What edge for tomatoes?

As long as the back bevel is thin, and the apex is clean, any grit will work for slicing. My old buck with hollow grind and 80 grit edge could slice translucent layers off a ripe tomato. I wouldn't bother going to a high polish as long as the geometry is thin. If its needed for dedicated chopping, then a higher polish is better, for basic kitchen prep (slicing tomatoes) its unnecessary and won't hold the edge as long - assuming your friend has few skills for maintaining the edge in question I'd say a 600 grit/1k is plenty.
If its a relatively softer steel - mid range kitchen cutlery, a medium finish and a smooth steel or burnish on the rim of a coffee cup will work well. Realistically, any mid to low finish with no burr. High polish+softer steel = poor longevity, so type/brand of knife is a major consideration, as well as your friend's general handling habits (religious cutting board, no dishwasher etc).
 
I never cut tomatoes at work but sometimes I like to slice them thinly.

In my experience, highly polished edges will glide through without resistance while toothy will have a grainy resistance regardless of ease. It just doesn't compete with a nice polished edge.
 
bluntcut said:
Took me a long time to write this post... yep it's still sort of incoherent :rolleyes:

Tomato skin fracture Pressure threshold = (Force / edge_contact_Area). Let's qualify P need to be small, which won't smush the tomato. Also let's ignore force vector and toothiness rip/tear by-product.

For given F and A=(edge Width * Segments * sEgment length). To achieve atleast minimum P, you can play with W, S, E. Further more, if we reduce [E] = a point/sharp_tooth; what left is just W & S variables. Where:

* W=sharpness. Apex width.
* S=number of tooth. S increase as as the tooth size (more refine) decrease.

So certainly there are points where sharpness are insufficient for a given large number S. By decreasing S (larger; coarser teeth), would directly reduce Area, which possible to achieve sufficient pressure to fracture tomato skin.

A reasonable great edge for tomato = shape a 1K edge where every tooth is sharp as possible from crest/tip to trough.
Click to expand...


Apex width is the inverse of sharpness. The greater the apex width, the less sharp it is. So some of your reasoning is inverted.
Your argument doesn't prove that miniserrations are better, since pressure can be decreased in other ways, eg. decreasing apex width by sharpening & polishing.
 
A knife with very thin bevels and a clean apex will easily be able to cut tomatoes with an edge at a variety of grits.

For cutting roses out of tomato skins, I find that anything from a 1000 grit up to 8000 grit edge works pretty well. For cutting a tomato into very thin slices to make a garnish (imagine a torus made out of very thin tomato slices) I find that it actually needs to be 2000 grit or above in order to keep the skin neat and clean.
 
I think, we agree and are talking about the same thing; however you probably can provide a more coherent explanation/reasoning... Please do so :thumbup:

mtangent said:
Apex width is the inverse of sharpness. The greater the apex width, the less sharp it is. So some of your reasoning is inverted.
Your argument doesn't prove that miniserrations are better, since pressure can be decreased in other ways, eg. decreasing apex width by sharpening & polishing.
Click to expand...
 
bluntcut said:
Took me a long time to write this post... yep it's still sort of incoherent :rolleyes:

Tomato skin fracture Pressure threshold = (Force / edge_contact_Area). Let's qualify P need to be small, which won't smush the tomato. Also let's ignore force vector and toothiness rip/tear by-product.

For given F and A=(edge Width * Segments * sEgment length). To achieve atleast minimum P, you can play with W, S, E. Further more, if we reduce [E] = a point/sharp_tooth; what left is just W & S variables. Where:

* W=sharpness. Apex width.
* S=number of tooth. S increase as as the tooth size (more refine) decrease.

So certainly there are points where sharpness are insufficient for a given large number S. By decreasing S (larger; coarser teeth), would directly reduce Area, which possible to achieve sufficient pressure to fracture tomato skin.

A reasonable great edge for tomato = shape a 1K edge where every tooth is sharp as possible from crest/tip to trough.
Click to expand...


bluntcut said:
I think, we agree and are talking about the same thing; however you probably can provide a more coherent explanation/reasoning... Please do so :thumbup:
Click to expand...

I can't, because slicing a tomato is way to complicated. If I thought about it for weeks, I doubt I could achieve a rational & comprehensive description. It is much easier to pick shortcomings in the attempts of others.

If you wish to pursue your path of a rational, let me make 2 points, which you may use constructively to improve your argument.

1. W=sharpness. Apex width.
Sharpness does not = apex width, since sharpness increases as apex width decreases.
One might say: Sharpness = 1/apex width. Or, Sharpness x apex width = 1.

2. Your initial assumption is that P=F/A is applicable. It is only applicable if the style is of a push cut. This is unlikely, & it changes & complicates the entire process.

Good luck, I will help further if I can.
 
Thanks.

Let me clarify my first post. My intention was to keep thing simple and focused at the most important point of this tomato cutting interaction -> first of is to fracture the tomato skin.

1. It meant to be a snapshot of a single value point. Hence whatever given W = it's the sharpness for this W. Perhaps, I should just use W and not mentioned the word 'sharpness'.

2. Pressure is the same for push & saw at given time until the tomato skin is fracture. Once fractured, force vector(s) will be different for push & saw cut.

Yep, thing can get complicated really fast... e.g. ask about tomato: type, size, state, et... thick vs thin slices; horiz vs vertical-cut :p

mtangent said:
I can't, because slicing a tomato is way to complicated. If I thought about it for weeks, I doubt I could achieve a rational & comprehensive description. It is much easier to pick shortcomings in the attempts of others.

If you wish to pursue your path of a rational, let me make 2 points, which you may use constructively to improve your argument.

1. W=sharpness. Apex width.
Sharpness does not = apex width, since sharpness increases as apex width decreases.
One might say: Sharpness = 1/apex width. Or, Sharpness x apex width = 1.

2. Your initial assumption is that P=F/A is applicable. It is only applicable if the style is of a push cut. This is unlikely, & it changes & complicates the entire process.

Good luck, I will help further if I can.
Click to expand...
 
In my experence a finely sharpened edge without teeth will last longer than a "Toothy" Saw tooth type edge because there is less resistence.

As mentioned, experiment yourself and find what works best for you for each application.
 
blame it on god said:
I prefer a heavily serrated tomato knife. In my experience a high polish just slides off tomato skin.
Click to expand...

I can take my gyuto from a Naniwa Snow White 8k (which is ~1.8ish microns) to the strops and go from 1 micron DMT paste to 0.5 micron DMT spray (flawless mirror on bevel) to finish my edge. I can still cleanly slice grape tomatoes into moon shapes--a torus is really hard to do since a grape tomato is so small.

I mean, this guy does it with a sort of middle of the road Miyabi without difficulty:

[video=youtube;dCVsygvbbzI]http://www.youtube.com/watch?v=dCVsygvbbzI[/video]
 
blame it on god said:
My knives can tree top arm hair and I polish with chosera stones and balsa strops. So there is no rounding of the apex.
Click to expand...

I think the important point is that if your polished edge is just sliding off the tomato, it's not as sharp is it COULD be at that same level of refinement. Also, from firsthand experience, it is quite easy to accidentally round the apex with Chosera stones (or any stones, for that matter) ;)
 
bpeezer said:
I think the important point is that if your polished edge is just sliding off the tomato, it's not as sharp is it COULD be at that same level of refinement. Also, from firsthand experience, it is quite easy to accidentally round the apex with Chosera stones (or any stones, for that matter) ;)
Click to expand...

My hypothesis is that sometimes slurry can be a negative thing. It certainly helps at grits 4000 and lower when you are still forming and shaping an edge. I think that at higher grits the slurry can sometimes round apexes unless you are very careful--in particular, attempting to put microbevels on when the stone still has slurry covering it seems to be cause of many of my own rounded edges.
 
Cynic2701 said:
My hypothesis is that sometimes slurry can be a negative thing. It certainly helps at grits 4000 and lower when you are still forming and shaping an edge. I think that at higher grits the slurry can sometimes round apexes unless you are very careful--in particular, attempting to put microbevels on when the stone still has slurry covering it seems to be cause of many of my own rounded edges.
Click to expand...

I have had similar experiences, I even experimented finishing on a completely dry stone and had great results. I gave up on using microbevels for a while because I had so many failed attempts :o
 
The sound of steel on dry stone is a terrible sound! But I agree, light strokes on a dry 4000 has made some scary edges for me.
 
Meh, for kitchen knives I prefer a few passes with the medium stones on the sharpmaker.

Maybe it is the crappy thick skinned FLAVORLESS tomatoes we get down here. Stupid hybrid tomatoes!
 
bpeezer said:
I think the important point is that if your polished edge is just sliding off the tomato, it's not as sharp is it COULD be at that same level of refinement. Also, from firsthand experience, it is quite easy to accidentally round the apex with Chosera stones (or any stones, for that matter) ;)
Click to expand...

From my POV, the high polish edge in the kitchen is for chopping, mincing, dicing. For tomatoes and assorted prep, an edge with some bite is a better choice. My Chef's knife will push cut tomatoes, but my utility knife slices them just fine. There is no way I would sharpen a kitchen utility for a third party to a fine polish unless specifically asked. If the recipient can't describe the finish or describe how they maintain their own knives, they get a utility edge - that will slice the ripest tomato just won't push cut it.
 
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