Newbie- Stop and home switches questions

[coloradonewbie]

I'm the newb I know. I'm sure these are stupid questions to you folks that have been doing this stuff for a while.

I purchased a pre-wired Xylotex 3-axis system with the control box already complete with cables, connectors, etc. I'm sure it's possible to add stop and home switches to the board inside and run the wires out of the cabinet.

Anyway, they show wiring the switches in series with a resistor in the mix in case a wire goes to high voltage or whatever. My question is, "why do most DIY tables only have 3 switches. X,Y & the +Z? It would seem to me that you would need a stop switch at either end of X and Y with one at the top of Z for a total of 5 switches.

Also, Mach 3 says you can share the X and Y stop switches and make them home switches too. Again a question, if you were sending the machine to home and it reaches either one of the x or y switches first, wouldn't it just stop the machine or does Mach 3 know to touch the switch, back off and head for the other switch until it hits it?

Sorry for the dumb questions, but I like to have things straight in my head before I start assembling anything.

[Bubba]

Hi,
A switch can and many times is activated by axis movement in either direction! In my particular case, I have one switch on the X axis mounted in the middle of the saddle. Thus whenever either end is approached, it will trip the switch. I also did the same for the Y axis. However for me, it was easier on the Z to have a switch for each the Plus and Minus directions due to the way the machine is made.

As for homing, you tell your controller in which direction to move to home. The only time you will get into trouble with a system with switches on both ends is IF the switch is already tripped on the wrong end to begin with because the controller will think it has reached the home position and start to "back off" the switch but in acutallity, will drive further into that switch position. Having said that, I have not had that situation happen to me in the several years that I have had it setup. You just have to pay attention to what your doing.

[coloradonewbie]

Thanks for the reply.

I just can't see the one switch for both directions setup in my head. My head is broken thinking about all this stuff. Maybe I'll wait until the machine is complete to worry about it. I'm definitely installing switches though. I don't want to worry about it every time I run the machine. Plus I think homing will be nice to have. "One switch? Crazy man".

[Bubba]

think of it this way,

The switch is mounted to the stationary part of the frame. It can be activated from either direction. Then on the movable part of the axis, you have "stops" that will activate the switch when the table moves to that point from either direction. I use switches that have "arms" on them that will trip the switch from either direction.

[coloradonewbie]

Sorry, doesn't help. I'll look for some photos or drawings of that setup to get it out of my head.

So, if the software (Mach 3) knows it's on a trip to home (homing), it will touch the first switch it comes to, back off and move on to the next switch until it arrives and backs off right? If the switches are acting purely as stops, the machine will just stop if it hits any of them?

[coloradonewbie]

Bubba,

I see it looking like the drawing that's attached.

[Bubba]

OK, that is one way to do it! In your case, looking at it as a router, I think it makes perfect sense to do it that way.

[stevespo]

Originally Posted by coloradonewbie So, if the software (Mach 3) knows it's on a trip to home (homing), it will touch the first switch it comes to, back off and move on to the next switch until it arrives and backs off right? If the switches are acting purely as stops, the machine will just stop if it hits any of them?

Yes, you've got it right. Rather than call them "stop" switches, they're generally referred to as "limit" switches. You can have limit++ and limit--, where limit++ is at the far end of your travel (increasing XYZ value) and limit-- is towards the beginning of your travel (decreasing XYZ value). As you mentioned, you can have your home switches perform double duty to also limit travel in one direction.

A "stop" switch (to me) sounds like an "e-stop" (emergency stop) which is another useful thing to have.

I think the order that Mach uses is home Z, home X, home Y. When the switch is tripped, it backs off slightly and continues to the next switch.

Personally, I have 4 contact switches and a touch off pad to set the Z tool height, so effectively 5 switches. Xhome also configured as X--. Yhome also configured as Y--. Zhome is the touch off pad. Then I have X++ and Y++ wired in series and sharing a single input on the parallel port. So 5 switches (wired NC, normally closed) and 4 inputs. That's just one way to do it.

Steve

[coloradonewbie]

Thank you guys for all your help, I'm comfortable with it all now. I think I'm going to wire the 5 "limit" switches with the y-- and x-- shared as a home switch. Also adding a touch off pad for the z-- and an edge finder tool I've seen. Also an E-Stop "BIG RED BUTTON" for when I screw up everything.

It's great to have you folks out there for answers and support. I'm not at all scared to build this beast, and I'm sure it will work better than I'm expecting if I take my time and ask lots of questions.

Thanks again for your help and I'll let you know how the build is going.

Pete
Fort Collins, CO

[Big-tex]

Partially as using share wiring for X+ and X- is a I think parallel port limitation.
If you are building router for wood it would make sense to use proximity sensors or magnetic switches normally closed. What that would give you is additional safety if something goes wrong with circuit controller and Mach 3 will see limit switch triggered.