Limit/home switches

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ScotY
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Limit/home switches

Post by ScotY » Fri Oct 06, 2017 10:41 pm

Hello,

I'd like to have a single switch per axis on my mini mill, just to keep things simple. Looking at the standard connections wiring diagram, it looks like I should use supply +24vdc to input 24 and wire the switches to inputs 1-4.

I've browsed the CNC12 manual and I believe if you define the travel limits of the machine, when running a program, it won't exceed these limits and crash the machine. However, I haven't found if there is some means of limiting travel when jogging the machine so as not to exceed the limits on the side without the limit switch. Hope that makes sense? Aside from installing 2 switches per axis, is there a way to do this?

Also, can anyone recommend a good limit switch that's reasonably priced yet accurate? I think I only need to be concerned with accuracy for the z-axis limit switch for tool height consistency?

Thanks, Scot

martyscncgarage
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Re: Limit/home switches

Post by martyscncgarage » Sat Oct 07, 2017 9:51 am

Yamatake makes good reasonably priced limit switches.
Optical limit switches, and proximity limit switches have also been used.

Yes, limit switch at Z+, X-, Y- on a mill. Set software travel limits and you will be good to go.

HOWEVER! If you are using open loop steppers (no feedback to the stepper driver, but somewhat forgiving) if you loose steps, software limits may not work or work against you depending on the direction you lost the steps.

Close loop stepper motor systems, Clearpath SDSK and DMM Technology AC drives that take step and direction input are good compromises but cost more.

Marty
"Jack of all trades, master of none!"
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cnckeith
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Re: Limit/home switches

Post by cnckeith » Fri Oct 13, 2017 8:50 am

ScotY wrote:
Fri Oct 06, 2017 10:41 pm
However, I haven't found if there is some means of limiting travel when jogging the machine so as not to exceed the limits on the side without the limit switch.

Thanks, Scot
Scot,
Hello. CNC12 software travel limits WILL stop you from Jogging into either travel limit. software travel limits will stop you from jogging into the switch and it will stop you from jogging into the other end of the travel (hard stop or switch) no matter what jogging method you use (VCP, Keyboard, Xkeys, Xbox controller etc..) try it! it even decelerates into the soft stop! (i think marty made a video of this) the only time you can jog into a swtich or hard stop is right after boot up of cnc12 and BEFORE homing it out. but even then you are only allowed to jog the machine tool very slowly (fast jog is disabled). Once you home the machine the machine knows where it is at, Software Travel Limts "turn on" and take effect protecting you from crashing the machine into either end of the axis travel.

ScotY
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Re: Limit/home switches

Post by ScotY » Fri Oct 13, 2017 1:08 pm

Thanks, Keith. I realized this once I got it up and running and forgot to come back and mention that. It's quite an awesome setup!

I have a question though. Is there a way to prevent cycle start from running a part? I've been just setting things up, trying to learn CNC12, etc. and am usually using the MDI screen to make things move. After typing something in the MDI window, I think it would be nice if hitting enter would make the machine move. I'm assuming there's a safety reason why you guys did it the way you did, requiring cycle start to send the command.

Anyway, my PC is not in front of the mill so I need to turn back and type/press buttons, then turn the other way to see what it does. On several occasions, I've hit the cycle start when I was jogging, or hit cycle start once for an MDI, then accidently hit it again and it starts the job file that is there from an earlier session. This has caused me to crash my indicator a couple of times now. :lol: Which reminds me, I need to hook up a real e-stop soon.

cnckeith
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Re: Limit/home switches

Post by cnckeith » Fri Oct 13, 2017 1:44 pm

yeah.. to meet industry standards..any automatic motion must be initialed with the cycle start button.

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Re: Limit/home switches

Post by tblough » Tue Oct 17, 2017 11:38 am

Scott,

I have a lot of users that run into the same problem with the start button as you do. I've created a --NULL--.CNC file that does not contain anything. I ask that the users load that program when they are done running theirs. That way is someone is using the machine in manual mode and they inadvertently hit the start button, nothing happens.

Dashes around the NULL are just so that it appears at the top of the program listing.

Cheers,


Tom
Cheers,

Tom
Confidence is the feeling you have before you fully understand the situation.

ScotY
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Re: Limit/home switches

Post by ScotY » Sat Oct 21, 2017 1:12 am

Thanks, Tom...that's a great idea to help keep me out of trouble.

cut2cut
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Re: Limit/home switches

Post by cut2cut » Sun Jan 07, 2018 12:54 am

tblough wrote:
Tue Oct 17, 2017 11:38 am
Scott,

I have a lot of users that run into the same problem with the start button as you do. I've created a --NULL--.CNC file that does not contain anything. I ask that the users load that program when they are done running theirs. That way is someone is using the machine in manual mode and they inadvertently hit the start button, nothing happens.

Dashes around the NULL are just so that it appears at the top of the program listing.

Cheers,


Tom
Thank you for sharing this !!! In my opinion, this should really be a "STICKY" so every Newbie sees it before they crash their machine while trying to configure and troubleshoot a new conversion. This "answer" wasn't very easy to find !

Jake

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Re: Limit/home switches

Post by Roadstercycle » Sun Jan 07, 2018 1:17 pm

I second the motion on making it a sticky. That could save a lot of headaches for a newbie or oldie. Great thought.

Gary Campbell
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Re: Limit/home switches

Post by Gary Campbell » Sun Jan 07, 2018 2:46 pm

I too ran into this on my lathe. "Cycle Start to....." So I pressed cycle start. We all know what happened. Using the Edit command I opened a file, deleted all the lines of code and renamed it "None.cnc" Problem solved

My question is: Why does it seem there needs to be a job loaded until the operator loads one? Especially on a clean install of the software (and hardware) Excuse my ignorance, but I have never seen this before.
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