Tool wear study looks for new angles.

TOOL WEAR STUDY LOOKS FOR NEW ANGLES

Harold Stewart's research into rake and clearance angles could lead to longer tool life.

A research project on tool wear causes and solutions, which was partially funded by a $25,000 grant from the International Woodworking Machinery & Supply Fair - USA (IWF), is moving into its next phase of discovery.

A study on rake and clearance angle, initiated by Harold (Sandy) Stewart for a USDA project at the North Central Forest Experiment Station, Carbondale, Ill., has been completed and is being analyzed by Stewart, now a senior research assistant at Mississippi Forest Products Laboratory, Mississippi State University.

"Once the analysis is complete, we should be able to recommend a range of rake and clearance angles to increase tool life," said Stewart, who has been working on extended tool life solutions for a number of years.

The latest project is an extension of an earlier study, also partially funded by the IWF, which focused on tool wear from machining wood and composites, such as hardwoods and MDF.

That research, completed when Stewart was at the North Central Forest Experiment Station in Carbondale, Ill., investigated the basic mechanisms in tool wear on wood, based on the premise that composite board caused excessive wear. The woodworking industry previously believed these wood products were abrasive. Stewart's research proved that was unfounded and led him to determine tool wear mechanisms other than abrasion in wood machining.

"What we found was that the real culprits were high temperature corrosion and oxidation," Stewart said. "This is different from what we find when machining green wood, which shows regular corrosion because sap conducts electricity - providing electrical current between the workpiece and the tool."

In order for abrasion to occur, a harder material must indent a softer material to form a scratch. Stewart's study showed no evidence of that at the knife edge.

This realization led to a U.S. Forest Service-funded competitive grant which in turn led to a series of studies (in cooperation with Ohio State University) that presumed the main problem was chemical in nature. The follow-up research resulted in several tool manufacturing and tool material manufacturing companies changing their manufacturing procedures.

Two of those firms have each won the prestigious Challengers Award for their efforts. The Challengers Award is presented biennially by the IWF to manufacturers selected by a team of industry experts who judge their product to be highly innovative and beneficial to the industry.

Onsrud Cutter Inc. of Libertyville, Ill., won a Challengers Award in 1988 for its solid ceramic router bit which operates cool and claims a tool life three to 10 times longer than carbide.

At IWF |90, DML Inc. of Louisville, Ky., claimed a Challengers Award for its Golden Eagle saw using Dyanite, a carbide material developed by Vermont American as a result of Stewart's findings. These new materials reportedly extend tool life two to five times over what could be expected in the past.

There are now nine applications for new patents using these types of materials, all a result of Stewart's research which created a need in the industry. The new carbide materials are also applicable to aerospace industry in epoxy graphite composites, non-ferrous metals such as copper and in mining.

Now, Stewart is moving to the next phase of research and development - rake and clearance angle. He is also examining other types of corrosion.

"There are several kinds of corrosion taking place when machining MDF," he points out. "One is sulfidation, a result of a sulfur salt on the tool." Stewart is investigating this phenomenon now.

Stewart said his research "is also aiding in the development of adhesives for the woodworking industry by reducing or eliminating filler that can cause excessive tool wear."

In addition, Stewart's research has led to a comparison of high speed steels for wood machining. "We found that heat treatment is as important as the type of steel that is used," Stewart says. "The industry has been recommending more abrasion resistant grades of steel, but our research proved that the steel itself is not the only problem. Certain grades of steel have been recommended for the wrong reasons. Now tool makers must look at heat treatment of the steel, which gives it its hardness and toughness."

John Zinn, executive director of IWF, said, "This tool wear research has created more technical transference and more direct benefit to the industry in a shorter period of time than in any other government or IWF-sponsored project I have seen."

IWF has funded several research projects over the years including the Flexible Cell Manufacturing study at North Carolina State University.

PHOTO : Sandy Stewart's cutting edge tooling research was boosted by a $25,000 grant from IWF. The research into rake and clearance angles could lead to longer tool life.