Newbie introducing recurve to blade

[Tjudd]

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

[Sir Amwell]

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.

[HaioPaio]

Here is a helpful topic https://forum.tormek.com/index.php/topic,3055.msg16402.html#msg16402

[aquataur]

There is one thing that I did not see mentioned yet. At least not in this context.

Japanese sharpeners almost unanimously quote the following grit ranges:

Arato (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:

• 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.

[Ken S]

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

[3D Anvil]

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.

[Ken S]

Good point, 3D. Well stated.

Ken

[Tjudd]

I 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.

[tgbto]

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.

[Thy Will Be Done]

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

What do you mean by grinding the blade square? 

[Thy Will Be Done]

There is one thing that I did not see mentioned yet. At least not in this context.

Japanese sharpeners almost unanimously quote the following grit ranges:

Arato (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:

• 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.

[aquataur]

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.

SUN 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)

Another chart (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.

[Thy Will Be Done]

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.

SUN 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)

Another chart (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.

[John Hancock Sr]

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)

Another chart (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.

[cbwx34]

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.

Have you seen this one?

You cannot view this attachment.
https://www.bladeforums.com/threads/abrasives-in-micron-scale-glgc-revision-14-2022.1779773/