Operator`s manual

Advanced Haas Mill Programming Techniques Training Manual Page 25
Arc On, Arc Off with Tool Compensation
When finish machining a part a rule of thumb is always leave equal amounts of stock on all features in
milling or turning. The reason for this is because of tool pressure. Tool pressure is the amount of force that
is generated on a tool when it is cutting. A deeper cut creates more force on the tool than a smaller cut.
Tool pressure has a tendency to deflect the tool away from the part. The larger the tool pressure the larger
the deflection of the tool. If there is more stock on one feature than another the tool is deflected further
away from the part creating possible out of tolerance conditions. Another aspect is that once a tool
becomes dull the larger the tool deflection. Out of tolerance conditions may develop as tools becomes
duller where they may not be seen with new sharp tools. Because of tool deflection it is prudent to evenly
distribute tool pressure throughout a single machining operation. To accomplish this, a roughing pass may
be used so that the same amount of material is left for the finish pass.
When finished machining a contour or pocket, witness marks or slight gouges occur when the tool ends at
the start position. At the end position the tool is not cutting material, no tool pressure and therefore there
is no tool deflection. Because it is not deflected it will cut off more at the end point than when travelling
around the part cutting a certain amount of stock off. Below the tool ends up where it starts when using
G41 cutter compensation for contour cutting the outside of the part below.
Using an arc on the part and an arc off minimizes this effect. When the tool arcs on to the part it slowly
cuts off more and more material until the full depth of the stock is reached. The opposite happened when
it arcs off the part. Less and less material is removed until the end position is reached. The approach and
retract movements are smooth and less likely to leave a witness mark.
When manually programming an arc on and arc off the radius of the arc must be greater than the radius of
the cutter. It is easier to program a 90 degree arc. On the next page a ½ inch arc and arc off is
programmed starting ½” away from the part.