Thomas Industrial Library

Disregard wheel color when selecting grinding wheels.

Wheel color is virtually meaningless.

Avoid using extremely thin cutoff wheels. (See Fig. 14-18)

F IGURE 14–18 Abrasive cutoff wheels in the .060”–.070” thick range can be fed fairly aggressively. Thinner cutoff wheels, such as the one shown on the right, work well in hand-held spindles.

Abrasive cutoff wheels under a 1 ⁄ 16 9 thick flex a lot under load.Wheels in the .070 9 thick range work well for most parting off jobs. Thinner wheels work well in hand held air spindles for cutting off small pins. Unlike many machinists, I prefer feeding a cutoff wheel down in the “Z” direction with the hand crank rather than moving the stock into the wheel in the “X” direction. I believe you can get a better feel for the amount of load you put on a cutoff wheel if you feed down on the stock.

What does friable mean?

Friable means brittle. Friable abrasives break easily forming new sharp edges. In a grinding wheel there are two things that break down. One is the abrasives themselves and the other is the binder. For best results, both should break down at about the same rate.

What is the difference between aluminum oxide and silicon carbide?

Silicon carbide crystals are harder and fracture more easily than aluminum oxide crystals. Silicon carbide wheels are used to grind hard, brittle material such as carbide, stone and ceramic. The common “green”wheels used in pedestal grinders for grinding carbide consist of silicon carbide crystals. Aluminum oxide crystals are tough and resist fracture. They are gradually dulled by hard material.When grinding pressure is great enough they will eventually fracture to present new cutting edges. Aluminum oxide wheels are identified by the letter “A” and silicon carbide wheels by the letter “C” within the wheel designation shown on the side of most wheels.

What is the difference between vitrified bonding and resinoid bonding.

Vitrified bonding material is glass like and brittle. Vitrified bonded wheels are commonly used in surface grinders. Resinoid bonding material is flexible which enables it to withstand harsh treatment. Resinoid bonded wheels are commonly used in pedestal grinders for off hand grinding.

32. What’s the purpose of grinding on the skew? (See Fig. 14-19)

F IGURE 14–19 Blocks can be set at an angle on a magnet to avoid concentrating heat in one area during grinding which may help reduce heat distortion.

You’ll occasionally see machinists set blocks at an angle on the magnet when surface grinding. Heat and warp are reduced using this technique as a result of the shorter contact time the wheel has with the part and the fact that heat is not being concentrated in one area. The technique is more effective on long thin parts that have a tendency to suck or expand into the grinding wheel from heat buildup.