Friday, October 10, 2025
Z-Touch Foil Thickness/Deviation Test and Accidental Accuracy Finding
The objective was to find out how consistent the μRepRap was when using an aluminium foil touchplate. Simultaneously an overall difference in height was observed on the Z axis when the X axis was displaced.
A glass slide with UV resin-bonded aluminium kitchen foil burnished in place was placed on the stage and connected to the Z-Touch ground probe. 0.5mm approx of one edge of the foil had been bend right over prior to burnishing, presenting two layers of foil. There is a limitation here in that irregularities in the foil will cause cumulative errors in the height of the second layer of foil.
cnc-js was then used to position the probe over the foil, and Z-Touch data noted at 300μm intervals along the X axis on single and double layers of foil. The separation in the Y axis was 300μm, however it had to be manually adjusted in cnc-js by approximately 50μm due to inconsistencies in the preparation of the foil edge in the XY plane.
Repeated probing of the same point was not possible. The probe point cannot be instantaneously stopped, and deceleration after time of contact results in holes being poked in the foil.
The resulting data were crudely spreadsheeted.
Analysis shows that the difference in probe heights between the one layer and two layer probe points on the X axis was in the range of 10-11.7μm, suggesting that this technique is likely capable of locating initial probe Z height to within 2μm.
Closer examination showed the Z values decreased as X displacement increased at what appears to be a linear rate given the sample size. Maximum vertical deviation was 28.5μm over an X distance of 2.1mm
Concluding, Z-Touch capability is suitable for at least initial probe height determination, and possibly may be sufficiently accurate for subtractive operations. If the probe tip is to be kept within 1μm of the surface, a working area of +/-75μm could be covered without compensating in software.
Note that the cause of this error is unknown. It may be that the stage is slightly tilted, or that tilting the stage will fix the issue regardless. However the Stage can reliably relocate within 50μm when homed, less than the distance for 1μm Z deviation. If the error really is relatively linear it will be possible to consistently compensate within 1μm accuracy - at least on the X axis.
