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Limit switches for book build CNC machine

Limit switches for book build CNC machine

Postby mza1979m » Mon Nov 09, 2015 12:27 pm

Hi everyone... I've pretty much completed my book build and all 3 axis are moving using the Planet CNC software. Now, I don't know why, but I never received any limit switches with my order when I ordered the electronics kit from the website, but anyways, I found 6 normal limit switches I had on a couple old 3D printers I had laying around, and if possible, I'd like to use them for the CNC machine... So 2 questions... First of all, IS this possible? Using just regular 3D printer limit switches (has 3 prongs) on a CNC machine? Or are they supposed to be special limit switches? Secondly, I couldn't find any information on the website on how to wire limit switches to a USB BREAKOUT BOARD. I found a diagram for the parallel breakout board but not for the USB breakout board. Any help would be appreciated.
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Re: Limit switches for book build CNC machine

Postby rob3662 » Mon Nov 09, 2015 5:13 pm

I can't help with the wiring to your usb breakout board, but you can use those limit switches. One of the prongs is the common connection and the other two are the normally open and normally closed connections. I have all of my limit switches ran in series using the normally closed connection. If you use the normally closed connection then your machine will let you know if a wire is broken because it will think a limit switch is pushed.
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Re: Limit switches for book build CNC machine

Postby mza1979m » Mon Nov 09, 2015 6:10 pm

Thank you for that. It helps. So are you able to tell me in a little more detail how your setup is wired? It's not too hard to figure out where the wires go on the USB breakout board as they are clearly marked. But are they polarity sensitive? And how are the limit switches wired together (if at all)? Or maybe you or someone can direct me to a location on the website that might contain more details.
Thanks.
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Re: Limit switches for book build CNC machine

Postby airnocker » Tue Nov 10, 2015 5:59 pm

Everyone has their own concept of implementing limit switches on their CNC machine. I prefer the minimalist approach of using the fewest number of switches needed to do the job. It does require a bit more planning, however.

The first image shows how the three axis limit switches are wired in series in the normally closed (n.c.) position, using the Common and Normally Closed pins. The end of the last switch is connected to Ground relative to the +5v supply and the end of the first switch connects to the designated break-out board input pin. With nothing connected to this input pin as shown, it is pulled "High" to +5v. With the series of limit switches connected to it as shown, they pull the pin "Low" to Ground. Therefore, the software is signaled that a position limit is reached if any switch changes from normally closed to open.

The second image shows how one switch can be used per axis to indicate a position limit is reached from either direction. In this case the switch is placed at or near the center of travel for the given gantry axis. Deflector or switch actuator arms are mounted at the end of travel points for each axis. I used cut-off pieces of PC edge connector slot tabs for these actuator tabs. The tab are slotted so their hold down screws can be loosened and the tab slide back-and-forth to adjust it's proper position, then re-tightened.

The other concept uses two switches per axis with each switch pair located at opposite ends of the gantry travel. This method requires six limit switches wired in series.

I hope this helps.
Attachments
LimitSwitches-2.jpg
Switch layout concept
LimitSwitches-1.jpg
3 switch solution
airnocker

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Re: Limit switches for book build CNC machine

Postby mza1979m » Wed Nov 11, 2015 2:19 am

Thank you SO much for this useful information.
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Re: Limit switches for book build CNC machine

Postby mza1979m » Sat Nov 14, 2015 12:57 pm

Thanks so much for the info.
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Re: Limit switches for book build CNC machine

Postby mza1979m » Sun Nov 15, 2015 11:56 am

I'm using a USB breakout board so I can't use Mach 3. It seems I have to use the Planet CNC software. I just paid 69 Euros for it yesterday so I can test it. I'm still waiting on them to email me the registration code (like seriously? It's 2015!).
But anyways, before I read your response on hooking up the limit switches, I had already hooked them all up, but as Normally Open instead of Normally Closed. Yes, I realize it's a mistake now. It seemed to be working initially. When 1 axis reached its limit on either end, it would press the switch and only that motor would stop. But it's so intermittent, I'm not sure why. Sometimes things would work the way they're supposed to, othertimes they just won't work at all and the axis keeps going past its limit even if the switch got pressed. So something is obviously wrong. So I'm going to re-wire all my switches to NC and see what happens.
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Re: Limit switches for book build CNC machine

Postby mza1979m » Sun Nov 15, 2015 12:40 pm

Ok, honestly, I'm still super confused how to actually physically wire the switches to the board and to each other. Putting aside all the advanced stuff and recommendations, I'm just looking for the basics. As in, "Connect wire from X++ on board to NC on limit switch 1. Connect wire from GND on board C on limit switch 1, etc." I don't know how to connect switches in parallel and how to connect them in series.
I have the USB breakout board, not the parallel breakout board, so I have the following pins on the board for my limit switches: X++, X--, Y++, Y--, Z++, Z-- and GND.
Thank you.
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Re: Limit switches for book build CNC machine

Postby Awesomeness » Sun Nov 15, 2015 8:07 pm

At this point, maybe you should Google "wiring switches in parallel", then. We're happy to help, but if you're getting frustrated because there isn't a step-by-step instruction guide for exactly your hardware and situation, you probably shouldn't have ever considered a DIY or kit build. I'm not saying that to provoke you... the desire to learn about and do this stuff your self is a prerequisite for having fun and being successful with this, as it's the trade off for not buying a $20,000 machine that shows up in a crate via FedEx.
If you don’t have time to do it right, when will you have time to do it over?
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Re: Limit switches for book build CNC machine

Postby mza1979m » Sun Nov 15, 2015 8:44 pm

And why do you assume that I haven't Googled a hundred thousand terms to try to figure this out myself? I have spent a week looking at a hundred diagrams from Google, and have spent countless hours attempting to wire it myself and have switched from a NC circuit to a NO circuit and back again, and have done TONS of troubleshooting. I don't see anything wrong with coming to the forum to try to get a little help with an issue I'm having. That's what it's for after all.
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