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| A Low Profile CNC Tool Height Setter. |
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| Tweakie:
My existing ‘touch plate’ has served me well over the years but as this relies on electrical contact between the ‘tool’ and the ‘plate’ it was just not possible to use it with the diamond and ceramic tipped tools I now have occasion to use. Something a bit more sophisticated was required and an active, ‘probe type’, low profile, tool height setter seemed to be on the cards. This is my first prototype and as luck would have it, works just as intended. It is still work in progress, as testing is on-going, but so far so good. An internal contact ring rests on 3 contacts under spring pressure and the overall height of the completed probe entered into my probing script as ‘plate thickness’. Any downward movement of the plate breaks one or more contacts for the G31 detection. Although the contacts are ‘normally closed’, the transistors invert this logic so the probe output is normally a weak High and only taken to a strong Low (GND) when contact is broken. The amount of movement necessary to operate the probe is incredibly small but it is largely dependant on the flexibility in the top cover and operational movement is currently smaller than two of my Z axis micro-steps. It does not seem to make any difference if the plate movement is parallel (centre contact) or tilted (off-centre contact) there is never any contact bounce – it either makes contact or it doesn’t. This type of ‘contact-break’ detection is used in some of the Baumer Electric limit switches – OK they have far more accurate manufacturing facilities than I have but they claim 1 micron repeatability. My Z axis only moves in steps of 0.001875mm (although the accuracy of micro steps is a long standing point of discussion). Jogging downwards with the axis set at 0.0010mm step size and zeroing at the exact point of electrical contact a further 2 steps were required to trigger the probe with the Z axis DRO now reading -0.0037mm. Of no practical purpose this 0.5mm text was engraved to a depth of 0.05mm just to see if it could be done. Tweakie. |
| PekkaNF:
Hmm. Looks good. Any chance of a photo of contacts/mechanics? How do they relate to those three screws wired to two transistors? PekkaNF |
| Swarfing:
Tweakie Looks great and would be very interested in the drawings and BOB if your willing to share please? :drool: |
| Tweakie:
Thanks guys. Once I have finalised the design and have completed a few more tests I will post the full constructional details, drawings etc. for those who wish to make this device (or something similar). Here is a pic of the completed contact ring assembly and another of the machined parts. Tweakie. |
| philf:
Hi Tweakie, The Height Setter looks very nice. :thumbup: One question - Is it failsafe? (If a wire breaks does it already think it has sensed the tool?) How much overtravel have you built in? Mine (which also doesn't need continuity through the tool) isn't very low profile (- about 30mm tall) uses an opto-isolator to pass the signal to the breakout board which doesn't invert the signal. If I don't plug the setter in or don't turn it on then the Z-height setting routine doesn't run. :beer: Phil. |
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