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"It starts with knowledge..." is more than a motto to us- it's how we do business. Our first goal is to share some of what we have learned about our trade with you.
How to Calculate the Right Chip Load
All good tools require some care in use to work to their best. In your wood shop, cutting edge maintenance is a variable cost that can be controlled by optimizing the chip load of your cutting tools.
The combination of three factors will affect the life of the cutting tools before renewal of the edge (either by replacing an insert knife, or having a fixed tool resharpened). These factors are:
1. The rotation speed of the tool.
2. The number of cutting edges on the tool.
3. The feed rate of the material past the cutting edges.
How Knives Dull
The formation of the wood chip at the cutting edge generates significant friction and flash heat. This sudden and extreme heat acts to form corrosive compounds from resins, glues etc. in the wood. Processed wood, like plywood or MDF, will contain more of these compounds than solid wood, but all timber will contain some. This corrosive action breaks down a cutting edge to what we see, feel and hear as a dull tool.
While a tool is rotating and cutting, the wood chip which is created works as a heat sink, absorbing the heat from the cutting edge. The larger the average chip thickness, the greater the capacity to absorb heat and to protect the sharp cutting edge. You may know that a rotating tool cutting against the feed direction will create a chip that starts thin as the knife edge starts the cut, and finishes thicker as the edge exits the cut. This chip load is measurable, and can be calculated. We use a formula that tells us the average thickness of a wood chip.
Adjusting Your Chip Load
Without yet going into the requirements for various operations (cutting-cross grain versus with grain) or materials (softwoods, hardwoods, and composites), a very small load will generally reduce tool life, while an optimal chip load will maximize tool life. It's a balancing act- more isn't always better. A very large chip load may give good tool life, but will most likely result in a coarse cut and poor surface finish. Finding the optimal chip load will depend on the needs of your project.
If you're planning a new project, working with an Application Specialist can help you calculate optimal chip loads for different types of woodworking applications and wood types before the first cut is ever made- for these professionals, it's down to a science. If you're already working with your tool, here are some helpful guidelines that can help you easily improve your chip loading.
Assuming a fixed number of cutting edges on a tool,
1) Increasing the tool RPM will decrease the chip load, while decreasing the tool RPM will increase the chip load.
2)Increasing the feed rate will increase the chip load, while decreasing the feed rate will decrease the chip load.
The simplest control method on most machines is feed rate, whether the adjustment is made by hand, a power feeder, or the feed control on a moulder. We suggest to keep increasing the feed rate until you notice the surface finish of the material beginning to degrade. This may be due to tear out, roughness, or other reasons. At this point, reduce the feed rate by 10%. If you are now satisfied with the finish, maintain this feed rate. The chip being produced will be large enough to protect the cutting edge for the longest possible time, and you will be maximizing the edge life and controlling your tooling costs.