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 Post subject: Convex edge on an EP
PostPosted: Fri Jan 24, 2014 1:46 am 

Joined: Sat Aug 24, 2013 2:42 am
Posts: 200
I have a tanaka 210mm blur #2 gyuto that came with a convex edge which cut like a monster.
When it was time to re sharpen I used the EP and put a V edge on it but the knife didn't cut the same. Performance was noticeably down. Not terrible but not as good as OOB.
I use an EP Pro and sharpen no more than 1" off center, slowly moving the knife across the table to hold the angle as close to true as possible.
Today I decided to put a convex on it with the EP.
Instead of stroking in the middle of the table, I swung the arm from the middle of the table to 6-7" out. The farther the arm swings out the less the angle. Kept moving the knife to keep a consistent convex.
Under the 60 power loop it looks good,even and smooth.
Didn't have anything to cut up but tomorrow I'm going shopping. Hopefully the supermarket will have produce that they're throwing out 'cause I'm gonna be doing some serious cutting.Oh Yeah..Serious :mrgreen:
Can't wait to try it out.

Douglas


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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Jan 24, 2014 3:13 pm 
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Douglas - Nice!! There's always something to learn on the EP. I'd say you're on the EP sharpening 201 track ;-). Let us know how she cuts.

So as I get your concept, your starting the stroke in the middle of the table and then swinging out on the push or draw? Do you do this in reverse on draw vs. push for a back and forth motion, or are you just doing, say a push stroke and lifting for the return?

Thanks


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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Jan 24, 2014 5:25 pm 
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Joined: Mon May 27, 2013 6:39 pm
Posts: 258
Even if your 12" away from the blade table you would have a hard time measuring any degree of differentiation. Less that 1/10 of a degree. The Swivel and guide rod have more play that that making it a moot point.



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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Jan 24, 2014 5:31 pm 

Joined: Sat Aug 24, 2013 2:42 am
Posts: 200
Steve;
I'm push out 6-7" then draw on the way back. Then move the knife just a little as normal.
The theory is that I'll be hitting the edge at my measured angle on the cube then as the arm swings waaaaayy out ,the angle will become more acute in a smooth convex all along the edge as I move the knife.
I don't have room for a Kalimazoo and I like the V edge anyway but this knife was a killer OOB and maybe it just cuts better with a convex...........convex fanatics please don't take this as open season :lol:
Turns out I can't get to the supermarket today but I'll be there tomorrow fer sure.

Douglas


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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Jan 24, 2014 5:39 pm 

Joined: Sat Aug 24, 2013 2:42 am
Posts: 200
Sadden;
Just threw the EP together to measure and at the EP center line the angle was 17.80° then 6" out it was down to !3.08° so I'm getting a convex. Don't know if it will make the knife cut any better but I get to play with it.


Douglas


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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Jan 24, 2014 5:52 pm 
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Sorry but your measuring wrong. It doesnt work like that.

Keep the angle cube parrell to the blade table and not the stone arm.



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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Jan 24, 2014 7:45 pm 
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Sharp Knives wrote:Sadden;
Just threw the EP together to measure and at the EP center line the angle was 17.80° then 6" out it was down to !3.08° so I'm getting a convex. Don't know if it will make the knife cut any better but I get to play with it.


Douglas



Even if it works for you, repeatability matching the angles is the problem when resharpening the same knife.....


:)



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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Jan 24, 2014 10:12 pm 

Joined: Sat Aug 24, 2013 2:42 am
Posts: 200
Sadden;
I disagree.
Sharpening with the EP is done 2 dimensionally on a right (90°) triangle.
The 90° side going from the mast base to the edge I'll call the base side.
When the base side gets longer as it does when sharpening farther from the blade table center line, the angle opposite the 90°(where the stone hits the knife edge) becomes more acute while the angle at the pivot
gets more obtuse, So measuring parallel to the table instead of the arm would be inaccurate. We need to measure to the apex of the triangle where the stone is hitting.
MR...I am thinking that repeatability error would be dependent on the number of strokes when doing the sweeps.
When I sharpen normally I stay very close to blade table center line and move the knife slooooowly to keep the base line(above) the same distance.
When I did the sweeps on the knife yesterday, I moved the knife the same but pushed and drew the stone as I was sweeping. So I think that it can be repeatable.When I put the 60x loop on the edge, it has a convex reflection instead of a flat V.
With the EP at least I know that the edge of the edge is what I set it for. How much of a convex? More than 1/10 degree for sure but a Kali pro could give a better answer by looking at it.

Douglas


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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Jan 24, 2014 10:34 pm 
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I'm curious how you handle the heel area. Do you move the heel well off the base for the sweep. If so, any stability issues w/blade on table. Also, what about the parts of the blade that aren't going to get that far from the center of the table platform. I'm just trying to visualize it. If you are so inclined after getting more comfy w/the process, I'd love to see a video of your technique.

I'm going to get out the cube - this concept has the gears going in my head ;-).


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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Jan 24, 2014 11:44 pm 

Joined: Sat Aug 24, 2013 2:42 am
Posts: 200
Steve;
I hang the heel out as far as possible for the swing, Stability wasn't a problem as I don't use much pressure anyway.
It will be interesting to see how the knife cuts.
This convex thing wasn't to say this is how anyone should do sharpening...more of ."I wonder how this will work out."
I've never had anything that I didn't mess with.

Douglas

If they didn't want you take it apart they would have welded it together.


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