Published on Nov 9, 2012
This is a very short and simple video which shows a few key points of sharpening :
1) Destress the edge by grinding off all weakened metal by cutting into the stone
2) Grind the apex bevel until it stops reflecting light, this is just getting the edge to the right shape. It does not take an overt amount of attention or focus.
3) Finish the apex to the desired grit paying attention to minimize the burr.
To simplify the process the finishing grit was kept at the shaping grit (200 SiC) which leaves an edge with a very aggressive slicing finish but also can easily shave, slice newsprint, and is very close to a true push cut (90 degrees in all three planes) on the newsprint.
In this case when finishing the apex the angle was raised to 15 dps (the bevel was shaped at 10 dps). The increase in angle is just to add durability to the edge as this is used very roughly in the kitchen by friends and family, i.e. it will scrape out pots and the like, it isn't restricted to just cutting.
In order to get to a true 90 push cut on the newsprint all that has to be done is be a little more careful on the final finishing which means :
1) Clean the stone
2) Reduce force to the absolute minimum (5-10 grams)
3) Go very slow with short travel on the stone.
4) Change the presentation angle of the knife to the stone to make the scratch patterns cross over.
To maximize the cutting ability the 15 dps bevel would also be minimized to a true micro-bevel by back sharpening at 10 dps.
As noted in the video, a few other details :
1) The benchstone used is extremely cheap and thus it cuts slow, loads easily and is conditioned with a 200 grit SiC waterstone to give it some fast cutting swarf. Without this step the time would be increased ten fold on the benchstone it cuts that slowly.
2) Grinding to form a significant burr stresses the edge heavily and leads to premature failure of the knife edge, especially if it is done with very coarse stones. The edge should only be shaped until it forms an apex, no further. The point of sharpening is to minimize a burr, the best way to do that is not form a large one in the first place.
This is the same process used on any style of knife, machete or axe, the only thing that changes are the grits used based on what is desired and the angles used in the shaping stage. If the knife is used more for push cutting then higher cutting ability and edge retention will be produced with a finer polish and as less durability is required the edge can be set to a lower angle.
This technique was developed to fill the goal of being able to sharpen knives for friends in two minutes or less even though they may come very dull and damaged. By starting with the right abrasive for the shaping stage even very dull knives can be brought back to life very quickly. The extra step to get a true push cut finish will take an extra 30-60 seconds on the stone using the above four techniques.
Discussion :
http://www.cliffstamp.com/knives/forum/read.php?7,6571
