Yes, they are not cheap, but they make finishing tasks in metal carving and jewelry work much faster and better. I look for them in boxes or 100 on ebay at good prices.
First, some nomenclature - like Kleenex and Xerox, people tend to call all rubberized abrasive wheels Cratex, when only the ones by the CRATEX company are truly Cratex. The others may be just as good, or not. I have always preferred the real Cratex. If not in a yellow box and marked Cratex, they may or may not be the genuine thing. This is the problem with people who pack them in bags of a doze. If the price is crazy good and they look OK, go ahead and try a few dozen, but at $100-150 a box for the 1X1/4" wheels .... I want to see the original CRATEX box.
The grades are C,M,F,XF. IIRC, the colors are Green for coarse, dark brown for medium, reddish brown for fine, and light green for X fine. There are other colors used by different manufactures of abrasive wheels, so look at the listings to see what the grit or grade is. Coarse is about 50 grit. medium is 80, fine is 100-120, and X fine is around 180 ( IIRC). That sounds rougher than you would think, as they leave a very smooth finish compared to a grinding belt. A fine grit will leave metal ready to buff, and XF will be shiny.
For carving on steel, you want Small Wheels ( sizes 1" and below) in coarse grade and the medium grade. Fine is nice to have if you can get it at a good price, but you don't need it. After you do some work, you will find the grits that best suit your steel type and work methods.
If they mention hardness, the grade you want is HARD. The soft wheels won't last a minute on steel, and medium isn't much better.
The most useful size is the 1" X 1/4" straight (flat) edge wheels. I prefer the 1/8" hole and 1/8" shank mandrel, as you need the heavier mandrel for working steel. If you can get a good deal on a box of wheels with the 1/16" hole, get them and drill the hole out with a 1/8" drill. The stock number I use is Q88-2, which is the 1X1/4 wheel with a 1/8" mounting hole. On gold I use M and XF most, on steel, I use C and M most. Get three or four of the 1/8 X 1/8 mandrels and keep several wheels of different worn diameters in the box. Switch off as needed for grinding in various curves.
Sometimes you can find a real deal on a different size, like a 5/8" wheel, or knife edge. If the price is right, get them, as they all have uses. The knife edge wheels wear down pretty fast and become flat edge wheels.
Also not cheap, but very useful for doing the knapped effect are the large Cratex wheels. They come in 1.5" to 6" and can be mounted on a arbor or small grinder. Most folks just put an shaft adapter arbor on a 1/4HP to 1/2HP motor and mount the wheel. I have a coarse and a fine 6" wheel mounted on a cheap HF bench grinder with the guards removed. The 6" wheels cost between $50 and $100, but the smaller ones start at less than $10. They will last a very long time if used with care. For general shop use, I like the 1" wide by 6" wheels. The smaller and thinner wheels are good for doing the clean-up in knapped blades. These size wheels can occasionally be found really cheap on the auction sales sites.
