I have just completed my first ceramic knife repair and sharpening by following Vadim's procedure described on his web site (http://knifegrinders.com.au/06Procedures_ceramic.htm). I'm pleased how it worked out so thought I'd share my experience and results.
The knife, which belongs to my sister-in-law, is about 8 years old so was showing signs of wear with a broken tip and chipped edge.
She claimed it was still quite sharp so out of curiosity I perfored a BESS test along the edge at the tip, middle and heel before I got started. I'm pleased I did as I recorded 1025, 1165 and 1085 BESS respectively so knew anything I did would be a great improvement :P
Firstly I fixed the broken tip.
As I am not a skilled freehand sharpener I chose to undertake this repair on the side of a CBN wheel, edge-leading, using the Tormek SVX-150 scissor plate to provide better support and control. Initially I started the grind with a CBN #400 grit wheel but it was slow going so switched to a CBN #80 which surprisingly was not as aggressive as I expected - ceramic is harder than I realised!
Once the tip had taken shape I reverted back to the #400 to finish off the repair. All in all this repair took around 10 minutes.
Next I repaired the edge to remove the chips using the SVM-45 knife jig and a pivot collar to maintain the curved edge. This was done edge-trailing at 30 degrees per side using the CBN #80 wheel. It took around 10 alternating passes to remove the chips so the process wasn't too slow.
Next, the setting of the new edge at 15 degrees per side, was done edge-trailing with two alternating passes on a CBN #400 and finished off with two alternating passes on a CBN #1000 grit wheel.
The honing was likewise straightforward and followed Vadim's procedure using a progression of finer diamond compounds on slotted paper wheels, except I stopped at 2.5 micron as I had a balance issue with my finest 0.5/0.25 micron paper wheel.
Here is the final result
Summary of BESS scores
|Set Edge #400
|Set Edge #1000
|Hone 10 micron
|Hone 5 micron
|Hone 2.5 micron
|Hone 0.5/0.25 micron
It's clear from the variations in BESS readings along the edge that I still have work to do on my technique so will buy a knife to practice so more, nevertheless there was convergence so got there in the end!
The edge of a ceramic knife that is this sharp will probably be extremely fragile. Fun to cut with if you are very careful.
John, I'll know soon enough if I'm asked to fix it again :) You have a point though. I'd be interested to see how stable the edge is after some use as it was originally 38 degrees included. I used 30 degrees included as that is what Vadim recommends for ceramic knives.
Good Josb Smurf.
The Tip has been perfect. But, for me, the really difficult is to make the entire length of the edge maintaining a coherent line.
I can see that your work is perfect.
Thanks for the progressive Bess Scores. ;D