The MCHTOL Command [MLPC]

The MCHTOL command allows the user to define the acceptable machining tolerance, measured as the maximum allowable error from the programmed tool path due to machine slide dynamics. It is valid for contouring machines, hybrid punch/contouring machines, lathes and mills.

The following MCHTOL functions are available:

Exact-Stop Machining Tolerance

Sharp changes of feed rate during corner cutting may result in out of tolerance machining due to roundness or overshoot. This is because the machine motion will lag the actual commanded motion by some amount. Exact stop codes (for example, the G09 code) can be used to decelerate all axes (usually to zero) at the end of the move, providing a good finish at corners.

\textbf{MCHTOL /} \begin{pmatrix}\,\begin{array}{l} \mathit{toler} \\ \textbf{FINE} \\ \textbf{COARSE} \end{array}\,\end{pmatrix}

The toler value specifies the magnitude of allowable error measured in part reference units. FINE specifies that the allowable error shall be minimized. COARSE specifies that a normal amount of error can be tolerated.

High Speed Machining Tolerance

HSM (high speed machining) implies faster than normal cutting, often requiring specialized controllers, machines, tooling and cutting fluids. GENER can support HSM controllers and emulate HSM capabilities on non-HSM equipped machines. HSM processing is restricted to feed interpolation motions only; GENER does not account for acceleration and deceleration on rapid positioning motions. HSM is not supported for polar interpolation, SmartCUT and SmartFEED.

\textbf{MCHTOL / CONTUR}, \Big[\,\big[\,\textbf{FEED},\big]\,\mathit{toler}\,\Big] \; \big[,\textbf{RAPID}\,\big] \; \big[,\mathtt{<\!options\!>}\,\big]

\textbf{MCHTOL / CONTUR}, \begin{pmatrix}\begin{array}{l} \textbf{ON} \\ \textbf{OFF} \end{array}\end{pmatrix}

[FEED,] toler specifies the magnitude of allowable error measured in part reference (CL file) units. This option activates HSM analysis and output for cutting motions. Depending on Icam Post QUEST settings the result will be a modified tape output featuring HSM adjusted feeds (so called emulation mode) or only reported machining time adjusted by machine dynamics (so called simulation mode).

RAPID option is activating HSM analysis for rapid positioning sequences. This mode is available only in HSM Simulation mode that is causing adjusted motion time being reported. This option never impacts tape output.

ON enables HSM at the last specified tolerance. OFF disables the HSM feature.

The <options> provide detailed control over the parameters used to measure and compensate for machining error. These parameters are defined in the post-processor but can be modified on the MCHTOL command to simplify calibration of the post-processor.

\textbf{OPTION},\textbf{0}

When emulating HSM, selects machine acceleration.

\textbf{OPTION},\textbf{1} \; \big[,\mathit{feed,time,toler}\,\big]

Selects linear acceleration and optionally specifies the acceleration rate as feed/time. Toler specifies the allowable difference between the emulated feed curve and the actual machine acceleration, in CL units per minute (this parameter must be specified but is ignored for true HSM machines).

\textbf{OPTION},\textbf{2} \; \big[,\mathit{feed,time,toler,bell}\,\big]

Selects bell-shaped acceleration and optionally specifies the acceleration rate as feed/time. Toler specifies the allowable difference between the emulated feed curve and the actual machine acceleration, in CL units per minute (this parameter must be specified but is ignored for true HSM machines). Bell specifies, in terms of a percentage (0 to 100), the total amount of time not spent at a constant rate of acceleration.

\textbf{OPTION},\textbf{3} \; \big[,\mathit{eaccel,toler}\,\big]

Same as option 2, but specifies the acceleration as a fraction of Earth acceleration.

\textbf{TYPE},\textbf{1} \; {\small \sim}\!\begin{pmatrix} \!,\! \begin{array}{l} \textbf{ON} \\ \textbf{OFF} \\ \textbf{RECALL} \\ \textbf{LINEAR},\mathit{max} \\ \textbf{REV},\mathit{max} \end{array} \end{pmatrix}

Enables (ON), disables (OFF) or resets to the QUEST default (RECALL) the HSM feed control error setting. LINEAR,max defines the maximum change in velocity for linear axes (in CL units per minute). REV,max does the same for rotary axes (in degrees per minute).

\textbf{TYPE},\textbf{2} \; {\small \sim}\!\begin{pmatrix} \!,\! \begin{array}{l} \textbf{ON} \\ \textbf{OFF} \\ \textbf{RECALL} \\ \textbf{LINEAR},\mathit{max} \\ \textbf{REV},\mathit{max} \end{array} \end{pmatrix}

Enables (ON), disables (OFF) or resets to the QUEST default (RECALL) the HSM acceleration error setting. LINEAR,max defines the maximum acceleration for linear axes (in CL units per minute). REV,max does the same for rotary axes (in degrees per minute).

\textbf{TYPE},\textbf{3}, \begin{pmatrix}\begin{array}{l}\textbf{ON} \\ \textbf{OFF} \end{array}\end{pmatrix}

Enables (ON) or disables (OFF) the following error control setting.

\textbf{TYPE},\textbf{4}, \begin{pmatrix}\begin{array}{l}\textbf{ON} \\ \textbf{OFF} \end{array}\end{pmatrix}

Enables (ON) or disables (OFF) the overshoot table control setting.

\textbf{SCAN}, \begin{pmatrix}\begin{array}{l}\textbf{ON} \\ \textbf{OFF} \end{array}\end{pmatrix}

Enables (ON) or disables (OFF) the feed-forward scanning control setting.

\mathtt{'}string\,\mathtt{'}

Activates specialized logic to better estimate the machining time and velocity for true HSM equipped controllers. Valid strings are: SN840D98 for the Sinumerik 840D; FNC15M98 for the Fanuc 15-M; and ICAM98 for the default generic calculations.