Hi all,
I am a new owner of the T8 trying to perfect my sharpening. I find that I keep introducing a slight recurve near the heel of the knife (1/16" or so). What is the best way to fix this? Any tips for preventing it from happening?
Thanks all
This has been covered I think a few times but I don't have the savvy to link you to relevant posts. Someone will I'm sure.
Personally I have overcome this problem in a couple of ways.
Firstly, ALTERNATE.
By this I mean flip the blade over at the end of each pass rather than focusing on one side till you reach a burr. Eventually you will reach a burr by flipping ( though it seems counterintuitive) and it won't take real time any longer. By doing this you are negating the overgrind in the middle of the blade near the heel.
Secondly, as advocated by Wootz and others, grind the first heel section of the blade up to 2 inches or so, pivot up and start again at the heel and work forwards.
Personally the first method works well and in my experience I've never had problems with smiles (as I call them) when adopting this approach.
Other than that, don't overgrind. Only enough to produce the burr then concentrate on areas of the edge that haven't. Then a full pass to even things out.
I'm sure that others on the forum will give further advice soon.
Here is a helpful topic https://forum.tormek.com/index.php/topic,3055.msg16402.html#msg16402
There is one thing that I did not see mentioned yet. At least not in this context.
Japanese sharpeners (https://japanesechefsknife.com/pages/how-to-sharpen) almost unanimously quote the following grit ranges:
QuoteArato (Rough Grit) has a rough surface. An Arato is useful for repairing chips, fixing a broken tip, and making an angle for a sharp blade.
Nakato (Medium Rough Grit). Sharpening with Nakato makes blade more sharp and good shape (angle) for sharp blade.
Shiageto (Fine Grit) is used for finishing the process. This work is necessary for keeping a sharp blade.
This translates into the following grit numbers:
Quote- rough grit: < 400 JIS ≡ ca. F240
- medium rough grit: 800-2000 JIS ≡ ca. F360 bis F600
- fine grit: > 3000 JIS ≡ F1000
(Note that according to Dictum in Germany Tormek stones are gauged in JIS, which makes sense since they are selling several stones of genuine Japanese origin.)
The above link has a couple of videos where Great Master Nagao (President of Hiromoto Company) says, that 95% of the sharpening happens on the middle stone, and that any further refining is reserved for specialists.
This clearly unveils that the Tormek standard stone is too coarse for sharpening. If falls under the Arato range and no amount of dressing it will change this.
I have been in contact with two local manufacturers of stone wheels who do custom jobs, and they state that there is no such thing as making the grit finer. The grit stays as coarse as it is, but the peaks are shaved off. (Note that this only works as long as the grain is softer than the one of the dressing stone. It will
not work with SiC wheels, since the dressing stone is SiC too.)
Dressing works to an extent, but there is the danger that with heavy dressing the stone untrues and that rough spots are breaking out I was told.
Theoretically the #800 grit Matsunaga stone would be ideal from the grit range perspective, but it is not since it is optimized for sharpening
carbon steel plus it is very soft and quickly reacts to pressure. I personally do not get on with those stones.
On the other hand, Dictum sells a #1000 Japanese stone, which has no Tormek complement, but this is hard bond so it is better used for polishing purposes. I have a honing stone from a big Japanese maker #1000 grit medium soft, but this behaves much different and truly falls into the Nakato range.
One after market seller tells me has a #600 JIS SiC stone custom made that works for all steels and that he never dresses it. The amount of "grip" is regulated by the pressure.
So besides all the valid things that have been mentioned in the links further up, this may be another thing to be kept in mind.
I have the suspicion that (like the case with the SiC wheel) the type of bonding of the grain plays a huge role and modulates the required pressure/the amount removed.
Keep in mind that the above quoted grit ranges stem from Japanese, who traditionally use
soft stones that wear quickly but remove a lot of material. Similar attention upon assessing the grit (yet towards the hard bonded end) may apply when using diamond or boron wheels.
I use the SG for setting bevels. For badly damaged chisels I use an even coarser grit.
I once had a very delicate, very thin high quality short chopping knife that went hollow no matter what I tried. I ended up sharpening it on the face of the stone. Next time I try the hard #1000 stone.
I have had a very rare opportunity to gain insight into this recurve issue. I have been spending this week in Sweden as a guest of Tormek. Part of the program was an all afternoon sharpening session with Tormek's sharpening experts. We were encouraged to bring tools which we found difficult to sharpen. The session was held in Tormek's sharpening studio, where the online classes are produced.
Wolfgang addressed the issue of unwanted "recurving" in knives. He demonstrated the importance of correcting the shape of the knife edge BEFORE AND INDEPENDENTLY OF SHARPENING. Although it might seem that combining the two operations might be quicker and remove less steel, trying to combine them actually worsens the situation. The shape of the blade urge must be corrected first by grinding the blade square. Once the shape is corrected, reestablish the bevel and sharpen.
Ken
I think what Tjudd is talking about is not correcting a preexisting recurve, but rather, creating an unintended recurve through repeated sharpening on Tormek. I experienced this issue when I started, too. The solution for me was to take Wootz's advice: apply a little extra pressure on the knife handle when sharpening the heel-end of the blade, sometimes going as far as tilting the knife down (ever so slightly) at the handle end when sharpening that first inch of the blade. In other words, just as you would raise your elbow slightly toward the tip of a curved blade, lower the elbow very slightly when doing the heel.
Good point, 3D. Well stated.
Ken
Quote from: 3D Anvil on September 01, 2023, 07:09:23 PMI think what Tjudd is talking about is not correcting a preexisting recurve, but rather, creating an unintended recurve through repeated sharpening
Exactly this! Thanks 3D and all. I will give Wootz' advice a try and see if it helps.
I think Tormek also mentions that rounding off the edges of the stone helps preventing this phenomenon by lowering the risk of unadvertently applying high pressure when laying down the blade on the stone.
Quote from: Ken S on September 01, 2023, 07:49:47 AMI have had a very rare opportunity to gain insight into this recurve issue. I have been spending this week in Sweden as a guest of Tormek. Part of the program was an all afternoon sharpening session with Tormek's sharpening experts. We were encouraged to bring tools which we found difficult to sharpen. The session was held in Tormek's sharpening studio, where the online classes are produced.
Wolfgang addressed the issue of unwanted "recurving" in knives. He demonstrated the importance of correcting the shape of the knife edge BEFORE AND INDEPENDENTLY OF SHARPENING. Although it might seem that combining the two operations might be quicker and remove less steel, trying to combine them actually worsens the situation. The shape of the blade urge must be corrected first by grinding the blade square. Once the shape is corrected, reestablish the bevel and sharpen.
Ken
What do you mean by grinding the blade square?
Quote from: aquataur on August 31, 2023, 10:30:35 AMThere is one thing that I did not see mentioned yet. At least not in this context.
Japanese sharpeners (https://japanesechefsknife.com/pages/how-to-sharpen) almost unanimously quote the following grit ranges:
QuoteArato (Rough Grit) has a rough surface. An Arato is useful for repairing chips, fixing a broken tip, and making an angle for a sharp blade.
Nakato (Medium Rough Grit). Sharpening with Nakato makes blade more sharp and good shape (angle) for sharp blade.
Shiageto (Fine Grit) is used for finishing the process. This work is necessary for keeping a sharp blade.
This translates into the following grit numbers:
Quote- rough grit: < 400 JIS ≡ ca. F240
- medium rough grit: 800-2000 JIS ≡ ca. F360 bis F600
- fine grit: > 3000 JIS ≡ F1000
(Note that according to Dictum in Germany Tormek stones are gauged in JIS, which makes sense since they are selling several stones of genuine Japanese origin.)
The above link has a couple of videos where Great Master Nagao (President of Hiromoto Company) says, that 95% of the sharpening happens on the middle stone, and that any further refining is reserved for specialists.
This clearly unveils that the Tormek standard stone is too coarse for sharpening. If falls under the Arato range and no amount of dressing it will change this.
I have been in contact with two local manufacturers of stone wheels who do custom jobs, and they state that there is no such thing as making the grit finer. The grit stays as coarse as it is, but the peaks are shaved off. (Note that this only works as long as the grain is softer than the one of the dressing stone. It will not work with SiC wheels, since the dressing stone is SiC too.)
Dressing works to an extent, but there is the danger that with heavy dressing the stone untrues and that rough spots are breaking out I was told.
Theoretically the #800 grit Matsunaga stone would be ideal from the grit range perspective, but it is not since it is optimized for sharpening carbon steel plus it is very soft and quickly reacts to pressure. I personally do not get on with those stones.
On the other hand, Dictum sells a #1000 Japanese stone, which has no Tormek complement, but this is hard bond so it is better used for polishing purposes. I have a honing stone from a big Japanese maker #1000 grit medium soft, but this behaves much different and truly falls into the Nakato range.
One after market seller tells me has a #600 JIS SiC stone custom made that works for all steels and that he never dresses it. The amount of "grip" is regulated by the pressure.
So besides all the valid things that have been mentioned in the links further up, this may be another thing to be kept in mind.
I have the suspicion that (like the case with the SiC wheel) the type of bonding of the grain plays a huge role and modulates the required pressure/the amount removed.
Keep in mind that the above quoted grit ranges stem from Japanese, who traditionally use soft stones that wear quickly but remove a lot of material. Similar attention upon assessing the grit (yet towards the hard bonded end) may apply when using diamond or boron wheels.
I use the SG for setting bevels. For badly damaged chisels I use an even coarser grit.
I once had a very delicate, very thin high quality short chopping knife that went hollow no matter what I tried. I ended up sharpening it on the face of the stone. Next time I try the hard #1000 stone.
Can you provide a reference citing where Dictum mentions that Tormek wheels are graded in JIS rating system? It makes sense but seems a bit at odd with prior comments from Wootz at Knifegrinders stating that they use the FEPA rating scale. I do tend to agree that the wheels are rated JIS from what I've seen, this would make the 4000 grit Tormek stone extremely fine grit in JIS scale if that was rated that number in FEPA scale.
Thy Will Be Done,
I wrote to them and asked their customer service. That´s what they came back with: Tormek stones are JIS rated.
Their reply was unmistakable, I have no doubt that is true.
The #800 and #4000 Matsunaga (Sun Tiger) stone are genuinely Japanese, and have labels in original language on them. I have serious doubts that they label in FEPA.
Quote from: wootz on February 04, 2016, 10:38:21 AMSUN TIGER 800 grit compared to finely graded SG
Note that Japanese grit JIS #800 corresponds to US ANSI #600, and European FEPA #1200, i.e. is somewhat finer than 'finely' graded Tormek #1000.
If you refer to the above document: Wootz unfortunately got the numbers twisted.
JIS #800 = ANSI #400-500 and FEPA #360-400. (Conversion Chart Grit Sizes (https://www.fine-tools.com/G10019.html))
Another chart (https://www.knivesandtools.com/en/ct/expressing-grain-sizes-sharpening-stones.htm) (Beware! They have many numbers wrong too)
The chart I have attached (it does not show the origin so I cannot quote) clearly reveals that a JIS#800 can be compared to a
P#1200 which is a
paper gauge. This is what Wootz misread.
A F#4000 stone would correspond to JIS#16.000 (according to the questionable source above), which would be ridiculously fine. It is also not logical that they term the stone "Japanese" and gauge it in some western grit unit.
Quote from: aquataur on September 06, 2023, 10:13:23 PMThy Will Be Done,
I wrote to them and asked their customer service. That´s what they came back with: Tormek stones are JIS rated.
Their reply was unmistakable, I have no doubt that is true.
The #800 and #4000 Matsunaga (Sun Tiger) stone are genuinely Japanese, and have labels in original language on them. I have serious doubts that they label in FEPA.
Quote from: wootz on February 04, 2016, 10:38:21 AMSUN TIGER 800 grit compared to finely graded SG
Note that Japanese grit JIS #800 corresponds to US ANSI #600, and European FEPA #1200, i.e. is somewhat finer than 'finely' graded Tormek #1000.
If you refer to the above document: Wootz unfortunately got the numbers twisted.
JIS #800 = ANSI #400-500 and FEPA #360-400. (Conversion Chart Grit Sizes (https://www.fine-tools.com/G10019.html))
Another chart (https://www.knivesandtools.com/en/ct/expressing-grain-sizes-sharpening-stones.htm) (Beware! They have many numbers wrong too)
The chart I have attached (it does not show the origin so I cannot quote) clearly reveals that a JIS#800 can be compared to a P#1200 which is a paper gauge. This is what Wootz misread.
A F#4000 stone would correspond to JIS#16.000 (according to the questionable source above), which would be ridiculously fine. It is also not logical that they term the stone "Japanese" and gauge it in some western grit unit.
I misunderstood, thinking that you meant Tormek produces their own wheels and the grit rating they use is JIS scale. The question is more to do with the Japanese waterstone they sell labeled at 4000, that has to be 4k JIS or you'd have something like 15K equivalent as you mention.
Quote from: aquataur on September 06, 2023, 10:13:23 PMIf you refer to the above document: Wootz unfortunately got the numbers twisted.
JIS #800 = ANSI #400-500 and FEPA #360-400. (Conversion Chart Grit Sizes (https://www.fine-tools.com/G10019.html))
Another chart (https://www.knivesandtools.com/en/ct/expressing-grain-sizes-sharpening-stones.htm) (Beware! They have many numbers wrong too)
I have been trying to make a comparison chart for myself and have found contradictory grit to micron charts. When I get the time I will try to source the standards and see if I can come up with an authoritative version. I suspect that some of the confusion is between the coated and loose abrasive which in some standards has differing particle sizes.
This whole stone grade is extremely confusing and one day I will do a video attempting to place it in perspective. I have never seen a clear definitive explanation that I find does more than make it even more confusing. Maybe I will succeed and maybe I will just make it more confusing. I attempt to try in any case.
Quote from: JohnHancock on September 07, 2023, 01:52:23 AMI have been trying to make a comparison chart for myself and have found contradictory grit to micron charts. When I get the time I will try to source the standards and see if I can come up with an authoritative version. I suspect that some of the confusion is between the coated and loose abrasive which in some standards has differing particle sizes.
This whole stone grade is extremely confusing and one day I will do a video attempting to place it in perspective. I have never seen a clear definitive explanation that I find does more than make it even more confusing. Maybe I will succeed and maybe I will just make it more confusing. I attempt to try in any case.
Have you seen this one?
MicronScale.png
https://www.bladeforums.com/threads/abrasives-in-micron-scale-glgc-revision-14-2022.1779773/
Quote from: JohnHancock on September 07, 2023, 01:52:23 AMQuote from: aquataur on September 06, 2023, 10:13:23 PMIf you refer to the above document: Wootz unfortunately got the numbers twisted.
JIS #800 = ANSI #400-500 and FEPA #360-400. (Conversion Chart Grit Sizes (https://www.fine-tools.com/G10019.html))
Another chart (https://www.knivesandtools.com/en/ct/expressing-grain-sizes-sharpening-stones.htm) (Beware! They have many numbers wrong too)
I have been trying to make a comparison chart for myself and have found contradictory grit to micron charts. When I get the time I will try to source the standards and see if I can come up with an authoritative version. I suspect that some of the confusion is between the coated and loose abrasive which in some standards has differing particle sizes.
This whole stone grade is extremely confusing and one day I will do a video attempting to place it in perspective. I have never seen a clear definitive explanation that I find does more than make it even more confusing. Maybe I will succeed and maybe I will just make it more confusing. I attempt to try in any case.
The problem really lies in the fact that even among the obvious difference in how the various grit scales relate to each other, there is also the issue of the fact that any given grit rating is referring to a wide range of particle sizes. Micron is the only measure that actually gives a specific particle size specification which lists a single number. 400 grit will be something like a range of xxx micron to xx micron.
This is why Hap Stanley, who worked for Shapton on their line of stones for many years and later founded Nano-Hone has made an effort to encourage companies to list the actual micron rating of their stones. He claims the technology will support this with how they can very finely separate particle sizes now but I suspect that this may be something that other manufacturer's simply do not pay much attention to and are perfectly happy to state a grit range instead as they don't have to be as stringent in production.
All Nano-Hone products list the actual micron rating and the approximate grit range of what that amounts to for those who are accustomed to reading grit numbers for reference. When they say that they are a certain micron, they are ACTUALLY 100% or as much as possible within reason, that specific size abrasive particle contained within the product. This is also why switching between manufacturers stones/wheels can be problematic as you work up in finish is that without the actual micron range you can be way off.
The confusion with grain may be even worse. A hard bonded stone releases grain more reluctantly than a soft one. The latter will offer freshly released sharp grain more eagerly.
Hard stones are said to be more forgiving for this reason. Besides that, such a stone gives a different grinding surface pattern, suggesting a finer grain than there actually is.
To return back to the point of the original subject, I think the SG-2x0 is too coarse for
knife sharpening overall and for what the Japanese call "the middle stone", despite all dressing measures.
I am ready to believe that it makes micro-serrations and thus yields a subjectively perceived good cutting action fast, but it may get there too fast for its own merit in unexercised hands (me not excluded).
It was meant to be the end-all solution for all cases, which cannot be.
BTW, I don´t see a comparably small company like Tormek genuinely producing their own stones. There are time-honored companies that do nothing but that.
And you would be surpised how cheap a custom job is, even at low quantities...
Quote from: Thy Will Be Done on September 07, 2023, 03:13:15 AMThis is also why switching between manufacturers stones/wheels can be problematic as you work up in finish is that without the actual micron range you can be way off.
Totally agree. Even their own blackstone (silicon carbide) is said to behave differently.
But as Master whats-his-name earlier in this thread says, for all practical reasons sharpening happens on the middle stone.
I also noticed, that upon starting a grinding pass (such as after flipping sides) it takes a second or so to align the knife optimal to the circumference.
More often than not you are hitting a corner before the blade "pulls in". By this time, you have overground that spot.
One could insert a foot operated switch for that, but then the blade runs dry for a moment.
Has anybody tried such a thing before?
Quote from: aquataur on September 07, 2023, 09:36:44 AMOne could insert a foot operated switch for that, but then the blade runs dry for a moment.
I'm not sure I totally understand your foot pedal suggestion, but if you mean "stop the rotation, lay down the blade, start the rotation", then I think it is problematic for several reasons :
- You will start in a "static friction" situation instead of the dynamic one when the wheel is turning. This will be compounded by the stone being drier. So the friction coefficient will be much higher and the natural tendency when starting (when sharpening edge leading) will be the blade digging in the stone then the jig being pulled away from the USB. If you apply strong pressure on the USB you will prevent this but the higher friction coefficient will mean .. overgrinding.
- At least in the way I feel things when sharpening with the Tormek, the water flow is a great indication of whether or not everything is going smoothly (squareness of the blade wrt the stone, lifting vs pivoting, pressure applied, etc.). I would hate to loose that instant feedback for the time it takes for the water to creep back up the stone.
I think what you're referring to here is one of the places where experience and muscle memory are needed with the Tormek. For me it happens in the fraction of a second where the blade gets close enough to the stone that the water starts to flow over the edge, but before the actual grinding with pressure happens. I kind of eyeball whether the area that is going to contact the stone is the right one, correct roughly, then make a second check/adjustment when the blade contacts the stone with so little pressure hardly grinding is happening at all. Then only when I'm satisfied with the water flow do I stop fighting gravity and actually apply pressure over the contact area.
I also found that rounding edges *a lot* solved my "hollowing" issues on straight-/almost-straight-edged blades. I'm not sure it is a grain/grit/micron issue as it is a grinding efficiency issue: if you want to grind efficiently, you take the risk of any slight mistake having a bigger impact. The sharper the corners, the higher the instant pressure, the quicker the overgrinding.
Quote from: aquataur on September 07, 2023, 09:26:03 AMThe confusion with grain may be even worse. A hard bonded stone releases grain more reluctantly than a soft one. The latter will offer freshly released sharp grain more eagerly.
Hard stones are said to be more forgiving for this reason. Besides that, such a stone gives a different grinding surface pattern, suggesting a finer grain than there actually is.
To return back to the point of the original subject, I think the SG-2x0 is too coarse for knife sharpening overall and for what the Japanese call "the middle stone", despite all dressing measures.
I am ready to believe that it makes micro-serrations and thus yields a subjectively perceived good cutting action fast, but it may get there too fast for its own merit in unexercised hands (me not excluded).
It was meant to be the end-all solution for all cases, which cannot be.
BTW, I don´t see a comparably small company like Tormek genuinely producing their own stones. There are time-honored companies that do nothing but that.
And you would be surpised how cheap a custom job is, even at low quantities...
Quote from: Thy Will Be Done on September 07, 2023, 03:13:15 AMThis is also why switching between manufacturers stones/wheels can be problematic as you work up in finish is that without the actual micron range you can be way off.
Totally agree. Even their own blackstone (silicon carbide) is said to behave differently.
But as Master whats-his-name earlier in this thread says, for all practical reasons sharpening happens on the middle stone.
I don't agree that the SG-250 is too coarse for knife sharpening in the least. In fact, I would argue that it is exactly the type of stone that actually would give the highest edge retention and cutting ability for MOST people's day to day knife use.
There are certain types of knives/cutting that would benefit from the Japanese waterstone's inherent qualities, such as kitchen knives or woodworking tools. Low polish/coarse finish is not a sign of a poor sharpening job when it comes to tools that are made for slicing.
I do feel that something around 400 grit may be a bit more well rounded of an edge but for pure slicing the coarser finish will always outperform the finer finish at the apex. Many people believe EDC type work knives need a polished edge but that works against performance for most tasks other than push cuts.
One of the pervasive myths about the SG is that it is 220 OR 1000. Those two numbers are a convenient approximation of the range of the stone with the stone grader. For several years, some Tormek users have used the term "600 grit" meaning a middle grit. The numbers are not exact, nor do they need to be exact. The SG is more versatile than just a two trick pony.
Ken
Quote from: Ken S on September 07, 2023, 03:02:59 PMOne of the pervasive myths about the SG is that it is 220 OR 1000. Those two numbers are a convenient approximation of the range of the stone with the stone grader. For several years, some Tormek users have used the term "600 grit" meaning a middle grit. The numbers are not exact, nor do they need to be exact. The SG is more versatile than just a two trick pony.
Ken
Do you happen to have any information as to whether the SG-250 is made with seeded gel alumina rather than conventional? The experience I have with the wheel is suggestive of this fact and even the labeling 'SG' itself is short for Seeded Gel which is seen with abrasives from Saint Gobain, etc.
https://www.abrasivematerials.saint-gobain.com/articles/understanding-seeded-gel-micro-abrasive-technology
If this is in fact how the stone is produced and perhaps custom made for Tormek by a similar producer, this could explain how the stone can itself be graded as it would crush and separate the microscopic particles that together form each individual grit particle and allow the stone to cut finer.
I have not seen the stone stop cutting and begin burnishing in my experience, which is exactly what happens with conventional abrasives over time without truing and lapping. The wheel behaves how I would imagine SG abrasives work by continually releasing fresh abrasive as it grinds.
The traditional meaning of "SG" at Tormek is "SuperGrind", a term going back to the introduction of the present man made aluminum oxide SG wheels. The original grinding wheels used bu Tormek were natural stones mined at Gotland Island. They were finer grained than the SG. The SG, being more coarse, cuts more efficiently.
I have always thought that Tormek introduced the stone grader to be able to have the SG imitate the smooth finish of the natural stone. I asked at Tormek, although no one seemed to remember this.
Ken
Quote from: aquataur on September 07, 2023, 09:26:03 AMThe confusion with grain may be even worse. A hard bonded stone releases grain more reluctantly than a soft one. The latter will offer freshly released sharp grain more eagerly.
Yes the actual cement that holds the grain does make a difference but also the friability of the grains within the abrasive. For instance the white aluminium oxide (used in the SG and SJ) is more friable and the grains crack revealing sharper edges. The grey aluminuium oxide wheels have less friable grains and thus wear less but create more heat and friction.
Quote from: Thy Will Be Done on September 07, 2023, 03:13:15 AMThe problem really lies in the fact that even among the obvious difference in how the various grit scales relate to each other, there is also the issue of the fact that any given grit rating is referring to a wide range of particle sizes.
I don't doubt that. Each standard does specify a micron range so if the maker conforms to that standard then the particle size will not vary that much.
I think that the issue is not small variations within a standard but the vast differences between standards. For instance 1,000 grit in one standard is 5,000 grit in another standard. With the lower grits the differences tend to be smaller but in the higher grits they can be significant. So sharpening to 5,000 grit really makes no sense unless you specify which standard you are using.
I first came across this when I was selling engineer supplies in about 1980. We sold Norton abrasives and they went from the old (ANSI I believe) standard to the "P" standard. We were given comparison charts and the differences did not become important till about 500 grit. Can you imagine the confusion when trying to explain to a customer that the 500 grit wet and dry was no longer 500 grit but 1,000 grit. In the end it was less hassle just to give them what they asked for. I recall that only one person came back and complained so we exchanged it for the P equivalent. The Metric vs imperial debacle has nothing on the grit confusion!!!
I have no information as to whether or not the SG wheels use seeded grains.
Ken
Quote from: Ken S on September 01, 2023, 07:49:47 AMI have had a very rare opportunity to gain insight into this recurve issue. I have been spending this week in Sweden as a guest of Tormek. Part of the program was an all afternoon sharpening session with Tormek's sharpening experts. We were encouraged to bring tools which we found difficult to sharpen. The session was held in Tormek's sharpening studio, where the online classes are produced.
Wolfgang addressed the issue of unwanted "recurving" in knives. He demonstrated the importance of correcting the shape of the knife edge BEFORE AND INDEPENDENTLY OF SHARPENING. Although it might seem that combining the two operations might be quicker and remove less steel, trying to combine them actually worsens the situation. The shape of the blade urge must be corrected first by grinding the blade square. Once the shape is corrected, reestablish the bevel and sharpen.
Ken
Hi Ken,
Asking again because it seems you may have missed this but I don't follow what you mean exactly by grinding the knife square first to remove recurves. Do you grind the knife at a 90 degree angle with the edge direct into the stone?
Quote from: Thy Will Be Done on September 08, 2023, 09:57:59 AMHi Ken,
Asking again because it seems you may have missed this but I don't follow what you mean exactly by grinding the knife square first to remove recurves. Do you grind the knife at a 90 degree angle with the edge direct into the stone?
I don't want to speak for Ken, but there is a lot of useful information in this video with Wolfgang (https://youtu.be/oUnosmAngJw?t=364)
Yes, using the support bar in the horizontal position, place the knife under the support bar. This will hold the knife in place. Grind at 90° to restore the blade curve. Once the curve has been reestablished, regrind the bevels..
The video with Wolfgang is well worth watching.
Ken
That´s what I ended up with a really delicate chopping knife.
There is a huge downside to this method: the face of the stone will deteriorate, and there is no elegant way to rectify it.
Theoretically you could use the diamond, but there is no support for the jig.
I tried a makeshift support using a XB-100, but there was always something in the way that hindered.
Wootz has a video where he tried that trick on a single bevel knife and he landed with the same conclusion.
For my needs I managed to rectify this problem, but the result is nowhere near as perfect as the guided diamond.
Quote from: JohnHancock on September 08, 2023, 02:29:56 AMThe grey aluminuium oxide wheels have less friable grains and thus wear less but create more heat and friction.
Is this relevant in a slow running wet grinder? I know this to be the reason for all masons, who sharpen their chisels on a fast running bench grinder, to choose a white alumina stone...
Quote from: aquataur on September 08, 2023, 09:18:50 PMQuote from: JohnHancock on September 08, 2023, 02:29:56 AMThe grey aluminuium oxide wheels have less friable grains and thus wear less but create more heat and friction.
Is this relevant in a slow running wet grinder? I know this to be the reason for all masons, who sharpen their chisels on a fast running bench grinder, to choose a white alumina stone...
It wouldn't be a problem with friction generating heat but it would still have the detriment of burnishing the steel (ie. pushing it around) rather than cutting it cleanly. This will only serve to weaken the steel at the apex and slightly behind it so it's never really a good thing to have a glazed or worn abrasive. That is my concern about the stone grader is I'm still not convinced it isn't doing just that, glazing the stone. We have companies investing large amounts of research into making abrasives that continue to fracture and renew themselves to present aggressive cutting particles. This whole concept just seems to fly in the face of what I think I know to be true.
Quote from: Thy Will Be Done on September 08, 2023, 09:46:07 PMThat is my concern about the stone grader is I'm still not convinced it isn't doing just that, glazing the stone.
That is certainly a valid concern.
It should be seen in context with the real live experince of a significant number of SG-250 users.
Please be so kind to provide facts for the Tormek SG-250.
Quote from: HaioPaio on September 08, 2023, 09:54:14 PMQuote from: Thy Will Be Done on September 08, 2023, 09:46:07 PMThat is my concern about the stone grader is I'm still not convinced it isn't doing just that, glazing the stone.
That is certainly a valid concern.
It should be seen in context with the real live experince of a significant numer of SG-250 users.
Please be so kind to provide facts for the Tormek SG-250.
And what are the facts? That people use it and claim it's just fine? I would not call that a fact but more of an subjective opinion on the matter. I would suggest that if anybody has to provide facts for the SG-250 it would be Tormek who in fact has the burden of proof on that issue to actually convince it's customer base that it's just as good as a dedicated medium grit wheel. I've seen no such supporting data or studies to even begin to have an educated conversation on the matter so what we're left with is entirely internet conjecture and anecdotal reports suggestive of performance.
Even if the stone cuts in a way that leaves a finish that is very close to 1000 grit or whatever equivalent, the difference would be completely undetectable to a casual user who would almost certainly not even be aware of the differences between a strong cutting abrasive and one that strongly burnishes. I will admit that I have not experimented much with this but the fact that you take a very coarse abrasive and make it cut like a medium abrasive is almost by definition what happens when abrasives get glazed over. If I simply let my SG-250 wear on a D2 blade rapidly I can see and feel the aggression lost.
I just did one yesterday and it sure felt and looked like the stone was burnishing a fair amount so I'll just recut the surface and renew it. It strikes me as rather odd that Tormek offers three grades of Diamond wheels and only a very coarse or very fine option for ceramic or silicon carbide wheels respectively. I don't see anybody here seriously suggesting taking a fine diamond plate to their diamond wheels in order to have it cut finer and finish cleaner. That would just be ridiculous but it does get recommended in other places often enough at various forums. That is the same line of thinking...
Quote from: Thy Will Be Done on September 08, 2023, 09:57:14 PMAnd what are the facts?
No, I meant, what are your facts? Is your single personal experience opinion supported by scientific data or by experince of multiple experienced users?
I hear what you are saying, and do not have any reason not to trust you.
I'm just asking for the many others, supporting your concern.
Quote from: HaioPaio on September 08, 2023, 10:34:47 PMQuote from: Thy Will Be Done on September 08, 2023, 09:57:14 PMAnd what are the facts?
No, I meant, what are your facts? Is your single personal experience opinion supported by scientific data or by experince of multiple experienced users?
I hear what you are saying, and do not have any reason not to trust you.
I'm just asking for the many others, supporting your concern.
Both scientific fact and experience of users that I trust who have done a lot of research themselves but I want to be clear that this is not Tormek specific and speaking of abrasives in general. It may be just a small problem and I may begin to experiment myself compared to 800 grit JIS King wheel I have not used yet but the reality is most end users understand little of abrasives technology and/or metallurgy and it requires knowledge of both in order to make an informed observation/judgement in the matter. It may be a complete non-issue but in general consumers should take information provided by manufacturer literature with a grain of salt as it can easily be full of truths that are not quite true.
I have bought an aftermarket F360 (JIS600) SiC stone. I trued it with the diamond no problem, but trying to put the dressing stone onto it resulted in a desaster. The dressing stone was grooved immediately, being of the same nature (the wiser gives way...)
This process I saw named here in this context with the term "glazing", and it sure looks glassy, but I do not know what it means technically in conjunction with a grinding stone.
I have a similar wheel on the (fast) bench grinder (green SiC) which I can only true with a tetra-boron grader stick.
The prior wheel btw is medium hard bond (grade "J") and reacts to pressure, so you can adjust how much it "grips". The SB wheel appears to have that feeling too. Maybe this is a peculiarity of the abrasive in conjunction with fairly weak bonding. That said, the SB is much coarser too.
The re-seller of those (he has them custom made from a huge manufacturer of abrasives in Germany) is a professional sharpener and he had them made because of the very dilemma you outlined above, namely having only coarse grits and very fine grits available and nothing inbetween.
Said sharpener told me that he never uses the grader, because it does not really change the grit (how could it?) but shave off the peaks. The inherent danger is said to be two-fold:
- the wheel can become untrued by heavy grading
- spots can brake free that release fresh sharp material thus making the perceived roughness uneven across the circumference
The #800 Matsunaga stone you mention has been tested by Wootz (linked to by my reference further above) and was found useful only for carbon steel.
It does seemingly little on soft steels. Just to keep in mind.
I was intrigued to get a similar stone in white alumina from the same source (and they are reasonable...)
but the burnishing bit you mention irritates me. I do not know technically what this means.
All I know is every mason I know has one of those (albeit on a fast bench grinder) and every manufacturer claimes "a cooler grind", but I have never read a first-hand explanation for that, particularly in context with wet grinding.
If what you say (that burnishing weakens the steel) is applicable here, than this is an argument that has to be taken serious.
Quote from: aquataur on September 09, 2023, 08:10:37 AMI have bought an aftermarket F360 (JIS600) SiC stone. I trued it with the diamond no problem, but trying to put the dressing stone onto it resulted in a desaster. The dressing stone was grooved immediately, being of the same nature (the wiser gives way...)
This process I saw named here in this context with the term "glazing", and it sure looks glassy, but I do not know what it means technically in conjunction with a grinding stone.
I have a similar wheel on the (fast) bench grinder (green SiC) which I can only true with a tetra-boron grader stick.
The prior wheel btw is medium hard bond (grade "J") and reacts to pressure, so you can adjust how much it "grips". The SB wheel appears to have that feeling too. Maybe this is a peculiarity of the abrasive in conjunction with fairly weak bonding. That said, the SB is much coarser too.
The re-seller of those (he has them custom made from a huge manufacturer of abrasives in Germany) is a professional sharpener and he had them made because of the very dilemma you outlined above, namely having only coarse grits and very fine grits available and nothing inbetween.
Said sharpener told me that he never uses the grader, because it does not really change the grit (how could it?) but shave off the peaks. The inherent danger is said to be two-fold:
- the wheel can become untrued by heavy grading
- spots can brake free that release fresh sharp material thus making the perceived roughness uneven across the circumference
The #800 Matsunaga stone you mention has been tested by Wootz (linked to by my reference further above) and was found useful only for carbon steel.
It does seemingly little on soft steels. Just to keep in mind.
I was intrigued to get a similar stone in white alumina from the same source (and they are reasonable...)
but the burnishing bit you mention irritates me. I do not know technically what this means.
All I know is every mason I know has one of those (albeit on a fast bench grinder) and every manufacturer claimes "a cooler grind", but I have never read a first-hand explanation for that, particularly in context with wet grinding.
If what you say (that burnishing weakens the steel) is applicable here, than this is an argument that has to be taken serious.
If you've ever bent a metal coat hanger back and forth until it breaks then you've demonstrated what is at work with burnishing. You're basically flexing the metal back and forth at the apex and every bend further weakens the steel and the end result is fracture of the metal.
Anytime you are not actually cutting the steel with abrasive that is cutting then you are merely pushing the steel, this is the basic mechanism of a sharpening steel to align the apex as it rolls, dents, etc. It can help things in the short term but in the long term it degrades edge retention.
Hmm. The apex is basically thin as paper. This makes sense.
Quote from: aquataur on September 09, 2023, 04:00:34 PMHmm. The apex is basically thin as paper. This makes sense.
It's actually much thinner than paper at the apex, strength of steel is nonlinearly related to thickness so that small increases in thickness can have very large increases in strength. There would be very little strength at the actual apex because of this and it is generally easy to deform and/or fracture as you see quickly misusing almost any knife which is not absurdly overbuilt as to make it more of a knife-like-object... silly things like cold-chisel edge geometry that you find on many 'tactical' knives.
Glazing is more than just wearing the abrasive so that the edges round over, the pores of the abrasive clog with the material being ground. This will happen if you are using an abrasive that is too soft for the material being ground. You will see this on the SG or SJ wheels when trying to grind HSS (high speed steel) for instance. You see a dark patch on the wheel and as that patch travels under your tool being sharpened the sound changes from a grinding to a smooth sliding sound. This is when you need to dress your stone.
The most obvious time this happened to me on the Tormek was when I was sharpening a Japanese knife. I don't know the hardness but it was obvious to me that the wheel was too soft for the steel. It did sharpen but took a lot longer then it should have and glazed the wheel.
This is why I bought the diamond wheels. I also sharpen HSS drill bits, HSS planer blades, and some high hardness chisel and hand plane blades all of which sharpen better on diamond. The SB wheel would also have been suitable being silicon carbide but I opted for Diamond since the geometry does not change therefore giving me a more accurate grind.