# Why use stones for double bevels knives instead of a slack belt grinder??



## gic (Jun 17, 2016)

Don't get me wrong, I like using stones - I have a pretty crazy of collection of them by now. They remain my drug of choice for touchups and when I just feel like mellowing out

But I recently learned how to sharpen on a 1x42 slack belt grinder and, objectively speaking, the edges I am getting on the knives I am practicing on are pretty insane. They are at as good as the edges I get on stones and, if I am being honest with myself, given that they are so convex, they may well be better. It also takes almost no time at all to do a practically dead knife. So except for the need to keep on dipping the blade into water on each pass to avoid heat buildup, and needing to develop enough skill so as not to do an overgrind or otherwise ruin the knife, what is the downside for any knife you would otherwise have to use a full progression on? 

Thinking through some obvious objections:

Cost doesn't seem much of an issue: A good quality 1 x42 slack belt grinder like the Viel or the Kalamazoo and a bunch of belts from Klingspoor doesn't cost any more than a good set of stones - maybe less!

Space could be an issue of course but I mounted my 1x42 on a piece of plywood and with a few clamps, it's pretty portable. You do need to wear a mask and have a bucket of water available but that isn't too bad. 

Belts do make more of a mess. (So my girlfriend won't let me do it in the kitchen like my using stones.)

So, what are the advantage people see to stones over a slack belt grinder for double bevel knives assuming (1)equal skill levels (2)working on a knife one would have to use a progression of stones on and not just doing a touchup?

(Oh: one downside I've noted is that I am listening to a lot less music which I put on when I sharpen on stones and can't really hear with the grinder going )



(Note I do pull out a really high grit stone to put a microbevel on when needed.)


----------



## aboynamedsuita (Jun 18, 2016)

I recall a very thorough write up by Dave Martell about this, it was fairly recently if memory serves. I don't think I'd want to use it on thin delicate edges, but if you're sharpening mass amounts of cheaper generic "work knives" such as vnox probably makes sense


----------



## gic (Jun 18, 2016)

Yep: Here's some of what Dave said there: "So using a belt grinder is all about speed (quantity vs quality)? Nope, not at all actually. Depending on one's approach, a fantastic edge can be made with belts, in fact I'd go so far as to say in some cases a better edge can be made with belts than with stones. " 

So in a sense my new post is to start a dialog to delve further into what Dave said in his post here: http://www.kitchenknifeforums.com/showthread.php/27549-Interesting-sharpening-video-by-J-Nielsen


----------



## malexthekid (Jun 18, 2016)

I guess some of it comes down to why, are you sharpening large amounts of knives or knives for work?

From my point as a home cook that just loves sharp pointy things, sharpening on stones is something i enjoy. I find it quite relaxing.


----------



## gic (Jun 18, 2016)

Well I am actually sharpening large numbers of knives from friends and thrift shops to learn how to use a grinder so I can start making knives! But I am still interested in the question of the convexity of a belt grinder edge being "better" than what I cna do on stones.

But I agree it isn't relaxing at all to use a belt grinder - as opposed to stones, which I find very relaxing, especially on muddy stones...


----------



## ecchef (Jun 18, 2016)

To me, sharpening with a 1 inch wide belt would be like sharpening on a 1 inch wide stone.
If I were to use a belt grinder, I'd go with a 4" belt and horizontal platen. Something like this:



My muscle memory is already conditioned to work in a horizontal plane anyway.
I don't know if this size has enough variety in available belts though.


----------



## XooMG (Jun 18, 2016)

Dust, noise, power usage are practical concerns for me. I also don't think complex "progressions" are necessary for sharpening, but stones are more interesting to have lying around the house than used belts...and some of the natural stones smell better.

I also sharpen single bevel and razors, and so the stones will be there anyway.


----------



## LifeByA1000Cuts (Jun 18, 2016)

+1 noise! Sharpening and knife work is night work to me (full time employed in non-food job).

Also: I wouldn't trust myself with a belt not to cause overheating...


----------



## Sharpchef (Jun 18, 2016)

I regularly use a machine like this, in my opinion much better then a Beltgrinder!

http://www.dick.de/en/tools-for-chefs-and-butchers/products/sm-90-lamellar-grinding-machine

I have a water cooled bench grinder for knifemaking but never use ist for sharpening just for thining blades, because my good knives would loose too much metal within no time!

These Machines (DICK) are a joy to use, quite simple btw., the lammelar air condition somewhat cooles the blade down, but i use it only for soft butcherknives and the typical german thick knives....... that need to be konvex grinded. Even with this machine you need to cool down the blade regularly, and even this will not prevent your steel from loosing massive hardness......
You will also need a polish wheel like on this machine, to deburr the edge, with beltgrinders no matter how fine the belt is, you will have massive burr.


You have to aknowledge that if the steels starts to throw out sparks, it is already too hot! This is nearly melted steel! at least 1500 Celcius! So not for expensive knifes, never!
A Blacksmith knows what i`am talking about, when the steel gets too hot in the forge at about 1190 Celcius it starts throwing out sparks (Carbon explosion included). So if this happens right on the edge, it is ruined, and you have to grind down even more.

Greets Sebastian.


----------



## Dan P. (Jun 18, 2016)

Why use a grinder instead of felt and/or leather wheels? etc. etc.


----------



## Dan P. (Jun 18, 2016)

Sharpchef said:


> A Blacksmith knows what i`am talking about, when the steel gets too hot in the forge at about 1190 Celcius it starts throwing out sparks (Carbon explosion included). So if this happens right on the edge, it is ruined, and you have to grind down even more.
> 
> Greets Sebastian.



I think these are two very different kinds of sparks!


----------



## Sharpchef (Jun 18, 2016)

Dan P. said:


> I think these are two very different kinds of sparks!



you are right, but both where only Carbon explosions affected by heat. And the heat is almost the same so i took it as an simple explanation. I am no metallurgiest or pro blacksmith, this comes to my mind after reading Roman Landes Books.

Back to topic, why is this just meant for double bevel knifes, a single bevel knife can also be sharpened on a belt grinder...... Very good btw. (if slow working and watercooled!)

Greets Sebastian.


----------



## gic (Jun 18, 2016)

No disrespect meant but find it hard to believe j Nielsen a master smith who sharpens with a Kalamazoo 1x42 belt would be ruining the edge and screwing up his heat treatment.


----------



## LifeByA1000Cuts (Jun 18, 2016)

Hardened steel is already too hot when it approaches 200°C, even less for some alloys (ZDP is rumored to lose ...or gain... its temper very quickly)....


----------



## osakajoe (Jun 20, 2016)

ecchef said:


> To me, sharpening with a 1 inch wide belt would be like sharpening on a 1 inch wide stone.
> If I were to use a belt grinder, I'd go with a 4" belt and horizontal platen. Something like this:
> View attachment 32309
> 
> ...



I have this exact ryobi machine. But only use it for repairs. Blade gets extremely hot fast if you don't know what you're doing


----------



## natto (Jun 21, 2016)

gic said:


> No disrespect meant but find it hard to believe j Nielsen a master smith who sharpens with a Kalamazoo 1x42 belt would be ruining the edge and screwing up his heat treatment.



I agree, but how do less experienced people know what is too much? Which belt produces less heat? When is a belt too dull? Which speed is proper? Thin ground knives are easier to burn. Carbon is annealed lower than ss and so on. To me it would be a lot of work, to examine the point until which I believe HT to stay untouched.


----------



## gic (Jun 21, 2016)

I've been following Nielsen's advice on the 1x42. One quick pass, dip in water repeat, seems to keep the plade cool enough.


----------



## Kippington (Jun 21, 2016)

natto said:


> I agree, but how do less experienced people know what is too much? Which belt produces less heat? When is a belt too dull? Which speed is proper? Thin ground knives are easier to burn. Carbon is annealed lower than ss and so on. To me it would be a lot of work, to examine the point until which I believe HT to stay untouched.



Metal will change color when you heat it enough to change its temper. It also hurts like hell if you touch it. Heat management on a grinder is easy enough if you're not in a rush.


----------



## Sharpchef (Jun 21, 2016)

natto said:


> I agree, but how do less experienced people know what is too much? Which belt produces less heat? When is a belt too dull? Which speed is proper? Thin ground knives are easier to burn. Carbon is annealed lower than ss and so on. To me it would be a lot of work, to examine the point until which I believe HT to stay untouched.



That brings it on the point!, sure guys like Jurgen Schanz (german Grinding Master) can thin out a blade even with sparks, but he just knows what he is doing. Give a Beltgrinder to a nooby and he will ruin the temper within seconds!

@Kippington: You are right!, but this are straight blanks.... On a belt grinder with no cooling the edge will suffer the most damage due too the heat. You will not recognize the fact of overheating with your fingers! 

As an example the edge of a knife can be nearly as thin as a piece of Aluminum foil, try to put it in an oven with 200 Celcius, put it out and recognize that you could hold it in yout hand, it cools down so quickly....

Greets Sebastian.


----------



## natto (Jun 21, 2016)

Kippington said:


> Metal will change color when you heat it enough to change its temper. It also hurts like hell if you touch it. Heat management on a grinder is easy enough if you're not in a rush.



Afaik tempering colors are a reaction with air oxygen. The color is a result of temperature and time. Is straw yellow after a second indicating the same annealing like after an hour? And how can I see the color on the very edge, the hot spot? With a proper test against overheating power tools would be much more fun.


----------



## gic (Jun 21, 2016)

Does the fact that the blade is a little wet when using Nielsen's method of "quick pass, dip, repeat" mean the blade is less likely to heat up?


----------



## natto (Jun 21, 2016)

It cools the edge down after the quick pass but I don´t know reliable info about heat absorption of wet blades. Follow the essential tips of the pros, check your results and you´ll be fine.


----------



## Kippington (Jun 21, 2016)

gic said:


> Does the fact that the blade is a little wet when using Nielsen's method of "quick pass, dip, repeat" mean the blade is less likely to heat up?



It helps for sure. Water sitting on a blade surface can indicate the temperature of the spot it's resting on by how it behaves, while also actively working to cool it by sucking out the heat and dissipating into the atmosphere. Its called _*'enthalpy of vaporization'*_, if my thermodynamics is correct. 



Sharpchef said:


> You are right!, but this are straight blanks.... On a belt grinder with no cooling the edge will suffer the most damage due too the heat. You will not recognize the fact of overheating with your fingers!
> 
> As an example the edge of a knife can be nearly as thin as a piece of Aluminum foil, try to put it in an oven with 200 Celcius, put it out and recognize that you could hold it in yout hand, it cools down so quickly....
> 
> Greets Sebastian.



There will always be a thicker part of a knife to pull heat away from a thin edge like a heat sink.

If an area is so thin that you are worried about it heating up too quickly, it would mean that the edge geometry must be flat enough to safely place a finger directly on the other side of the blade that's touching the grinder, less then a millimeter away from where the grinding is happening. The heat shoots though thin metal fast enough to hurt before it affects a temper.



natto said:


> Is straw yellow after a second indicating the same annealing like after an hour?



Pretty much yes. You can get thin metal to change color to purple in under 5 seconds if you want... or don't want.
It happens in front of your eyes on the side that faces you, just after you pull your hand away because it's getting too hot to touch.

By the way, 'annealing' is a earlier part of heat treating (before the quench) that happens at much higher temperatures compared to tempering. You won't be able to affect an annealed blade with a belt grinder.

There's a better explanation of the differences *here*.


----------



## LifeByA1000Cuts (Jun 22, 2016)

"hurts like hell if you touch it"

If there is truth to claims of some steels even suffering at upper two digit centigrades... metal at these temperatures can feel perfectly harmless to the frequent cook, let alone to pros


----------



## natto (Jun 22, 2016)

So the stuff I looked up is not common sense. I´ll keep this in mind and never ever more mix up annealing with tempering:whistling:


----------



## daveb (Jun 22, 2016)

What's a centigrade?


----------



## Dan P. (Jun 22, 2016)

LifeByA1000Cuts said:


> "hurts like hell if you touch it"
> 
> If there is truth to claims of some steels even suffering at upper two digit centigrades... metal at these temperatures can feel perfectly harmless to the frequent cook, let alone to pros



Upper two digit centigrade like the inside of a roast?? Seems like the wrong steel to use!


----------



## LifeByA1000Cuts (Jun 22, 2016)

There's been conjecture about ZDP-189, for example, being very sensitive to overheats even in that temperature range... and as a layman, I would interpret a temper curve, as found in datasheets, which is non flat below 150°C as "heat sensitive stuff indeed"....


----------



## LifeByA1000Cuts (Jun 22, 2016)

@daveb I thought that slur for "degrees Celsius" was very commonly known worldwide and still chic to use, sorry.


----------



## Kippington (Jun 22, 2016)

LifeByA1000Cuts said:


> There's been conjecture about ZDP-189, for example, being very sensitive to overheats even in that temperature range... and as a layman, I would interpret a temper curve, as found in datasheets, which is non flat below 150°C as "heat sensitive stuff indeed"....



You are, quite literally, missing the point of a temper curve.

Almost all blades have been tempered to increase toughness. If you know what steel a knife is made of and what HRC the maker was aiming for, you should be able to pick the right point on a curve that tells you which temperatures are safe to get the knife to.

Take a look at *this ZDP data sheet* at the graph on the bottom of the second page.
According to this information, if I heat a ZDP-189 blade to 200°C my blade will still be at *66-67* Rockwell C. If I screw up and overheat it to 300°C (the steel would look purple at this stage! :shocked3, a look on the graph will show us what Rockwell the blade is now... *65* HRC. I would hardly call that a ruined knife. If anything, the toughness of the steel has probably _increased_ as a result.

*Here's a data sheet for VG-10*, page 5 has some interesting information on tempering. Take a look at what 300°C does to VG-10, and _then_ tell me that ZDP-189 is sensitive to overheats! :razz:


----------



## Keith Sinclair (Jun 22, 2016)

Gig I use the same Kalamazoo 1x42 to thin knives. Of coarse there are are knives I would not put on a belt. I do that same technique bucket of water the knife & belt get wet. Never let the blade get hot. Not using gloves can feel the temp. I even have a 1x42 leather belt can get hair splitting edge with it. Use it to sharpen Macheti's, Axe, & hatchet too.

No problem using a 1 inch belt for thinning as long as you make even passes good for convex edges large & small. Larger belts you have to be extra careful can generate heat quickly. Like the control I have with the kalamazoo.


----------



## gic (Jun 22, 2016)

Saw a picture of a guy recommending somehow clamping a wet sponge to a belt, I wonder how that could work...


----------



## Dave Martell (Jun 23, 2016)

I'm here to attest to being able to sharpening on belts without wrecking the temper...totally doable, even without water.

Of course I'd also have to attest to how easy it is to trash the temper sharpening on belts, even using water.

You have to have a light touch, that's the ticket to win.


----------



## LifeByA1000Cuts (Jun 23, 2016)

@Kippington to be a bit tongue in cheek: I thought people buy ZDP for the bragging rights (nothing wrong with that!) to that last tenth of a HRC grade, not for the toughness


----------



## Sharpchef (Jun 24, 2016)

Sharpening on a beltgrinder is doable for a pro! who knows what to do!

But i still say if there is a spark the steel has reached at least 600 Celcius!

This affects to O2 toolsteel when reached the 600 Celcius, from HRC 62 to HRC 55 within a second! All scientific researched!

For the german speaking members here`s a very informative discussion on the german Messerforum with lots of PDF`s regarding the scientific reseraches:

http://www.messerforum.net/showthread.php?44974-Schleifen-%DCberhitzen-H%E4rteverlust-ein-quot-heisses-quot-Thema

greets Sebastian.


----------



## malexthekid (Jun 24, 2016)

Sharpchef said:


> Sharpening on a beltgrinder is doable for a pro! who knows what to do!
> 
> But i still say if there is a spark the steel has reached at least 600 Celcius!
> 
> ...



so you say i can get steel to 600C with a hand file?

if the edge was at 600C then the guys doing the sharpening would have no finger tips.


----------



## Sharpchef (Jun 24, 2016)

malexthekid said:


> so you say i can get steel to 600C with a hand file?
> 
> if the edge was at 600C then the guys doing the sharpening would have no finger tips.



Ernst Stüdemann , Ernst Lauterjung and Volker Grube did researches about the affects of grinding in the steel, and they reached up to 900 Celcius with a handfile! but only on the first few my of the surface!

You can`t measure heat especially in steel with your fingertips, the head flows through the steel too quickly!



here you can buy the ebook, don`t know if it is available in english.........

http://link.springer.com/chapter/10.1007/978-3-322-88475-6_6

I use a watercooled beltgrinder for thining hardened knifes, and there is still a risk of ruining the temper!, but i am only hobbyist not a pro, but i would never use it for sharpening......

For more information i would like you to read Roman Landes books.

This is not my wisdom, it is from germanys steels specialist, like Ulrich Gerfin, Roman Landes etc.!

Believe it or not.

Here is an english text about grinding and talking about 1000 Celcius and more using a grinding wheel:
http://www.abrasiveengineering.com/therm.htm

you can find more if you search.....

Greets Sebastian.


----------



## malexthekid (Jun 24, 2016)

of course they can reach those temperatures with continuous grinding.... but quick passes are a lot different.

and sorry but you would definitely feel 600C in a knife blade. not that much steel to dissipate the heat.


----------



## Sharpchef (Jun 24, 2016)

malexthekid said:


> of course they can reach those temperatures with continuous grinding.... but quick passes are a lot different.
> 
> and sorry but you would definitely feel 600C in a knife blade. not that much steel to dissipate the heat.



The feelings in my hand (as pro chef) is another one then a not heat "resistant" guy.... so if the blade gets too warm for my fingertipps (maybe over 120 Celcius just on the surface (where it is touched), it is allready too hot on the edge (if sharpened). I can easily take out a Metal sheet (the thing you put the meals on, sorry for my english) out of the steamer with 100 Celcius, it looses heat after seconds........ with my hands...

And again, i don`T want to offend! this is simply the truth, if you don`t believe, you don`t have to.

Greets Sebastian.


----------



## malexthekid (Jun 24, 2016)

Sorry but it isn't the truth but a statement of your opinion.

Sorry but have you studied heat transfer?

if your fingers are only a few mm away then no the blade would not have reached that temps.

but then again feel free to dispute what those that have actually done this have experienced.

as you said not looking to offend but i do not accept anecdotal opinion or statements made as fact.

yes you can get very high temps grinding. that is simple energy transfer. the question is time and what us the max. would be interesting what the combustion temps of the belts are.


----------



## Sharpchef (Jun 24, 2016)

Ok, if i use a firesteel to make wood burn (wood starts to burn at about 600 Celcius, this is a fact, not my opinion), it is startet with a spark flying through the air and loose temperature on the way, right?.

If the fire gets started, we have to believe that the spark still has about 600 Celcius, right?

If we sharpen on a belt grinder there will be sparks, right? can we start a fire with this sparks ? (yes we can!) try to use some wood shavings and place it under your beltgrinder, it will start too burn. So we have reached at least 600 Celcius. And you have just too look on datasheets for maybe O2 Steel, and will find out this will increase the rockwell hardness within seconds!


And again this is not my opinion, it was researched in a scientific way......

btw. Have you ever used a lighter? and burnt your hands?, i guess no........ But the sparks are just melted metall over 1200 Celcius......

You can PM me and i give you Email adresses of guys that can explain that in a more scientific way, the steel gurus of germany like Achim Wirtz, Ulrich Gerfin, Roman Landes etc.

Greets Sebastian.


----------



## malexthekid (Jun 24, 2016)

hi Sebastian.

don't mean to seem abrupt and lets just say we are both right in different ways and let this topic get back on track.


----------



## Matus (Jun 24, 2016)

Sharpchef said:


> ... If we sharpen on a belt grinder there will be sparks, right? can we start a fire with this sparks ? ...



I am no promoter of belt sharpening, but I would only like to make the point, that practically all knives we buy and use were ground on belt grinders (partially or completely) or grinding wheels (OK, those are water cooled/lubricated) after HT. One just needs to be careful and be slow. Even if a spark leaves the blade here and then, then it only means that on a very localized point the metal got hot and very most of that heat was taken away with that spark. There is a reason why one has a bucket of water stading next to the belt grinder. Keeping the blade wet allows to cool it during the grinding as the water evaporates.

If I were planning to sharpen blades on a belt (I do not) I would probably use slow speed and some sort of compound on some flexible belt.

Where I do agree compleltely is that the thinner the steel, the easier to overheat because there is no heat sink and cooling via air is very slow. But there are options one can get a for a belt grinder for cooling . like a nozzle that sprays water on the belt.

In other words - there are ways to sharpen knives with belts, but the main component is to be careful.


----------



## Sharpchef (Jun 24, 2016)

Matus said:


> I am no promoter of belt sharpening, but I would only like to make the point, that practically all knives we buy and use were ground on belt grinders (partially or completely) or grinding wheels (OK, those are water cooled/lubricated) after HT. One just needs to be careful and be slow. Even if a spark leaves the blade here and then, then it only means that on a very localized point the metal got hot and very most of that heat was taken away with that spark. There is a reason why one has a bucket of water stading next to the belt grinder. Keeping the blade wet allows to cool it during the grinding as the water evaporates.
> 
> If I were planning to sharpen blades on a belt (I do not) I would probably use slow speed and some sort of compound on some flexible belt.
> 
> ...



I own a water cooled bench grinder.... but can ruin tempering with using that too..... Just a matter of belt speed, ineed.

@Matus:as you are are german guy too, you may just read the thread i shown and tell the guys here (because i a`m a nooby) that what i tell here is not complete rubbish..... with a researched backround, if you like, cause the Topic is sharpening not grinding( you are right every knife is made with belt grinders..... even after heat treatment.)

Greets Sebastian.


----------



## XooMG (Jun 24, 2016)

It's very localized and at a small scale, but sure you can get some parts of the edge to achieve a very high temperature.

At a small enough scale (i.e. when carefully done with reasonable effort to keep cool), the effect becomes pretty negligible and does not appear to alter the performance of the edge very noticeably. An occasional spark site will be at temp for a very small fraction of a second, and the entire edge would not be uniformly changed, nor change deeply enough to affect overall edge integrity. A spark in the air remains at temp much longer.

It takes a little bit of carelessness to affect the edge performance at normal geometries, but it certainly can be done.


----------



## Dan P. (Jun 24, 2016)

As it is being cut from the blade, the small particle of metal being removed accumulates heat, hence sparks. With sufficient care the parent metal does not accumulate heat. Remember there is a tremendous difference in size between the little sliver of metal being abraded and the parent metal.
A good example of this that is more observable is to use a scraper or, more commonly available, a coarse file. Using a single vigorous stroke you can remove a dusting of short swarf that will be blue with heat. The parent metal will be cold. You can try that at home, you don't need steel gurus.


----------



## Kippington (Jun 24, 2016)

Dan P. said:


> Using a single vigorous stroke you can remove a dusting of short swarf that will be blue with heat.



Absolutely. Take a look here as metal chips fly off, heating up from yellow to purple then blue in a fraction of a second - all while the parent metal does not change color as it retains little heat.

[video=youtube;-Nw32lstErA]https://www.youtube.com/watch?v=-Nw32lstErA[/video]


----------



## Matus (Jun 24, 2016)

Sharpchef said:


> Sharpening on a beltgrinder is doable for a pro! who knows what to do!
> ...
> http://www.messerforum.net/showthread.php?44974-Schleifen-%DCberhitzen-H%E4rteverlust-ein-quot-heisses-quot-Thema
> 
> greets Sebastian.



The first sentence is the core of the solution. Sharpening on a belt requires knowledge and experience. I have a belt grinder (since about 4 weeks - so I am noob), but seen how little mistake leads to very fast overheating of the edge (in particular once it gets thin) and burning my fingers in the process, tells it all. There are pros that can sharpen blade on a belt - one sees this more often with outdoor knife makers (hint - blades that are considerably thicker than Japanese kitchen knives), but if one watches their youtube videos, one can see how carefully they do that.

I agree that sharpening and grinding are 2 diametral different things and the main difference is the thickness of the material being worked on, because the material of the blade is also the heat sink for the created heat and if one is working on a blade that is very thin (close to the edge) then there is basically no way to disperse the heat generated and overheating can happen extremely fast. I fully agree with that.

The only reason why this can actually be (with all that care and experience) done is what Dan just said - the tiny steel particle that got hot is TINY (probably in the range of few micrometers) and comparable amount of heat (if not less) was deposited to the blade at the point where the particle was removed is thus also small, extremely localised and dissipated quickly even close to the edge.

Thank you for the linked article - I will definitely read it (even if I am not a German - if you could hear me you would know right away  ). But yes, if it was written by Achim, than it is probably worth taking seriously.

I would say - what was said and discussed is all right - we are balancing literally on a knife's edge because this is a topic where only very little stands between sharpened and overheated edge.

Does this make sense to you guys?


----------



## Matus (Jun 24, 2016)

But is is probably fair to say that those blades on the cutting head are made from high speed tool steel - steel that can handle higher temperatures without loosing its properties. Still - your argument applies here as no steel would handle being heated to that temperature without changing its properties.



Kippington said:


> Absolutely. Take a look here as metal chips fly off, heating up from yellow to purple then blue in a fraction of a second - all while the parent metal does not change color as it retains little heat.
> 
> [video=youtube;-Nw32lstErA]https://www.youtube.com/watch?v=-Nw32lstErA[/video]


----------



## Matus (Jun 24, 2016)

I am just doing my best so this while a bit heated, but very interesting discussions remains worth reading.


----------



## gic (Jun 24, 2016)

I wonder if the fact that J Nielsen uses a 1 x 42 for sharpening as opposed (I am sure) to a bigger 4" belt grinder for shaping makes a difference. Logically a pass on a 1x42 touches the steel of the knife to the belt only 1/4 the amount of time that a 4 inch belt does and so heats up much less rapidly.


----------



## Kippington (Jun 25, 2016)

Matus said:


> But is is probably fair to say that those blades on the cutting head are made from high speed tool steel - steel that can handle higher temperatures without loosing its properties. Still - your argument applies here as no steel would handle being heated to that temperature without changing its properties.



I think the head is made from high speed tool steel (they specify the screws as M3 steel, which gets tempered at about 550°C), whereas the attached blades cutting though the metal are made from something else, carbides probably.
My point of the video was to show that in grinding and milling; just because there are sparks or bits of purple metal flying off, it's not a good indication of the temperature of the actual work-piece. It only indicates the temp of the bits that are flying off it.

It also helps to address Natto's question about how quickly tempering colors change. The video has to slow down to see how quickly the oxidization happens.



gic said:


> Logically a pass on a 1x42 touches the steel of the knife to the belt only 1/4 the amount of time that a 4 inch belt does and so heats up much less rapidly.



Once you consider we are not machines and can vary the speed and pressure of a pass at a whim, your logic breaks down very quickly! :rofl2:


----------



## natto (Jun 25, 2016)

Tempering colors can change fast, no question. To read them is my point. A good edge is around 1/1000mm wide, 1/100 should be dull. This 1/100mm does the cutting and is most critical to be affected by heat. With a loupe I might judge the color of 1/10mm, less would be guessing. 

Further up the blade the thicker geometry can take more heat without damage. If I remember correctly, the tempering colors near the edge indicate the higher temperatures. Then visible colors would indicate lower temperatures than what the edge got.


----------



## gic (Jun 25, 2016)

I wonder if one of those hand held laser beam thermometers often used for barbecue could help settle the issue, if one person shines it on the blade edge as the other sharpens the blade could one begin to get a sense of the temperature gradiant


----------



## LifeByA1000Cuts (Jun 25, 2016)

Even small thermal imagers are affordable nowadays... Calibrating them properly on metal (same problem with IR thermometers BTW) and making sure you are not actually reflecting another heat source in will be the tricky part if you want any accuracy.


----------



## Sharpchef (Jun 27, 2016)

Just to clarify once more, i believe that a pro can thin a blade on a dry beltgrinder, with speed regulation!, with water cooled Benchgrinders also sharpening is no problem at all.

I just want to say that this is not good for anybody! The chance that you ruin your knives is very high!.

Greets Sebastian.


----------



## natto (Jun 29, 2016)

Sharpchef said:


> Just to clarify once more, i believe that a pro can thin a blade on a dry beltgrinder,...



If pro can sharpen on a belt sander without damaging the edge, everyone who knows what to do can. I am interested to learn what might work for me. 

From your link to abrasiveengineering.com/therm 


> The use of grinding fluids is effective in preventing thermal damage since fluids not only remove heat from the grinding zone but also lubricate to reduce the friction between the wheel and the workpiece. There are, however, limitations on the ability of the fluid to cool. Shafto et. at. (1975) have shown that for creep-feed grinding, water-based fluids cool effectively only when the workpiece surface temperature is below a critical value of about 130°C. Once this temperature is exceeded, the fluid loses its ability to cool, and the workpiece temperature rises steedly to a temperature which could be expected under dry grinding conditions (see fig. 1).


 Thank you, this I didn't know


----------



## LifeByA1000Cuts (Jun 29, 2016)

Interesting... I would have assumed water based coolants to clamp the temperature to a 100°C or below ... by using the excess heat up through evaporating.


----------



## goatgolfer (Jun 29, 2016)

daveb said:


> What's a centigrade?



Two Centigrades are just your two Cents.. said JJ Celsius


----------



## Matus (Jun 29, 2016)

LifeByA1000Cuts said:


> Interesting... I would have assumed water based coolants to clamp the temperature to a 100°C or below ... by using the excess heat up through evaporating.



Once the water starts the boil the heat transfer sinks a lot, because the workpiece will be isolated by the vapour from the surrounding liquid coolant. The same effect allows one to (for a very short period of time) to dip a finger in a liquid nitrogen without damage.


----------



## LifeByA1000Cuts (Jun 30, 2016)

Would have expected all the motion in a grinding scenario to force new coolant against the hot surfaces... I mean, the boiling water in a pot boils instead of comfortably hovering on a steam layer like some urasuki and letting the pot beneath melt


----------



## Matus (Jun 30, 2016)

LifeByA1000Cuts said:


> Would have expected all the motion in a grinding scenario to force new coolant against the hot surfaces... I mean, the boiling water in a pot boils instead of comfortably hovering on a steam layer like some urasuki and letting the pot beneath melt


Yep, but the temperature gradient between the pot and the water is not large enough to create a complete layer of wapor between the water and the pot. It is the convection that tranports most of the heat and the process is still relatively slow. But drop a little water on a surface with some 200+ degrees Celsius and it will 'glide' on a wapor on it. But if you pour a large volume of water inside a over-heated pot the vapor creation upon the contact with the pot will cause the surface to cool down very fast and the since the pot material has rather limited heat transfer it will not be able to allow for sufficient heat transfer to keep the temperature of the inner surface of the pot high enough to sustain the behaviour (if it would the whole water volume would burst into your face as the vapor would be expanding)


----------



## Dan P. (Jun 30, 2016)

More speed/lower grit, more coolant. It's not rocket surgery!


----------



## WingKKF (Jun 30, 2016)

I've done some reading on the subject from Verhoevens writing and as I understand it, there are two scales he is talking about when discussing overheating during grinding. On the macro scale, if you are careful about grinding and keeping the blade cool, the temper of blade itself should not be affected but at the micro scale, the surface of the metal being ground will be trashed metallurgically speaking as there is no way to prevent that top layer of steel (couple of microns probably) from overheated above temper temperatures during grinding. Verhoeven usually talks about edges 1 micron or so thick, so the very edge of any belt ground knife will be compromised no matter what. This is why I believe, the final finish should be done manually of a waterstone if you do care about the final few microns at the edge.


----------



## malexthekid (Jun 30, 2016)

I really want to see someone skilled in this set up with a highly accurate thermal imaging camera just to see if the steel is getting to those temperatures.


----------



## XooMG (Jul 1, 2016)

malexthekid said:


> I really want to see someone skilled in this set up with a highly accurate thermal imaging camera just to see if the steel is getting to those temperatures.


Thermal camera in a microscope? How do you plan to get the blade from grinder to scope before it cools?


----------



## LifeByA1000Cuts (Jul 1, 2016)

Normal microscope optics will be black to thermal radiation, so thermal imaging would be mostly useful for macro level effects. There are thermal microscopes, no idea what they cost...

You'd focus the microscope straight at the grinding site as it happens... problem: Thermal imaging optics are rather less resilient to sparks etc than glass...


----------



## Sharpchef (Jul 1, 2016)

Another point that speaks against sharpening on beltgrinder (no matter what speed/cooling fluid is used), is that the belts always do a little jump, everytime the glued part is reached. Not that much matter while sharpening konvex grinds, but using the hard grindtable it can cause problems.

Greets Sebastian.


----------

