife flip. After a couple of times it becomes second nature when sharpening a knife.

As for the burr. I don't look for it until I finished 1 flip. I always sharpening against the wheel and getting very small burr.

As for original factory angle I find it not so important as individual preferences are also to consider, as well as the steel quality.

[Jan]

Wolfy,

thanks for sharing your unique procedure!  It is of course a possible way to compensate for an asymmetrical montage of the blade into the knife jig.

May be you know the rule of thumb I posted previously: "When we turn the adjustable stop one turn, we shorten the projection length by 2.5 mm (0.1"), which will typically cause an increase of the bevel angle by 1.5 degrees".

The stumbling stone for me would be to remember the number of turns and to turn back after every knife flip. 

Jan

[WolfY]

Jan,

Remembering the no. of turns is good for the brain exercise especially when doing mechanical/ casual work And there is always a paper sheet to use if necessary. It's also a good idea to write a small notation that only you understand and glue it to the Tormek. E.g 40mm/40dgr - 2 turns. Etc...
I don't pay attention to the value of 1 turn as it would be too much science in it. Although it is good to know the value of it.
Problem is when attaching the knife is to be concistant. Do you align the knife face to the jig or try to center it? How wide is the knife? Etc...
This differences can move the center of the edge and differ how much to compensate. So I either measure with the WM-200 both sides (only 1 time) to know how much to turn the jig or I just use my feeling. 1 dgr or so is accepted as difference of edge angles. If difference is too big you see it direct on the bevel.

[Jan]

Do you align the knife face to the jig or try to center it? How wide is the knife? Etc...
This differences can move the center of the edge and differ how much to compensate.

Wolfy,
I always try to centre the blade between the jaws of the knife jig.

For edge angle setting I mostly use the kenjig approach which is quick and accurate.
If knife blade thickness is between 2 and 3 mm I mount it into the knife jig without any doubts. 

If the blade is thinner than 2 mm I use a suitable shim as described by Wootz.

If the blade is thicker than 3mm and if necessary I slightly correct the kenjig angle setting of each side individually using the Anglemaster and do not apply the frequent jig flipping method. Alternatively I use my home made platform without the knife jig.

I think Wootz is perfectly equipped for thick knife sharpening. 

Jan

[Jan]

1 dgr or so is accepted as difference of edge angles. If difference is too big you see it direct on the bevel.

Wolfy,

I agree with you that 1 degree difference between the bevel angles of opposite sides is acceptable tolerance. 

For my thin Victorinox knife the bevel width is circa 0.5 mm (0.02") and changing the bevel angle by 1 degree will change the bevel width by some 15%. This is not visible by naked eye, only under strong loupe or microscope. Good laser goniometer will also detect this difference provided the bevel is honed.

Jan

[Ken S]

I believe the poll results are conclusive; use of the kenjig technique has become an important part of sharpening among the top expert sharpeners in the Czech Republic. Can the developing world be far behind? 

In all seriousness, Jan has not copied a forum idea; he has made substantial improvements. To me, that captures the soul of the forum, working for the common good.

Keep up the good work, all.

Ken