MachPro Spindle Calibration
These instructions apply to all VFDs where the spindle is controlled through the MachPro Control Spindle tab
Why calibrate your spindle?
Does your CNC control need it? Yes - it needs to be accurate enough to meet your needs.
- The rated speeds and feeds for your tools and materials should perform as expected.
- You should have comparable performance across all your machines when running the same spindle speed.
- Accurate spindle calibration enables you to make cleaner and more accurate cuts – improving the quality of your final product.
- Scheduled preventative maintenance should include verification of the accuracy of the system, including the spindle speeds.
This documentation focuses on knee mills as a common example and is adaptable to other machines.
Prerequisites
- Your spindle needs to be configured according to your motion controller's capabilities for spindles.
- The axes need to be calibrated
- Machine zero and soft limits need to configured
- The I/O, particularly limits, need to be connected and working
Definitions
Machines often have both gears and speed controls.
The control needs to know which physical gear is engaged to control the spindle motor for the correct speed. If you use multiple gears on your machine, there will be gear change buttons on the screen, and you can also
The speed control is a set of variable diameter pulleys that provide a variable speed within each gear. We often set this to the maximum RPM. Then we use the VFD to provide the full speed range within each gear.
Set MaxRPM values for each gear
If you do not have a tachometer
Pull down Configure | Control | Spindle tab
If your machine only has one range (no pulleys or gears), then enter the minimum and maximum RPM for the spindle in the Range 1 row.
If you have multiple gears, enter the rated maximum RPM for each gear into the MaxRPM column for each gear.
If you have a tachometer
Use the steps below to set the MaxRPM:
- Set the spindle override knob on the operator control panel to 100%
- Temporarily set all MaxRPM values to twice the labeled RPM on the speed control. This is not to destroy your machine. For calibration purposes this forces the VFD to the maximum hertz output - therefore the maximum tool RPM. We use that to calibrate accurate tool RPM for normal production.
- Verify that the VFD is sending the maximum Hz to the spindle (see next section)
- Run your machine in each gear range with the temporary MaxRPM values you used above. Verify that the VFD is putting out maximum Hz. Record the actual MaxRPM values from the tachometer for each gear range.
- Enter the actual MaxRPM values that the tachometer reported in the spindle tab.
If it is not safe to run this spindle at its maximum RPM, please contact MachLabs for assistance with calibration.
Verify that the VFD is sending maximum speed commands to the spindle
You need to know that the VFD is telling the spindle motor to run at full speed. Assuming the motor is configured to run at 60 Hz, then if the VFD is sending 60 Hz, the motor is running at full speed. You just entered the MaxRPM values into the spindle config. Set your machine for one of the gears and run the spindle at the MaxRPM. You can check the VFD output two ways, and both are equally accurate:
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With the enclosure door open, check the LED on the VFD. This VFD is running at P44.59% of 60 Hz = 26.754 Hz. The "P" prefix on the number indicates the number is a percentage.
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Open a web browser and enter this IP address in the search bar 192.168.208.90. It will open a welcome page for the VFD with two buttons at the bottom. Click the Monitor button and look for the Output Frequency line. This is the same machine running at the same time, and it also reports 44.59% = 26.754 Hz. |
Adjust feedback ratios for TSpeed
The formula is MaxRPM / Maximum Motor RPM = feedback ratio
Pull down Configure | Control | Spindle tab
Check the ID plate on the spindle motor for RPM values. In this image we are running at 60 hertz; so we use the second value: 1735
MaxRPM from tachometer / Maximum Motor RPM = feedback ratio
4485 / 1735 = 2.5850144092219020172910662824207
You can paste the the full value into the spindle FeedBack Ratio field for this range, or just 2.58501
Note: the feedback ratio only adjusts the value in the TSpeed field. It does not have any effect on the actual RPM of the spindle. If the spindle speed reported by a tach does not match commanded speed, then go here: Set MaxRPM values for each gear
Operating the spindle
Use M-Codes to operate your spindle during production: M3, M4, and M5 (relevant portion of the G-Code and M-Code Reference)
You can manually control the spindle with the buttons on your operator panel.
Changing Gears
The gear ranges can be changed from the control by using M40-M45 in your G-Code file. These macros can be used to just change ranges or they can be used to automatically change gears on the machine if it has an automatic gear changer. To shift the machine range 0, run M40. M41 is range 1, M42 is range 2, and so on. You will be prompted to change the gear manually. M40 P# can also be used where # is the gear range to use.
Special situations
Overspeed a spindle motor
If you want to command your spindle motor or grinding wheel to go faster than the base frequency, command the spindle to go max RPM and use a tachometer to measure the speed. Then use the following formula to calculate your new Max Output Frequency (Hb105):
Desired Max RPM * Current Max Frequency / Current Max RPM = New Max Frequency
For example, if your Current Max Frequency is 60 and you measure the spindle runs 1030 RPM but you actually want it to go 1515 RPM, calculate your new Max Frequency as follows:
1515 * 60 / 1030=88 Hz.
Make sure to recalibrate your RPM feedback and your spindle speed as shown below.
Set a spindle to always run at maximum RPM
In some cases, a machine was originally configured to run the spindle motor at full speed, and the gears and speed controls are used to bring the RPM down to the required value. A motor running this way will always generate its maximum torque, which is very helpful when using large tools.
Pull down Configure | Control | Spindle tab
Set your MinRPM and MaxRPM for each gear to the same value.
Set your Max Spindle Motor RPM to the rated value listed on the spindle motor plate.
Leave the FeedBack Ratio values alone as they are no longer meaningful.
The spindle section of you screen can now be ignored. You will adjust your spindle speed entirely through the gears and speed control.
The rest of the spindle configuration above is not needed when it is configured to run maximum RPM.
Auxiliary Spindle MaxRPM
If your VFD is enabled as an Auxiliary spindle (under MachPro settings), set the Auxiliary Control Max RPM to the max RPM of the tool or table. Use this value both in the VFD configuration, and in the sub spindle configuration. Also see this section on sub spindle configuration
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