Why NO home switches?

[Wolfesmetalfab]

I have searched, and cannot seem to find the answer, just repeats saying use NO for home and NC for limits. I see why using NC for limits makes sense, cause if I wire breaks, it trips the limits. Why is it important to use NO for homes? i have the Soundlogic Bob C. BOB and it is for a plasma table.

I am curious, cause the switches I ordered, the NC switches will give better repeatability cause the arm is stiff compared to the NO switches I got, and I have extra.

Oh and Im using mach 3.

Anyone know why?

Thanks
Brian

[LaserImage]

Originally Posted by Wolfesmetalfab I have searched, and cannot seem to find the answer, just repeats saying use NO for home and NC for limits. I see why using NC for limits makes sense, cause if I wire breaks, it trips the limits. Why is it important to use NO for homes? i have the Soundlogic Bob C. BOB and it is for a plasma table. I am curious, cause the switches I ordered, the NC switches will give better repeatability cause the arm is stiff compared to the NO switches I got, and I have extra. Oh and Im using mach 3. Anyone know why? Thanks Brian

I have three NC switches that are used for both limit and home switches. I don't know why NO would be advisable. The wire breakage issue seems like it would make sense for limit and home.

Gary

[Wolfesmetalfab]

thats what I thought, but i see lots of people saying NO for home. Anyways with the soundlogic board has anyone successfully used NC switches hooking them to their designated home and limit inputs on the BOB? It says in the manual, that if you use NC tell Mach in the active low settings. I did and it wouldnt work. I believe if i read and am thinking right, that the home and limits on the soundlogic are connected onboard in parallel and this is why the NC switches do not work, but NO do?

Can anyone verify what I am thinking, so I dont go and buy more NO switches if I dont need to cause I have a bunch of NC. Or how did you hook your NC up to the Soundlogic.

Brian

[vger]

Brian, Not sure exactly why. It could be the way the home sequence is done. Move untill home is activated then move back slow untill deactivated and it's home?

Steve

[Bubba]

I think it is more a matter of choice. Sometimes people look at a thought and then it becomes gospel. You are correct in the reasoning for the operation of the limits. In the case of home switches, it is less of a "hazard" if the system doesn't work due to a broken wire. However having said that, I agree it will help point to a problem if you try to home and it goes in the wrong direction; so this is one reason why mine are also NC switches for homing also. As long as you properly configure your system, it should work just fine.
I cannot help you with your particular bob as I don't have one.

[LaserImage]

Originally Posted by Wolfesmetalfab I believe if i read and am thinking right, that the home and limits on the soundlogic are connected onboard in parallel and this is why the NC switches do not work, but NO do?

I don't know that board, but I don't know of any reason that they have to be connected in parallel. Connect them in series and NC works perfectly. It also can make life easier by only needing three switches that are used for both home and limits.

Gary

[Wolfesmetalfab]

but I don't know of any reason that they have to be connected in parallel

What I mean, is that the BOB has screw terminals for x,y,z,a home and x,y,z,a limit, so it would have 6 pairs of wires going away from it since I am not using the a axis.

What I am thinking I will do, is use 3 pairs of wires going out from just the limit connections and wire 2 switches NC in series and not hook anything to the Home inputs on the BOB, and then tell mach what Im doing for home direction, and I think it should all be good.

[Crevice Reamer]

Here's a good discussion of home/limit switches:

http://www.cnczone.com/forums/showthread.php?t=24432

CR.

[LaserImage]

Originally Posted by Wolfesmetalfab What I mean, is that the BOB has screw terminals for x,y,z,a home and x,y,z,a limit, so it would have 6 pairs of wires going away from it since I am not using the a axis. What I am thinking I will do, is use 3 pairs of wires going out from just the limit connections and wire 2 switches NC in series and not hook anything to the Home inputs on the BOB, and then tell mach what Im doing for home direction, and I think it should all be good.

If you use Mach then you don't need the inputs on the BOB. Simply wire them in series and tell Mach what input you are using - it can figure out what is what. Here is a quote from the thread CR is referring to:

Some software packages can use a single switch for both a reference home switch and a limit switch. Mach software is one of these. Check the software that you wish to use to see the support for limits and homing functions. There is not really a standard among hobbiest CNC software packages, so it is your obligation to research all software available for something that will work for you. One can choose to have a single home switch, two home switches, three, or none at all. Same goes for the limit switches.