Friday, September 16, 2011
START WITH SHARP Tools !
Every carver's got his own recipe for proper sharpening. You'll develop your own as you get more and more into carving. That's why I only gave you a 'short list' above.
You'll also find that some tools react well to one abrasive medium, while others sharpen better with another, even though all the tools are of good quality and proper hardness. This is because the tools are probably made of different steel alloys (of which there are many). Let's visit some of the tools and techniques. Read the rest of the article...
1. Bench Stones– Bench stones are used to sharpen straight chisels, skew chisels, and the outside edges of vee parting tools and gouges. I kept it pretty generic in my recommendations: 'bench stones– coarse, medium and fine'. I could have called out grits, or told you to get Arkansas stones, or Japanese water stones, or plain old-fashioned oil stones. This would have done nothing but confuse you.
All sharpening is about 90% skill and experience and 10% personal preference. Start with a set of readily available name-brand stones and learn how to use them. By the time you feel comfortable with your results you'll also have concluded what you don't like about them. Then try something else. Here are a few of the many iterations of bench stone:
a. Water and oil stones– the water (or oil) lubricant helps cool the tool as you sharpen, and mixes with the grit that's generated to form an abrasive slurry which in turn helps the cutting action.
b. Diamond stones– diamond 'dust' of controlled grit size is electroplated to a metal honeycomb which is in turn bonded to a stiff composite backing. Water is used as a lubricant. The honeycomb allows the grit to clear itself while sharpening. Stones come in several grits from med-coarse to fine.
c. Ceramic stones– not good for coarse cutting, but excellent for medium to very fine finish sharpening. These stones tend to clear themselves very well.
d. Cast iron 'stones'– these are a variation of the old machinest's lapping plate. They come with a diamond pattern of grooves machined into the surface (for coarse lapping and grinding) or a smooth top for fine lapping. Oil is the lubricant; carbide abrasive dust is used for coarse work, while diamond dust is used for fine.
2. Slip stones– slips come in various materials and grits: vitrified (kiln-fired clay/abrasive mix), ceramic, diamond, etc. Shapes include radiused and knife edged (both of these in straight and tapered versions), cylindrical, triangular, square and tear drop cross-section. Additionally, there are tapered slips with combo knife edge and radius.
There are also combination inside/ outside tapered radius slips for sharpening the inside and outside of gouges. I personally find these somewhat clumsy to use, and more suited for larger gouges.
3. Strops– stropping (sometime referred to as honing) does the same thing for your carving tools as it does for the barber's razor- gives it that final keen edge. The strop is impregnated with honing oil (light engine oil works too) and abrasive powder to form an abrasive slurry. As with the coarse, medium, fine routine mentioned above, the powders come in graduated grits.
I use the backside of the belting for medium honing and the face for the final strokes. I also use short pieces of belting as 'slips' to hone the inside radius of my gouges.
Additional approaches to stropping are continuous belts which will fit on a 1" belt grinder, as well as laminated leather wheels for your bench grinder.
4. Buffs– buffing is another good way to get that final edge on your tool. Again, whether to use buffing or stropping sometimes depends on alloy of the tool in question. I buff when I can– it's faster! Use buffing compound liberally (available at Sears Hardware outlets among others).
5. Grinding setups– there are several grinding approaches that apply. One thing to remember when using power equipment such as grinders, buffing heads, drill presses etc.– ALWAYS WEAR SAFETY GLASSES!:
a. Conventional bench grinders are a possibility, but I don't use one too often. The only way you can grind the bevel is with a 'hollow' grind, which weakens the cutting edge. You can grind a flat bevel on the side of the wheel, but this is a dangerous approach and doesn't allow good control for an accurate grind. Note: most of these grinders run at 3450 rpm. You're better off with a 1725 rpm grinder, and these are available.
b. Flat belt grinder– this is a viable approach for the bevel of flat chisels and the outside bevel of gouges and vee tools. Use medium to fine grit belts. A word of caution– the direction of belt travel must be going away from, rather than into the cutting edge of the tool.
c. Arbor-mounted grinding wheels or abrasive-impregnated rubber (or composition) wheels running on a drill press. This approach positions the wheel horizontally, unlike the bench grinder, allowing good visibility and control for grinding bevels.
Run at around 400 to 800 rpm for added safety and to keep the tool temperature down. For safest operation, the direction of rotation should go away from rather than toward the cutting edge of the tool. Also, apply only light pressure to avoid breaking the wheel and/or causing possible injury. You'll find that light pressure gets the job done a little slower, but it's a lot safer and will tend to keep the temperature of the tool lower.
d. Wet grinders– These specialized grinders feature a large diameter low speed grinding wheel which rotates in a water trough so that it's always wet. They come with either horizontal (preferable in my opinion) or vertical wheels, and give a very fine finish to the tool. Some even have a second built-in spindle mounted with a rough grinding wheel or a buffing head.
e. Oscillating Honer– This little machine features interchangeable stones (about the same size as a bench stone) which oscillate similar to an orbital or oscillating sander. I saw this machine advertised in the catalog of a company that went "belly-up" before I could order one. (If anyone out there knows where I can get such a machine, please let me hear from you!)