Thanks, Terry

Cutters are the most difficult tools to sharpen. I have written a detailed article on the topic, but we are not supposed to advertise companies and unfortunately, my articles is on a commercial website. I am going to assume you have a proper stone and that you are familiar with sharpening other tools, such as shears.

Sharpening concave cutters

For curved blade tools such as knob or concave cutters it's a little harder. This requires a little more experience. I certainly don't recommend practicing your skill on an expensive pair of cutters, but you can certainly do this yourself. Take your time and look closely at how your cutters are made before you begin.

The first step in sharpening concave cutters is to use a cylindrical stone to sharpen the interior surface. The objective is to remove as little material as possible with your stone while keeping the original bevel.

Don't try to change the angle or fix your tools bite. The two sharp edges on your cutters should meet exactly. One edge should just barely overlap the other so that when they snap through a branch one edge will not jam into and dull the other. They should close so precisely that you cannot see any light between the edges when they are closed.

Take your time and sharpen the inside until you can feel a burr. Once you feel a burr, it's time for the water stone. Lightly roll the outer part of you concave surfaces against the stone, one side at a time.

All your trying to do is smoothes the surfaces and remove the burr. Again, Do not attempt to correct the "overbite" of concave tools. After sharpening, apply light coating of oil to prevent your tools from rusting.

Hoppefully this helps a little. Start slow.

Others have written articles on the topic and i'm sure you can find them with a quick google search. try searching for something like "Staying Sharp In Your Bonsai Garden"

Ashley

Anyway, I had a pair of concave cutters and some rugrat used it to cut wire. Well this left a huge divit in both blades. I broak out my japanese slip stones. The ones I have were about $5 each, they measure 6x2". One long edge has a large curve and the other has a smaller curve. I have 3 of them, 800, 1000 and a 1200 grit.
I would just sit and widdle or file away the cutting edges to remove the divit. You will have to stop, open and close the jaw and hold it up to light to see where your going. You need to look where the jaws are touching and determin where to file down to make it better. Once I got the shape back, wich took about 2-3 hours over a few days I went to a higher grit. Kept going, not changing the shpae now but getting the edges back. This took about just as long. Then went to the final grit and polished the edge very nicley, this only took about 1/2 hour. Its about as sharp or a bit sharper than new.
I think the best way to do this is to know your tools. I like to see the mechanics of what I have so when I bough the tool new. I would watch at all angles when cutting something. I knew how this tool cut, with that, I was able to reshape it back to what it was after the damage.

Bottom line, have patience with what your doing. If you start to feel rushed, put it down till tomorow. Look at it again and continue.