Reply To: Preventing Micro chips while sharpening
TL;DR Which I think stands for “Too long, didn’t read.” which I’m sorry for, but I’m way behind on my forum reading, so I’ll jump in here, not knowing if what I have to add has been discussed or not.
Serious chipping is a problem that nagged me for the first two years of WE sharpening and it changed my approach entirely. It popped up again this last week, when I hurriedly sharpened my Delica in ZDP-189. For those not familiar, Spyderco’s ZDP-189 blades to at least RC64. I think that maybe both of my problems are happening here with Trevor.
The first is related to stones which hadn’t been completely broken in. These diamond stones have a tendency to have clusters of diamonds which resist efforts to knock them free from the surface matrix of diamond particles which are correctly positioned and attached to the platen. Clusters which stand proud of the surface can easily tear out chips at the edge of blades which are very hard, and/or have a very low included apex. If you can feel a “clicking” sound as the stone(s) move over the edge, you may have one of more clusters that still need to be knocked off. Try to pin-point the location of the cluster and try to knock it off on some hard steel. I use a piece of glass.
The second problem lies simply with the hardness of the edge and the direction of stone movement. Edge trailing (upward) strokes have a greater chance of tearing chips from the edge than edge leading strokes. Edges which are very hard (as with one made from a file?) and which have incomplete crystallization along the edge also have a greater tendency to have chips break free. As I was sharpening my Delica, I was focused on a rather deep defect in the edge and carelessly switch to a scrubbing action with my (well-broken-in) 400 grit stones. When I re-checked with my USB ‘scope, I found the edge was now riddled with small chips. Never happened before with higher grits and downward strokes, except where a cluster refused to leave a new set of 800s.
Normally, 400 grit is the lowest grit I’ll use on any knife, unless I’ve filed the edge flat and can clearly see when I am well clear of the edge center-line. This was the first time I had ever used the 400s on this knife. Clearly, it didn’t like it, and my guess is that it sure didn’t like the upward strokes.
My suggestion is to knock off any remaining clusters and to switch to edge leading (downward) strokes only, if only for this particular knife.
