Burnt Cutters and Tool Life

      "Burning" or overheating a cutter edge, during grinding or regular use, can significantly degrade the service life of the tool. February 24, 2008

I am doing a study on the effect of run time and knife deterioration if your knives get burnt whilst grinding. Have you carried out any study on this issue? I would very much appreciate any input you may have on this subject.

Forum Responses
(Solid Wood Machining Forum)
From Dave Rankin, forum technical advisor:
Burning cutters while grinding does primarily one bad thing to the tool. This fractures the cutting edge some. Due to the temperature that the tool steel is heat treated at and the temperature reached during grinding, the tool steel's heat treating is generally not reduced. This is most true when wet grinding.

I have done a lot of testing and study on the effects of grind burns as well as run burns. As a general rule you will see some significant tool life in both cases. Depending upon the depth and color of the burn, the resultant of tool life effect differs. For example, if the burn is less than .5mm or .020", the effect is very minimal. If you plunge ground the tool and the burn is 3mm or 1/8" deep, then you can expect to see a reduction of tool life of up to 50%.

What affects the life of the tool more is the heating that occurs during the running of the tool. It is very common for tools to be run slower than they are designed for. For example, a 6,000 rpm machine with 2 knives (1 effective knife cutting, or single knife) needs to run at a minimum of 22-23fpm. Once you go below this point the tool sees a significant temperature increase. Also, if the wood piece stalls in the machine and the tool is allowed to run for 3 seconds, the temperature increases. This temperature increase can reduce the life of the tool up to 70% depending upon the tool design and the type of tool material. Tools that have 90 degree cuts, such as some tongue and groove profiles, can show up to the 70% life reduction.

A few things that can help here include:
1. Use the correct grinding wheel for the tool steel.
2. Use a proper coolant at the proper ratio.
3. Keep the grinding wheel clean.
4. Use the correct rotational speed for the grinding wheel.
5. Clean your machine regularly to eliminate the return of contaminants to the grinding point.
6. Do not stall wood in the machine.
7. Run the machine at the proper feed rate.
8. Use the correct tool material.

When selecting the tool material, think about the length of run. Longer runs may benefit from some of the advanced tool materials available. Tools such as:
1. Diamondback from Centric in WI.
2. Badger from WKW
3. DGK from MSI
can offset the effect of heat in the tool.

Most scientific analysis has been performed for specific applications for customers and the test results are their property and not available for print. From experience, some of the advanced tool steels can increase the tool life up to 12 times.

From contributor H:
The long and short of it is not to burn your knives, and if they get burnt, re-grind to fix the knife. I try never to start with a defective knife, because I know it may work for a while, but it will cause issues for sure!

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