At the May 1998 meeting we had a presentation on sharpening by Charles Cooley. We have had Charles present at our meetings in the past and he has always been very informative. Some of us have had the pleasure of visiting his shop and seen the hundreds of hand planes that he has tuned up and ready for planing. Some of the planes he bought at flea markets and some he has made. He has planes for every use you could imagine. His tools are sharp enough to shave with.
When sharpening chisels the following angles are suggested:
Sharpening tools consists of grinding the bevel and honing the edge. When grinding, "thou shalt not burn the steel". Use the right stone and grit, the right angle, and grind the whole bevel, not the edge.
Charles advised us that most grinding wheels that come with the cheaper grinders should not be used in sharpening. The wheels should be 8" to 10" in diameter and run at about 1700 to 1800 RPM or slower. Most of the cheaper grinders have 5" to 6" wheels and run at 3450 RPM. The Cheaper wheels are carborundum, which he does not recommend for tool sharpening. Charles recommends the 120 grit aluminum oxide wheel (white) because the binder that holds the aluminum oxide together is soft and as you grind it breaks off keeping the tool cooler. It is also a good idea to have water flowing over the wheel, as this also keeps the tool cooler. Delta has a wet/dry grinder that has a 2" wide wheel that is 10" in diameter. This type of wheel is better because it has a speed of 70 rpm. The TOMEK grinder also has a 2" by 10" wheel that has a speed of 90 rpm. Both these machines allow you to use water in the trough that will keep the edge cool and prevent "bluing".
After grinding, you can use a water stone to hone the edge. Water stones come in grits from 250 to 8000. You can start with an 800 then 1200 then 4000 and finish with 6000 or 8000. You only have to do a few strokes on each stone. Once you have honed a good edge you can maintain the edge with the 8000 stone. The 8000 stone will give you a mirror finish on your tool; this is what you want.
There are also diamond honing stones that you can use. These stones will cut faster than the water stones and will not hollow out like the water stones will. The extra-fine diamond stone is about equal to 1200-grit water stone. You can hone on the extra-fine diamond stone then finish on the 8000-grit water stone. This method will be faster because the diamond will cut faster The polycrystalline diamond honing stones seem to work the best. They are the ones that are on a 3/8" milled steel plate
After the 8000 grit Charles strops the edge on leather. The bevel on his tools looks like a mirror. One way to check to see how sharp your edges are is to offer the tool very carefully and gently on your thumbnail. The lower the angle you can achieve between thumbnail and the sharpened edge, the sharper it is. Remember that the back of the tool must be flat.
As always, Charles gave an informative presentation with demonstrations of sharpening a few tools and showing how well they perform when properly sharpened.