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| A Low Profile CNC Tool Height Setter. |
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| Noitoen:
You can use a piezzo disc from a buzzer as a sensor mounted on some spring suspension just to act as a little over travel damper, with a little metal disc glued to the piezzo. Anything that touches the sensor will generate a voltage spike to be amplified and generate the home reset pulse even if the tool pushes the damper springs. |
| Tweakie:
Hi Phil, Good points you have raised and thank you for your comments. Yes, I have incorporated what I consider to be ‘fail safe’ characteristics but these are not totally 100% foolproof and I am sure could be improved upon in the light of experience and others suggestions. Currently the probe is connected to the machine with a 3 core cable and miniature jack plug, there is no on/off switch and it is always active. If either the Positive or Ground wires were cut (or the probe not connected at all) this is detected (at the breakout board end) and the probing script reports ‘probe already grounded’ and no Z axis movement will be made when operating the ‘auto tool zero’. If the Sense wire is cut the script runs as normal but the contact plate then over travels onto one or more of 3 ‘over travel’ mechanical switches. This is sensed (at the breakout board end) and in turn, triggers an ‘immediate stop’ by activating a machine limit. The over-travel switch feature, operating a machine limit was, I must admit, not part of my original design but has subsequently been added (as a result of a suggestion made on the Artsoft forum) to protect the tool from damage in the unlikely ? event that the G31 command (or associated probing script) goes wild. My available ‘over travel’ distance is currently 2.0mm but this will be reduced to approximately 0.5mm (before the over travel switch is contacted) when the updated switch PCB is fitted. As always, this is an ongoing project and I am learning as I go but so far so good. Tweakie. |
| philf:
--- Quote from: Tweakie on June 18, 2012, 01:41:59 AM ---Hi Phil, Good points you have raised and thank you for your comments. Yes, I have incorporated what I consider to be ‘fail safe’ characteristics but these are not totally 100% foolproof and I am sure could be improved upon in the light of experience and others suggestions. Currently the probe is connected to the machine with a 3 core cable and miniature jack plug, there is no on/off switch and it is always active. If either the Positive or Ground wires were cut (or the probe not connected at all) this is detected (at the breakout board end) and the probing script reports ‘probe already grounded’ and no Z axis movement will be made when operating the ‘auto tool zero’. If the Sense wire is cut the script runs as normal but the contact plate then over travels onto one or more of 3 ‘over travel’ mechanical switches. This is sensed (at the breakout board end) and in turn, triggers an ‘immediate stop’ by activating a machine limit. The over-travel switch feature, operating a machine limit was, I must admit, not part of my original design but has subsequently been added (as a result of a suggestion made on the Artsoft forum) to protect the tool from damage in the unlikely ? event that the G31 command (or associated probing script) goes wild. My available ‘over travel’ distance is currently 2.0mm but this will be reduced to approximately 0.5mm (before the over travel switch is contacted) when the updated switch PCB is fitted. As always, this is an ongoing project and I am learning as I go but so far so good. Tweakie. --- End quote --- Thanks Tweakie, Mine has an overtravel of 2mm but hopefully I never need to worry about it. In operation I can't see any movement at all. When I first set mine up I didn't realise the significance of some of the numbers in the macro and entered a number less than than the height (then 30mm) of my height setter. The 2mm of overtravel soon disappeared followed by the "ping" of another 2mm carbide cutter as it tried to bury itself in the top of the plate. :doh: After cleaning up the plate the setting gauge is now only 29.74mm! :beer: Phil. |
| AdeV:
Ooh, eck, I've got all this to come, haven't I? Luckily, my controller is so old, it doesn't have a tool height setting program; I do have a rather accurate handwheel thingy though, so I can manually set tool heights without having to worry about overtravel. How repeatable are microswitches? I'm guessing they must be reasonably repeatable as my machine uses them as both limit switches, and reference marks, when setting itself up. It had occurred to me if they were good to, say, 0.01mm, they'd make an ideal tool height setter without having to worry about conductivity. |
| HS93:
Ade would this do, Knowing you you probably have half a dozen already http://www.machine-dro.co.uk/z-axis-dial-tool-setting-gauge-aluminium-body.html Peter |
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