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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Feb 21, 2014 12:55 am 

Joined: Wed Feb 20, 2013 2:22 am
Posts: 851
As promised here is a diagram in .pdf format. Pretty shameful work actually, considering I'm an engineer. Best I can do with MS Office and Iron Maiden in the background.

2.5mm sounds in the ballpark using my highly calibrated eyeball. Maybe more.

Sadden, good observation on the longitudinal movement of the block. If you can come up with the solution for a reasonable price I will log onto PayPal. Judging from your kit we have differing views of reasonable. :lol:

Cheers,

Rick


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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Feb 21, 2014 12:58 am 

Joined: Wed Feb 20, 2013 2:22 am
Posts: 851
FML give me a minute.


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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Feb 21, 2014 1:16 am 

Joined: Wed Feb 20, 2013 2:22 am
Posts: 851
Looks like this miserable pic is all you're gonna get.


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EP Apex error sources.jpg [12.09 KiB]
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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Feb 21, 2014 1:47 am 

Joined: Tue Jan 21, 2014 9:19 am
Posts: 15
@Sadden:
Oh, dang. I thought the block was metal, not plastic. I don't own an Edge Pro Apex, I just had friends measure theirs for me.

@Tall Dark and Swarfy:
Thanks for the picture! :) That really clarifies things a lot. I'm rather surprised to hear about 2.5mm being approximately what you actually see for play. I guess you need to consistently press in such a way as to remove the slack the same way throughout a stroke.

One would think there should be a good way to fix this... Such as MadRookie's modification? Sliding parts will always wear out, especially when there is a cloud of abrasive dust and swarf. Even so, a metal guide should last longer than a plastic one, I think...

btw, Clay Allison says he uses a tiny bit of Dawn dish soap when sharpening. The generated foam prevents the dust and swarf from going airborne, and then rinses off with water. I like his idea.


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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Feb 21, 2014 2:00 am 

Joined: Wed Feb 20, 2013 2:22 am
Posts: 851
There's no way to stop the block assembly from falling once you hit a certain point. Certainly, with pressure the assembly stays up, but once you reach equilibrium it falls. And at some point you no longer have any lever against the fulcrum.


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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Feb 21, 2014 4:12 am 

Joined: Tue Jan 21, 2014 9:19 am
Posts: 15
Oh, I was thinking that if you had a third arm, you could push down on the back of the sliding arm, or on the joint block itself. :) But since we only have two arms, one hand will be used to hold the knife, while the other is used for the sliding arm... I suppose a really crude idea would be to use a bungee cord or spring. Probably a more wear-resistant replacement would be better (like MadRookie's mod).


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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Feb 21, 2014 5:00 am 

Joined: Wed Feb 20, 2013 2:22 am
Posts: 851
OMG I was thinking rubber band just before I read your bungee cord suggestion. But is it worth the flailing? I really want a Mad Rookie solution for the Apex. It should be easy enough. I'll look into it this weekend.


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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Feb 21, 2014 6:59 am 
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I had made a mechanism similar to the EP block for the Gizmo sharpener I built. To reduce play, I drilled out a plastic block and glued and inserted a brass sleeve with more precise clearances to remove the play almost entirely. If there is zero play, the friction easily increases with any contamination / grit / dirt that gets on the rod. This is temporarily alleviated by polishing the rod as needed with some 400 grit sandpaper.

I'm not convinced that Mad Rookie's modification of centering the pivot point is of any critical importance (I could be wrong), but if it only reduces the play in the mechanism, for that alone, I give it full kudos as an excellent idea !! One of many that he has introduced that has redefined the EP as an instrument of extreme precision.

---
Ken



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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Feb 21, 2014 5:55 pm 

Joined: Tue Jan 21, 2014 9:19 am
Posts: 15
I would say the following about MadRookie's modification:

(1) Replacing the pivoting mechanism of the Edge Pro with a spherical joint is an improvement for sharpening straight edges. (See my technical report for details.)

(2) In theory, centering the spherical joint has no effect. However, in practice, it could improve stability of the knife on the platform.

(3) From our discussion, it seems that a precision spherical joint would reduce the amount of play.

In the sharpening rig I built, I use spherical joints with metal balls and metal rods. I have not had problems with friction. I believe the rods-diameter and the bore-diameter of the balls are designed for a "slip fit" as machinists would say. One could always polish the sliding surfaces and/or use a small amount of lubricant.


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 Post subject: Re: Convex edge on an EP
PostPosted: Sun Feb 23, 2014 4:33 pm 

Joined: Sat Aug 24, 2013 2:42 am
Posts: 273
How I found the tweaked stone holding rod was to pull the arm al the way out then took readings
at the ball handle end of the rod, behind the stone holder then at the end behind the pivot.
Next, I pushed the rod back and took readings at the ball handle end-in front of the stone- and at the end behind the pivot again.
If there was any play in the pivot rod holder it was made worse by the slightly bent rod.
Not neccessarly the answer but worth checking.

Douglas


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