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True 90 degree push cutting

Posted by SecondCrack 
True 90 degree push cutting
January 03, 2015 04:42AM
I've been trying to get a true 90 degree push cut with and against the grain on phone book paper, without much success.

I've been sharpening stainless knives on a variety of stones, the best result so far being with a stainless opinel no. 8, push cutting with the grain only, DMT plates then micro bevelled on Spyderco ceramics (M through to UF).

Is anyone else struggling to attain this sharpness? Has anyone got any tips to how they achieved this?

I'm thinking my problem is a combination of not maintaining a consistent enough bevel angle and subsequently not refining the scratch pattern on the apex enough.

My goal is filming from dull to push cutting free standing paper in under 7 minutes: has anyone done this?
Re: True 90 degree push cutting
January 03, 2015 05:05AM
It should not require a very fine grit see for example : [www.youtube.com] where it is done with a Norton Economy fine (320 grit / 46 micron).

I would suggest :

-set the edge at 10 dps
-refine the edge with a muddy stone at 10 dps
-micro-bevel at 15 dps and use various burr minimization techniques
Re: True 90 degree push cutting
January 03, 2015 09:00AM
Funnily enough, I just retried the knife, and it push cut with and against the grain just like in the video above.

It was sharpened at around 8 degrees per side, micro bevelled around 12 or so (roughly estimated) and I used crossed scratch patterns, high angle passes, pressure was only barely enough to keep the knife on the stone, and back-bevelling.

The knife didn't effortlessly push cut though, and I know that with the decent knife and equipment I have, I should be able to get it there.
Re: True 90 degree push cutting
January 03, 2015 12:30PM
All my efforts have been documented here. I've never been close to cross grain push cutting or push cutting away from the point of hold.

I have gotten better with time though, and I imagine I'll get there sooner or later. I feel like the main thing that has helped (as my process hasn't changed much...or rather my approach to doing things) is probably more practice and so more likelihood of holding a consistent angle.

_______________________________________________________________________________________________

Always in search of a good choppa'
Re: True 90 degree push cutting
January 04, 2015 07:05PM
A perfect case where if you believe it is possible to due, you can do it. If you have doubts, you are often unsuccessful. Doesn't sound scientific, but it is, go figure.



Edited 1 time(s). Last edit at 01/05/2015 01:07AM by jasonstone20.
Re: True 90 degree push cutting
January 04, 2015 08:33PM
Quote
C Amber
All my efforts have been documented here. I've never been close to cross grain push cutting or push cutting away from the point of hold.

I've done it with the Havalon Piranta spinning smiley sticking its tongue out and I've done it after sharpening the cKc Victorious, however I can't repeat it at will. I just sort of luck into that level sharpness.


Chumgeyser on Youtube
E-nep throwing Brotherhood. Charter Member
Re: True 90 degree push cutting
January 04, 2015 08:40PM
That's great Chum. It's only bound to happen more and more as you keep at it then!

_______________________________________________________________________________________________

Always in search of a good choppa'
Re: True 90 degree push cutting
February 28, 2015 03:53AM
I haven't had time to post in quite a while but I think I can usefully contribute to this one.

I would by no means consider myself highly skilled at sharpening, yet I have little trouble achieving push cutting sharpness on a number of my knives (and stubborn issues with a few, but that's another issue).

For me, I find it easiest to obtain high levels of push-cutting sharpness by polishing the edge bevel as finely as possible prior to setting the micro-bevel, so I would find it easiest to get a push-cutting edge by going through an Atoma 400 -> Atoma 1200 -> DMT F -> DMT XXF -> Spyderco M -> Spyderco F -> Spyderco UF progression, and then micro-beveling using a Spyderco Sharpmaker on the M -> F -> UF rods (using 5-10 pps on the rods at each stage).

This is a bit time consuming, but because the edge-bevel itself becomes very highly polished, it becomes much easier to form a mirror polished micro-bevel. While in theory the micro-bevel could be done with the UF rods alone, they remove so little material that it's just faster to use the M-F-UF progression on the rods.

Using this progression I find it easy to get most of my knives to where they will do push-cuts with and across the grain on newsprint.

A faster method, adapted from Cliff's thoughts on accelerating the process of getting to a Henckels 8000 micro-bevel is to go Atoma 400 -> Atoma 1200 -> DMT F -> DMT XXF on the edge-bevel and then do 20-30 pps on the Spyderco Sharpmaker M-F-UF rods to set the micro-bevel. I find this progression a bit more difficult skill wise, but significantly faster in terms of time (because getting a true UF edge-bevel finish requires a significant amount of passes on the M-F-UF benchstones to polish out the scratches from earlier stones).

Now, at best I'm getting my knives to push-cut newsprint at a true 90 1/4-1/2" from the point of hold across the grain, but still, I wouldn't at all consider it difficult in terms of skill. For instance, I'm basically hopeless at identifying burrs, so I typically use 1-2 high-angle pps at each micro-beveling stage (i.e. with the second method, 20pps, deburr, 10pps then move to next rod).

My edge bevels are typically in the 5-7dps area and I use the 15 dps setting on the Sharpmaker for setting the micro-bevels. I'll also note I typically find this way easier to achieve successfully on steels like Aogami Super, 8cr13mov and 52100 than on 154CM or S30V.
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