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Power sharpening: how fast is too fast?

Posted by WobblyHands 
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Power sharpening: how fast is too fast?
October 30, 2016 11:10AM
I find that I often have to grind away a lot of metal when sharpening. E.g. sharpening for friends where the edge is about as sharp as the spine, reprofiling, zeroing, etc. So I am thinking of an electric sharpener. The knives involved are mostly VG10 and lower carbide steels.

The model I am looking at is like this:



On low setting it has a 1450 rpm with a 100mm diameter diamond coated disk. So the edge of the disk would be 7.6m/s or 25f/s. No cooling except maybe I can put some grease on the disk.

Is that going to ruin my edges?
cKc
Re: Power sharpening: how fast is too fast?
October 31, 2016 03:46AM
Without cooling there is a very high chance of damage to the edges. you cannot discount the skill of the operator exerting the pressure which increases the heat and friction.

there are systems like this that have water cooling in them as well.

----------------------------------------------------------------------
It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
Re: Power sharpening: how fast is too fast?
October 31, 2016 07:33AM
Quote
cKc
Without cooling there is a very high chance of damage to the edges. you cannot discount the skill of the operator exerting the pressure which increases the heat and friction.

there are systems like this that have water cooling in them as well.

Thanks.
I know the water cooled systems with waterstones, drippers and slower speed. But they are messy and I live in an apartment. No workshop or garage sad smiley
Re: Power sharpening: how fast is too fast?
October 31, 2016 09:11AM
1500 fpm isnt terribly fast, but would depend on the operator and abrasive too.

You cant be sure of that spec, either. A high quality unit run by a skilled operator would likely be fine at that speed. If it runs very fast then bogs down, it would be very difficult to do nice edges with.

It isnt so much about the speed, but the combination of speed, time, and metal removal. The faster the thing spins, the less time you have before damaging anything. For cheapo knives though, it probably doesnt matter much.

I dont think there is a cheap, good way of doing all you want, especially without a place to do it. I dont like them, but the Worksharp may come closer to your goals.
Re: Power sharpening: how fast is too fast?
October 31, 2016 10:53AM
Quote
Any Cal.
1500 fpm isnt terribly fast, but would depend on the operator and abrasive too.

You cant be sure of that spec, either. A high quality unit run by a skilled operator would likely be fine at that speed. If it runs very fast then bogs down, it would be very difficult to do nice edges with.

It isnt so much about the speed, but the combination of speed, time, and metal removal. The faster the thing spins, the less time you have before damaging anything. For cheapo knives though, it probably doesnt matter much.

I dont think there is a cheap, good way of doing all you want, especially without a place to do it. I dont like them, but the Worksharp may come closer to your goals.

Oh sorry I haven't made myself clear. By ruining the edges I mean overheating them and messing up the temper.

It spinning too fast for me to control metal removal isn't a concern for now. I have experience with a 3000rpm bench grinder with paper wheels (which I've learnt later not to use because of the heating problem) and also I plan only to do rough shaping with it. Apexing will be done on stones freehand.
Re: Power sharpening: how fast is too fast?
October 31, 2016 04:48PM
I would try a proper very coarse stone first before I went to power sharpening for rounder kitchen knives. Around 90-220 grit, ex: Garden & Scythe stone (Norton, TASK, Gator brands), Coarse India (Aluminum Oxide), Coarse Crystolon (Silicon Carbide), XXC or XC Diamond plate, King or Sun Tiger Waterstone, Cheap Hardware Store combination hone.

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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Edited 1 time(s). Last edit at 10/31/2016 04:49PM by jasonstone20.
Re: Power sharpening: how fast is too fast?
October 31, 2016 07:18PM
Quote
jasonstone20
I would try a proper very coarse stone first before I went to power sharpening for rounder kitchen knives. Around 90-220 grit, ex: Garden & Scythe stone (Norton, TASK, Gator brands), Coarse India (Aluminum Oxide), Coarse Crystolon (Silicon Carbide), XXC or XC Diamond plate, King or Sun Tiger Waterstone, Cheap Hardware Store combination hone.

Thanks for the suggestions smiling smiley

I have the Shapton Kuromaku (=Shapton Pro?) 120 and 320, as well as a Lansky XC diamond. Sometimes I use p60 SiC sandpaper glued to a flat surface.
After zeroing a few knives (some high carbide admittedly - a zdp spyderco dragonfly and super blue stretch) the Shapton 120 dished around 4mm in the center. Also the Lansky diamond lost quite some of its aggression. Yet with all these the tasks took a lot of time.

One time I tried to sharpen for a friend. He had a Tojiro (VG10 I think) that would would tear printer paper a bit even when held tight on both sides.
I held the Lansky on my offhand and did very quick and light passes. After 5k pps it still didnt apex. (I don't have very good skills but I'm not clueless either)

That's why I am thinking of a machine.
Re: Power sharpening: how fast is too fast?
November 01, 2016 08:51AM
I sharpened knives in my shop for about 8 months. The only way to get dull knives sharp in a reasonable time is with power tools. You will not overheat the edge with proper abrasives and technique, though some think otherwise.

Use an abrasive that cuts well, and do not spend long on it, you will be fine. Especially if you finish the edge by hand. Buy some knives at a thrift store for spare change and practice on them. You will get a feel for it quickly, especially if you managed to make paper wheels work!

I prefer to use a coarser abrasive, as it creates less heat, to form bevels, then clean up apex with finer hones much like a microbevel.
me2
Re: Power sharpening: how fast is too fast?
November 02, 2016 01:14AM
If the lubricant supplied with the higher quality paper wheels is used, I don't think overheating would be a problem. If you already have the wheels, try an experiment. Sharpen a knife with the wax/lube supplied with the wheels. Aim for about a 15 degree per side edge. Then get some bamboo skewers and try cutting through them. Then try with your water stones. If the paper wheel edges get dented, you may be over heating them. That's why I quit recommending a HF belt sander for sharpening. My carbon and low alloy steel knives would always dent after belt sander sharpening. Some knives it doesn't matter, since their use is so rough anyway. Some steels don't get bothered either, like the high speed steels knives I've made. Most steels I've checked carefully will have an issue.
Re: Power sharpening: how fast is too fast?
November 02, 2016 02:13AM
I think most paper wheels will be 3500-6000 fpm. Massively fast.

I checked the belt speed I was using today to set bevels on two knives- it was 680 fpm on my belt grinder. Very safe, very controllable, doesn't impart significant heat to the blade.

I have done blades on 2k fpm sanding belt, but it is really not doable.

The 2k fpm might have worked on a disk, but the belt made it very difficult. Mostly, you just have to move very quickly, and there is no margin for error.
Re: Power sharpening: how fast is too fast?
November 02, 2016 04:32AM
Quote
Any Cal.
I sharpened knives in my shop for about 8 months. The only way to get dull knives sharp in a reasonable time is with power tools.

It is possible to sharpen a dull knife back to shaving sharp, easily in under 2 minutes with just hand stones. It takes many times longer to unpack/pack up a blade than to sharpen it .

Quote

You will not overheat the edge with proper abrasives and technique, though some think otherwise..

I would like to know what is the supporting data for that conclusion.
Re: Power sharpening: how fast is too fast?
November 02, 2016 08:26PM
Quote
CliffStamp
Quote
Any Cal.
I sharpened knives in my shop for about 8 months. The only way to get dull knives sharp in a reasonable time is with power tools.

It is possible to sharpen a dull knife back to shaving sharp, easily in under 2 minutes with just hand stones. It takes many times longer to unpack/pack up a blade than to sharpen it .

Quote

You will not overheat the edge with proper abrasives and technique, though some think otherwise..

I would like to know what is the supporting data for that conclusion.

Supporting data is lack of data to contrary. Also, physical amount of work being done vs. ability of that amount of energy to create heat. We have Roman's scissors, and blue tips, there is no controlled experiment I am aware of to show anything to the contrary. I would like to have you at my shop, personal experience changed some of my views on this considerably.

I assume the 2 minute figure is dependent on bluntness and edge thickness. As I am sure you are aware, many knives come in much like butter knives. Are those also a 2 minute job with the same technique? I had no issues with knives that were simply dull, it is the DULL knives that are time consuming due the amount of steel being removed.
cKc
Re: Power sharpening: how fast is too fast?
November 02, 2016 10:25PM
Any Cal, I think the issue with the statement that Cliff quoted is that its too vague to be defensible conclusively.

some steels might be tempered at 160c, some at 500c.. if you are regrinding a knife not made by yourself, do you know the tempering temperature. do you know based on the steel and hardness (if you know it) what the ideal abrasive grit is to use to cut the most with the least friction? there are too many variables to say you will not overheat an edge.

I guess the next bit is that you said with proper abrasives, and "proper" technique... Certainly, tecnhique plays an important factor in how easily you overheat the steel. a poor technique, an accidental addition of force could lead to an edge burn in a blink of an eye. I've seen it happen with people I'm teaching.

but even with a perfect abrasive, and a perfect computer controlled blade holder that can run the blade across the abrasive at a specific force and feed ratio, the cutting action of the abrasive is causing a lot of heat on a small region.

Coarser grits that bite deeper cause greater heat because of the force required to remove the metal.


when dry grinding, the risk is that the finer grits, which have less heat from removal cause more friction from rubbing.. this is where the cooling comes in. if you grind wet, you notice very quickly that you can grind longer, with less heat, with finer belts..

so with proper abrasive and technique, we cannot exclude time.. are you refinishing in 1 minute, or 10.. meaning less time on the belt giving time to cool down, and is this considered part of technique. I can grind wet in 5 minutes what can take 30 dry, with must less risk of damage.

there is a wealth of information about heat build up on steel.. this is why drills, grinding wheels, and all cutting tools have so much information about correct type of coolants, and feed speeds to reduce heat..

----------------------------------------------------------------------
It's not Cliff, its Dr Stamp
#kebabstickcut, it's a thing - make it happen
Re: Power sharpening: how fast is too fast?
November 03, 2016 04:24AM
No, the statement is vague enough to leave the OP the opportunity to fine tune his process, and indicates that one size would not fit all.

I am well aware of how heat flows in grinding and cutting operations. I do appreciate the chart, but it is missing quite a bit of important info. Speed and material would be especially useful.

Proper abrasive and technique includes time, which is why I stated it that way. More than anything, it would be time spent on the abrasive on each pass, which would be much more important than time spent overall.

I really don't care to repeat my posts from several months ago, but the gist is that despite abrasives causing heat, and industry in the past using coolant, neither of those prove the need to wet grind to prevent damage to blades. It is understood that cooling is more about part distortion than anything else, that the coolant is not present in the cut area at the time of the cut, and that the tooling has no need for the cooling.

Your (cKc) experience with wet grinding knives proves nothing except the ability of water to cool metal. The metal that was abraded was never reached by coolant until after the damage had been done. Also, the entire knife blank could be 400f for an extended period, and as long as the edge was no hotter, it would remain undamaged. I have used wet grinding in the past, and use it on occasion today- in some circumstances it has no more (or less) effect than dipping the blade in a bucket.

Lathe tooling, industry slitting knives, and hard use all have the opportunity to reduce the temper more than careful sharpening on a machine of proper speed. Obviously this can be taken to a slow extreme (120fpm) or a high extreme (2000fpm), and neither would be applicable to the discussion- which is part of the issue. Powered sharpening at 10fps is likely beyond safe, while proper technique and abrasives may let 20+fps work. Until there are at least a couple controlled experiments proving otherwise, saying that powered sharpening with *reasonable technique and tools* is bad is not defensible. The only argument can be over "what is reasonable?", and without hard data, is likely going nowhere.
Re: Power sharpening: how fast is too fast?
November 03, 2016 02:18PM
Quote
Any Cal.

Supporting data is lack of data to contrary.

No it isn't.

A position isn't rationally justified because there isn't data to its contrary. If you actually accepted that is valid reasoning then you would accept that I have rational basis to take the position you are a terrorist.

This is a positive claim :

"You will not overheat the edge with proper abrasives and technique, though some think otherwise.."

If you don't have any data to actually support that then this isn't the forum to make the claim, go to another forum where they are comfortable with claims without empirical data.



Edited 1 time(s). Last edit at 11/03/2016 02:27PM by CliffStamp.
Re: Power sharpening: how fast is too fast?
November 03, 2016 03:21PM
Unless we are meta-debating, I don't think it is absolutely necessary to be fixated on on whom does he burden of proof lies.

Usually the person making an assertive claim has the burden of proof, other times it depends on whether the positive or the negative is provable.

But on this matter, for me, I am happy that someone is giving me any information at all, whether it be "it's possible to burn the edge" or "it is not a certainty that you will burn the edge" or anything in that level of precision.

I really appreciate all for the information and advice you guys have given. grinning smiley
Re: Power sharpening: how fast is too fast?
November 03, 2016 03:45PM
One of the things I think causes confusion and friction about the powered/unpowered and wet/dry grinding/sharpening is a few things:
  • A standard or reference point for being able to speak on common terms.
  • The ability to measure for the layman
  • The size and scope of what's happening

People have different reference points and what's acceptable for sharp or edge retention, and without controls, it's easy to talk about the same thing but not be on the same page, or the opposite. My acceptable sharpness level and edge retention isn't only different from someone else's, it differs from knife to knife and the role or current use of thee knife.
Physics and science aren't subject to someone's will or opinion. It has taken people who work in the industry and/or have degrees in these field that we have the information thay we have. They would probably be the first to admit that they don't know exactly everything, or exactly how everything works. Repeated, repeatable observation are what we do have, and should be explored, understood, and not dismissed in a whim.
What we are trying to measure and observe is happening on a small level and very quickly, and without proper techniques, making absolute, far reaching claims don't help anything.

If something works for you, great. If you have no problems with it, great. Let's all try and be respectful and continue to expand our knowledge and experience.

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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Re: Power sharpening: how fast is too fast?
November 03, 2016 05:11PM
I'll agree with Jason...when making the assertion I try to think of it from a practical point of view.

1. If you can go wet, why not do it? I do understand it's messier, but if you really want to make the best product possible it seems like a reasonable step...just like using West Systems over say Gorilla Glue. I doubt the former is needed, but why not<
2. If you can't go wet, well, then you have to consider your time and effort...maybe it's worth doing some dry power sharpening when thinning edges..then hand finish. If you're careful, even if you overheat the edge hopefully it goes away after a couple of hand sharpening.
3. Lastly, are you likely to notice the difference? If you're just talking cheap knives anyway, try it out. It seems to me you likely are burning the edge if grinding dry....the question is whether it makes a noticeable difference in performance? It may not, especially if you're careful (by which I mean lower speeds, work slowly, fresh belts).

Like with everything related to knife performance, I'm not sure the absolute answer in terms of material science is really the one we need to live by (just consider how it contributes)...you have to consider how practicality, along with design and the way it's used contribute.

_______________________________________________________________________________________________

Always in search of a good choppa'



Edited 1 time(s). Last edit at 11/03/2016 05:13PM by C Amber.
Re: Power sharpening: how fast is too fast? (3 fps dry)
November 04, 2016 03:05AM
Quote
Any Cal.
.. Powered sharpening at 10fps is likely beyond safe ... hard data ... saying it is bad is not defensible ... Supporting data is lack of data to contrary.
Hi,
Ever seen flint (rock) and steel (iron, carbon steel) throwing sparks?
Ever done it?
Thats just a sharp rock (abrasive) hitting the blade (steel)
at less than 5 feet per second (maybe 2 fps)
About 2 fps is a comfortable hand grinding speed



Tempering happens above 300° Fahrenheit / ~149° Celsius

Appendix D: Dusts with Cloud Ignition Temperatures Lower Than Their Layer Ignition Temperatures | Classification of Dusts Relative to Electrical Equipment in Class II Hazardous Locations | The National Academies Press
Quote

iron 450 ignition powder versu 500/530 layer
The layer ignition test (LIT) test determines the lowest temperature at which a layer of dust of specific thickness, usually 5mm

1964 EXPLOSIBILITY OF METAL POWDERS 20010917 067
Quote

Table 1. Ignition and explosibility of metal powders
Iron, carbonyl .................. cloud 320° Celsius layer 310° Celsius
TABLE 4. - Ignition and reaction temperatures of metal-powder layers in an air, carbon dioxide, or nitrogen atmosphere
Iron, hydrogen-reduced 290° Celsius

These data apply to relatively coarse dust (through a No. 200 sieve) but not to submicron powder.
Sieve Size and Mesh Designation
says No 200 sieve is 74 micron opening
74 micron is about P200 grit
Research of minimum ignition energy for nano Titanium powder and nano Iron powder
Quote

Fe powders with diameters of 150 μm, 15 nm, 35 nm, and 65 nm.
the Minimum Ignition Energies MIEs for all the nanopowders were less than 1 mJ; the low MIEs of these powders indicate that they are extremely combustible.
150 micron is about P100 grit
1 mJ millijoule is 7.376×10^-4 foot pounds‐force thats 0.0007376 fpf


So, in summary, since apex is about 1 micron,
using hand grinding only
its definitely possible to overheat (above 300° Fahrenheit / ~149° Celsius) ,
the flint/steel sparks are the proof

so something something INSERT energy work force speed calculation HERE , VAGUELY (lack of clear understanding + fatigue)
1lb at 2fps = 0.0137 pound‐force seconds or 0.2765 joule seconds per meter or 276.5 millijoules...
20 grams (0.044 lb) at 10fps, thats 0.0137 pound‐force seconds or 0.06094 joule seconds per meter or 60.94 millijoules...

____
Thanks
I don't mow smiling smiley
Re: Power sharpening: how fast is too fast? (3 fps dry)
November 04, 2016 10:02AM
That's something. The dust cloud data is to show? Temp of spark...320c

The question is whether significant tempering happens. Significant being such that it has a measurable effect on the steel. Measurable could be in a lab setting with micro hardness testing, or could be measurable in cut testing.

As I understand it, and Cliff may have an answer, 1 hrc difference would not be measurable in cut testing. The difference in cutting ability would be less than the scatter. If this is the case, we would have to be tempering beyond the manufacturers draw temp enough to create a 1 hrc draw.

Today I had 5 knives being tempered at 400f in shooting for an RC60. As you are likely aware, tempering is time AND temp dependent. Not only do they have to be at 400f, it could take 30+ minutes before they show a drop from their as quenched hardness. To reduce the time needed to temper, you could temper at a higher temp. This would speed the process.

In looking at the generic HT sheet, running the temper 180f hotter (for 2 hrs) would drop the hardness 4 points, or 45f per HRC. So in this little exercise, my blades could sit for hours at 445f with a max 1hrc drop. If these were cheap knives at rc 56, it would take 100f additional to drop 1 hrc. Simple exposure to the temp wouldn't do it, a brief exposure would have to be significantly higher to cause ANY difference. Possibly, a 320c/608f spark could be generated and still not be producing enough heat to effect the temper at the micro level due to the time at temp. .020" edge at 10fps is .002 seconds, minus the cooling of the blade heat sink. Additionally, no heat is being generated at the apex if it is leading, the heat is generated as the cut progresses. Now we are looking at less time at temp AND more heat sink.
Re: Power sharpening: how fast is too fast?
November 04, 2016 10:50AM
That just made me think of a question, probably already asked, but in dry grinding, at the very apex, is there a larger difference in temperature with hand vs powered grinding?

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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Re: Power sharpening: how fast is too fast? (3 fps dry)
November 04, 2016 01:37PM
Quote
Any Cal.

Today I had 5 knives being tempered at 400f in shooting for an RC60. As you are likely aware, tempering is time AND temp dependent. Not only do they have to be at 400f, it could take 30+ minutes before they show a drop from their as quenched hardness. To reduce the time needed to temper, you could temper at a higher temp. This would speed the process.

In looking at the generic HT sheet, running the temper 180f hotter (for 2 hrs) would drop the hardness 4 points, or 45f per HRC. So in this little exercise, my blades could sit for hours at 445f with a max 1hrc drop. If these were cheap knives at rc 56, it would take 100f additional to drop 1 hrc. Simple exposure to the temp wouldn't do it, a brief exposure would have to be significantly higher to cause ANY difference. Possibly, a 320c/608f spark could be generated and still not be producing enough heat to effect the temper at the micro level due to the time at temp. .020" edge at 10fps is .002 seconds, minus the cooling of the blade heat sink. Additionally, no heat is being generated at the apex if it is leading, the heat is generated as the cut progresses. Now we are looking at less time at temp AND more heat sink.

it seems we have reached the point in discussion where you are going to do it your way no matter what. tempering is temperature dependent, tests we did on HF after discussion with R Landes(http://www.hypefreeblades.com/forum/viewtopic.php?f=4&t=640&hilit=80crv2), showed 80CrV2 needed 2 15 minute tempers with quench between to reach desired hardness.
800°C with a holding time of around 5-8 minutes does not create retained austenite in a 0,8C steel.
It will create fine austenite ad thus fine martensite after oil quench in an section smaller or equal to 5mm max.
so the only thing you need to do is to temper the virgin martensite after the quench.
This would be finished after a few minutes in a preconditioned cline.
But, I would make the few minutes a half an h. to be sure all, even the thicker crossections, have reached the tempering temp. of 180-200°C.

I grind at low speed wet to prevent the chance of overheating. If have spent the last 5 hours heat treating a blade and getting the hardness I want, why risk overheating and creating soft spots on the edge.

scott
[www.etsy.com]
Re: Power sharpening: how fast is too fast? (3 fps dry)
November 04, 2016 08:58PM
Quote
Any Cal.
That's something. The dust cloud data is to show? Temp of spark...320c

The question is whether significant tempering happens. Significant being such that it has a measurable effect on the steel. Measurable could be in a lab setting with micro hardness testing, or could be measurable in cut testing.
...more heat sink.

in previous discussion of burning blades
someone mentioned sparks dont mean edge gets burned,
thats just the burr burning (the burr thats part of edge)
so its supposed to show the lowest temperature at which steel/iron shavings/dust can ignite
and that it doesnt take much energy to raise 150 micron dust , larger than apex at ~1 micron or dull plateau reflection ~20 micron to the temperature where it starts combusting in air
the burning spark is much hotter, internet says over 1000 °C or 700°C
but its closer to 1200 degrees Centigrade

Cliff said it takes something like $5-$10 (canadian?) to get microhardness testing done smiling smiley hint hint

____
Thanks
I don't mow smiling smiley
Re: Power sharpening: how fast is too fast? (3 fps dry)
November 04, 2016 09:15PM
Quote
oldsailorsknives
Quote
Any Cal.

Today I had 5 knives being tempered at 400f in shooting for an RC60. As you are likely aware, tempering is time AND temp dependent. Not only do they have to be at 400f, it could take 30+ minutes before they show a drop from their as quenched hardness. To reduce the time needed to temper, you could temper at a higher temp. This would speed the process.

In looking at the generic HT sheet, running the temper 180f hotter (for 2 hrs) would drop the hardness 4 points, or 45f per HRC. So in this little exercise, my blades could sit for hours at 445f with a max 1hrc drop. If these were cheap knives at rc 56, it would take 100f additional to drop 1 hrc. Simple exposure to the temp wouldn't do it, a brief exposure would have to be significantly higher to cause ANY difference. Possibly, a 320c/608f spark could be generated and still not be producing enough heat to effect the temper at the micro level due to the time at temp. .020" edge at 10fps is .002 seconds, minus the cooling of the blade heat sink. Additionally, no heat is being generated at the apex if it is leading, the heat is generated as the cut progresses. Now we are looking at less time at temp AND more heat sink.

it seems we have reached the point in discussion where you are going to do it your way no matter what. I do it the way I want now, but asked for references to see if there was any reason to do it the way some here believe in. No matter what? No, it just takes data to change my mind rather than rhetoric.

tempering is temperature dependent, AND time, otherwise tempering would take seconds, not minutes. Most industry sheets recommend 1hr per inch of thickness, Roman isn't comfortable recommending 1/2 that.

tests we did on HF after discussion with R Landes(http://www.hypefreeblades.com/forum/viewtopic.php?f=4&t=640&hilit=80crv2), showed 80CrV2 needed 2 15 minute tempers with quench between to reach desired hardness.
800°C with a holding time of around 5-8 minutes does not create retained austenite in a 0,8C steel.
It will create fine austenite ad thus fine martensite after oil quench in an section smaller or equal to 5mm max.
so the only thing you need to do is to temper the virgin martensite after the quench.
This would be finished after a few minutes in a preconditioned cline.
But, I would make the few minutes a half an h. to be sure all, even the thicker crossections, have reached the tempering temp. of 180-200°C.

I grind at low speed wet to prevent the chance of overheating. If have spent the last 5 hours heat treating a blade and getting the hardness I want, why risk overheating and creating soft spots on the edge.And you mistakenly believe that grinding wet is changing anything because you can't see the sparks. You are grinding dry, and wetting the blade immediately after, you are just unaware of it
Re: Power sharpening: how fast is too fast? (3 fps dry)
November 04, 2016 09:31PM
Quote
ShaperAndMower
Quote
Any Cal.
That's something. The dust cloud data is to show? Temp of spark...320c

The question is whether significant tempering happens. Significant being such that it has a measurable effect on the steel. Measurable could be in a lab setting with micro hardness testing, or could be measurable in cut testing.
...more heat sink.

in previous discussion of burning blades
someone mentioned sparks dont mean edge gets burned,
thats just the burr burning (the burr thats part of edge)
so its supposed to show the lowest temperature at which steel/iron shavings/dust can ignite
and that it doesnt take much energy to raise 150 micron dust , larger than apex at ~1 micron or dull plateau reflection ~20 micron to the temperature where it starts combusting in air
the burning spark is much hotter, internet says over 1000 °C or 700°C
but its closer to 1200 degrees Centigrade

Cliff said it takes something like $5-$10 (canadian?) to get microhardness testing done smiling smiley hint hint

I am interested in the Micro Hardness testing. Any info available on that would be appreciated. Never even considered that it would be available. Will Google it shortly.

If we use your arguments as a baseline, it can be concluded that 1) if there are no sparks, there is no overheating going on, or 2) hand sharpening is already imparting hundreds of times more energy than is needed to overheat the blade, or 3) power sharpening imparts much less energy to the blade than hand sharpening due to the lower forces involved. It seems that there is a flaw in there somewhere.

To everyone, I am really not trying to argue so much as learn what I can. I am not attacking anyone for their views, but hoping to learn what the data is that supports them. The discussion forces me to consider my methods and the reasoning behind them, and I assume does the same for you. We could find the best way, and some could ignore it because 1)they figure the old way was good enough, 2) old way was beneficial in other ways, 3)the old way just seems better. Discuss and enjoy, we all get to learn things. The dust ignition data was interesting, and was the first I have ever seen of it. The flint and steel spark analogy forced me to think. None of it needs to be a personal attack.
Re: Power sharpening: how fast is too fast? (3 fps dry)
November 05, 2016 12:10AM
Hi
Quote
Any Cal.
I am interested in the Micro Hardness testing. Any info available on that would be appreciated. Never even considered that it would be available. Will Google it shortly.
This is where I think I read about it
site:cliffstamp.com "$5" micro hardness testing ->
Extreme Regrind : Pacific Salt, Small Sebenza, Meadowlark, Delica, Vapor, Fulcrum
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Microhardness testing is fairly inexpensive, $5-$10 per spot, locally.

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priced it locally (relatively) in Charlotte, NC, about 1.5 hours from here (Spartanburg, SC). The cost was reasonable, but not what I'd call cheap. It was about $125 for a hardness profile from spine to edge.
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Chris, in regards to micro-hardness, or any other kind of work, it has to be critical what you are requesting. In this case you don't want the equivalent of a stamped document which could be used as expert testimony, all you want at most is informal data. The costs are radically different.



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Any Cal.
If we use your arguments as a baseline, it can be concluded that 1) if there are no sparks, there is no overheating going on,
Nope smiling smiley I dont think so
Steel wool from super fine (00000) to fine(0) is in mm 0.025 / 0.035 / 0.04 / 0.05 , or 25/35/40/50 microns thick
the length of each of these strands is many thousands of microns long
when its burning (hot rusting ) you can see that its burning (hot rusting ) because there is a lot of it
if you watch globs fall of, sparks, they're always bigger than 2-3 mm (2000-3000 micron)

when dudes are using the back of a mora to throw sparks (hot rusting )
the sparks are weak and small and short lasting,
they don't throw/fly much past 1-2cm (1000-2000 micron)

the apex on a knife is 1 micron, by eye you can't see reflection with a flashlight past ~20 microns
ending in apex of 1 micron
so when sharpening apex you're scraping/balling up steel from maybe 2mm(2000 micron) toward 20micron toward 1 micron, as you're doing that its oxidizing/rusting/generating heat

so if you can't see sparks,
well that just means you can't see sparks,
it doesn't mean the apex wasn't overheated



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Any Cal.
2) hand sharpening is already imparting hundreds of times more energy than is needed to overheat the blade,
Not sure about hundreds, but ENOUGH smiling smiley energy to overheat the apex for sure

Recently I was hand shaping a blade using p150 sandpaper
about 2 - 4 feet per second
had my finger on the blade
i burnt my finger a bit (i said ouch out loud)
it wasnt red like sunburn but it was bit tingly the next day
if i was hitting the apex i believe i would have overheated it
but stainless won't show color change at tempering temperature


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Any Cal.
or 3) power sharpening imparts much less energy to the blade than hand sharpening due to the lower forces involved.
I dont think so speed is much faster (10fps) and force used is the same as hand sharpening
~1lb or more for shaping ~1oz for apexing







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Any Cal.
To everyone, I am really not trying to argue so much as learn what I can. I am not attacking anyone for their views, but hoping to learn what the data is that supports them. The discussion forces me to consider my methods and the reasoning behind them, and I assume does the same for you. We could find the best way, and some could ignore it because 1)they figure the old way was good enough, 2) old way was beneficial in other ways, 3)the old way just seems better. Discuss and enjoy, we all get to learn things. The dust ignition data was interesting, and was the first I have ever seen of it. The flint and steel spark analogy forced me to think. None of it needs to be a personal attack.

Yeah I know you are ,
posting on the internet,
but so am I tongue sticking out smiley

____
Thanks
I don't mow smiling smiley
Re: Power sharpening: how fast is too fast? (3 fps dry)
November 05, 2016 04:22AM
here is a long discussion about Unwanted Tempering Whilst Sharpening [www.hypefreeblades.com]
when my grinder is set up for low speed, my belt speed is 2.5 to 3.5 fps, the belts i use are 180 grit or finer, and they are wet. running the belts wet adds a minute or two to setup time, 3fps is slow enough that the water stays on the belt and is not flung into my face. maybe this is belt and suspenders territory but it works and does not add time or expense to the process. this is for final finishing and sharpening.
over the years working in electronics calibration and industrial maintenance and production, because of my ADD I get best results by establishing a process, fine tuning it, then following it.

scott
[www.etsy.com]
Re: Power sharpening: how fast is too fast? (3 fps dry)
November 05, 2016 07:37AM
Thank you Scott for that link, hadn't looked at that thread in years.

Shaper, good responses.

After reading the thread Scott linked, it brings up a couple issues.

1) Cliff couldn't tell (at the time?) a 1 hrc difference in cutting tests. Maybe a 2 hrc difference. Makes the definition of significant degradation important.

2) Microhardness testing can't test at the edge, can only test a ways back. Basically can only tell if you really blew it, effecting hardness 50 microns back or something. Still interested though. If they can test on a bevel, maybe a long chisel grind on 4 sides of a plate or something. Need to talk to live person to understand some of the price lists I found.

Lastly, on Shaper's response.

If hand sharpening can overheat the edge, it would seem that rapid cutting of cardboard or carpet would do the same, as it is often done quite a bit faster with more force involved. Once again, what is significant?

I don't have the answers, and I expect we may all have different ones, but am interested to hear what they might be.

Scott, 3fps is pretty good! I can run mine that slow, but it is so close to stopping that I can't actually work on the belt at that speed. This discussion makes me want to play with it a bit and see what could be done about that.
Re: Power sharpening: how fast is too fast? (3 fps dry)
November 05, 2016 12:32PM
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Any Cal.
Thank you Scott for that link, hadn't looked at that thread in years.
I read that thread when I was a newbie and took the conclusions to heart.

Scott, 3fps is pretty good! I can run mine that slow, but it is so close to stopping that I can't actually work on the belt at that speed. This discussion makes me want to play with it a bit and see what could be done about that.

I achieve 3fps in 3 ways. VFD to control motor frequency. 3" drive wheel. An 800 rpm 3 phase Leeson motor, someone on Ebay was selling new old stock and was selling the motor which was a special order. Leeson does not make an 800 rpm motor this small(56C frame, 1Hp) for stock. 3fps is enough power to pull a blade from your hand and drive it 1/2" deep in my plywood shop floor. I seem to be one of the few voices on BF or KD who recommends smaller slower motors to newbies. I have see recommendations to newbies of building a grinder with a 3600 rpm motor, a VFD set to 120Hz, and a 6" drive wheel, my math says a belt speed over 150fps.

scott
[www.etsy.com]
Re: Power sharpening: how fast is too fast?
November 06, 2016 04:05AM
This may be helpful guys

Grinding wet does greatly reduce the risk of burning edges, but does not make it impossible. You can still burn edges if using dull belts and pushing hard, even under coolant.

But back when I was using an abrasive cut off wheel to sharpen serrated knives at 1700 rpm I would see some of the serrated knives peaks turning brown. When I switched to using a mist coolant being sprayed on the wheel at the edge there were no more issues w/ discoloration. It is a drastic and significant difference I experienced in my opinion.

Now I grind under coolant at about 1400 fpm when doing primary grinds, and about 800-1000fpm when sharpening - all under coolant w/ sharp abrasives. I have also found that the coolant prevents clogging of the belts w/ the metal, especially as you get to 220 grit and above.

Lastly, I recall cliff having done some testing within the past year that showed cutting cardboard fast or slow made no difference in edge retention, although I don't remember which video this was in atm.