Chilling blade before using a powered belt?

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Pendexter

Joined
Aug 20, 2018
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I did google search, which is how I came up with my specific questions at the bottom of the post. I'm trying to make my posts more concise, so here goes:

- belt grinding causes heat due to friction.
- the thinner the cross-section, the easier it is to overheat metal due to the less thermal mass.
- the thinnest part of a blade is at the apex, where the cross section is only a couple of microns across.
- temper occurs at between 350 and 500 degrees for many common types of steel.
- belt sanding can allegedly get the apex above the tempering temperature without the rest of the knife being noticeably warm.
- using ice water to cool the blade seems like a good idea to prevent the blade from overheating.

I started sharpening two knives at a time, leaving one in the ice bath while sharpening the other to keep both from overheating at the edge.

Questions:

1. is there any drawback to letting the blade sit in ice water for a while before grinding? i.e. micro-fracturing of the metal due to thermal stress... etc.
2. is this much ado about nothing? I have read that many knife makes use chiller platens and wet belt grinding systems, so there is obviously a subset of makers that think that temperature control is important.
 
#2. How hot the blade gets is totally dependent on the skill of the person sharpening. It's that simple.
 
If you are using power tools to sharpen you must have the skill not to overheat or chew up the blade. Power tools are very unforgiving and many people stay away from them. It takes time and a whole lot of practice to learn. If you're not using power tools then heat issues are null.
 
At the thin apex of the edge, soaking in ice water will make no difference.
You can cool sanding belts with a water spray or drip to keep the edge cool when sharpening.
Knife maker who use water cooled belts generally do so to keep down dust and keep from burning themselves while grinding. Some makers grind their blades from steel that is previously heat treated, and this keeps the grinding from altering that heat treatment.
 
SOLEIL said:
If you are using power tools to sharpen you must have the skill not to overheat or chew up the blade. Power tools are very unforgiving and many people stay away from them. It takes time and a whole lot of practice to learn. If you're not using power tools then heat issues are null.
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Soleil: I've been working with the KO Worksharp (powered belt), Sharpmaker and diamond stones. At some point, I may settle on one system, but for now, I want to learn as much as I can about the different systems.
In your signature, you write that "Life is dull without Paper Wheels". Are you of the school of thought that paper wheels won't overheat the apex? What RPM are you running the wheel at? 8"?
I'm trying to learn the techniques required to prevent overheating of the edge.

Bill DeShivs said:
At the thin apex of the edge, soaking in ice water will make no difference.
You can cool sanding belts with a water spray or drip to keep the edge cool when sharpening.
Knife maker who use water cooled belts generally do so to keep down dust and keep from burning themselves while grinding. Some makers grind their blades from steel that is previously heat treated, and this keeps the grinding from altering that heat treatment.
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Bill: When you say that knifemakers use water-cooled belts to keep down dust and burning themselves while grinding, am I correct to assume that you mean pre-heat treat?
And when you say that water spray or dip can keep the edge cool, is that because the steam point of water is 212 degrees F. and the belt won't get above that temp without turning into steam, and therefore the metal in contact with the wet belt also won't be raising about that 212 degree point?
I can see how a wet belt in contact with the blade while grinding would be more effective than pre-cooling the blade and then grinding on a dry belt.
 
Even the KO worksharp has high enough rpm to cause overheating the fine edge ... and can affect the heat treat quite quickly ...

also the KO worksharp can burn up being ran to slow ... there have been a few threads on that recently ...

I don't use belt sanders for sharpening anything other than an axe in bad shape or a mattock or tool that doesn't need the finest edge ... and after I fix damage I still hand file and sharpen ...

but from what I have been told and read ... something in the area of 150 to 200 rpm with water cooling as you grind is best to avoid affecting the heat treat.

I'm sure some makers or professional sharpeners will be better able to dial in on the exact process and rpms etc ...
 
115Italian said:
Is cold metal more brittle than warm?
Click to expand...
Did a quick google search. Very interesting question...
Yes, there is a "ductile to brittle transition" of steel. It depends on the specific composition, amount of impurities, etc. that will determine the transition temperature. But I'm not sure if the brittleness of cold steel is affected by rapid heating via the friction of belt sharpening.

Maybe less plastic deformation and more chipping in terms of stock removal at extremely low temperatures (below negative 50 degrees Celsius)?
 
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JJ_Colt45 said:
Even the KO worksharp has high enough rpm to cause overheating the fine edge ... and can affect the heat treat quite quickly ...

also the KO worksharp can burn up being ran to slow ... there have been a few threads on that recently ...

I don't use belt sanders for sharpening anything other than an axe in bad shape or a mattock or tool that doesn't need the finest edge ... and after I fix damage I still hand file and sharpen ...

but from what I have been told and read ... something in the area of 150 to 200 rpm with water cooling as you grind is best to avoid affecting the heat treat.

I'm sure some makers or professional sharpeners will be better able to dial in on the exact process and rpms etc ...
Click to expand...

I also read about the Worksharp motors wanting to run at full speed. That's what got me thinking about temper in the first place. I think that I'm mentally transitioning away from powered tools, but I'm not there yet.
 
If you haven't come across the below researches yet, they are worth a look:

LaTrobe Specialty Steel Company, Bulletin 104, Improper Grinding of Tool Steels
http://customer.cartech.com/assets/documents/datasheets/Bulletin_104.pdf

W B Rowe “Temperature case studies in grinding including an inclined heat source model.” School of Engineering, Liverpool John Moores University UK
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.895.1681&rep=rep1&type=pdf

New Zealand WAIKATO University website:
The Measurement of Knife Sharpness and the Impact of Sharpening Technique on Edge Durability

Scientific studies on grinding, interpreted for knives, tell us that the blade is not overheated if pulled across an 8-10” wheel at a feed rate of approx. 10cm per 1 second on full speed grinder/buffer, and 5cm on half-speed.

We sharpen and hone on wheels, and I had no need to translate the research data into the belt speed. Obviously, the blade feed rate not to overheat the edge on 10" paper wheels on a half-speed buffer is not the same as for your belt grinder.
One has to interpret the grinding speed and the workpiece feed rate in the W. B. Rowe experiments to pulling the knife blade across the belt on his belt grinder, to ensure the sub 200C heating.
For a given grinding/honing speed there is a certain safe feed rate, and if you pull the blade slower than that across your belt or wheel, the friction becomes detrimental to the edge temper.

BTW our fingertips get burning sensation at 70C - when the blade feels warm during honing it is not a worry, but when burning, the very edge temeprature may reach the "de-tempering" range.
 
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wootzblade said:
If you haven't come across the below researches yet, they are worth a look:

LaTrobe Specialty Steel Company, Bulletin 104, Improper Grinding of Tool Steels
http://customer.cartech.com/assets/documents/datasheets/Bulletin_104.pdf

W B Rowe “Temperature case studies in grinding including an inclined heat source model.” School of Engineering, Liverpool John Moores University UK
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.895.1681&rep=rep1&type=pdf

New Zealand WAIKATO University website:
The Measurement of Knife Sharpness and the Impact of Sharpening Technique on Edge Durability
Click to expand...

Thanks for all the info! I'll be attempting to digest it in the next couple of days.

I've read a lot of your posts and articles, it was one of the reasons that I started exploring sharpness at a more granular level. I can get hair whittling, but don't have any rolling papers yet :)
 
No worries. It depends on steel, but generally, partial annealing (read: the edge apex softening) starts at over 200 C.
 
Pendexter said:
Hi.
Click to expand...
Hi
1. The only risk to a blade from sitting in salty ice water BEFORE touching abrasives is rusting, but seeing how cold slows chemical reactions, its nothing to worry about if it sits a few minutes

Water, esp ice water, is a risk to a blade if it has been overheated, like to the point you cannot touch it with your skin -- you gotta let that air cool to the point you can touch it before quenching in water


You can burn the apex (not entire blade) even if wet grinding if you try,
but dry grinding is guaranteed to burn it, cause its so small ( 1 micron x 1 micron).
but you cant never be sure how burnt it is
in happens in milliseconds (that is 1/1000 second) and it cools off just as fast

Its not trivial to know you have a burned edge unless its really burnt.
Sure sign is heat discoloration/scale

More obvious sign would be
edge rolling/chipping/reflective after light cutting/chopping of clean materials
and that lessens and goes away after a few subsequent hand sharpenings

Less obvious sign
edge burrs easier in hand sharpening
and that lessens or goes away after a few sharpenings

Less less less obvious sign
less edge retention on average, fewer cuts on average in cutting cardboard/rope/...
but casual observation won't do, its very easy to fool oneself, so you gotta be scientific



pre-chilling is useful cause it allows you to grind more passes before having to dunk the blade after air cooling
lubrication (ex water drip) keeps the dust down and allows your belts to last longer (like free money)

See
Simple HF 1x30 mod for water cooled grinding. | BladeForums.com
and Harbor Freight 1x30 Belt Sander ...


Will I feel the edge of my knife overheating from grinding with bare hands?
knivesandstuff
knivesandstuff
Published on Sep 5, 2016

Many times I have heard an rationalization about grinding dry without using wet grinders that a steel has to reach the tempering temperature before you can do any damage to the steel. This is then often followed by a claim that with bare hands touching the steel you can feel the knife, and your hand would be burning off before the steel could reach that heat.

This proposition misunderstands a lot about thermal dynamics and the transfer of heat. I think it also intentionally ignores the fact that typically people are speaking about damage to the thinnest most important part of the cutting knife, the steel behind the apex.
Heat interestingly behaves differently in different materials especially ones that have different thicknesses.
When heating steel which is thick in one part and very thin in another part, the thin area does not have much material to absorb and disperse heat, and so it can get hot very quickly, but is also able to release that heat very easily faster to the air around it than to the thicker material its connected to, depending on the type of material.
Aluminium is a very good thermal conductor and so heat can travel very well.

In this experiment, I am using a heat treated piece of Elmax, ground down in a similar cross section to a Scandi Ground knife with a fuller and 3mm spine. I am holding the steel in a similar location to where one might hold it if grinding.. infact much closer and with more contact than many.

The point I am making is that it is not a reasonable statement to say that because you are touching a knife somewhere that you can feel if you are damaging it. I can with absolute ease, and intentional lack of skill make a knife blade burn and discolor on a grinding belt by applying slightly incorrect technique, and see the blade glow momentarily if I want to.

Yes, often the damage may only be at the very apex. just enough to make that edge chippy, or rolly, or whatever, and some sharpenings may take off the bad steel.. every hand ground knife faces its own challenges. Wet grinding can still have issues, but far far less.

Please observe and come to your own conclusions.
 
bucketstove said:
Hi
Sure sign is heat discoloration/scale

More obvious sign would be
edge rolling/chipping/reflective after light cutting/chopping of clean materials
and that lessens and goes away after a few subsequent hand sharpenings

Less obvious sign
edge burrs easier in hand sharpening
and that lessens or goes away after a few sharpenings

Less less less obvious sign
less edge retention on average, fewer cuts on average in cutting cardboard/rope/...
but casual observation won't do, its very easy to fool oneself, so you gotta be scientific
Click to expand...

Hey Bucketstove, thanks for the thorough explanation. I suspect that I've been burning my edges. I went straight to the supersteels, but haven't been impressed with the performance. I wish Pete from Cedric & Ada's Youtube channel would do a test on the same steel, Lansky vs Worksharp since I know that he has both of those sharpening systems. I'm not at the point where I could confidently freehand to the same level of sharpness as I can with the belts.

I actually have an HF 1x30 sitting under the Christmas tree. I read Cliff Stamp's thread yesterday and was thinking about doing a drip mod. That was also part of the reason that I'm investigating this issue.
 
Pendexter said:
Hey Bucketstove, thanks for the thorough explanation. I suspect that I've been burning my edges. I went straight to the supersteels, but haven't been impressed with the performance. I wish Pete from Cedric & Ada's Youtube channel would do a test on the same steel, Lansky vs Worksharp since I know that he has both of those sharpening systems. I'm not at the point where I could confidently freehand to the same level of sharpness as I can with the belts.

I actually have an HF 1x30 sitting under the Christmas tree. I read Cliff Stamp's thread yesterday and was thinking about doing a drip mod. That was also part of the reason that I'm investigating this issue.
Click to expand...
Hi,
Well, add some lube to your worksharp and see what happens :)


Well, stream, pete did do it for a faulty knife (not steel)
See Problems With D2 Steel What on earth is wrong with this D2 steel by Cedric & Ada Gear and Outdoors


See also
Does Power And Dry Sharpening Lower Edge Retention?

Maybe even KnifeNews Article on Cedric&Ada Edge Retention Test




Pendexter said:
I'm not at the point where I could confidently freehand to the same level of sharpness as I can with the belts
Click to expand...
Maybe you are?
When using worksharp blade is more or less vertical right? cause the worksharp guide touches the blade..

Can you hold blade more or less vertical while you slide it against a pen/pencil?
Say you hold pencil in left hand, tilt it about 10 or 15 degrees ,
then "sharpen" a blade by keeping it vertical?

Thats about all the freehand control required if you got the stones :eek: :D
dont have to be super precise if you use the worksharp to sharpen at ex 14 or 10 degrees per side
and then the next 5 or 10 sharpenings freehand at 15 degrees per side
 
There's a lot to this topic, just because you're throwing sparks doesn't mean you've heated the steel to its melting or combusting temp any more than than you've done so when striking steel with flint. While you can ruin the temper on a hardened piece of steel, the likelihood the apex is reaching some astronomical temp while the steel behind it isn't even warm seems like a huge stretch to me.

I suspect much of the reduced longevity reported from belt grinding is due to improper finishing technique rather than loss of temper.

That said, for dedicated sharpening it really helps to have fresh, sharp abrasive and ability to reduce speed if necessary. Although, running at lower speeds increases glazing of the abrasive. While friction induced temp increase might be lower initially, there is a possibility you'll soon be generating more heat at a given speed due to less efficient cutting action.

I don't notice any difference in longevity with a belt sharpened edge, but then I do all my finish work manually on a stone.
 
The paper wheels I use are 8" at 3400+ RPM. I also use 6" wheels. I do not know the RPM of my other grinders as I made them myself from old motors. I have read here numerous times that my type of setups are too fast, too much HP and not at all the way to sharpen. I prefer higher RPM but can sharpen at any speed. I really don't understand the hype about wheel RPM, wheel size and heat problems. I've been using motorized tools to sharpen my knives for 40+ years. The key is practice, knowing how the particular steel of your knife will work and feel. I can tell many steels just by the way they sharpen. Great caution should always be used when running high RPM, especially with 3/4 or 1 HP motors. If something catches and you lose control of what your sharpening things will fly faster than you can see them. If you use the proper safety equipment you will be OK. None of my grinders have shields, as I like to reverse polarity for different methods. Safety glasses are a must. I also wear a face shield when buffing or using wire wheels.
 
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