Diamond Wheel Wear while Grinding Carbide Knives

Diamond grinding wheels can fail prematurely for different (preventable) reasons. April 11, 2008

We have a diamond wheel which completely wore out halfway through a carbide knife. We are new to grinding carbide. What could have caused this? I realize that at $300 a wheel, they should last longer, so what did we do wrong?

Forum Responses
(Solid Wood Machining Forum)
From contributor R:
Many things could have caused this to happen. The things that come to mind first are too aggressive grinding and not enough coolant, and maybe the wrong RPM while grinding. While grinding the carbide you should be at 3000 RPM. Slower RPM will wear the wheel down. There should be no spark while grinding carbide and each pass you should not be taking more than .004". Clean the wheel with a cleaning stick to eliminate buildup of deposits. If you're grinding inlaid carbide, you will need a combo wheel. This type of wheel grinds both steel and carbide at the same time. If you're grinding the euro style or bak pak style, you will need to grind the backer like high speed steel and the carbide with a diamond wheel. I use a 4mm for roughing and a 2mm for finishing. Back grind angles for Euro or bak pak carbide should be around 18*. The backer around 23*.

A few notes about the backer and carbide two knife system. While grinding the backer, use 2mm pin and 4mm wheel. This will distort the backer, leaving 1 mm on each side bigger than the carbide. This is to allow for wood chip flow on the carbide. When grinding the carbide, use a 4mm square pin to rough and a 2mm round pin and wheel to finish grind.

From contributor C:
Were you using a roughing wheel? There are two grades of diamond, one for roughing out and one for finishing. I can imagine that a finishing wheel wouldn't last long at all if used to hog out a profile.

As contributor R said, keep an eye on the RPM of the wheel - it needs to be much higher with diamond than it does with a HSS vitrified wheel.

Does your grinder have the option of reversing the rotation of the grindwheel? If it does, you'll find you get a better edge if you use the reverse on the finish grind only. I personally don't use it for the roughing out, as it has a tendency to snatch upwards.

From Dave Rankin, forum technical advisor:
I agree with contributors R and C and will add a question. What concentration of diamond were you using?

There are three basic types of superabrasives:
CBN for grinding steel
DIA (diamond) for grinding carbide only
CDX (combo) for grinding carbide and steel at the same time.

My first thought is that you may have been using a CDX wheel for a DIA application or a DIA wheel for a CDX application.

Another problem that I have had with superabrasives is the type of rim that the abrasive is attached to. I use steel rim wheels only. I have had problems with flex in aluminum wheels and this has caused premature wear.