A question for Deckingman (ian)

tierod

Hello Ian, I wonder if you can help me with something? I’m building a cnc and in order to have a decent homing speed my carriage is so heavy it won’t stop instantly and gives my end stop switch a decent whack. So I was thinking about making my own plunger style normally closed switch so a little overrun didn’t matter. I designed a couple different ones but am not satisfied they will have good repeatability.I have a 2 motor , 2 endstop system and need something easily adjustable to square the carriage. I read a post recently where you had commented about making your own endstops with copper plates. Your posts indicate you are knowledgeable about these things (I see you hand build a lot of things) and I wonder if you could show and explain how you built yours? I would appreciate it immensely! Thank you,
Rod

oliof

I am not Ian, but you could also consider a non contact end switch (optical/hall) the system can pass by/through to avoid the whack/crash

deckingman

@tierod I'm currently 10,000 miles away from my printer and PC so have limited access to files and images. However, I don't think my Z homing switch would suit your application. Essentially I use the nozzle as a probe. So the hot end is mounted on a kinematic pivot which allows some movement in Z but none in X or Y. It's held against the stop with springs and the stop itself is a brass plate which abuts a brass bolt. By connecting wires to the plate and bolt, this makes both an electrical switch as well as a physical stop. When homing Z , as soon as the bed touches the nozzle, the hot end pivots and the electrical contact is broken. In practice, the physical movement is immeasurably small.
What might suit your application better would be my fast homing switch which is a "flag" made from thin sheet aluminium which passes through a slotted opto switch. The idea is that the initial fast homing moves the bed in series of 100mm moves and repeats until the opto switch triggers. This gets the bed somewhere close to the nozzle before the slow homing using the brass plates.

tierod

@deckingman
Thank you for your answers.
I’ve thought of trying the Opto switches but I thought they were normally open switches and I’m very paranoid about having faults in either open circuits or faulty cheap Opto sensors. I’ve experienced a few crashes from inexperience with the software side. I use nema 32 steppers and they crash hard! A couple more questions, are there any normally closed Opto switches and what specific switch would you recommend? At this point I don’t care about cost and I’m only worried about accuracy on my dual motor axis anyway. And do you have any thoughts on debris interfering with the Opto?
Thanks!
Rod

tierod

@oliof
And thank you too oliof!

deckingman

@tierod Yes, on a CNC machine, swarf or debris could be an issue so maybe not such a good idea.
Maybe the arrangement I used before changing to a slotted opto switch might work for you. This was a "normal" micro switch mounted on an arm that could pivot against a spring. So to get the bed somewhere close to the nozzle at high speed, I did a series of 100mm moves, and checked the state of the switch after each move. If the switch was open, I'd do another fast move. If the switch was closed, I'd do the slow homing using the nozzle as described earlier.
So effectively the carriage could continue to travel some distance after the switch triggered without anything crashing. The arm holding the micro switch would just pivot against it's spring

tierod

@deckingman
Right, I have decided to try(already started)design an enclosed Opto switch with a guided plunger. I just printed a boot out of tpu to seal off everything but the boot is pretty stiff. I’ve designed it to be internally adjusted and have a spring under the boot to help return the stiff boot. Looks good so far on fusion but so did all the other designs . I’ll see how it goes . Thank you, I don’t know what I’d do if this forum and all the excellent advise I’ve found didn’t exist, well I do know, I never would have been able to design and build my own 3d printer and my cnc. Kudos to all!!
Rod