Grinding Wheels for Carbide Knives

      Advice on grinding wheel choices and grinding techniques for carbide tooling. March 9, 2010

Question
How long can I expect a diamond grinding wheel (4 mm rough) to last? We will be grinding carbide inlay, deep profiles 1/2 inch plus. How long do finish wheels and 2 mm rough wheels last? Please assume that grinding will be done as quickly as possible due to time constraints, so they will be pushed to cut a little faster than some people may push them.

Forum Responses
(Solid Wood Machining Forum)
From David Rankin, forum technical advisor:
If you are grinding carbide inlay, you will need to use a CDX wheel to grind. Depending upon the manufacturer of the wheel, you can expect a wide range of life possibilities. Here is the way I grind carbide inlay in my shop.

1. I rough out with a ceramic wheel. The wheels I use will normally last for about 15-20 inches of grinding (average depth 1/2-5/8").

2. I finish with a CDX wheel, 120-220 grit.

Most grind shops use a roughing CDX wheel, but I have found with the correct rpm and motion the ceramic wheels we use here work well and it saves us money.

When finishing only, we get a life of the wheel that is several weeks of steady grinding. When roughing with a CDX we can see a life from several hours up to a couple of weeks if we are grinding hard. It depends on which make of wheel we use.



From the original questioner:
Is there a rough figure I can plan by for the number of inches I will get using a CDX wheel to rough 1/2 inch to 7/8 inch deep profiles? I get my wheels from Global Tooling. They are cheaper than other sources, but I'm not sure how quality compares.

The ceramic wheels you are describing... I was under the impression from various sources that normal wheels would not work for carbide. What brand are you using? RPM?



From contributor R:
The life of any grinding wheel depends mostly on the habits of each grinder person. Everybody develops their own style of grinding. To say a wheel is going to last any particular amount of time is guessing at best. There are so many companies that make wheels now; which one lasts the longest is anybody's guess.

Although I have a great deal of respect for Dr. Dave's knowledge in this field, I would caution you on using a ceramic wheel to hog out inlaid carbide. The steel cools much faster than the carbide does. This could cause fracturing of the carbide, resulting in loss of product and waste of your time. Grinding carbide is a time consuming process. Trying to rush this process will only cost you more money in the long run. Dave might have a way that works best for him, or maybe it's a new process I have not tried. I am not saying it won't work; but you could crack the carbide without even knowing about it.

I would use a 4mm square pin to hog out and a 4mm CDX wheel to match. The wheel will go square over time, so save yourself the hassle and use a 4mm square pin when hogging. I prefer the Euro style carbide over the inlaid because the inlaid carbide tends to eat your wheels quicker. The place you're getting your wheels from I am sure has different grades of wheels. The better the grade, the more expensive.



From David Rankin, forum technical advisor:
Contributor R is correct about most ceramic wheels when it comes to grinding carbide. I have worked for many years developing different silicon carbide grinding wheels and ceramic blends for different applications.

I have used silicon carbide wheels for roughing out carbide and they work very well but typically do not last very long. The ceramic blend that I use we call the Magic wheel. I use it for HSS and coated steels on a daily basis. Contributor R is correct about the steel and carbide heating at different rates. When I grind carbide inlay with the Magic wheel, I use the following key factors:

1. Heavy clean coolant flow.
2. Do not force the grind; allow the wheel time to remove material.
3. Clean the wheel with a cleaning stick more regularly than when grinding HSS.
4. Allow about 1/8" for the CDX wheel to clean up.
5. Run the wheel at the max RPM the wheel is rated at. For my Weinig, that is 2760rpm.

Remember, the wheel is not going to last as long as it would for HSS.



From contributor R:
Thanks for the explanation. 95% of the carbide that I do is in the Euro style carbide with the micro corrugations - better grade carbide, easier to grind, more flexibility on depths of cut, wheels last longer, but more money. Downfall is, you must be gentle with it or it will shatter. No banging of boards together, no impacting while feeding, no using a hammer (ha ha) when the feed stalls. Whatever works best for your application. There are many choices for what you are doing - all have pros and cons.

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