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Setup Tool Length

An-114, Copyright © by Gil Hagiz
Last updated Dec-22-2005
For version 6.01 and higher


While many machine shops use tool room to set and measure tool length there are many others that measure the tool on the machine, manually or automatically.
NCPlus has basic built-in procedures to measure and enter tool length into the tool table, but it is recommended to use the more advanced routines that are provided by the machine files.

Tool Table

Tool data is given in a tool-table. Each tool is identified by its number, holder (if exists), radius or diameter, length, and ball/bull radius if applicable.
The tool table is opened by F12.

Tool Table

Tool data is given as follows:

T    Tool number. 
H    Holder (pot) number. If minus, the tool is deleted. Holder #0 denotes the spindle tool. 
R/D  Selects Radius or Diameter. R or D value: +-9999.9999.
I/M  Inch or MM for tool radius or diameter.
Z    Tool length value: +-9999.9999.
I/M  Inch or MM for tool length.
Ball Ball or bull nose radius, same unit as R or D.
Name Description, up to 25 characters. Not used by NCPlus.

Editing Tool Table


What is Tool Length?

Tool length is entered in the tool table so that the program deals with Z relative to the work-piece and the control adds the tool length to the Z-axis position (tool length compensation).
When tool length is set in a tool room the length is measured from the spindle face. These are called Qualified Tools.
If the tool length is measured on the machine the length value of all tools will be relative to the length of the tool with which the measuring device was set.

A and B heads

The absolute length of the tool is essential for 4 and 5-axis machines with rotary axes A or B in the head.

Regular Machine

For a machine where the tool is always in the -Z direction absolute tool length value is less important because the Z-position is the sum of tool length and Z-offset (assuming that tool length compensation is active).
In short: if we enter a longer tool length we can set a lower Z-offset.
For example, a combination of tool length value of 1" and Z-offset of -1" results in same Z as 100" and -100", regardless of the actual tool length

It is important to remember that if we set the Z-offset with a tool having an arbitrary length all other tools will be relative to that tool.

Ball and Bull Nose

Compared to a face mill where tool length is measured to its face, for these tools the length is measured to the center of the ball/bull radius.
However, for 3D contouring, ball and bull nose cutters require 3D radius compensation, either pre-calculated by the post or dynamically calculated by the control.

Basic Tool Length Entry

To measure and enter tool-length proceed as follows:

Insert Tool Length

This feature lets you insert tool-length automatically into the tool table in two ways:

To insert tool length proceed as follows:

Automatic Tool Length Measurement

Automatic tool length measurement requires a probe (touch or laser), permanently attached to the table, preferably outside the regular working area.
A generic ATLM.CNC utility is available for automatic tool length measurement.
This utility can be modified by the retrofitter according to the type of probe.
It can be used for one tool or for a range of tools if ATC is available.

Like the Z-now in the Insert command the probe's Z-position must be known. Before the probe can be used it must be calibrated with a tool whose length is known.

The ATLM utility can either measure a tool or calibrate the position of the probe.
If the calibration has never been performed it goes directly to calibration.
Otherwise either measurement or calibration is selected from a menu.
For calibration the program uses current tool length, assuming that it is correct, but let you modify it. Whatever you call it, this will be the length of this tool after the calibration is done, and all other tools are later measured from the same zero point as the calibration tool.
In Calibration you jog XYZ so that XY are those of the probe and Z is about 10-40 mm above it.
When ready hit CS to measure the probe and save XYZ for subsequent measurements.
It is recommended that the calibration tool will be the longest tool because if a new tool is entered in the tool table with zero length it will approach the probe from same position as the calibration tool. (Of course an approximate length can be entered).

Once the calibration is done other tools can be measured.
To save time the current length of each tool is used to position the tool above the probe.
The tool is then lowered slowly until it hits the probe, saves the Z-position, and retracts.
The Z-position and the probe calibrated position are used to calculate the new length, which is saved into the tool table.