I don't think that the shape of the bevel is a concern because the radius of the stone is so large that the bevel is flat for all practical purposes.
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Convex stones. New trend for the end users?
- Thread starter Acmemfg
- Start date
I calculated the radius at 26' using the 1mm crown over 10" figures.
Ok. But what value is this
If they wanted the razors to be dead flat they could easily use a belt bench sander to achieve this. Like the knife sharpeners use. The entire bevel would receive equal grinding as opposed to the current method.
And I’m not sure why they don’t do this. I suspect that for whatever reason they’re just dead set on their traditional methods. I’ve wondered why someone hasn’t tried making SR’s with CNC marching yet. Might not be worth the cost based on market demand though.
From this, can we go so far as to say that the convexed stone is still flat as well for practical purposes? In any case, I had heard the bevel's resultant concavity being touted as an advantage and wondered why. I suppose it has to do with the summit of the bevel leading to the apex or edge being thinner, but this would appear to be at the cost of being less forgiving as to shaving angle and the edge being more prone to collapsing.
I think that a straight edge on a convex hone is all about mimicking the rolling x of a smiler on a flat stone.
Even if your straight edge razor is perfect in all ways there are advantages to this style of honing IMO.
Even if your straight edge razor is perfect in all ways there are advantages to this style of honing IMO.
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A problem with grinding full hollow blades is deflection of the thin blade as you are grinding. The double wheel grinder addresses this deflection by grinding both sides at the same time so the wheels back each other up. The set up is still unstable in twist though and the same deflection problem prevents ideas of holding the spine or tang rigid from working. At least that is the way I see it.
Yes! Hone the blades as they are! Lol.
I agree, as I mentioned in my first post (#20). But can't this be done on a cylindrical-shaped stone as well? No need for the spherical gradient in other words...
Yes, I would agree with the honing aspect of the cylindrical hone, but lapping a hone to an accurate spherical surface is much much easier than to an accurate cylindrical surface, and the process is well established from the lapping of telescope lenses and mirrors. Two surfaces lapped together until they mate in all orientations always results in a spherical interface with the case of a flat interface represented by a sphere of infinite radius.
Do go on, I'm all ears; but please be more specific, if not more basic, as to an explanation of the respective areas and substances of the two surfaces being lapped together. Are they the same or do they differ? I have a vague recollection of small convex lens manufacture involving something akin to a kettle drum for lapping/polishing.
Well, most people start with something relatively small say 4" in diameter to sort of artificially start the dish in the concave piece. One guy was starting with pitch filled dog food cans, IIRC. When making a concave mirror once they have the shape they use pitch as the convex side to carry the grit for polishing. I ran across this when I was researching the three stone method for making flat lapping plates. The grit that I bought was mostly sold to telescope makers which is what got me interested in this technique. There are several videos on mirror lapping for telescopes.
For making convex hones I would think of using anything to start with to get close to the spherical concavity and then start using the actual hone as the convex piece. The basic premise is that the larger piece goes concave and the smaller goes convex. When they mate in all directions they are spherical. Our purposes are much less demanding than telescope mirrors.
As all of my razors smile I have no need to try this, but I do find it interesting.
In one of Jarrod's videos he said that the Germans told him to use as little convexity as possible. For what its worth.
For making convex hones I would think of using anything to start with to get close to the spherical concavity and then start using the actual hone as the convex piece. The basic premise is that the larger piece goes concave and the smaller goes convex. When they mate in all directions they are spherical. Our purposes are much less demanding than telescope mirrors.
As all of my razors smile I have no need to try this, but I do find it interesting.
In one of Jarrod's videos he said that the Germans told him to use as little convexity as possible. For what its worth.
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Thanks, that is helpful. Perhaps you mean pitch-filled dog-food bowls rather than cans? If this is all about a concave underlying support as the base for lapping, then I don't see why arriving at a cylindrical shape, if it would serve the same end, would be any more difficult. One could find the requisite tube or pipe of a gross diameter, scatter some grit inside and introduce the flat stone.
The problem I have with a convexed hone with a spherical gradient is that here we are no longer talking about something analogous to a rolling stroke on a relatively large, flattened honing surface, but something more akin to a rolling stroke on a large postage stamp, as the effective length of the stone in addition to the effective width is also coming into play with a spherical gradient, resulting in a peak at the center or middle of the honing surface. Not that honing on a large, flat, postage-stamp-sized hone can't be achieved, of course. I like to goof around with honing on large coticule slurry stones from time to time; but these remain flat at a cost of around $20 per slurry stone, whereas the asking price of an analogous large convexed coticule as claimed would be well into $$$.
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No, he actually used the whole can and felt that the metal can helped during the rough in stage. It wore to convex in due time.
I don't get your postage stamp analogy or the peak reference. The radius that we are talking about is large enough that it would barely be noticeable in use except in its benefits IMHO. A radius is a radius and I don't see why this wouldn't work the same on a 2x6. Jarrod talks about always honing toward the peak to keep the angle right, but this makes no sense. Imagine honing on a 50 foot diameter sphere. The angle stays the same no matter where or which direction you hone, short or long strokes. There is no peak on a sphere. Jarrod also started lapping his concaves with TWO 12x12 tiles?????Duh!
Smiles on flat stones accomplishes the same benefits, but smiling razors are harder to manufacture in quantity and don't lend themselves to the double wheel grinders in use.
I don't get your postage stamp analogy or the peak reference. The radius that we are talking about is large enough that it would barely be noticeable in use except in its benefits IMHO. A radius is a radius and I don't see why this wouldn't work the same on a 2x6. Jarrod talks about always honing toward the peak to keep the angle right, but this makes no sense. Imagine honing on a 50 foot diameter sphere. The angle stays the same no matter where or which direction you hone, short or long strokes. There is no peak on a sphere. Jarrod also started lapping his concaves with TWO 12x12 tiles?????Duh!
Smiles on flat stones accomplishes the same benefits, but smiling razors are harder to manufacture in quantity and don't lend themselves to the double wheel grinders in use.
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Not that I have done this, so I am supposing that when you take a flat, rectangular stone and introduce a spherical gradient to the honing surface relative to the flattened base on the other side, there would be a more pronounced area towards the middle area of the honing surface than on the sides and ends relative to the flattened base underneath. That is what I am talking about when I wrote "a peak." Maybe this was taken from Jarrod's original description, I don't remember.
As for the postage stamp reference, let's first recall your acknowledgement that a cylinder would work in much the same way as a sphere, and your recent remark that "[t]he angle stays the same no matter where or which direction you hone, short or long strokes." We both seem to agree that a convexed surface, be it spherical or cylindrical, is essentially forcing one to use a rolling stroke by default in that the arc is no longer being introduced during the gest on a flattened stone but is inherently there as part of the pass on a convexed stone. And if this is the case, then we are essentially honing on point-by-point (or section-by-section) basis in relation to the spine and edge considered on the lateral bias (i.e. from side to side of the stone rather than from end to end) during the stroke. This can be demonstrated in the example where someone marks off a flattened 3" x 8" hone into two 1-1/2" x 8" sections and hones with a rolling stroke leaving swarf traces in only one of the 1-1/2" x 8" sections. Here I would suggest that this example is more analogous to a cylinder than a sphere in that the gest introducing the arc locating the pressure as given is laterally biassed while the stone remains flat. And it is also assumed that most of the length of the stone is being used during the stroke. From here, let's say that we are perfectly comfortable with using a rolling stroke in this way, so a 3"-wide hone no longer becomes necessary; we can now comfortably hone in the 1-1/2"-wide range. Following this, we start to realize that given a razor's 3"+ length, or little more than a pocket knife, we really don't need an 8" length of stone; something more like 5" would suffice just as well. So now we are down to honing on a 1-1/2" x 5" stone. We can continue to hone like this using the full length of the stone or we can introduce more laterally-biassed passes, effectively shortening the length of the stone being used to 3"; and at around 1-1/2" x 3", we arrive at what I would call "honing on a postage stamp" or maybe "honing on a postage label." All of this is fine with relative finishing stones like coticules and purple Welsh slate, but it still remains analogous to honing on a cylinder as far as I can perceive. And what to do if one has a 1-1/2" x 3" hone and one wants to set a bevel with it? One solution would be to introduce torque biassed towards edge in making the pass. This is finally what I would consider as analogous to honing on a spherical surface; it's no longer just analogous to a rolling stroke but more analogous to a rolling stroke to which torque biassed towards the edge has been applied. This also might explain Jarrod's claim that the stones work much faster when convexed.
As for the postage stamp reference, let's first recall your acknowledgement that a cylinder would work in much the same way as a sphere, and your recent remark that "[t]he angle stays the same no matter where or which direction you hone, short or long strokes." We both seem to agree that a convexed surface, be it spherical or cylindrical, is essentially forcing one to use a rolling stroke by default in that the arc is no longer being introduced during the gest on a flattened stone but is inherently there as part of the pass on a convexed stone. And if this is the case, then we are essentially honing on point-by-point (or section-by-section) basis in relation to the spine and edge considered on the lateral bias (i.e. from side to side of the stone rather than from end to end) during the stroke. This can be demonstrated in the example where someone marks off a flattened 3" x 8" hone into two 1-1/2" x 8" sections and hones with a rolling stroke leaving swarf traces in only one of the 1-1/2" x 8" sections. Here I would suggest that this example is more analogous to a cylinder than a sphere in that the gest introducing the arc locating the pressure as given is laterally biassed while the stone remains flat. And it is also assumed that most of the length of the stone is being used during the stroke. From here, let's say that we are perfectly comfortable with using a rolling stroke in this way, so a 3"-wide hone no longer becomes necessary; we can now comfortably hone in the 1-1/2"-wide range. Following this, we start to realize that given a razor's 3"+ length, or little more than a pocket knife, we really don't need an 8" length of stone; something more like 5" would suffice just as well. So now we are down to honing on a 1-1/2" x 5" stone. We can continue to hone like this using the full length of the stone or we can introduce more laterally-biassed passes, effectively shortening the length of the stone being used to 3"; and at around 1-1/2" x 3", we arrive at what I would call "honing on a postage stamp" or maybe "honing on a postage label." All of this is fine with relative finishing stones like coticules and purple Welsh slate, but it still remains analogous to honing on a cylinder as far as I can perceive. And what to do if one has a 1-1/2" x 3" hone and one wants to set a bevel with it? One solution would be to introduce torque biassed towards edge in making the pass. This is finally what I would consider as analogous to honing on a spherical surface; it's no longer just analogous to a rolling stroke but more analogous to a rolling stroke to which torque biassed towards the edge has been applied. This also might explain Jarrod's claim that the stones work much faster when convexed.
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Wow. Congrats on getting that written down in a readable, digestible manner. I especially liked this part;
" We both seem to agree that a convexed surface, be it spherical or cylindrical, is essentially forcing one to use a rolling stroke by default in that the arc is no longer being introduced during the gest on a flattened stone but is inherently there as part of the pass on a convexed stone. And if this is the case, then we are essentially honing on point-by-point (or section-by-section) basis in relation to the spine and edge considered on the lateral bias (i.e. from side to side of the stone rather than from end to end) during the stroke."
To expand a little. When honing a smile, it doesn't matter (wear patterns on the stone aside) whether the contact point of the stone is all along one side, as in your marked off example, or a diagonal path from corner to corner, and this would be the same with a straight edge on a cylindrical surface. I think that we agree that when honing a straight edge in this "section by section" manner on a flat stone, we are concentrating the pressure point towards the very edge of the stone and a slight rounding here would be beneficial.
I once calculated the effect of a slight dish of constant radius on the bevel angle, assuming a smile and a rolling X, and it was on the order of .1 degree for an 8" stone with a 1mm dish. Of coarse if one was using a straight back and forth stroke with a straight edge razor this same dish would cause all sorts of problems due to heel leading angles taking the middle of the edge off of the stone. My point is that a large radius (~ 25 FEET!) crown would have negligible effect on the bevel angle and not cause problems with heel lead or lag angles. Problems do arise if the radius is not constant and this is where I see the advantage of a spherical shape over a cylindrical one. Where a constant radius spherical shape is the natural defalt. How does one lap a cylindrical surface and insure a constant radius (flat in this case) from end to end.
" We both seem to agree that a convexed surface, be it spherical or cylindrical, is essentially forcing one to use a rolling stroke by default in that the arc is no longer being introduced during the gest on a flattened stone but is inherently there as part of the pass on a convexed stone. And if this is the case, then we are essentially honing on point-by-point (or section-by-section) basis in relation to the spine and edge considered on the lateral bias (i.e. from side to side of the stone rather than from end to end) during the stroke."
To expand a little. When honing a smile, it doesn't matter (wear patterns on the stone aside) whether the contact point of the stone is all along one side, as in your marked off example, or a diagonal path from corner to corner, and this would be the same with a straight edge on a cylindrical surface. I think that we agree that when honing a straight edge in this "section by section" manner on a flat stone, we are concentrating the pressure point towards the very edge of the stone and a slight rounding here would be beneficial.
I once calculated the effect of a slight dish of constant radius on the bevel angle, assuming a smile and a rolling X, and it was on the order of .1 degree for an 8" stone with a 1mm dish. Of coarse if one was using a straight back and forth stroke with a straight edge razor this same dish would cause all sorts of problems due to heel leading angles taking the middle of the edge off of the stone. My point is that a large radius (~ 25 FEET!) crown would have negligible effect on the bevel angle and not cause problems with heel lead or lag angles. Problems do arise if the radius is not constant and this is where I see the advantage of a spherical shape over a cylindrical one. Where a constant radius spherical shape is the natural defalt. How does one lap a cylindrical surface and insure a constant radius (flat in this case) from end to end.
Very well, and thanks for the appreciation. If the main benefit is with a smiling edge, the irony is that the Solingen production tends more towards a blade that has a parallel relationship between edge and spine, and yet Solingen is the source from where the convexed hone is being celebrated. Meanwhile, Thiers production, at least of old, tended more towards a smiling edge. I don't want to press the issue much further as my understanding of geometry and physics is limited and I am a little bit burned out after my last reply, other than to say that if we are talking about a radius of something like 25 feet, then for all practical purposes the stone surface might be said to be reasonably flat. Maybe there is a slight gain there, but we are really splitting hairs. As for lapping a cylindrical surface, it might be illustrative to study how sharpening-stone manufacturers arrive at their various diameter stones for gouges and the like, particularly the slip stones which would not be achieved with a lathe. For a far greater diameter or radius, I have imagined that placing some grit in the interior of a section of very large section of tubing (or, if we are talking about an extremely large radius, how about the inside of skateboard stunt ramp?) and moving the stone up and down or from side to side while respecting the parallel nature of the concave lapping surface would achieve the desired effect. But if I understand from you that so doing would invariably introduce a slight convexity from end to end as well, then so be it, just as long as such convexity isn't negligible, practically speaking.
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At the risk of beating this dead horse back to life. I maintain that there is no benefit with a smiling edge, and that the benefit is being able to hone a straight edge with the same 'section by section' sequence as if it were smiling.
In the interests of clarity, I'm quoting one your earlier messages. What you mean is that "there is no benefit [to honing with a convex surface] with a smiling edge[.]" Correct? For me, it's all the same really, that "section by section" lateral bias of the rolling stroke with a narrow flattened stone goes on regardless.
