Help a sharpening dullard

I've been trying to sharpen my 6" jointer blades with the the sandpaper/scary sharp method as described here:
http://www.taunton.com/finewoodworking/pages/w00003.asp
but for the life of me I cannot get them sharp. If anything they are duller than they were when I started. I have a set of Hirsch chisels that I use the same technique on and they will get sharp - very sharp. But after going through the grits 80, 120, 220, 320, 400 the jointer blade are just plane dull, heck the factory square edges are sharper than what I did.
I hold one blade flat along the glass with the front bevelled edge acting as a guide for the one I am trying to sharpen. As near as I can tell the blade stays in this position - I don't let it rotate on edge. In the article they don't even use a guide, they just "feel the beveled surface on the paper". I even mark the edges with a marker to make sure surface wears evenly. How long am I supposed to stay on each grit - seconds? minutes? hours? Is it even possible to sharpen jointer knives this way? I'm doing something wrong I know but can't tell what.
Dukester
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Is there any chance you have carbide jointer blades?
David
Dukester wrote:

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I suppose it's possible. How would I tell?
They are factory blades from a Ridgid 610 jointer. The manual (page 23 of http://www.ridgid.com/CatalogDocs/jp0610_6442_eng.pdf states that they can be honed on an oilstone and reground.

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If they are the original blades, they are not carbide. I'd have to say the problem is just technique. I spent a lot of time getting a couple of jointer blades sharp because I found holding them at the correct angle was problematic. I have no trouble with my chisels and plane blades because I've got a honing guide.
It should only take a few minutes per grit.
David
Dukester wrote:

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I just got an old jointer from my father in law; never used one before. But I do know what the terms mean. Honing and regrinding are entirely different. Regrinding means you take the knives to a sharpening place where they "grind" the cutting edge. Honing, means you leave the knives in the arbor, wrap paper around most of the the stone so that it won't ruin the table, raise the table and move the arbor so that the stone fits flat on the knife bevel, and slide the stone sideway across the knife.
I suggest you go talk to a saw and knife sharpener (a real one that uses expensive tools). It cost me $6.60 to grind my three 4-3/8" blades which were in terrible shape. I don't see how you could grind the cutting edge parallel with the back unless you have a highly accurate jig.
Dukester wrote:

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you roll them a bit, they'll end up dull. Before I got the Makita, I cut a saw kerf in a board at the proper angle to make the bevel on my blades parallel to the bottom of the board, then mounted a cone stone in my drillpress, sliding the blades back and forth, then adding a piece of paper underneath as a shim did them very well. I believe I picked the idea out of FWW tips section. Lapping the wire edge off completed the job nicely.
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Dukester wrote:

A local sharpening shop does a really nice job on mine for $0.90 an inch. I have two sets, when the new set goes in, the other goes to the sharpener.
I've gotten good at chisels of all types, plane irons, etc... but find the cost of a pro doing my jointer and thickness planer blades well worth it. They usually return better than any new set I've ever purchased.
Barry
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Think about something here. You have a jointer to give you accurite edges in a timely fashion. The wetstone or other hand grinding operations are always going to be a problem in attempting to sharpen jointer knives as all three edges need to be hitting the wood flat and square as well as sharp If one blade is a little longer you are not going to get a good edge.
The solution is easy send them to be sharpened. This is an easy proposition to a tool and die maker with a surface grinder, so the charge is nominal and the job is perfect. The tool maker will set the blades on a fixture that will hold them precisely and he just grinds them untill they all match with a machine that can move the grinding wheel down in increments of 1/10,000 of an inch at a time. You can never come close to that kind of precision by hand.
The wheels are also not the kind of wheel that you find on a bench grinder. They are designed to be dressed with a diamond to flatten the face of the stone leaving extremely sharp edges. The surface grinder also grinds under a flood of coolant so that all of the heat generated in the grinding process is removed. (This is a really cool machine.)
Do your self a favor and don't waste your time dinking with the jointer knives.
--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
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Roger Shoaf wrote:

...
...
Yeah, buy yourself one of those precision grinding gizmos! That sounds like a machine no good dorker should have to do without. :)
(Put it right next to your 16" TS and 12" jointer. :) )
Cool description. I love a good tale of a ridiculously expensive machine I'll never be able to even dream about owning in my wildest fantasies.
--
Michael McIntyre ---- Silvan < snipped-for-privacy@users.sourceforge.net>
Linux fanatic, and certified Geek; registered Linux user #243621
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