Sorry if this is a repeat. I want to automate my machine to raise to max z height, move to home position and then zero height without connecting a probe to the milling bit.
I have a Rambo board and believe there is a max height switch input. Is it supported in the firmware?
Does anyone have links to a probe that detects pressure maybe or maybe there is a version that has a switch inside that is accurate?
About the only pressure-sensitive switch that I can think of is https://www.precisionpiezo.co.uk/
I have a couple of versions of these and have tried them with different setups. I can’t think of a good way to set these up with an MPCNC though.
You could probably do something with a load cell. You may be able to scavenge one from a kitchen scale or inexpensive bathroom scale (one that does not use a spring) and come up with a switching circuit.
In many ways though this is a bad idea. By definition, a pressure sensitive sensor needs pressure before it switches. you are dealing with a point, so how much pressure is enough? It takes very little pressure to push a sharp bit, particularly, say a 20° engraving point into something like softwood, say pine. you will need many different calibrations for different bits and different materials. Those piezo sensors are intended for something like a printer hotend nozzle against tempered glass or steel, where it is nearly impossible for it to actually puncture the surface.
For a max limit switch, people have implemented those. I think it takes a reasonably simple edit of the marlin firmware.
Now consider this: Professional machines don’t use pressure switches because they don’t do a good job. We don’t use pressure switches because there aren’t really any good ones to use.
The professional machine approach is usualy to use a bit setter so that the endmill is always a known distance from the max. this means that as soon as you home the machine to its max position, you know exactly what the height of the milling bit is above your spoilboard.
We use a touch plate so that we know how high the bit is above the work. We use a plate that we know is hard enough not to be dented when the bit touches it, so long as the circuit is completed and the machine stops pushing.
I have my machine set up so that it will do what you are seeking. I outlined most of what I did in this topic. After @jamiek 's comment in that topic about clearance height, I decided to add a limit switch on the Z axis. I mounted a roller-type limit switch, which I trigger with a prism shape “stop.” The prism shape, at is max depression of the switch, does not damage the switch. This setup protects the switch in case I make a mistake, and allows me to quickly swap my Z axis for my laser. I’m away from home at the moment, but if you like, I can post a picture of the Z limit switch when I return home.
After verifying everything is working, I haven’t used the bitsetter or the Z limit switch. In other words, my setup is not well tested. You don’t need to mess with workspaces to get your specific need to work, but you will need to enable probing in the firmware.
Note I don’t use the Z-MAX limit switch plug. My bitsetter, touch plate, and my Z max limit switch all use the Z-Min plug. For moving to the max, I just probe up until the Z limit switch is triggered.
Thanks for the replies. It stopped me going down the pressure sensor rabbit hole. In the end I used a fixed location and adapted my initial script to move to that position to zero with a metal plate and a croc clip. I did not mess with max height limit. I instead just relied on me moving it up to the right initial position before homing.