Grinding Wheel Glazing
Tips to minimize the problem of knife-grinding wheels loading up with metal during use. September 17, 2008
Question
I run a Weinig Rondomat grinder with their premium blue vitrified wheel (54 grit) on M3 HSS. My wheel seems to load up or glaze over in a very short time. Are there any tricks of the trade to keep this from happening?
Forum Responses
(Solid Wood Machining Forum)
From contributor R:
Yes, there are a few things you can do. Weinig makes a Rondor stone wheel dresser just for this purpose. Dress the wheel a few times by hand with this while you're rough grinding. This will help reduce metal buildup on the wheel. Rpms should be at or around 2000 while roughing out a pattern and should be at or around 3000 when finish grinding.
From contributor S:
Make sure that your stone is not oil contaminated, and that what you are sharpening doesn't have any oil on it either. Oil causes the stone to load up with debris from grinding.
From David Rankin, forum technical advisor:
My experience with the premium blue wheel is to run a little slower on the RPM. I generally start at 1400rpm and go up to 2000 if needed. One thing to remember is the harder the knife steel, the softer the wheel needs to be. To make the wheel softer, slow it down. When a wheel is running too fast it will load quickly. Other causes of loading include incorrect grinding wheel vs the steel, plunge grinding, and over aggressive grinding. The proper coolant is also very important. Check your ratio to assure that you have proper cooling action.
From contributor A:
I would just like to add a few things to the good responses above. First, it would help to know when you are getting the loading. Is it when you are hogging or finishing? If it is when you are hogging, then increasing aggressiveness (how hard you push), increasing coolant flow, and decreasing RPM's may help. A trick I use when hogging new knives is to run the wheel into the factory edge of the steel kind of quickly, which can break the glaze usually pretty good. (Yes, your wheel can explode if you do this too hard, so be careful.) Also, try not to let your wheel slow too much from heavy hogging. If it does, let it come back up to speed before proceeding. Increasing the distance from your tool rest to the wheel a hair can help the amount of coolant that can get to the cut. This will help with loading and burning.
If it is loading while finishing, this might just be relatively normal for a vitrified wheel, especially with some of the harder steels out there today. If I have more than about a 5" flat to finely finish, I will usually switch to a CBN (Borazon) wheel. Also grinding wheels will vary from batch to batch from all suppliers. You may have just gotten a very hard batch.
From contributor J:
Just a little tip. When your diamond dresser gets to the point where it needs replacing, keep it. You can do a quick un-glaze with that, without altering the shape of your wheel.
From contributor T:
I like the ceramic grinding wheels. They seem to do a better all-around job with little buildup, but you must find the sweet spot of speed, proper technique, and operator comfort or experience, whichever you want to call it. I have seen some of the best cutting knives ground with the wrong or worst looking wheels we could find. Granted they all do not turn out that way all the time, but I think it's got a lot to do with the operator(s).
