limit switches fitting and wiring

[deannos]

OK, I have dropped the idea of cannibalising printers and scanners and will be building this-
http://buildyourcnc.com/latest.aspx
I have most of the hardware already in the shed, so just need the electrics and a few other bits. But having checked prices out on e-bay I reckon this could be done for under £200. The OH will let me spend that. But having spent nearly 4 hours watching the build videos and having a good feeling about this, there is one thing I'm not clear about. It was mentioned, but never went into detail on how to fit or wire them in, and that is limit switches. Now I under stand you need 2 per axis, one at each end of travel but that is all I know. I used the search facility on here but as of yet haven't found anything that helps.

Dean

[amishx64]

Originally Posted by deannos OK, I have dropped the idea of cannibalising printers and scanners and will be building this- http://buildyourcnc.com/latest.aspx

Awwww man why not? I'm using the 8mm rods and steppers outta printers and scanners for my build. Take a look in my signature.

I'll post info on limit switches in about an hour I'm going to be a bit busy in a few minutes. Just a heads up.

[amishx64]

ok so here's what's up. You need a type of standard, normally open switch. All this means is that there is no internal connection when the button is not being pushed down. Don't worry its hard to find switches that aren't like this.

Here's an image of a good switch type for CNC purposes.



This is called a tactile switch. Notice the lever.

You need 6 of there on your machine. Two per axis, as you stated.

Every switch has two terminals. They are both electrically the same, so it doesn't matter which wire goes where exactly. You'll need to attach one wire to each switch and connect all those wires together. That'll be your ground, typically black wire. Each switch should now have one remaining terminal. You need to connect one individual wire to each on these remaining terminals. Make sure the wires are long enough for axis movement and back to the controller. Each of these individual wires now corresponds to a limit on an axis.

Label wires as follows for simplicity purposes:
Wire #

1. -X axis limit
2. +X axis limit
3. -Y axis limit
4. +Y axis limit
5. -Z axis limit
6. +Z axis limit

Next connect wires 1 - 6 to spare pins on your DB - 25 (parallel port) connector. Go into Mach 3 or whatever program you are using and set these pins as limit switches. When a pin is grounded, that means the axis has reached its limit at that switch.

To mount a switch, screw it down lightly and have the machine axis frame able to hit it when it gets close. Nothing to it.

If you want greater reliability (in case a switch fails) put two in parallel. I can draw you up a diagram if you want.

Hope that helps.

- amishx64

[FandZ]

You don't have to have limit switches, at least you don't have to have them with Mach3. You do have to have Home switches. Home switches can be thought as your 0 point for all your axis. I'm sure you probably understand what your home switch is by now.

In mach 3 you can set up software limits (soft limits). Basically the software will stop the machine at whatever point you set it to be. I've also read other software will do this too but I can't remember the names at the moment.

I've bought limit switches for my machine but haven't gotten around to installing them yet. I've used only soft limmits and so far have been very impressed with the function. It stops the stepper motors cold. But I have crashed my gantry before I figured out how to set up my soft limits. Not fun...

Now I believe I've read with servo motors that limit switches are practically a must. If a servo motor gets an order from the control software to say rapid @ 100ipm but then the control software crashes, it'll keep going and crash. With steppers it won't happen because the commands come in steps so if the software crashes it'll just stop with the last step. Someone please correct me if I'm wrong in my understanding.

Originally Posted by deannos OK, I have dropped the idea of cannibalising printers and scanners and will be building this- http://buildyourcnc.com/latest.aspx I have most of the hardware already in the shed, so just need the electrics and a few other bits. But having checked prices out on e-bay I reckon this could be done for under £200. The OH will let me spend that. But having spent nearly 4 hours watching the build videos and having a good feeling about this, there is one thing I'm not clear about. It was mentioned, but never went into detail on how to fit or wire them in, and that is limit switches. Now I under stand you need 2 per axis, one at each end of travel but that is all I know. I used the search facility on here but as of yet haven't found anything that helps. Dean

[MadeInTheShed]

Ive just purchased 6 of these switches that are NC for $1 each. Im going to connect them in series, and then input just one hardware limit signal into MACH3. If one of the limit switches is pushed, the circuit is broken, and the machine stops! Also if one of the wires is cut or one of the switches fails, the machine wont run till the limit switches are working. Thinking about that, I might go buy some spares in case one does fail...........
I know you dont have to have limit switches, but for $1 each, and a bit of cable, its pretty cheap insurance.

[FandZ]

Originally Posted by MadeInTheShed Ive just purchased 6 of these switches that are NC for $1 each. Im going to connect them in series, and then input just one hardware limit signal into MACH3. If one of the limit switches is pushed, the circuit is broken, and the machine stops! Also if one of the wires is cut or one of the switches fails, the machine wont run till the limit switches are working. Thinking about that, I might go buy some spares in case one does fail........... I know you dont have to have limit switches, but for $1 each, and a bit of cable, its pretty cheap insurance.

Just remember when you are setting them up, your home switch needs to be right before the limit switch. Meaning you want to trip your home switch first. Yo only have a 1/4 inch to play with on those things. That's why I never got around to installing them. But eventually I'll get around to it

[acondit]

Actually, you only need one switch per axis (if you design it correctly). You set it up so there are two activating stops, one near each end of travel positioned such that the single switch is activated as either end of the axis is approached. Exactly how you do it depends on how that particular axis is designed.

Implementation is left as an exercise for the student.

Alan

[FandZ]

Originally Posted by acondit Actually, you only need one switch per axis (if you design it correctly). You set it up so there are two activating stops, one near each end of travel positioned such that the single switch is activated as either end of the axis is approached. Exactly how you do it depends on how that particular axis is designed. Implementation is left as an exercise for the student. Alan

So you are saying, let the switch ride on the moving part of the axis and have little speed bumps to trip it on each end? I like it!!! Yes it deserved 3 exclamation marks.

[acondit]

Originally Posted by FandZ So you are saying, let the switch ride on the moving part of the axis and have little speed bumps to trip it on each end? I like it!!! Yes it deserved 3 exclamation marks.

Yes and no. Like I said it depends on the design of the particular axis. For example on a mill for the X-axis the switch could go on the saddle and the stops on the moving mill table. For a router with a moving gantry the X-axis switch would probably go on the moving gantry and the stops on the table or base (depending how it is set up).

Alan

[deannos]

Thanks for the replies, the fitting of the limit switches is not a mystery anymore and is it seems very easy. I have another question, i was nosing on ebay and came across these and wonder if they were any good for the machine i'm hoping to build-
http://cgi.ebay.co.uk/800-step-Very-...d=p3286.c0.m14

Any thoughts or ideas on these. I admit to not having a clue about stepper motors.
Dean

[amishx64]

Originally Posted by deannos Thanks for the replies, the fitting of the limit switches is not a mystery anymore and is it seems very easy. I have another question, i was nosing on ebay and came across these and wonder if they were any good for the machine i'm hoping to build- http://cgi.ebay.co.uk/800-step-Very-...d=p3286.c0.m14 Any thoughts or ideas on these. I admit to not having a clue about stepper motors. Dean

NO. NO. NO.

Not unless you have a very high voltage power source, say 60 volts and a driver to handle it. Even if you did, the motors would burn up. These motors will be much too weak to be any good for you. Look for motors under ~8 ohms, more towards 4 or so. The motors should also be much bigger.

This motor has too high of a resistance, and too low of a max amperage rating (.3).

If you need help determining if a motor is OK, give me the motor specs and your power supply specs.

[GeeksGoneBad]

I thought I'd add my $.02

I have my switches set up on the machine (I have a moving gantry) two for the X and two for the Y - at each end... the limit switches in the negative direction on each axis are doubling as a home switch as well - this is fairly easy to set up in Mach 3

and if I can add one more tip - Don't - whatever you do - run your limit switch wires along with your motor wires - creates a ton of false trips because of the noise (my switches are wired N.O. - not sure if noise affects N.C. though)