My next addition to my CNC is going to be a touch plate for setting Z2 height.
My machine like most requires me to connect a wire to the spindle to complete a circuit.
I was wondering does anyone have any plans for one that doesn't need the wire connected? I'd like to just change bits and hit go, so it will check the height and then move and start machining.
The only way i know of to avoid a spindle connection is to use a high precision switch mounted such that a touch plate actuates the switch. A very long time ago we did this on a precision lathe with a Baumer precision switch. In this case it probed the parts position pre and post, setup cut to figure out where the tool was. In a mill you could probe the cutter directly. The biggest problem really is designing the mechanism to hold the switch, the switch was very expensive considering it repeated to one Micron and had a sapphire tip. So you need to prevent over travel to protect the switch.
I suppose you could do an electronic equivalent of connecting a wire to the spindle by having an isolated touch plate that makes the circuit in the same way as the spindle would. That is the plate gets pushed into contact with the other end of the circuit. At that point though you have made a switch so why not just buy a switch like the above.
Im certain there are other ways to accomplish this but a precision switch giving you an off/on signal is pretty simple implementation wise.
CNCdrive sells a wireless version: Wireless tool length sensor - CNCdrive - webshop considered using this when I was setting up mine as I wanted to avoid the same thing; connecting a wire to the spindle. I don't know what kind of Breakout board you have. But a good BOB will have good isolation between the sensors and the machine and as such there is no way to use the machine as a direct part of the sensor circuit without defeating that isolation. I ended up using a touch plate that requires you to connect a wire to the spindle for the touch plate, and a high precision switch for the fixed location probing. My touch plate uses a magnet to contact the spindle so it breaks away before something gets broken if I forget to remove it. The high precision switch needs no connection to the spindle and works similarly to what Wizard described, and maintains the electrical isolation of the machine and the BOB. This is the fixed position switch I use. The maker sells it on Ebay: www.youtube.com/watch?v=OzYhfOBJW1w
Thanks for those links. I found another site where someone was using a high precision switch, like wizard had talked about. I was able to buy the same switch for $35.00 on eBay. I am going to give that a try. The manufactures website states it accurate to 3 microns (an OMRON D5A-8511 the big one in the picture). The guy using one said it's better than that.
If I'm not happy with it I will probably get the WS one as that looks exactly like what I'm looking for. The price is a little higher than what i was hoping to spend, but time costs a lot to.
Z2 Height Touch Plate w/o spindle wire
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