KJ-140 middle gap normal?

[Kenshiro_Joestar]

Hello everyone,
I ordered a KJ-140 jig for grinding thin, wobbly blades (like from carpet cutting knives) and when I received it today, it is curved and the gap in the middle is 1,4 mm wide.
Can someone please tell me if this is intentional or did I receive a faulty product?
Greetings
Eric

[RichColvin]

Eric,

I have the predecessor products (the SVM-100 and SVM-140).  Both of them are the same way.  

When I use them, the ends "flex" out so that there is a consistent edge against the blade.

Rich

[Ken S]

Eric,

I agree with Rich. With traditional hand woodwork, glue ups for tabletops are usually "sprung". This means being planed so that the two ends of the board protrude ever so slightly beyond the middle of the board. When the boards are clamped together, the middle is compressed enough to be together and the ends are under pressure.

This is notquite the same as the knife jig jaws; however, extra pressure on the ends of the jaws will make the clamp more secure.

Ken 

PStoTormek: This would be good to include in the instruction sheet.

[Kenshiro_Joestar]

Thanks Rich and Ken!
I will tinker around some more with the jig. It seems I need to shim it, even cranking it uncomfortably hard won't close the gap enough and the blade isn't fully supported in the middle, creating a small "smile" in the grind.
Eric

[HaioPaio]

Eric
Please try sharpening with much less pressure. The smile is very likely not caused by the jig.

[Kenshiro_Joestar]

Hello HaiPaio,
thanks for your comment. Almost the whole blade is not fully supported in the jig, which makes the blade move and making it slightly wider in the middle (smaller edge angle). The gap, after cranking the screw down, is 1,25 mm while the blade is 0,6 mm thick. Only the outmost parts contact the blade. Thanks to Rich and Ken I could confirm the clamp is in spec, so no big (or even small) deal. Some cardboard was enough to solve that.
Eric

[Ken S]

I would like to add my thought that I believe the middle gap in the longer Tormek knife jigs was an intentional design feature. When I visited Tormek, I was included in a design committee meeting. The members are an incredible, very experienced group. I have great confidence in them.

Ken

[HaioPaio]

while the blade is 0,6 mm thick.

If I had known that, I wouldn't have posted.

I'm glad you found a solution that meets your needs. I have never sharpened a knife with a spine thickness of 0.6 mm, so I can't really contribute a solution.

Personally, I believe that the jig for long knives is not designed to support extremely thin blades. I haven't seen a specified lower limit for suitable spine thickness, but it seems obvious that sharpening something as thin as a piece of aluminum foil would be difficult to work with the setup.

That said, I've never tried it myself, and I don't know the practical limits.

[Ken S]

I sharpen only my own knives. The only thin knife I own is the Henckels boning knife which is part of the set I purchased in 1990. My wife and I eat very little fish, so I have never added a fillet knife.

I have SVM 100 and 140 jigs, as well as a KJ-140. My boning knife is not long enough for either 140 jig. In hindsight, I would not purchase either of the long knife jigs, although I like the regular knife jigs.

Ken

[Sir Amwell]

Surely the answer here is to use the tried and tested 'increase the spine thickness by adding layers of tape to the desired tolerances' which I think is between 2 and 3 mm?