21" paper cutter knives

[thats sharp]

Hello forum members. I have used the Tormek jig for my 12" planer knives and like how well they worked.
But, I have been approached by a local non-profit organization and asked if I can sharpen their paper cutter knives. The Tormek is too small for the 21" knives but I was wondering if anyone on this forum would have some suggestions as to how this could be done. I do have some other sharpening equipment- belt sander, Thorvie av-40, bench grinder but I'm just not sure how to get started. Would anyone be willing to chat about this type of sharpening. With the wealth of knowledge on this site I figure someone would have some answers.
thanks in advance

[Elden]

Mike, following is a link to a previous thread that discussed this topic:

http://forum.tormek.com/index.php?topic=1684.msg7941#msg7941

I have tried sharpening a hand operated unit before using a hone without removing the blade from the unit. I didn't score very high on the success scale. It had a nick or two that really needed a grinder to remove them. Tension on the arm seemed to be an issue as well.

[thats sharp]

Thanks for the reply Elden and the link to the previous posts regarding this problem.
The paper cutting knife has a 5/8" primary bevel on it. It's from a commercial cutting machine. The difficulty I'm having is trying to find a stone or wheel that will cover the full 5/8" bevel. I have tried to use a ceramic cone but find I must grind to an extremely high degree (70 degrees) to cover all of the bevel but the fine edge chips easily.
Most of the information I have suggests that a common angle for these knives lies somewhere around 24 degrees so I'm uncertain if I need a different sharpening wheel or if a completely different machine is used (CNC comes to mind).
Again, I appreciate your reply.

[jeffs55]

Sounds like you need a belt sharpener or a sanding wheel, anything that does not hollow grind like the Tormek.

[sharpnails]

,.. (..) ..  cutting knife has a 5/8" primary bevel on it. ...(..))..extremely high degree (70 degrees) ...(..)... common angle for these knives lies somewhere around 24 degrees so I'm uncertain if I need a different sharpening wheel ...

To quote Ken S from some of his previos posts "I'm lost..."   

Can you post a photobucket pix of this assembly ?   If i can see what your up against i might have a specific suggestion., otherwise i'd just be guessing in the dark

- Dan

[Elden]

With a bevel that wide, probably a grinding machine with a cup wheel would be required. For example:

http://www.google.com/search?ie=UTF-8&source=android-browser&hl=en-US&q=foley+bedknife+grinder#imgrc=24GwJkByl369qM%253A%3Bundefined%3Bhttp%253A%252F%252Fwww.ozarkwoodworker.com%252Fimages%252Fadphotos5%252F384ad.gif%3Bhttp%253A%252F%252Fwww.ozarkwoodworker.com%252FFOLEY-384-Bed-Knife-Grinder-Operators-Parts-Manual_p_312.html%3B616%3B348

That type of machine grinds straight blades. The grinding head moves manually on a rail setup as I recall, but it has been years since I have seen one. The price would not be cheap. Google bed knife grinder.

As Dan stated a picture would be helpful.

[thats sharp]

Thanks Jeff, Dan and Elden. I think I've been able to attach photobucket images of my current attempt to sharpen the paper knife. Elden, the machine I am using (AV-40) is similar to the bed knife grinding machine that you refer to but on a much smaller scale.
I clamp the knife on the rails, adjust my motor to the desired angle and manually move my cone wheel into the bevel. Once I have the contact I move the jig manually across the rails. Hopefully you can see the images of my two different angle settings. One is at 24 degrees (recommended) but only touches the very edge of the bevel. The other angle is set to 70 degrees which allows me contact across the entire bevel. I can get a good edge with 70 degrees but it wears and chips easily.
Tried to speak to the knife maker but they were less than co-operative.
Thanks again
I may need to load the second image in a separate post

[Elden]

Thanks for posting the picture Mike.
   I have not personally sharpened blades like that so I can't really offer advice. About 25 years ago I attended Foley Belsaw' s sharpening school. I believe they touched on that subject, but I had no reason at that time pursue the topic to a greater depth.
   I have a friend who has been involved in the printing industry. I think I remember him saying they had their power shear blade sharpened. The sharpener change the bevel a 2-3 degrees from the manufacturers stated bevel. He said it didn't work. It had to be redone.
   Have you tried contacting Thorvie? I have heard of those sharpeners in years gone by, but all I had was Foley Belsaw. Thorvies sounded like good machines however.