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 Post subject: Re: Convex edge on an EP
PostPosted: Mon Feb 17, 2014 6:37 pm 

Joined: Sat Aug 24, 2013 2:42 am
Posts: 174
I can't measure the convex but after following the procedure in my original post there is a convex reflection on the edge, Give it a try.
I'm not saying that it's a ytreich convex but it's there.
I'm sticking with Lagrainian.

Douglas


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 Post subject: Re: Convex edge on an EP
PostPosted: Mon Feb 17, 2014 6:49 pm 

Joined: Wed Feb 20, 2013 2:22 am
Posts: 662
Yup, very similar to your mod Rook, but designed towards the Apex. If I have seen further it is by standing on the shoulders of giants.


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 Post subject: Re: Convex edge on an EP
PostPosted: Mon Feb 17, 2014 7:10 pm 

Joined: Tue Jan 21, 2014 9:19 am
Posts: 15
Hi everyone,

Still catching up on this thread, but just a quick note:

I would be curious to get some real-world measurements on how much play there is in these sharpening mechanisms. Mechanics and metal workers do this all the time with dial indicators and dial-test indicators.
https://en.wikipedia.org/wiki/Dial_indicator

A dial indicator has a sliding rod with a tip. As the rod slides up and down, a dial shows how much the tip has moved, typcially to 0.001", 0.0005, or 0.0001" resolution. A dial-test indicator is similar, except that it is based on a pivoting lever rather than a sliding rod. Mechanics typically measure things like total-runout and back-lash with these. We should be able to do the same.

I have a cheap (ie: made in China) dial indicator, and will measure my home-built rig when I have time. But I don't have access to other rigs (like a WEPS or EP). If any of you have indicators, it would be interesting if you could measure the play in your sharpeners.


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 Post subject: Re: Convex edge on an EP
PostPosted: Mon Feb 17, 2014 7:42 pm 

Joined: Wed Feb 20, 2013 2:22 am
Posts: 662
As I stated, my rig has 0.75 degree play. Measured from when the rod is fully extended to when the rod is fully collapsed with no pressure other than an angle cube on the very end.

The play is in the height adjusting wing nut, the pivot screw, and the oversize guide hole the sharpening rod fits into.

When the rod is fully extended the proportion of the mass past the fulcrum that is the edge of the sharpening table or blade keeps any play in the assembly under pressure at its highest point (numerically lower angle). As one pushes the rod in, the mass moves to the opposite side of the fulcrum and the assembly drops, resulting in a numerically higher angle. Keeping downward pressure on the stone will counter this drop to a point, but is contrary to desired technique.

I can try to draw a picture, but I'm no da Vinci.


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 Post subject: Re: Convex edge on an EP
PostPosted: Mon Feb 17, 2014 11:54 pm 

Joined: Tue Jan 21, 2014 9:19 am
Posts: 15
Hi Tall Dark and Swarfy,

Could you post a sketch? I'm reading your description but feeling a little confused. I would say, don't worry about making a super nice sketch or not. Many of us, myself included, are terrible at drawing! I sometimes try to compensate by using Adobe Illustrator, or software.

Sincerely,
--Lagrangian


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 Post subject: Re: Convex edge on an EP
PostPosted: Tue Feb 18, 2014 12:57 am 

Joined: Wed Feb 20, 2013 2:22 am
Posts: 662
I'll see what I can do, but it will be a day or two. Maybe a video would be better? But I'm no Darryl Zanuck.


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 Post subject: Re: Convex edge on an EP
PostPosted: Tue Feb 18, 2014 1:02 am 

Joined: Wed Feb 20, 2013 2:22 am
Posts: 662
Also, I dicked up the angles in my explanation above. As one pushes in the rod (giggity) the assembly drops lower and thus the angle becomes numerically lower, or more acute.


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 Post subject: Re: Convex edge on an EP
PostPosted: Tue Feb 18, 2014 5:58 pm 

Joined: Sat Aug 24, 2013 2:42 am
Posts: 174
TD&S;
I don't know how, but I tweaked my first arm and took it out of straight. Not much but a little. New arm measured straight. I'm not a heavy EP user so I imagine that slop will eventually develop.
It's time for Mark or somebody to make up MRs' mod .

Douglas


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 Post subject: Re: Convex edge on an EP
PostPosted: Thu Feb 20, 2014 5:58 pm 

Joined: Tue Jan 21, 2014 9:19 am
Posts: 15
Hmm... 0.75 degrees sounds too big to me?

Please check my math:

The closest distance from the vertical mast to the edge of the table (for Edge Pro Apex) is 8 inches. Converting to metric (8in)*(25.4mm/in) = 203.2mm.

Next we'll convert 0.75 degrees to radians:
(0.75 deg)*(pi/180) = 0.01309... rad

Small angle approximation:
For small theta, in radians, sin(theta), tan(theta) are approximately equal to theta.
(0.01309 rad)*(203.2mm) = 2.6599... mm

This would suggest that the guide rod has play of roughly 2.5mm near the vertical mast of the Edge Pro Apex. This seems, to me, to be way too huge? Maybe something else is going on as well? If you really do have 2.5mm of play, then you should order a replacement joint from Ben Dale. They do wear out, and Ben Dale does sell replacement parts.

Naively, I would expect play to be much smaller, like a tiny fraction of a millimeter.

Sincerely,
--Lagrangian


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 Post subject: Re: Convex edge on an EP
PostPosted: Fri Feb 21, 2014 12:35 am 
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Joined: Mon May 27, 2013 6:39 pm
Posts: 258
Its a metal guide rod passing through a plastic guide. It wears out quick , and comes with play brand new anyways making order a factory replacement a moot point for the purposes of this discussion. I have a machinest buddy coming over to take some measurements here in a few days. Sometimes this weekend hopefully.

2.5mm doesn't sound too far off for a well used unit likes TD&S's machine.

Another interesting thing , the guide block rotates around the mast. Meaning as you move back and for that in and of itself introduces variation , as the block moves infront of to behind the mast. Yet another reason to upgrade.



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