Re: reshparpen knifes as good as new?
There are many sharpening options and most will get the job done IF you devote the time and attention to it.
I am a knifemaker and would use my Bader B3 (2x72 belts)for a blade that had never been sharpened or was heavily chipped and mangled.
If you are re-sharpening a dull blade, you (hopefully) won't need to re-create the secondary bevels and or utilize a belt grinder.
I use a Gatco diamond (medium) to clean up the bevels and sharpen the blade. The edge will be functional but not quite shaving or at least not shaving cleanly. Now I switch to a white ceramic on the Gatco (or Lansky though I think the Gatco is a bit more user friendly)
The blade will shave nicely after using the white ceramic stone. I would then usually make a pass or two across a loose buffing wheel (this can be EXTREMELY dangerous)for a literally "hair popping" edge.
(I challenge customers at knife shows to find a blade on my table that wont shave cleanly. No one has found one but if they do, it will be promptly removed and not offered for sale until corrected!)
A few tips-
I suggest a marker to place a few dots along the edge of the blade. This will make it easy to see if your grind angle matches the existing edge. (Otherwise you might not notice until you have removed enough to screw up the edge and or cosmetically blemish an otherwise flawless bevel)
Run both ways (sawing motion) with the Lansky/gatco until you have intersected the bevels (creating a bur). Kill the bur by running a push only motion or by sawing very lightly only a few passes each side before switching sides.
Have good lighting because it will enable you to see mistakes that you would swear didn't exist in average lighting conditions.
Or, the easiest technique to a sharp blade...offer a knifemaking buddy a bottle of something nice in exchange for a razor sharp blade.