So how do i sharpen a knife like this

[wootz]

I tried to word the procedure I follow myself for sharpening concave blades on Tormek.
Feel free to ask if unclear in any part.

Knives I sharpen using the below procedure.


The stone must be graded fine and the stone corner must be smoothed out, just a little.


Grind away from the edge.
Set grinding angle at the concave trough, with the jig adjustable stop pressed against the Universal Support.
Mark the line of contact (LOC) with a laser.
Lock collar at the ends of the concave (crests), with the collar pressed against the Universal Support.


The concave is sharpened near the edge of the stone on the side of the handle.
E.g. with tip pointing to you right, sharpen near the left stone edge area ~5mm wide.

1.
Start at the bolster end of the concave (crest), i.e. with the locked collar pressed against the Universal Support, positioning the blade at the point where the laser LOC crosses the stone edge, and tilting the blade just enough not to touch the stone with the rest of the blade.

Do the descending part moving the jig with lateral and forward movement, maitaining the blade contact with the stone at the LOC crossing the stone edge, and not tilting unnecessarily.
E.g. with tip pointing to you right, move the jig left-and-forward; maintain the jig position perpendicular to the Universal Support.

2.
Do the trough segment with the jig adjustable stop pressed against the Universal Support.

3.
Then continue to the ascending part, moving the jig with lateral and backward movement.
At the end of the ascending part you reach the locked collar.

These steps are illustrated on the next 3 photos.




Similarly sharpen the other side of the blade on the opposite stone corner.

Hone on a tapered felt wheel with 0.5 micron diamond paste.

[Jan]

Wootz, thanks for posting a detailed description of your procedure for sharpening concave blades. 
I was also pleased to read that you are using a laser line. 

I would like to ask you how much you charge for a single concave blade sharpening. In my opinion, the preparation of the rounded edge of the grinding wheel and subsequent truing is quite a costly affair. I assume that the rounding and truing procedure will cost you at least 2 mm of grindstone diameter which represents more than 2% of its total capacity. 

It would be good to have one grindstone dedicated to this work. Do you think that a worn grindstone would it be appropriate for this purpose? 

Jan

[wootz]

Hi Jan, haven't spoken with you for long.
You guess right, I have two alumina SG stones, one with square corners, and another with rounded. This covers all knife shapes, the rest is technique.
What to charge depends both on the time and consumables spent; to sharpen a short karambit like pictured might cost more than an 8" kitchen knife only because the karambit takes longer to set up.

[Jan]

Wootz, thanks for your clarification! 

Jan

[WolfY]

Just yesterday as I was demonstrating and sharpening at a knife and cold weapon fair, and had some queries for shaping and sharpening concave blades. I tried to avoid it as I knew I have to use the edge of the stone and didn't want to round it. And today I see this post

So, after lots of thinking about the necessity of it my q. is: Is it really necessary to have a straight 90 dgrs edge for knife sharpening, for ex. or the rounded edge don't make a different, leaving the necessity of either truing (not an option) the stone or having 2 stones. I even think it will be an advantage to have it rounded always.

The other thing I noticed is the use of laser line marker. Can you pls, show and explain how you added it to the machine?

Thanks in advance

[SharpenADullWitt]

Won't having rounded corners, just make the stone narrower? (for sharpening purposes)
Trying to remember what JF said about minimum stone size.  Because I am thinking that maybe one could make a spacer and use a T-4 wheel, with rounded corners on the T-7 and the spacer could give clearance on both sides of the wheels, for unusual profile knives.

[Jan]

Just yesterday as I was demonstrating and sharpening at a knife and cold weapon fair, and had some queries for shaping and sharpening concave blades. I tried to avoid it as I knew I have to use the edge of the stone and didn't want to round it. And today I see this post

So, after lots of thinking about the necessity of it my q. is: Is it really necessary to have a straight 90 dgrs edge for knife sharpening, for ex. or the rounded edge don't make a different, leaving the necessity of either truing (not an option) the stone or having 2 stones. I even think it will be an advantage to have it rounded always.

The other thing I noticed is the use of laser line marker. Can you pls, show and explain how you added it to the machine?

Thanks in advance

Wolfy,
Ad1) Having the stone corners rounded you cannot sharpen the edge near the handle. 

Ad2) Laser line is a battery powered laser line module mounted on a bar which can be attached to Tormek housing e.g. via the USB sleeve. It is good for freehand sharpening, belly sharpening, platform sharpening and in many other situations.



For more info read
http://forum.tormek.com/index.php?topic=2562.135


Jan

[WolfY]

Ad1) Having the stone corners rounded you cannot sharpen the edge near the handle. 

Of course losing 3 mm of the corner will decrease the sharpening area and the ability to fully get close to the start/ end point of sharpening near the handle. Normally it's not a problem for me as I don't sharpen the closest 5mm near the handle for user safeness

Ad2) Laser line is a battery powered laser line module mounted on a bar which can be attached to Tormek housing e.g. via the USB sleeve. It is good for freehand sharpening, belly sharpening, platform sharpening and in many other situations.

I have other thoughts of use this kind of attachment. Not for freehand sharpening purpose.
Can you provide a link to where I can get one of those?

Thanks.

[Jan]

Wolfy, the laser line shown is my homemade prototype. Your interest may inspire some manufacturer. 

Jan

[WolfY]

Wolfy, the laser line shown is my homemade prototype. Your interest may inspire some manufacturer. 

Startup Kickstarter?
I'm signing up for one. Just name the price

[wootz]

I use this laser I sourced from eBay, cost me US$ 9.50 delivered
http://www.ebay.com/itm/Industrial-650nm-5mW-focusable-Red-Laser-Line-Diode-Module-w-AC-Adapter-13x42mm-/131790206137?hash=item1eaf4ef4b9:g:SyYAAOSw1DtXGuNH

Unlike Jan, I didn't attach it to the Tormek, but have it on a separate stand next to it.

Laser marking of the line of contact helps to properly do concave, pronounced convex and S-shaped blades.
But the locking collar is not as necessary, it's just an additional reference point aiding with a complex shape.

So grateful to this forum for this laser LOC idea. If I remember right, Ken first suggested it, and Jan realised.

[RichColvin]

Won't having rounded corners, just make the stone narrower? (for sharpening purposes)
Trying to remember what JF said about minimum stone size.  Because I am thinking that maybe one could make a spacer and use a T-4 wheel, with rounded corners on the T-7 and the spacer could give clearance on both sides of the wheels, for unusual profile knives.

I recently listened to a Fine Woodworking podcast where they discussed the advantages of rounding the surface of the grinding wheel.  They advocate that this makes sharpening easier & faster. 

[Ken S]

Rich,

I believe the podcast goes back to one of the Isles family of toolmakers. He puts a crown on his (dry) grinding wheels to minimize the contact area during grinding to keep the tool cooler. I will check. I printed the article. I believe it was on Tools for Working Wood. Here is the link. It is well worth your time for dry grinders.

http://www.toolsforworkingwood.com/store/blog/453/title/Further+Thoughts+On+Grinding

Ken

[RickKrung]

Disregard this post.  Had a question about how to power it, but found one that has the power adapter, so order it. 

Rick

[Ken S]

I recall a post where Jeff Farris, the founder of this forum and a very experienced Tormek user, stated that he had ground a small radius into the inside corner of his grinding wheel.

Ken