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View Full Version : Spine Thickness Does Matter



Marko Tsourkan
12-21-2011, 01:46 PM
So, while I still am trying to work out an optimal thickness for a pro environment knife (a good balance between weight and geometry thickness), I took a recommendation from one of the pro guys here who used my knives, and ground one slightly thicker what I normally grind.

After some cutting at home, I liked the performance. It had a solid feel and I didn't see much decrease of cutting performance over thinner knives. It would make a good line knife - no flex, solid feel and thin above the edge (right now it's under .005").

Then I ground another knife even thicker at the spine but thin at the edge, and put it through the same cutting routine - apples, carrots, potatoes and onions. I didn't cut any proteins, as the purpose of the test was for an all-around knife.

The performance difference between the two was quite noticeable. On a thicker knife, the heel and middle of the knife wedged where on a thinner it didn't.

Both knives were ground to the same thinness at the edge, and approximately same convex 2/3 up the blade. The difference in weight was pretty negligible (officially 8g, but the heavier knife has a shorter machi, which probably took off another 8g from overall weight).

So, it seems to point to one conclusion - spine thickness does matter, regardless how thin a knife above the edge is. Spine thickness affects geometry in mid-section, which in turn affects cutting ability of a knife to go through denser foods like apples.

Here as some shots of spine, heel, profile and measurements. The spine shot is a bit distorted - those are not as thick as they look, but you can see a contrast in thickness well. Also, I come to think that spine measurements on a thinner knife are similar to 260mm Mario's Carter.


M

3214

3215

3216

3217

Eamon Burke
12-21-2011, 02:11 PM
The spine should be as thin as possible while still achieving the weight/balance desired.
:2cents:

Marko Tsourkan
12-21-2011, 02:15 PM
Right, so it makes sense to make two different versions of the same knife. At the weight of 220g with a handle (thicker one), it will still be a pretty light knife. The thinner version will weigh about 200g or slightly less.
What I found interesting, is that you can have a negligible weight difference, but very different performance on similarly ground knives all due to spine thickness.

M

PS: the thicker knife that I tested will be reground

jmforge
12-21-2011, 05:31 PM
Interesting stuff, Marko. Have you messed around with different degrees of taper yet?

kalaeb
12-21-2011, 06:02 PM
Your dedication to r&d is phenominal. Definately commendable is the thought b ehind every aspect of your knives.

Marko Tsourkan
12-21-2011, 07:08 PM
Interesting stuff, Marko. Have you messed around with different degrees of taper yet?

I don't really measure it in degrees. I sort of grind it till it looks about right. Now that I set on a benchmark where it needs to be, I will start using calipers more often.

@Matt - now I have no excuse to procrastinate. This was the last question I needed to get an answer and I think I got it.

M

RRLOVER
12-22-2011, 08:10 PM
You have one blade going from 3.19 to 2.71 and the other 2.93 to 2.12,those grinds are not similar at all.Are you trying to compare a similar spine tapers but at different thickness,or just a thicker middle and tip spine with the same behind the edge grind.

MadMel
12-22-2011, 11:41 PM
I've just decided who I'm going to for my next knife.:idea2:

Marko Tsourkan
12-23-2011, 12:26 AM
You have one blade going from 3.19 to 2.71 and the other 2.93 to 2.12,those grinds are not similar at all.Are you trying to compare a similar spine tapers but at different thickness,or just a thicker middle and tip spine with the same behind the edge grind.

That is a conclusion I arrived after (thicker spine translated into thicker middle). I have not ground a thick knife before and was wondering how claims that spine thickness doesn't matter as long as a knife ground thin above edge (unless above edge means middle, or more precise, hollowed out middle like in Shigefusa :) ). The degree of convexing was similar on both knives, but that didn't seem to matter as the thicker knife wedged in it's mid section.

I already reground it and cut some vegetables with it. Definitely a difference.

M

RRLOVER
12-23-2011, 09:38 AM
I see now.The middle is my bane,to thin and it's flexy to thick and it wedges.

jmforge
12-23-2011, 08:26 PM
Marko, don't you have a TW 90? If so, have you bought the surface grinding fixture? I would think that might be handy for experimenting with things like this.

Marko Tsourkan
12-23-2011, 08:31 PM
$1000 surface grinding option is a bit too much for me, to be honest. I would rather save the money for another TW90 or a real surface grinder. :) I don't find it difficult to grind a distal taper by hand (I would be looking in other options, if I did).

Mario, just that we are on the same page, by midsection I mean half-way between spine and edge, and middle of the blade is halfway between handle and tip (approximately).

M

jmforge
12-23-2011, 10:17 PM
True. The easy to use sine block feature of the TW90 gadget seems kind of attractive though.
$1000 surface grinding option is a bit too much for me, to be honest. I would rather save the money for another TW90 or a real surface grinder. :) I don't find it difficult to grind a distal taper by hand (I would be looking in other options, if I did).

Mario, just that we are on the same page, by midsection I mean half-way between spine and edge, and middle of the blade is halfway between handle and tip (approximately).

M

Marko Tsourkan
12-23-2011, 10:49 PM
Sine block feature would allow you to set an angle, as on a sine magnetic chuck. I don't think you can do that on TW-90 attachment, at least I don't see it in a video.

To grind a distal taper on TW-90 surface grinding attachment, you would have to shim the blade, but I don't think the magnets on the chuck are strong enough to hold the blade with shims. Plus, you would need to buy a demagnetizer. I can think of better ways to spend 1K on tools.

M

jmforge
12-23-2011, 11:31 PM
You would have to shim the blade if you wanted to grind in the taper after your ground the bevels. Otherwise, I would think that it would be just like tapering a tang. It may be different with these thin kitchen knives, but I forge the taper into my blades before I forge out the bevels and the guys who I have seen making Japanese swords do the same thing. Of course, even if you ground your bevels halfway up, I think you might be able to do whatever taper you needed and then go back and finish beveling and blending. The only shimming you might have to do would be perhaps at the heel and maybe the tip to keep the flat of the blade stuck to the magnet and not the bevel.
Why would you need to buy a demagnetizer?
Sine block feature would allow you to set an angle, as on a sine magnetic chuck. I don't think you can do that on TW-90 attachment, at least I don't see it in a video.

To grind a distal taper on TW-90 surface grinding attachment, you would have to shim the blade, but I don't think the magnets on the chuck are strong enough to hold the blade with shims. Plus, you would need to buy a demagnetizer. I can think of better ways to spend 1K on tools.

M

jmforge
12-23-2011, 11:38 PM
I'm not trying to argue with you, Marko, just axing.:D There will come a time in the near future where I have to decide on whether to get another KMG chassis and motor and buy and modify a used surface grinder to run with 72" belts or just buy a full boat TW90 with the surface grinding attachment. Can't do both in the foreseeable future.

Marko Tsourkan
12-24-2011, 08:58 AM
I didn't interpreted as as an argument. You mentioned a sine block feature, so I clarified that TW-90 didn't have one.

A piece will be magnetized on the chuck and stay magnetized, so you need to demagnetize it. Same with all magnetic chucks. Less powerful ones, like on TW90, the level of magnetization will be smaller.

M

stevenStefano
12-24-2011, 11:07 AM
I think I generally like knives that are a little thicker than most people, but one thing I find problematic with knives that have a thick spine and thin behind the edge is that they are sometimes difficult to "aim." Might seem like an incredibly dumb/obvious thing to say but with some thick knives it is hard to know where the edge is if there is a big difference between the edge thickness and spine thickness

jmforge
12-24-2011, 12:37 PM
Maybe I am misusing the term, but I thought that the TW 90 had sine block ypte adjustment for tapering lengthwise.
I didn't interpreted as as an argument. You mentioned a sine block feature, so I clarified that TW-90 didn't have one.

A piece will be magnetized on the chuck and stay magnetized, so you need to demagnetize it. Same with all magnetic chucks. Less powerful ones, like on TW90, the level of magnetization will be smaller.

M

Marko Tsourkan
12-24-2011, 01:15 PM
Maybe it does, but I watched a video and Travis doesn't mention it, but is possible that it includes that feature.

M

jmforge
12-24-2011, 02:48 PM
He did a different demo of the sine block feature where he tapered a bar using a 2 1/2" Bader serrated wheel and a 300 micron Gator belt..
Maybe it does, but I watched a video and Travis doesn't mention it, but is possible that it includes that feature.

M

Marko Tsourkan
12-24-2011, 03:09 PM
Then is it is possible. There is no description on TW site and the last time I talked to Travis about the attachment, he didn't mentioned the tapering option, but I did know that he was working on some improvements to the jig. I just wonder how it works if you do a taper on both sides or a blade, as the second side's taper should be double the degree.

In any event, I would look for a real surface grinder before purchasing a 1K attachment.

M

jmforge
12-24-2011, 04:14 PM
Marko, the current version has a "registration" pin at 6 inches from the pivot point and one at at 3 inches, so you space it for the initial taper at 6 using a feeler gauge (?) and when you flip it over to do the other side, you can use the same spacer at the 3 inch mark. It also has a dial indicator. It would appear that Travis has really gone the extra mile to make this thing easy to use for the mechanically impaired like me.:lol2: My concern with a real surface grinder is how much it would cost to get one in good working order and then modify it to work with belts, especially if I am already looking to buy a second grinder and convert my KMG into a dedicated horizontal platen setup most of the time and possibly buy a KMG "flatbed" grinder too.
Then is it is possible. There is no description on TW site and the last time I talked to Travis about the attachment, he didn't mentioned the tapering option, but I did know that he was working on some improvements to the jig. I just wonder how it works if you do a taper on both sides or a blade, as the second side's taper should be double the degree.

In any event, I would look for a real surface grinder before purchasing a 1K attachment.

M

Marko Tsourkan
12-24-2011, 04:53 PM
Hard to say. There are some limitations to the jig that make it not very attractable at the current price. I would not think twice about getting another TW-90 though.

M

jmforge
12-24-2011, 05:41 PM
Of course there are going to be some compromises, but having done some preliminary research on the cost of doing the same thing even with an old "real" 6 x 12 surface grinder or one of the Chinese made benchtop grinders from Grizzly or HF and a sine plate /mag chuck plus belt conversion, the $1000 doesn't seem so quite so bad as long as it does what I need it to do, which would primarily rudimentary tapering and flattening and getting damascus billets in a flat enough form that stock removal guys could use them.
Hard to say. There are some limitations to the jig that make it not very attractable at the current price. I would not think twice about getting another TW-90 though.

M

Marko Tsourkan
12-25-2011, 05:15 PM
I am thinking 618 - 624 Brown & Sharpe Micromaster from 1970s if I end up going that direction - I have no money to waste on imports (ones that are made for the likes of Clausing might be an exception). Until then, I can get a very good distal taper without any jig.

M

mhlee
12-29-2011, 02:12 PM
That is a conclusion I arrived after (thicker spine translated into thicker middle). I have not ground a thick knife before and was wondering how claims that spine thickness doesn't matter as long as a knife ground thin above edge (unless above edge means middle, or more precise, hollowed out middle like in Shigefusa :) ). The degree of convexing was similar on both knives, but that didn't seem to matter as the thicker knife wedged in it's mid section.

I already reground it and cut some vegetables with it. Definitely a difference.

M

Marko - Will you be applying this to both your customs and your stock knives?

Marko Tsourkan
12-29-2011, 02:41 PM
Custom and ready-made (coming in the future when I figure how to manage my custom orders better) will be virtually the same knife with the only difference being that the latter I will make without an input from a buyer. So far geometry and profile selection has been left to me on most custom orders, so the two will be very similar in all respect, except ready-made will have handle material and combination selected by me.

I will have curly koa, curly maple, Arizona Desert Ironwood, Ebony as my wood staples. I might add a few other types of wood as time goes by. I will continue using horn, but will look for other materials, as well as other constructions of a handle as well.

Oval, and Western handles will be available shortly. A hybrid oval/Western wa is in works.
M

mhlee
12-29-2011, 04:46 PM
That's awesome.

Marko Tsourkan
12-29-2011, 05:59 PM
Ready-made knives will give me a little more flexibility on size, production time, etc. Communication and customization takes time - say you make 3 knives of same size, profile and geometry with handle material you have on hand, you get them done faster than 3 custom knives with different profiles, geometries and handles.

M

mhlee
12-29-2011, 06:23 PM
No question about that.

Thanks for the information. I'm looking forward to when you start working on these.