With GibbsCAM 11.3.x and later, there have been changes to how the system handles turning tools on machines that are capable of rotating the tool into different orientations.
This article covers issues that these new features expose relating to touch off points and tool program points.
Rotated Turning Changes
GibbsCAM v11.3 changed how turning tools are defined and used on machines with rotary axes.
Prior versions of GibbsCAM required a user to create a separate tool tile for each cutting orientation that a tool would be used in. The system treated these as separate tools, each with there own settings (such as offset registers).
v11.3 moved the "cutting B" field from the tool definition into the process. This allows a single tool tile to be used in any number of cutting orientations, simplifying tool setup for these customers. The tool dialog still contains a "Setup B" angle that tells the system what orientation the tool was when it was touched off, as well as what orientation to interpret any tool offsets in.
Tool Tip Confusion
The vast majority of turning posts are setup to output a posting program point to the rotated tool tip. For tools that do not rotate, this is the touch off point shown by the cross in the image to the right.
The touch off point is computed once for each tool tile based on the setup angle and tool orientation selected.
Tool Tip and rotating tools
This touch off point is attached to the tool, and when the tool rotates, it will rotate with it. This means that when using the Rotated Tool Tip output mode in the post processor, with a tool that is cutting at an angle that is different from the setup angle, the touch off point will be at a different location. The rotated tool tip output mode assumes the CNC machine has applied the same tool rotation to the touch off offset that it did to the tool using some kind of dynamic compensation mode (Such as TCP). The single tool tile only has a single tool offset register, so the same offset must be used for all orientations of the tool. The image below illustrates how the touch off point will rotate with the tool and how GibbsCAM's compensation for contact point can make the touch off point appear to be "inside" the part. This is requred because the touch off point is physically outside the tool and the actual tool radius must be compensated for in order to get the correct final cut dimensions.
Other Output Modes
Rotated Tool Tip as an output mode is not correct for all machines. Some machines that do a full tool radius compensation do not use a touch off point, they take input to the tool center. This allows the CNC to dynamically compute the full offset based on tip radius and orientation. Machines that require this type of input should use the Rotated Tip Center output mode.
Some machines require the type of output that was generated by versions prior to 11.3, a separate and unique touch off point for each cutting orientation. This type of output can not be supported by using a single tool tile in multiple orientations. GibbsCAM only supports a single touch off point for each tool tile, not one for each use in an operation. These types of machines must continue to use multiple tool tiles, one tile for each touch off needed.
Understanding Machine Requirements
Due to the number of new options available to customers, it is important that post developers understand what type of input the CNC machine needs when turning tools rotate. Once a developer understands what the required input is, and how it relates to the tool geometry, they can select the correct output mode in the post.