Grinding Wheel Selection

[DaveL]

I posted the following question on the WoodCentral Woodturning forum and am cross posting it here in hopes of exchanging data:
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I wrote a tool sharpening lesson for our woodturning club about 6 months ago and I was amazed at the lack of information available about grinding wheels and picking the right one for sharpening HSS.

While researching the subject I visited the Norton and Radiac websites and both sites state that the wheel speed is a determining factor in selection of the wheel hardness. Unfortunately there does not seem to be any guidance stating which harnesses should be used for different speed grinders.

1. Can someone explain the relationship between wheel speed and hardness of the wheel bond and how to select the proper wheel for a specific speed grinder?
2. Has anyone performed testing of grinding wheels on slow speed grinders?

Thank You,
Dave
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Thank You,
Dave Lauffenburger

 

[MichaelMouse]

Easy. Newton says the energy of collision divides, so 1/2 MV^2 is available to slap the wheel. Softer bond breaks easier. Faster speed breaks same bond easier still.

Tradeoffs include the oft-mentioned "friability" factor giving a continuously fresh grind surface versus stone life. New ceramic AlOx have harder bond for longer life, while allowing the grit to fracture rather than fall away. At a price and a half.

Friction is mostly a function of pressure, so with the same grinder/wheel, pressing harder will also increase heat. I suppose a really loaded stone surface might contribute, but it doesn't keep me up nights. Dress the wheel if it bothers.

Makes not a lot of sense to me to buy soft wheels designed to protect against ham-handed grinding on carbon steel for the purpose of grinding HSS, especially on slow-speed grinders. I use the green SiC wheels from Woodworkers' Supply. Make a nice edge, outlast the white Nortons fivefold. Of course, it was only after a number of years with the hard gray Nortons that I took the flyer on the white ones. Learned fast, though.