What's new
What's new

Recommended grinding wheel for sharpening HSS bits

Jeremy

Hot Rolled
Joined
May 19, 2002
What grit and style of wheel do you guys recommend for hand forming and sharpening HSS lathe bits? Bit's I'm using are 5/16". I have an old bench grinder that should do the job, just need the right wheels.
 
Which grinding wheel? Most any aluminum oxide abrasive wheel suited for off-hand grinding will work just fine.

Chances are your grinder was furnished with two wheels; one an A-46-O and the other A-60-O or P. These are as good as any providing the right balance of hardness and cutting ability for general off hand tool grinding as they have for generations.

The secret to grinding high speed steel is to remember that HSS is abrasion and heat resistant. These two properties make it resistant to grinding.

A grinding wheel is a cutting tool and the abrasive grains are in effect its cutting teeth. If the abrasive grains are dull from use they wear more then they cut causing friction thus heating the tool.

Look closely at your grinding wheel in grazing light and note the many shiny grains like little sequins. These are dull grains that need to be dressed off. You sharpen a grinding wheel by dressing off the layer of dull grains exposing the fresh sharp ones underneath.

Efficient grinding is accomplished with a clean, true, properly dressed grinding wheel. I know guys who spend hundreds of dollars on "low speed" grinders, exotic wheels, and so on thinking that somewhere there's a magic solution to off-hand grinding that doesn't require work. They're deluded.

The solution is a diamond dresser mounted in a handle. The dresser is a small 7/16 shank cluster diamond available from MSC for about $30. Mount it in a 7/16 hole drilled axially 1 1/4" deep in a piece of 7/8" dia barstock with a 10-24 setscrew cross drilled to hold the dresser in place. Make it a 16" long or so. Call this item a hand shank. Put a bicycle hand grip on it if you wish.

Don't even consider a star dresser or the so-called "abrasive truing sticks" for a grinder dedicated to sharpening HSS tools. the star dresser leaves a rough surface suited for soft steel and the truing stick glazes and dulls the abrasive grains it exposes. Use only a diamond dresser.

To dress the wheel, start the grinder, hold the hand shank firmly and position it in the tool rest so the diamond is presented to the wheel periphery. Start a side to side traversing motion taking about a second to cover the width of the wheel. Feed slowly in until you contact the wheel as you traverse the dresser. The wheel will rapidly dress away leaving behind fresh sharp abrasive grains.

Wear eye protection and position the shop vac hose to catch the abrasive so it doesn't fly all over the shop. By the way, your grinder should be isolated from the machine tools. The grit and dust are severly punishing to machinery.

If a grinding wheel is sharp you can sharpen a wood pencil on it without scorching the wood.

Plain vanilla M-2 ot M-4 HSS sharpens readily on a well dressed wheel. The harder more durable alloys may be much more difficult. I've had to dress the wheel every few minutes when grinding delicate tools from T-15.

Yes your grinding wheel will wear away with every dress. Grinding wheels are consumable items like hacksaw blades and sandpaper. Get used to buying a new wheel every now and then.
 








 
Back
Top