Convex club.

[Chan Eil Whiskers]

If bevel is already set on flat hones, is it necessary to reset bevel on convex? Or will results be similar finishing on convex?
What about taking previously finished edge, then just refinishing on convex?

I've discussed this with Jarrod.

He gave me a huge, long, detailed, deep, but not entirely clear to me answer, so I emailed him again.

I've now had a chance to read your long email response several times and to ponder it. Very good stuff I think, but I'm not 100% sure I entirely understand the answer to my questions.

If I understand correctly you're saying one can hone on the Ark finishing stones a stone previously honed from bevel setting on a flat stone.

You're also saying that it might be better (would be better?) to set the bevel on the soft convexed Ark before finishing on the hard Ark finishing stones.

Is my understanding correct?

This was Jarrod's response.

To summarize the prior communication as briefly as I can in one sentence, one can always refine flat upon convex but never the latter, one can go from flat to convex because the convex stone causes modern hollow ground razors to flex at their bevel plane to meet the stone shape, and it is better to set on convex if you've the time but not remotely a necessity.

I'm glad to have both sides of the Double Convex Ark as it is better to set the bevel on the convex.

When I'm honing on the DCA a razor with either of these

• a good bevel off a flat stone
• or a good bevel and a good and finished edge, off a flat stone

I start on the soft side of the DCA. Maybe it's not necessary, but it is better.

When I'm touching up an edge previously finished on a DCA I may go back to the soft side of the DCA (if it seems like a good idea) or I may just work with the hard side of the DCA (if I think the edge needs less work.

The soft side of the DCA is definitely a bevel setter. However, for removing chips I use a faster stone, the Chosera 1K and then both sides of the DCA. The soft side of the DCA can be used with pressure or used very lightly.

Just to be clear, I'm no expert on this, but I've been using the DCA a pretty good bit since I got it, and also discussing various aspects of its use with other users of the stone, including Jarrod.

Happy shaves,

Jim

 

[kohalajohn]

If bevel is already set on flat hones, is it necessary to reset bevel on convex? Or will results be similar finishing on convex?
What about taking previously finished edge, then just refinishing on convex?

if you have a healthy razor you can just go straight to the black convex finisher. It will finish the edge just fine. And over time the bevel will develop that very slight hollow arc that gives you a touch more acute angle. But that's not a hugely important thing.

The only advantage of a bevel setter that is convex, is that it sets you up at the beginning with that slight arc I mention above. Oh, and also if your razor has a slight warp, then the convex bevel setter is handy.

But if your razor is good, then no need to bother.

 

[Biglo13]

Ok. Math is not my forte. But my understanding is that jarrods master sagitta is 5cm on a 12 inch tile/ diameter. Curious what would be the equivalent sagitta for 9 inch diameter.

Correction .5 mm sagitta....

 

[bluesman 7]

Correction .5 mm sagitta....

I take it that sagitta is autocorrect for 'sag in the.....' Wikipedia just shows it as a constellation with no geometry reference.

 

[Namkcakram]

I take it that sagitta is autocorrect for 'sag in the.....' Wikipedia just shows it as a constellation with no geometry reference.

I dated a gently curved Sagittarius or two in my time, but I’ve never been into the curvy side of geometric nerd terms.

 

[kohalajohn]

sagitta just comes from the word for arrow. it's the straight line from the highest point of the curve of the lens to the bottom.

Jarrod has a .5mm sagitta in his foot wide concave granite tile. so that's just how deep the puddle of water would be. pretty shallow. But it took him 24 hours of labour to get it. and then he made a second one. whew.

and then he broke his second one when he took my advice about buying a variable speed potting wheel. I thought that would save him labour.

nope. the tile flew off it and broke on his tiled floor.

If you're reading this Jarrod, sorry about that.

the things I have to learn when I just wanted a good shave....

 

[Biglo13]

I take it that sagitta is autocorrect for 'sag in the.....' Wikipedia just shows it as a constellation with no geometry reference.

Sagitta (geometry) - Wikipedia

 

[bluesman 7]

Sagitta (geometry) - Wikipedia

Ah. Thanks for that. Learned something new. I'm surprised that it did not come up when I searched wikipedia.

 

[Chan Eil Whiskers]

sagitta just comes from the word for arrow. it's the straight line from the highest point of the curve of the lens to the bottom.

Jarrod has a .5mm sagitta in his foot wide concave granite tile. so that's just how deep the puddle of water would be. pretty shallow. But it took him 24 hours of labour to get it. and then he made a second one. whew.

and then he broke his second one when he took my advice about buying a variable speed potting wheel. I thought that would save him labour.

nope. the tile flew off it and broke on his tiled floor.

If you're reading this Jarrod, sorry about that.

the things I have to learn when I just wanted a good shave....

I'd heard rumors of his tile breaking, but the rest of the story is painfully way too real.

You'd think there'd be a solution (an anchor solution) to the flying tile problem.

Interesting stuff about exactly how small the sagitta in his tile is (and hence how small it is in our convexed Arks). Small, but just right.

Happy shaves,

Jim

 

[Biglo13]

If you have a master tile and a pottery wheel.... I have your mounting /anchoring solution/s PM me....

 

[bluesman 7]

Interesting stuff about exactly how small the sagitta in his tile is (and hence how small it is in our convexed Arks). Small, but just right.
Jim

Right! A .5mm dish over 12" is a 75' radius. I think that a lot of the knee jerk reaction against the convex hones is that it is hard to conceive just how large the radii are.

 

[Biglo13]

i am math challenged....
what would sagitta be for 9 inch diameter?

 

[bluesman 7]

For the same 75' radius the sagitta over a 9" chord would be .011" or .27 mm

 

[Biglo13]

For the same 75' radius the sagitta over a 9" chord would be .011" or .27 mm

Thanks ill let you know if my idea works out......

i just realized

different legnth stones should have different sagitta.

But prolly not enough to make that much of a difference

 

[Namkcakram]

Thanks ill let you know if my idea works out......

i just realized

different legnth stones should have different sagitta.

But prolly not enough to make that much of a difference

Well it should make no difference at all if you’re shaping based on radius, the blade would experience the same geometry on a 2” stone or a 12” stone. The total displacement would be higher on a bigger stone, but the radius of the surface would be the same.

.5mm on a 12” tile seems too small for the straight edge photos I’ve seen posted online. I know the backlighting exaggerates gaps, but even so it looks like more than a .5mm rise just over the length of an 8” stone. You guys sure it’s not more than that? I bet I’ve given a standard size waterstone more than a .5mm sagitta in one or two honing sessions before.

Maybe we need some engineers on here to get together and develop a less labor intensive process for Jarrod to make these stones now that they seem to be gaining a following.

 

[bluesman 7]

i just realized different legnth stones should have different sagitta.

But the radius should be the same.

Well it should make no difference at all if you’re shaping based on radius, the blade would experience the same geometry on a 2” stone or a 12” stone. The total displacement would be higher on a bigger stone, but the radius of the surface would be the same.

^This

 

[Chan Eil Whiskers]

Really nice edge!

Off the DCA yesterday.

Boker Tree.

 

[Biglo13]

Well it should make no difference at all if you’re shaping based on radius, the blade would experience the same geometry on a 2” stone or a 12” stone. The total displacement would be higher on a bigger stone, but the radius of the surface would be the same.

.5mm on a 12” tile seems too small for the straight edge photos I’ve seen posted online. I know the backlighting exaggerates gaps, but even so it looks like more than a .5mm rise just over the length of an 8” stone. You guys sure it’s not more than that? I bet I’ve given a standard size waterstone more than a .5mm sagitta in one or two honing sessions before.

Maybe we need some engineers on here to get together and develop a less labor intensive process for Jarrod to make these stones now that they seem to be gaining a following.

I rethought the process yes it is just a smaller slice of same ball......

I did notice some manual defects on my stone ... from human processing... ez enough to stay away or I’ll fix it when I finish my master tiles....

I was/am a potter I have a solution for fix the tile centered. On wheel. What he needs is a arm to hold the stone to spinning tile....

 

[bluesman 7]

What he needs is a arm to hold the stone to spinning tile....

The stone needs to swing though the radius to maintain and promote the spherical shape of the master. When the stone mates to the master regardless of orientation then the interface can only be spherical.

 

[Namkcakram]

I rethought the process yes it is just a smaller slice of same ball......

I did notice some manual defects on my stone ... from human processing... ez enough to stay away or I’ll fix it when I finish my master tiles....

I was/am a potter I have a solution for fix the tile centered. On wheel. What he needs is a arm to hold the stone to spinning tile....

If the tile is large enough and spherical enough, then the stone orientation doesn’t matter with regards to shaping only to the wear pattern created on the stones surface right? I’d bet your pottery skills would let you freehand darn close to a perfect hemisphere section on a spinning wheel.

A jig holding the stone would be best for sure though. The woodworker #1 rule to live by is that no matter how many tools you have or lack, you will never have enough clamps or fixtures/jigs.