You are the man!!! I have a bed size of 24" X 36" so ill have to find that config file and tweak it!
I dont have a Z home switch, come to think of it I dont believe ive seen anyone with a Z endstop…
Z endstops are usually touch plates. You clip a wire to your bit, clip a wire to a piece of foil or other metal, but the other ends in the Z_MIN endstop S and - and set the foil under the bit, on top of your work piece. A Z home then drops down until the bit touches the foil and you have an accurate 0 right at the top of your work. Jog Z up enough to keep things from bumping together and you are good to go.
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Can you somehow do a Z MAX so it doesn’t accidentally keep going up and up and push the ‘z’ to the ceiling? Either a physical switch or hard coded in the marlin firmware with MM value?
You could… But it would just unthread your lead screw and push your Z axis out of your gantry if your lead screw is long enough. If it’s shorter than your Z axis rails, then even if you unthread your screw, it won’t have enough travel to push the Z axis out of the center assembly. If it’s as long as your rails (or longer), you could push the whole Z axis out of the assembly, which could be messy…
But I’ll circle back to the fact that (in general) CNC doesn’t provide the safety rails that 3D printers tend to. You have to take responsibility to make sure you’re staying within the constraints of your machine, and then be responsible enough to attend to the machining process to shut things down if it all goes pear-shaped.
But sure, you could rig up a Z-max endstop. Maybe at the bottom of the Z axis/toolmount. Then you’d have to enable it in the firmware. Personally, I’d say keep your lead screw short enough not to fully disengage the Z axis if it unthreads. You shouldn’t be using that much Z travel anyway… 
Full disclosure: as it stands, my lead screw is longer than my Z axis; I need to cut a couple of inches off before I finish assembling things.
Very good points. When I put in the leadscrew I wasnt sure how much to cut off so I left enough on it so that the screw would not go past the router bit and could cut more later. Clearly I need to cut a bunch more off it. I built it to have roughly 3 inches of travel so I just need to burn into my mind never ever go past 70mm and watch for typos lol.
I would like to wire up an oh shit button but for now its gonna be on a switch on a surge protector for these moments.
I wouldn’t cut a bunch off of your lead screw. Just keep it a bit shorter than your Z rails. Maybe see where the top bearings still engage, and keep it around there. Granted, T8’s are pretty darned cheap, so hacking it down probably isn’t the end of the world, but if you cut off too much, you lose the Z travel you built into your Z axis.
Although talking it out makes me think that, for stability, you don’t ever want the Z rails out of the bottom bearings anyway, so if you shorten your lead screw to the point that it unthreads at or just after that point, you have a safety factor built in (even if your Z runs away, it should remain captured by the gantry), but can use your full designed Z travel. If you want to upgrade/lengthen your Z axis, you’ll have to spend another $10-15 on a new lead screw along with the rail material…
And if I’m blowing smoke, I’m hoping @vicious1 or some other more knowledgeable personage will come along and correct me… 
Im blind and cant find the file for this setting. Can somebody help me out with what folder I can find this config file in? Or is it in the settings of Repetier?
It’s in the Marlin source. If you’re using Ryan’s latest source (which is pretty close to the latest Marlin 2.x-bugfix with updated configs), it’s in the Marlin\Marlin directory (should be two config files, a makefile, a couple of misc files, and two directories, src and lib). Then you get to recompile the firmware and flash to your board! Have you been doing that already? It’s not difficult, but can seem daunting. I can do it, but I am a very intuitive computer/technology person, and it would behoove you to get someone else to help you with that (or to find other threads on the subject to read), if you need help. I’m your worst-case math/engineering TA. I do a lot of hand-waving of essential steps and “obvious” assumptions… 
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Well you had me until recompiling and flashing lol. I think I can wing it (I def done my share of computer tinkering…(flashing android roms, emulators, arcade cab front end configs, installing and running stand alone ecus in a few cars). However im a bit overwhelmed fixing the stupid stuff I keep finding with my build, understanding how to use ESTLCAM, and working with the damn endstops. Im gonna hold off from reflashing for now and leave it alone. Its working pretty well so far and I would hate to throw another kink in the works before I routed anything. I will be coming back to this once I feel confident in everything.
One more thing to note… Endstops don’t stop the machine at the end of it’s travel. They are only used for homing without quite a bit of modifying the firmware.
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Keerect-amundo! You can set “soft endstops” in the firmware that will prevent it from moving outside of the defined bed space, but those are really only useful if you are using the homing endstops so that the system knows where the X/Y origin is for the machine. Otherwise, it’s SOP to lie to your machine about where the origin is. At least, it can’t shouldn’t trust you. But with hardware endstops giving it the origin, it kinda has to go out on a limb and trust that you provided the correct bed size. In fact, I believe they are enabled by default with the dual endstops (DE), since that’s pretty much their raison d’entedre… Also why you can’t go into “negative space” when using DE.
You’re welcome,
Capt. Obvious Mansplainington, III
In regards to going negative. Can you start your zero in the cam software in the middle of the part if you set you G92 there as well? Or will it not go into the negative?
Sometimes its easier to start in the center but not the end of the world.
That is not the same. With dual endstops “home” is at the endstops, Zero is where ever you want it. You can even use workspace offsets. When you need to use it it will make sense. You just can not go past your endstops.
So im not sure if this is the correct way to use the endstops but I have a simple 90 degree fixture to lock a corner of the work piece in and set up the end stops to basically home right on the corner on work piece from that which would be my zero. If that makes any sense for a repeatable zero start point on the lower left corner of my wood.
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Hey Could you explain the G92 command process? I am new to Repetier Host and am having similar problems.
https://docs.v1engineering.com/learn/coordinates/
If you have more questions, I would open a new thread. This is pretty long and pretty old. I didn’t read through it to see if it was up to date.