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Limit switches for book build CNC machine

Re: Limit switches for book build CNC machine

Postby Awesomeness » Sun Nov 15, 2015 11:23 pm

You bought/built a DIY machine... the key word there is YOURSELF. You shouldn't get mad at other people if they don't solve your problems for you. And really, they've tried above.

The stuff you're confused about is extremely basic. I'm not kidding - I think I first learned it in 7th or 8th grade science class. It's very strange to see people here without those requisite skills, and you probably need to go brush up. If you already looked "at a hundred diagrams from Google", followed the advice here, and still can't get moving in a positive direction, I don't know where to point you next.

Maybe someone will go find all your parts, and make you custom diagrams and instructions. Besides the obvious "give a man a fish" kind of thing, I don't have time to do that right now, and know it wouldn't help many people if I did.

As an aside, I hold the opinion you really don't even need limit switches on these types of machines. I don't use them, your machine really isn't powerful enough to break anything, and there are few examples of times where you might be in danger of running into the limit of an axis. Consider just running without them.
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 » Mon Nov 16, 2015 12:42 am

Ok, first of all, I don't who the heck told you that I got mad at anyone in the first place. That's just nonsense. I was simply asking for help with an issue I'm having. If you don't want to help that's fine, I'm not forcing you to help. But please don't waste my time with your philosophical responses unless you have something useful to say. Goodbye.
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Re: Limit switches for book build CNC machine

Postby airnocker » Mon Nov 16, 2015 1:13 am

Awesomeness, you did weigh in a bit on the inpatient side. I must say mza1979m has been sincere in his effort for insights and assistance.

mza1979m, I do not have any experience the breakout board you are using or the CAM software, but that said:
1. There is nothing special about the limit switches used in DIY CNC machines
2. It is a good idea to implement them but as Awesomeness said, if you are diligent in you machine operation you don't HAVE to have them.
3. Try a Google on "Series and Parallel Switches"
4. You have a free choice of either wiring your limit switches in parallel or series. My example showed the series connection.

Most breakout boards use only one input terminal for series or parallel limit switch connection method. You mentioned your board has a terminal for the X, Y and Z limit switches. It is possible that you only need to use one of them.

If you have further question let me know.
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Re: Limit switches for book build CNC machine

Postby mza1979m » Mon Nov 16, 2015 1:32 am

Thank you airnocker, I appreciate that.
As you stated, I actually did try wiring several limit switches in series as a NC circuit and connected only one of the pins on the board. Not sure if I did it right but now none of the limit switches do anything.
Also, it's a 4x2 machine with one of the motors being a NEMA 34, so that's a pretty big motor that can do damage I think. But I might be wrong. But at any rate, I ran into much bigger issues after running the machine for the first time (without limit switches), and thought, forget it, I'm not troubleshooting THIS! So I purchased a new CNC router a few hours ago. Now I'll just wait until it arrives in the mail. Can't wait! I think I'll eventually dismantle all the electronics on my CNC build and use them for something else :)
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Re: Limit switches for book build CNC machine

Postby airnocker » Mon Nov 16, 2015 3:34 am

Damn. I had written a lengthy reply and suddenly it vanished. So I will begin again.

There are a number of different USB controller boards available and not knowing which one you have makes it difficult for anyone to help you with specifics. Tell us the make and model.

Regardless whether the controller board (or break-out board as it is often referred to) is the USB serial type or the parallel type they both do essentially the same thing, and that is, through a cable coming from the controlling computer, control signals are sent to the machine's electronics and event signals from the machine are passed back to the computer. Signals sent from the computer are OUTPUT signals and signals sent from the machine to the controller board and back to the computer are INPUT signals.

Controller boards have OUTPUT and INPUT terminals. Some OUTPUT terminals send signals to the stepper motor controllers, another might be used to turn the router ON and OFF as a control signal to a relay or something similar, another might send a speed control signal to the router speed controller. INPUT terminals receive signals, usually from switches on the machine, such as an Emergency Stop button, touch plates for zeroing the Z-axis router bit, homing switches and position limit switches. How these switches are used in a circuit that connects to the input terminals of the controller board are usually up to the user and/or the user's understanding for how the CAM software is configured in conjunction with the break-out (controller) board.

Inputs on the controller board usually have jumpers where one selects whether the "triggering" signal will come from a transition from a steady-state +5v DC value to GND or from a steady-state GND signal to +5V. This is described as an "active HIGH" vs. an "active LOW signaling method. (5v DC is a common value used, but it could be any positive direct current voltage).

In my simple circuit diagram, the line that extends to the left from the junction of the resistor and the switch connections that have there opposite end wired in series to GND is being "read" (or monitored) by the computer through controller board. If any switch opens, this causes a change in the "status quo" on the input port and the user must configure the CAM software to deal with it appropriately.

If this is helpful, let me know and I will continue.
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Re: Limit switches for book build CNC machine

Postby mza1979m » Mon Nov 16, 2015 11:59 am

Thanks for that. It does help in understanding how the board works, but in all honesty, like you suggested, for now I'm going to leave the limit switches off. And as I mentioned in the previous post, I found bigger issues (leveling the bed) that I need to deal with first.
And by the way, I have the USB breakout board from this website. The entire electronics kit was purchased from this website.
Thanks.
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Re: Limit switches for book build CNC machine

Postby airnocker » Mon Nov 16, 2015 6:01 pm

thanks
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