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TOPIC: Why convex isn't a "stronger" edge...

Why convex isn't a "stronger" edge... 2 months 1 week ago #17444

  • LeoBarr
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I did some Globals on an Edge pro and the way I did it was thinned at 10˚ to the edge then beveled the edge at 15˚just a couple of passes to put the bevel on and each subsequent bevel at -1˚ through to 11˚ the work was done with 1200 grit then I stropped out the transitions . Globals unlike Shuns come with a convex and in their literature they claim it goes from 10-15˚ .
I imagine the Shuns are sharpened on a wheel and the Globals on a belt .
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Why convex isn't a "stronger" edge... 2 months 1 week ago #17445

  • razoredgeknives
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LeoBarr wrote:
I did some Globals on an Edge pro and the way I did it was thinned at 10˚ to the edge then beveled the edge at 15˚just a couple of passes to put the bevel on and each subsequent bevel at -1˚ through to 11˚ the work was done with 1200 grit then I stropped out the transitions . Globals unlike Shuns come with a convex and in their literature they claim it goes from 10-15˚ .
I imagine the Shuns are sharpened on a wheel and the Globals on a belt .

sweet! I bet that was super sharp and efficient!
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Why convex isn't a "stronger" edge... 2 months 1 week ago #17446

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I was very happy with the result I did this whist waiting for the WE and having read about a method to convex decided to do it would be a little quicker on the WE probable with the low angle adapter.
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Why convex isn't a "stronger" edge... 2 months 1 week ago #17447

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ScreenShot2014-05-14at17.24.00.png

I just looked it up on the Ikea website it is the Slitbar series it is 36.48€ but interesting enough it carries a - 25-year Limited Warranty. Read about the terms in the Limited Warranty brochure. So it would be worthwhile seeing if they will exchange it.
I think at the rock bottom price they are made in China .- Core of hard steel that gives a very sharp edge,surrounded by softer steel that makes the blade durable.
For this price it has to be made in China or India I could not find any reference to VG10 steel like a Shun and it comes in a box with a weight of 1Lb so quite a heavy knife unless the box is heavy.
So the cracks could be due to lack of tempering or simple bad tempering.
Still damascus brings out the Magpie in us I admit I have 2 damascus Laguiole 1 Theirs ,a Shun and a Seki cut camping Deba now I actually prefer the look of plain steel especially when laminated so a hard carbon steel laminated with Iron I like seeing the line between the two different metals.
Last Edit: 2 months 1 week ago by LeoBarr.
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Why convex isn't a "stronger" edge... 2 months 1 week ago #17450

  • tcmeyer
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I should have stayed online to make sure the photos loaded. Strange that they didn't, as I compressed them quite a bit. Even cropped them. Here I'll try again. Since Leo already got the right overall, I'll skip it.

Non-magnified view of the heel area:

IMG_0120.JPG


Microscope pic of the same crack:

IKEACrackNo1.jpg



Yes, the knife is heavy. That bolster is a solid chunk of stainless, forged with the blade. The handle looks to be a micarta, maybe of ironwood. Again, I didn't sense that the edge was overly hard (untempered) but clearly, something's wrong.

Thanks for looking it up, Leo. I'll tell her to take it back and ask for a warranty replacement.

Josh, I completely agree with you that the convex cannot be stronger than a normal v-edge of the same angle. I'm simply offering that maybe the claim originally was made as compared to a knife which has an edge angle continued from the same primary grind planes. For example, if the 15-degree grinds had been continued out to the apex.
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Why convex isn't a "stronger" edge... 2 months 1 week ago #17451

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tcmeyer wrote:
I should have stayed online to make sure the photos loaded. Strange that they didn't, as I compressed them quite a bit. Even cropped them. Here I'll try again. Since Leo already got the right overall, I'll skip it.

Yes, the knife is heavy. That bolster is a solid chunk of stainless, forged with the blade. The handle looks to be a micarta, maybe of ironwood. Again, I didn't sense that the edge was overly hard (untempered) but clearly, something's wrong.

Thanks for looking it up, Leo. I'll tell her to take it back and ask for a warranty replacement.

Josh, I completely agree with you that the convex cannot be stronger than a normal v-edge of the same angle. I'm simply offering that maybe the claim originally was made as compared to a knife which has an edge angle continued from the same primary grind planes. For example, if the 15-degree grinds had been continued out to the apex.

dude that is jacked!!! yeah, good call on the warranty replacement!

yeah, full convex is definitely optimum! :)
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Why convex isn't a "stronger" edge... 2 months 1 week ago #17452

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ScreenShot2014-05-14at20.12.24.png

The handle is Pakka like Shuns so a goos resin based wood looking handle . That crack is as I would have said when playing Conkers that is a death crack it has gone through to the cladding the whole knife is toast.
It also looks as if there are stress fractures panning out from that running parallel every 1 / 2 mm it looks like a handsome edge although the knife looks way too thick to cut well I would say the secondary bevel needs raising to about 1/3 up the blade to get a descent profile .
This seems to be how cheap knives are shaped supermarket knives all seem to be like this they are fine for cutting pre siced foods or opening plastic wraps but they fail miserable for cooking .
Its a pity that they have produced a laminated knife with such a poor profile .It did say in the blurb

Designer thoughts
"My idea with the SLITBAR series was to create kitchen knives that you can have on show to give character to your kitchen. For their modern and distinctive look, I took my inspiration from Asian design. Of course it's just as important that the knives are functional, comfortable to use - and that they age well. I also wanted to include many different types of knives in the series, so that you always have the right one, no matter what kind of food you're cooking."
Designer Mårten Cyrén.

That essentially the knife is for show and I think this was the main design idea utility after .

Sorry to be so critical of the knife but unless you are going to thin the next on decently it is never going to be a good knife and I suspect that the next one will have the same cracking problems perhaps a better bet would be to ask for the money back and perhaps put it towards a good entry level Japanese knife like a Mac.
Last Edit: 2 months 1 week ago by LeoBarr.
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Why convex isn't a "stronger" edge... 2 months 1 week ago #17453

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I just want show you what I would consider a good blade shape this knife is a Mac and it was originally a Santuku that had a very large chip out to the centre of the blade from an Avocado stone over time I have got this knife right initially when I slowly ground off on an Edge Pro I had a reasonable edge but the edge was probable about a third up the blade it was sharp but pretty useless so eventually after a couple of goes I have got the right amount of taper and shape to the blade probable resembling the sort of profile it had when new once again it cuts properly passing through most things easily . These cheaper knives will never perform properly unless they are radically thinned and I am not sire that you can do the secondary bevel on the WE since it needs to be sub 10˚ probable 5-7˚ I would imagine having done this on bench stones I cannot say what angle it is on this knife probable about 1 coin thickness under the spine but I do not use coins the primary bevel is probable about 12˚per side as an estimate .

The spine mid way along the knife is 1.65 mm the thickness of the blade about 1cm above the primary bevel mid way along the knife is about 1.15mm - 2.5mm above the primary bevel the blade is 0.5mm. These are more the sort of proportions you should be looking for in a knife I think the Ikea knife is probable well over 1mm thick
IMG_1800.jpg


IMG_1802.jpg


IMG_1803.jpg

2.5 mm above the primary bevel
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