What is ProbeApp (Skip this Section if you know ProbeApp already)
The ProbeApp is an add-on for CNC12 that provides an enhanced, very user friendly Touch Screen User Interface for all kind of probing cycles specifically designed for CNC12 driven Routers and Mills. These are some of the benefits of the ProbeApp:
- All Probing Cycles can be called directly from the ProbeApp Button on the VCP (no need to dive deep into the function key structure of CNC12 to reach a probing cycle)
- Probing Cycles can be called directly from a running job file. As an example, the tool change script mfunc6.mac can directly initiate an automated tool height offset measurement of a tool if needed
- Support to touch off a Touch Probe on a Tool Touch off plate that has a pre-travel distance before it triggers. ProbeApp allows to compensate for the pre-travel
- Tool Library Offset Management with automated Tool Height Offset measurement for spindles with exchangeable tool holders
- Support for different type of Triple Corner Finder Touch Plates including the very popular Avid Touch Plate
- Automated Tool Height Offset Measurement supporting single and dual Touch Off Plate methods for collet type spindles. Checkout Guide on how to measure Tool Heights and set WCS Z0 on a Router or Mill with none-fixed Tool Holders most efficiently for more details
- Optimized probing cycles to set WCS 0 for all 3 axes at the center of a stock or any of the corners in one probing cycle (not available with CNC12)]
- Enhanced Probing cycles. As an example if the Z clearance height distance is set too low while measuring a boss, the CNC12 built in boss probing cycle will just error out. The ProbeApp Boss cycle has a retry function moving Z up until it can move across to the other side of the boss. It will only error out if a limit has been triggered during the retry phase or if an unexpected probe trip occurred
- Enhanced Bore Cycle that allows to find the center of a bore by measuring just 3 side in a case where the 4th side is not available for some reason
- Support for Tool Library synchronization between the CAM and the CNC12 Tool Library (there’s a fully automated tool library synchronization between Fusion 360 and CNC12)
- Optional Rack ATC Module for Fork and Drop-In type fix or actuated single racks mounted on any side of the table (Currently in Beta Phase)
What’s new in ProbeApp V3
The main screen hasn’t changed much. The former "Tool Offsetter” cycle has been renamed to “Tool Library Mgr” because that’s what it really is. Most of the new Touch Probe Calibration and Trip Map features are behind the Gear Box icon on the bottom left of the main screen:
ProbeApp V3 now supports the latest versions of CNC12 running on Centroid’s Acorn, OAK and AllIn1DC control boards.
The focus of Version 3 has been on testing and improving Touch Probe accuracy.
These are the functions that have been added (click the link to read the corresponding chapter in the User Guide):
Touch Probe Accuracy
Most manufacturer of Touch Probes will publish the repeatability of their product which is usually within a couple of micrometers which seems to be very impressive but this is only a small part of the whole story if you want to know what actual probing precision you can expect in real machine operations. If you measure the same feature multiple times and you get the same result within a variation of just a couple of micrometers, it really doesn’t tell you anything about the accuracy of the measurement, it just tells you that your machine can repeat the same measuring errors very precisely. If your repeatability is very bad, you will know for sure that there’s something wrong with your touch probe or with your machine but if you would like to know if great repeatability is in fact equal to great accuracy, you have to dig a little deeper.
What impacts the Accuracy of a Touch Probe
Most mechanical Touch Probes used in the DIY space are based on a design like this:
What seems obvious is that the center of the probe stylus ball must be concentric to the center of the spindle in order to give accurate measurements. Most touch probes do have adjustment screws to achieve this very important calibration. It’s also well known that a probe stylus will have some pre-travel distance from the moment the ball touches the surface and the point where the trip signal is actually being generated and this is caused by the geometry of the 3-leg trip mechanism and the deflection of the probe stylus. This pre-travel distance is compensated for by calibrating the probe stylus ball diameter which will always be a little smaller than the nominal diameter of the ball.
What is not so well know is the very important fact that the pre-travel distance can vary significantly based on the direction the probe stylus is being tripped. This again is being caused by the 3-leg design of the trip mechanism that has a significantly different trip force around a 360 degree circle. The required trip force in the area of one of the 3 legs is much higher than in the center area of two legs. Based on my measurements of some popular touch probes, the trip force difference between the lowest and the highest trip force can easily exceed 50g of force. This trip force difference alone can already generate significant probing errors based on the length and thickness of the probe stylus being used. If you would like to know what deflection variation 50g of force can cause on your stylus, plugin your stylus data in this Deflection Calculator and be surprised. This is an error that cannot be easily accounted for with any type of calibration.
Machine Factors that impact Probing Accuracy
Independent of the touch probe itself, there are several machine factors that impact probing accuracy:
- Lead Screw Turn Ratio. Of course the overall probing accuracy can only be as good as the precision of the lead screw. An accurate calibration of the lead screw is essential.
- Back Lash. In order to get the best probing accuracy, Back Lash Compensation should be activated and properly calibrated
- Spindle Tram. It’s very important that not just the spindle axis is perpendicular to the machine bed, but also the Z-axis column on which the spindle moves up and down.
Quick Probing Accuracy Test
Calibrating a touch probe is usually done with a Ring Gauge that has a well known diameter and a Bore probing cycle and if the calibration is done correctly and the machine has no mechanical issues, the repeatability of measuring the diameter of the ring gauge should be within a couple of micrometers. The issue with a Bore cycle is that the first probing cycle is always along the X-axis to find the center of the bore. The actual diameter measurement is always made along the Y-axis. Now if you are curious if you would get exactly the same diameter measurement along the X-axis, you can do a quick test like this:
- Use a Ring Gauge or anything else that has an exact round bore like a ball bearing and run a Bore Cycle
- Write down the Diameter that the Bore cycle reported
- The Slot Cycle should give you the exact same Diameter the Bore Cycle did. Any variance can be considered a probing error that most likely will impact most of your probing results
Get a better Picture about your Machine’s Probing Accuracy
In order to get a good picture about the real world Probing Accuracy you can expect on your machine, ProbeApp V3 has now a Trip Map Generator. You will need a Ring Gauge (or some kind of bore with a well known diameter) and a Center Finder. With the Center Finder in the spindle, you will adjust the X and Y-axis position so that the center of the spindle is exactly concentric with the gauge bore. You then switch out the Center Finder with the touch probe and start the Trip Map Cycle. This cycle will move around the 360 circle of the bore in a configurable step size of 1-45 degrees and will record at which point the trip and un-trip signal occurred, calculating the error between where the trip occurred compared to where it should have.
A typical Trip Map will look like this:
This Trip Map clearly shows the impact of the 3-leg design of the trip mechanism. As most of the probing moves are made along the X and Y-axis, you can see on this map how important it is to find the best possible position of how to place the touch probe in the spindle to average out the trip band error on both sides of each axis. It is also important to make sure the touch probe it mounted exactly the same way for every probing cycle.
In this Trip Map example, the trip map bandwidth (difference between the shortest and the longest pre-travel distance) is 40 micrometers. If an average pre-travel distance is used, real world probing accuracy of 20 micrometers (0.02mm, 0.0008”) can be expected.
Touch Probe Calibration
ProbeApp V3 now comes with a Touch Probe Calibration cycle that will make the calibration process of the pre-travel adjusted probe stylus ball diameter very easy. Normally a Boss Cycle is being used for the calibration process and as explained above, the Boss Cycle always uses the probing cycle along the Y-axis for a bore-diameter measurement. If you’ve done the Quick-Test as described above, you might have determined that the measurement along the X-axis shows an error compared to the diameter measurement along the Y-axis.
The Touch Probe calibration cycle does give the option to calibrate for diameter accuracy by just taking into account the measurements along the Y-axis or you can choose to average out the diameter dimension variation between the X and Y-axis for better averaged overall measurement accuracy:
Improve Probing Accuracy with Precision Probing
If the pre-travel distances of your touch probe differ significantly between the X and Y-axis probing directions, you might consider the Precision Probing Method that is now included in ProbeApp V3.
To activate the Precision Probing Method, the Precision Calibration cycles have to be completed first. Precision Calibration cycles will measure the exact pre-travel distances on the X+, X-, Y+ and Y- separately and will store those values to be used in the Precision Probing Method
After a Precision Calibration has been completed, the measured pre-travel distances for each side will be displayed. The values can be adjusted manually if further fine-tuning should be necessary:
After the Precision Calibration Cycles have been completed, all probing cycles that support the Precision Probing Method will show a “Precision Method” checkbox that can be used to force a Precision Probing cycle:
TP touch off on TT Cycle Improvements
Most Touch Probes (TP) and Tool Touch Off (TT) devices don’t have any significant pre-trip-travel in the axial direction so touching off a TP on top of the TT is not a problem in many cases as it doesn’t matter if the TP or the TT is generating the trip signal as long as both devices are connected at the same time.
If a control isn’t wired to allow the simultaneous connection of the TP and TT, then it needs to be determined which device has the weaker spring load as this will be the device that will generate the trip signal and just connect that device. This can be tested by placing the TP by hand on top of the TT, push down the TP slightly and see if the stylus of the TP moves up or if the plate of the TT moves down. In most cases, the TP will have the weaker spring than the TT.
Now a problem occurs when the TT does have a pre-trip-travel distance and the TP is creating the trip signal. The offset measurement will be incorrect by the amount of the pre-trip-travel which can be significant. As an example, the very popular, wireless DT02 is such a device.
The configuration screen now allows two different options to handle this situation. The first option is to configure the exact pre-travel distance of the TT that will be used to adjust the position when a TP touches off on a TT. The second option is to configure the full pre-travel adjusted TT height and force a manual touch off of the TP on the base surface where the TT is placed on:
Optional Rack-ATC Module (currently in Beta Phase)
The ATC Module is integrated into the ProbeApp-Tool Library Manager and can be activated with a license update. The Rack-ATC Module supports Fork/Finger as well as Drop-In Type racks positioned along the X or Y Axis and on the front, back, left or right side of the table.
With the Rack-ATC Module activated, the Tool Library Manager will expand with a Bin# Column as well as ATC specific Function Keys:
There’s one simple ATC Configuration screen to fill out. The Rack-ATC module will auto-generate all script files needed for proper ATC operations
Stay tuned for more updates on this ATC-Rack Module.
How to get the ProbeApp V3
At the moment, ProbeApp V3 is still a non-profit, donation based product. You can make a donation in the amount that is reasonable to you for this App.
Contact me at firstname.lastname@example.org if you are interested in the ProbeApp.
If you have any questions or comments, please post them in this thread for everybody to see.