i replaced the switch i destroyed above with one i bought off amazon and now when i run a homing sequence the z axis goes up and clicks the switch, comes down about 1/8" then goes back up and clicks the switch again and comes down, then does thattwo more times and then goes back up one more time and finally moves on to the X and Y axis
any idea why it does that now?
Did you update your version of grbl? Thereās a setting in the config.h that specifies how many times it engages and backs off from the homing switch.
i didnt make any changes to grbl. worked fine before the new switch went on
Donāt suppose anyone knows what spec the limit switches are? Managed to destroy one today and I suspect it wonāt be my last
Cheers!
Al
Are the limit switches worth the trouble? I did not order them with the upgrade and now I am thinking I should just keep manually homing the machine.
I am not sure I could stand the suspense of watching the spindle approach a hard limit just hoping everything works correctly.
For some they are others not so much. I played around with them and ultimately decided not to implement them. But to each his own.
I find that they are essential if you want to use multiple bits for a cut and want to recover your position after changing the bit. Also, if you home your machine when you turn it on, you can set āsoftā limits that will keep it from crashing into the ends.
@AllenMassey - I think it depends on how you use the switches. Wired and configured as homing switches they are useful for exactly that - HOMING, but will not stop you from destroying them if you tell the machine to go somewhere it should not go. Wired and configured as limit switches, which would require 6, they can tell your machine to stop moving when it hits them and maybe save the belt or some other part if you tell the machine to go somewhere impossible. All-in-all, the whole homing/limit switch debacle is something that requires a lot of reading and understanding before you will get the most out of it. I have seen some really great write-ups about how to wire them, and how to filter the circuit to avoid or eliminate noise, and whether to wire as NC or NO.
One of the forum posts I have bookmarked for later use
and another
and yes, another
Joined the smashed homing switch club the other day! Yay?
I really do think there should be a forum badge for it 
Along with your first deep plunge into the wasteboard, and your first snapped bit.
Breaking stuff is how we gain experience, I am just not sure I can afford much more experience.
Agreed, also had a plunge through my project into my wasteboard yesterday! No broken bit though, luckily!
snapped my 1/32" bit over the weekend, finished a cut in some acrylic, (a 3/4" pink flamingo) and had jogged the spindle up and the gantry back to look at the work, hit return to zero and before I knew it the spindle came down and the gantry rapided forward dragging that little bugger across one of the clamps.
They make a real nice pinging sound when they snap! 
It can be really exciting when one fragments at 10,000+ RPM. Not that Iāve done thatā¦a few timesā¦ 
Not sure if this info will help others or not - Iām gradually getting the limit switch thing closer to a resolution. Much of the info below is from another thread on the same subject.
On my machine (1000x1000 X Carve) Iāve installed additional limit switches, so I now have a switch on each end of both the X and Y axis and a single switch on the top of the Z axis. These are all Normally Open switches, wired in parallel pairs (the two X switches in parallel and ditto for the two Y switches)
Using Easel (through the Inventables site) I ran the Machine setup program which (for me) was the easiest way to āenableā the homing switches in GRBL. Iāve no doubt thereās probably a simple command for doing this via Universal Gcode Sender (UGS), however Iām all for taking the simple path wherever possible.
The advantages of using Easel to set up Homing is that it has a series of test sequences which allows you to
I then set up āSoft Limitsā by
I then enabled āHard Limitsā in GRBL by sending the ā$21=1ā command (GRBL should again respond with āokā)
So to summarise, Iāve now got:
Is this the final setup - certainly not. Iāve already had problems with false alarms due to noise issues with the switch wiring (I did use shielded cable for the new switches, but Iāve not yet connected to the controller - I assume this would go to ground, but thatās TBA). Iāll shortly be adding a DeWalt unit to replace the current tiny spindle, so Iām kinda hoping that running the power cable for this separately will reduce the noise a little also. Finally, Iām exploring the option of waiting in a capacitor & some additional resistors to reduce noise even further.
For reference, see here for a list & description of some of the GRBL commands and what they do Configuring Grbl v0.9 Ā· grbl/grbl Wiki Ā· GitHub
For interest, below are a couple of images on how I fitted the additional switches - not the neatest or best option, however it suited some of the restrictions I have with the way Iāve configured my machine.
Please also excuse the somewhat crude table set-up Iām using at the moment which is an odd combination of T Slot channels, threaded holes and multi-piece wasteboard. Iāll get around to something better when I stop tinkeringā¦
I have limit switches on my shapeOko2, I use NEMA17 motors and the limit switch wiring runs through the same cable duct as the stepper wires. This creates noise on the limit switch inputs. This was solved by installing a RC filter with a .47uf capacitor.
From Github:
Grbl v0.9j Atmega328p 16mhz 115200baud with generic defaults (2015-12-18) ā¦IMPORTANT INFO WHEN UPGRADING TO GRBL v0.9 :
ā¦Baudrate is now 115200 (Up from 9600).
ā¦Homing cycle updated. Located based on switch trigger, rather than release point.
ā¦Variable spindle is now enabled by default. Z-limit(D12) and spindle enable(D11) have switched to access the hardware PWM on D11. Homing will not work if you do not re-wire your Z-limit switch to D12.
This means that you have to verify your wiring if you upgrade Grbl.