Bergstrom quickly realized that his toolholder lacked the gripping power to hang onto his cutting-edge endmill, as the thing kept spinning right out of the holder. He took the end mill and ground a flat spot on its side of it's shank, giving the toolholder’s clamping screw a place to bite into. Bergstrom had invented the Weldon flat shank.
When rough machining and removing large amounts of material, Weldon flat holders can be beneficial. Particularly in the Aerospace sector when machining parts such as expensive wing spars, tool pullout can occur which can be very costly and damaging.
When machining materials such as Titanium, optimal machining parameters produce high torque forces on the cutter, Titanium requires an aggressive depth of cut at relatively slow spindle speeds and Weldon Flat holders are ideal for these types of applications.
However, Weldon Flat tools do have their disadvantages. Weldon-style endmill holders by their design push the cutter off centre which creates runout and can drastically reduce tool life. Tool Balancing (or imbalance) can also be a problem.
Standard Weldon Flat vs Advanced Performance Weldon Flat
The Standard Flat (WF) and the Advanced Performance Weldon Flat (AF) are essentially the same, but the length of the Weldon Flat to the cutting tool is different.
The Advanced Performance Weldon Flat (AF) is measured from the flute washout to the flat. This guarantees that the flute or flute washout will not be inside of the holder.
If the flute or flute washout is inside the tool holder, the chips can pack into the holder and cause the tool to break.