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In the Shop => Knife Sharpening => Topic started by: smurfs on January 16, 2020, 09:34:32 PM

Title: Ceramic knife repair and sharpening feedback
Post by: smurfs on January 16, 2020, 09:34:32 PM
Hi all,

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.

(https://i.postimg.cc/C1KpcDvZ/1-ceramic-knife-before.jpg)

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.

(https://i.postimg.cc/JndVvngp/2-tip-reprofile.jpg)

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.

(https://i.postimg.cc/mkzfs4WB/3-tip-reprofile-setup.jpg)

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

(https://i.postimg.cc/BbrWZzJD/4-ceramic-knife-finished.jpg)


Summary of BESS scores










Step
Heel
Middle
Tip
Dull blade
1025
1165
1085
Set Edge #400   
960
760
915
Set Edge #1000
595
400
520
Hone 10 micron
325
210
220
Hone 5 micron
165
105
175
Hone 2.5 micron
95
85
80
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!


Title: Re: Ceramic knife repair and sharpening feedback
Post by: Ken S on January 16, 2020, 11:15:47 PM
Well done,Smurfs!

Ken
Title: Re: Ceramic knife repair and sharpening feedback
Post by: john.jcb on January 17, 2020, 03:20:10 PM
The edge of a ceramic knife that is this sharp will probably be extremely fragile. Fun to cut with if you are very careful.
Title: Re: Ceramic knife repair and sharpening feedback
Post by: smurfs on January 17, 2020, 03:51:59 PM
Thanks Ken.

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.
Title: Re: Ceramic knife repair and sharpening feedback
Post by: Josu V on January 17, 2020, 05:52:52 PM
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

Regards