You most definitely should have received limit switches in your package. We will send you the missing limit switches.
But to directly answer your question; no, limit switches are not needed with CNC machines. You can set up soft limits to make sure the machine does not go out of bounds.
With that said, if the motors stall for some reason and the computer does not know the actual position of the gantry or the spindle, then the machine may actually go out of bounds and the machine may hit a physical limit. With or without limit switches, the machine will stop.
Please call the office so that we know who you are and we can send the limit switches to the correct person.
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There are no limit switches in my Greenbull 5x10 kit. Are these no longer needed?