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Newbie introducing recurve to blade

Started by Tjudd, August 29, 2023, 06:19:53 AM

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Thy Will Be Done

Quote from: aquataur on September 08, 2023, 09:18:50 PM
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...

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.

HaioPaio

#31
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.

Thy Will Be Done

#32
Quote from: HaioPaio on September 08, 2023, 09:54:14 PM
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 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...


HaioPaio

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.

Thy Will Be Done

#34
Quote from: HaioPaio on September 08, 2023, 10:34:47 PM
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.

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.

aquataur

#35
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.

Thy Will Be Done

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.

aquataur

Hmm. The apex is basically thin as paper. This makes sense.

Thy Will Be Done

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.

John Hancock Sr

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.