[CNC Lurker]

I got a 3-axis kit which includes a Gecko G540, power supply, and Nema 23 380 oz-in stepper motors. Now I need to buy the e-stop and limit switches. I've searched and read several threads on limit switches and e-stops, but I haven't found which ones to buy or where to get them from.

I've read it is better to get the e-stop that locks close when you hit it, and you have to twist it to unlock it, but where do you buy those at?

I've googled micro-switches and limit switches, and they range from $2.50 to over $100. There are also some with a roller on the lever/arm, and some switches don't have any rollers.

I'm in the states, TX actually, where would be a good place to get limit switches?

One last thing, I know I need 2 limit switches for each axis, so that is 6 switches. I've read where some are using them for "home" also. Would I use 1 of the limit switches as a "home", or would I need to add another switch to each axis (for a total of 9 limit switches)?

[brtech]

I got my e-stop on ebay. Something like this:
Emergency Stop Mushroom N/O N/C Push Button Switch - eBay (item 300498494577 end time Dec-28-10 14:24:18 PST)

For limit switches, you get "snap action" microswitches, and Digikey is a good place to get them. There are two types: a "lever" and a "roller". Opinions vary if you need/want a roller.
A sample part number is:
Digi-Key - SW873-ND (Manufacturer - SS-5GL2T)


You usually have one limit switch on each end of each axis. 3 axis, 2 per axis, 6 switches. You can use one of the two on each axis as home. You don't wire it differently, you just configure the home switch on the same pin as the limit switches.

[Torsten]

I got a 3-axis kit which includes a Gecko G540, power supply, and Nema 23 380 oz-in stepper motors. Now I need to buy the e-stop and limit switches. I've searched and read several threads on limit switches and e-stops, but I haven't found which ones to buy or where to get them from.

I've read it is better to get the e-stop that locks close when you hit it, and you have to twist it to unlock it, but where do you buy those at?

I've googled micro-switches and limit switches, and they range from $2.50 to over $100. There are also some with a roller on the lever/arm, and some switches don't have any rollers.

I'm in the states, TX actually, where would be a good place to get limit switches?

One last thing, I know I need 2 limit switches for each axis, so that is 6 switches. I've read where some are using them for "home" also. Would I use 1 of the limit switches as a "home", or would I need to add another switch to each axis (for a total of 9 limit switches)?

You actually only need one limit Switch per Axes.
Just have to make sure something triggers the switch as the travel nears each end.
You will want to design the trigger mechanism in a way that allows the axes to travel past for a short distance.
The controller needs a little room to decelerate once triggered.

[brtech]

Uh, if you want to stop motion on either end of the axis, you need two switches per axis. I think what you meant is you only need one INPUT per axis, with both switches wired to the same input.

[CNC Lurker]

I got my e-stop on ebay. Something like this:
Emergency Stop Mushroom N/O N/C Push Button Switch - eBay (item 300498494577 end time Dec-28-10 14:24:18 PST)

For limit switches, you get "snap action" microswitches, and Digikey is a good place to get them. There are two types: a "lever" and a "roller". Opinions vary if you need/want a roller.
A sample part number is:
Digi-Key - SW873-ND (Manufacturer - SS-5GL2T)


You usually have one limit switch on each end of each axis. 3 axis, 2 per axis, 6 switches. You can use one of the two on each axis as home. You don't wire it differently, you just configure the home switch on the same pin as the limit switches.

I looked at that seller fro the e-stop, from he's from Hong Kong and it would take about 10-21 days to get here. BUT you did give me the search term to look for and I found a USA seller of that exact same e-stop and I just ordered it.

For future reference, the Ebay seller's name is tree_kicker and he sells it for $7.99 with free shipping. He had it listed as "Emergency Stop Switch Push Button Mushroom PushButton".

I'll look at the Digikeys micro switches.

By the way, I see you built the FLA-300, I'm going to start a thread on the FLA-100 I'm building.

I got my 3-axis kit from FLA with the Black Friday $50 off deal :banana:: 3 Axis Electronics Kit

[JD_Mortal]

Remember, the purpose of an "emergency stop" is to kill power directly at the source. (As opposed to being an input to a digital readout, requiring the computer to act on that action. That is unsafe.)

That is why emergency switches are so expensive. They usually connect directly to the power, or a power-breaker, which has to handle high voltages and amps directly, and keep the operator safe from disconnect shocks. (When you abruptly stop power, the amps continue to flow, like momentum, and try to jump connections. Thus, the elaborate internal setups for industrial emergency switches. This often includes dual-line breaks, and a physical separation arc-gap wall between contacts. Possibly also some quick-snap springs to pull contacts to a non-arc distance.)

For these tiny devices, we don't need super-industrial, OSHA required emergency stop buttons. We simply need something that will handle 240vac @ 30a for most uses. It should be 4x your consumption. Though, you may want to get dual-contacts, and break the live-wire of the motor drivers/power and the spindle/power separately. Though, if they are all plugged into one location, like a power-bar or a rail, killing the rail is fine. (But you can get feedback from the spindle, pumped into your sensitive electronics.)

You do not, and should not, have to kill the computer. Just the power to the moving devices.

I got my hand crushed in a 6-on-6 web printing-press, hurt like a b***h because the one place that I was located, didn't have an emergency stop button. Every other location had one, except that one. So the conveyor grabbed hold of my rag, and pulled my hand inside the conveyor-belt, slowly... My hand wrapped backwards, popping and crunching, around a metal roller that was as wide as a beer bottle... Luckily, it was just tendons and knuckles popping. No permanent damage. It stopped when the circuit-breaker popped. No-one could hear me screaming.

You don't want to accidentally lean over, and your hoodie-tie gets grabbed by the 10,000 RPM spindle... Or accidentally "think" that it is safe to clear some debris, and the spindle decides its next move is up, and into your finger... and not have a stop-button handy for you to reach.

Sorry, got a little side-tracked... what was the question?

Oh yea... switches...

You can use one micro-switch for each axis, if you mount it in the moving mount. The switch, for example, would be in the center near the nut, and a pole extending off the walls would break the NC connection. That works for both the STOP and the LIMIT switches, which you should have both. However, I think it is better to have two LIMIT switches, so you can freely move them to the work-area-edges. That keeps the tools from having to travel all over, and gives you more options for mounting your material in any location.

EG... like this... (--- = rod) (# = switch) (=== = rail) ( [] = spindle)

|---     [  #  ]     ---|
|========[_____]========|

does this...

|-[--#  ]            ---|
|=[_____]===============|

and this...

|---            [  #--]-|
|===============[_____]=|

The STOPS should immediately stop the motors, as that is the crash border. Having enough room to decelerate is a thing to remember. The LIMITS should be prior to the STOPS, eg, hit first by the moving platform. They should be set to reverse the motors, or throw them into slow-mode, or some other corrective action. (You would/could also use those for your HOME switches.)

You don't need them both, but it makes it better and safer if you do have both STOPS and LIMITS.

[Fastest1]

Where in Texas? If Houston, try EPO or Ace Electronics. A latching Estop is safer but as long as it cuts the power til reset either style works.

[CNC Lurker]

Remember, the purpose of an "emergency stop" is to kill power directly at the source. (As opposed to being an input to a digital readout, requiring the computer to act on that action. That is unsafe.)

That is why emergency switches are so expensive. They usually connect directly to the power, or a power-breaker, which has to handle high voltages and amps directly, and keep the operator safe from disconnect shocks. (When you abruptly stop power, the amps continue to flow, like momentum, and try to jump connections. Thus, the elaborate internal setups for industrial emergency switches. This often includes dual-line breaks, and a physical separation arc-gap wall between contacts. Possibly also some quick-snap springs to pull contacts to a non-arc distance.)

For these tiny devices, we don't need super-industrial, OSHA required emergency stop buttons. We simply need something that will handle 240vac @ 30a for most uses. It should be 4x your consumption. Though, you may want to get dual-contacts, and break the live-wire of the motor drivers/power and the spindle/power separately. Though, if they are all plugged into one location, like a power-bar or a rail, killing the rail is fine. (But you can get feedback from the spindle, pumped into your sensitive electronics.)

You do not, and should not, have to kill the computer. Just the power to the moving devices.

I got my hand crushed in a 6-on-6 web printing-press, hurt like a b***h because the one place that I was located, didn't have an emergency stop button. Every other location had one, except that one. So the conveyor grabbed hold of my rag, and pulled my hand inside the conveyor-belt, slowly... My hand wrapped backwards, popping and crunching, around a metal roller that was as wide as a beer bottle... Luckily, it was just tendons and knuckles popping. No permanent damage. It stopped when the circuit-breaker popped. No-one could hear me screaming.

You don't want to accidentally lean over, and your hoodie-tie gets grabbed by the 10,000 RPM spindle... Or accidentally "think" that it is safe to clear some debris, and the spindle decides its next move is up, and into your finger... and not have a stop-button handy for you to reach.

I was thinking about that actually. If I hit the e-stop, it stops the steppers, but the router is still running. I was wondering if I needed a stop for the Porter Cable 690 router I will be using, something like this one from Rockler: Safety Power Tool Switch

I'm using an E-stop because in one of the builds someone posted, the z depth was set wrong and it kept on going down into the table.

I do plan on keeping all body parts out of the way. In a former life, I was a sheetmetal fabricator, and I've seen a few fingers crushed in slip roles, brake presses, and punch presses. I don't fear the machines, but respect them.

Sorry, got a little side-tracked... what was the question?

Oh yea... switches...

You can use one micro-switch for each axis, if you mount it in the moving mount. The switch, for example, would be in the center near the nut, and a pole extending off the walls would break the NC connection. That works for both the STOP and the LIMIT switches, which you should have both. However, I think it is better to have two LIMIT switches, so you can freely move them to the work-area-edges. That keeps the tools from having to travel all over, and gives you more options for mounting your material in any location.

EG... like this... (--- = rod) (# = switch) (=== = rail) ( [] = spindle)

|---     [  #  ]     ---|
|========[_____]========|

does this...

|-[--#  ]            ---|
|=[_____]===============|

and this...

|---            [  #--]-|
|===============[_____]=|

The STOPS should immediately stop the motors, as that is the crash border. Having enough room to decelerate is a thing to remember. The LIMITS should be prior to the STOPS, eg, hit first by the moving platform. They should be set to reverse the motors, or throw them into slow-mode, or some other corrective action. (You would/could also use those for your HOME switches.)

You don't need them both, but it makes it better and safer if you do have both STOPS and LIMITS.

That's kind of what Torsten was stating earlier:

Just have to make sure something triggers the switch as the travel nears each end.
You will want to design the trigger mechanism in a way that allows the axes to travel past for a short distance.
The controller needs a little room to decelerate once triggered.

I've read that there are hard switches (micro switches) and soft switches (in Mach3) and I believe having it slow down before it hits hard switches can be done in Mach3. I'll do some more reading on that.

I haven't bought Mach 3 yet, but I did get my Gecko and steppers yesterday, but I haven't hooked them up and tested anything yet. I'll have to read and see if they can move without an e-stop/fault error.

[CNC Lurker]

Where in Texas? If Houston, try EPO or Ace Electronics. A latching Estop is safer but as long as it cuts the power til reset either style works.

I'm in Rockwall, TX.

I did stop at a Radio Shack on the way home and I found these there (see attachment).

If rollers are not necessary, then I'll just pick these up.

[JD_Mortal]

Almost any type of switch will work, depending how you setup the contact point. The voltages/amps are low, and you will not be hitting them over 10,000 times under normal situations...

The only thing you have to worry about is "contact corrosion" (Get nickle-plated or gold plated if you are going for broke.)

As for impact ratings, and g-forces... Those can be issues depending on how much your machine vibrates and how you setup the contact of the switches. The roller is good because it allows you to use a spring-ramp and the roller itself is also on a leaf-spring arm. Thus, impact is nearly zero. (As opposed to a toggle-switch or a micro-switch which would require you to manufacture some form of leaf-spring to depress the contact.)

Secure it well and if possible, within a sealed enclosure with the switch-arm poking out through a slit that is cut in a piece of rubber or thin plastic. That will keep salty-humidity and dust away from the contacts inside. (The cheap ones at RS tend to have holes and poor push-clip seals which allow contaminants to enter the shell.)

[RomanLini]

These might look a little scary at first, but they are actually simple to work with as they just have 3 wires; +5v, ground and the output wire;
http://www.cnczone.com/forums/open_s...made_easy.html

Thye have no moving parts to fail (like microswitches) and they are much more accurate, mine tested as good as 0.01mm repeatability.

[ger21]

I was thinking about that actually. If I hit the e-stop, it stops the steppers, but the router is still running.

Here's what I'm going to do. my Motor power supply and router are both fed by the same 110V line. Putting an estop switch in that line will stop motion by killing power to the drives, and will shut off the router. Depending on the power supply, it may keep moving for a second or two though.

[CNC Lurker]

These might look a little scary at first, but they are actually simple to work with as they just have 3 wires; +5v, ground and the output wire;
http://www.cnczone.com/forums/open_s...made_easy.html

Thye have no moving parts to fail (like microswitches) and they are much more accurate, mine tested as good as 0.01mm repeatability.

Thanks for the reply, but it is pretty scary for a noob and I'll admittedly take the easier route right now, but I'll look at those again in the future when I'm a bit more confident.

Maybe someone could make those turn-key and sell them on here. Basically have it already soldered, assembled, and ready to mount.

[JD_Mortal]

Here's what I'm going to do. my Motor power supply and router are both fed by the same 110V line. Putting an estop switch in that line will stop motion by killing power to the drives, and will shut off the router. Depending on the power supply, it may keep moving for a second or two though.

If needed, for better safety, though not required...

An electronic break which "releases" whenever power is applied, will help reduce the router free-spinning. (Again, it is not needed.) This would be a cheap, low-power actuator that pulls-away from the spindle-shaft while the power is on. Once the power is killed, not just the spindle turning off, the actuator would spring into breaking position, and slow-down the router faster than free-spinning. Just a simple metal lever break will suffice.

If this is going to be around employee's then it may be a requirement. (Manual back-off knobs might also be a requirement too.)

[RomanLini]

Mechanical brakes can work well, but are complex to implement and expensive if you want electric controlled ones.

The very fastest way to stop stepper motors is to leave their power supply full on, and kill the step pulses to them. They will slam to a halt with the full magnetic power of the driver.

Ger21's idea of cutting all the power will allow the steppers to coast a bit, maybe for a couple inches or more. It might not be the best for safety, but it's easy.

On my machine I just kill the power to everything, (similar to what Ger21 suggested) but in my case it kills the step pulses too as they are generated by a "brains on board" inside my machine. That stops everything pretty much instantly, although the router will take a few seconds to spin down if there is not much load on it.

If you use a relay to disconnect the mains power to the router you can electrically brake the router by switching a large resistor across it, this can all be done easily with one relay.

[ger21]

Ger21's idea of cutting all the power will allow the steppers to coast a bit, maybe for a couple inches or more. It might not be the best for safety, but it's easy.

If you get an Estop with multiple contact blocks, just add one for the Estop input to Mach3. Then, while killing power, it'll also stop the step pulses, as well as stop your g-code from continuing on while the machine is stopped..

[hemsworthlad]

On my machine I just kill the power to everything, (similar to what Ger21 suggested) but in my case it kills the step pulses too as they are generated by a "brains on board" inside my machine. That stops everything pretty much instantly, although the router will take a few seconds to spin down if there is not much load on it.

Erm . . But that mean your steppers are still under software control which hisn't a safe state to be in.?

[JD_Mortal]

Coasting without power is safer than holding position, while it pins-down your hand, and needs to be programmed back-out. Without power, unless you have a mammoth-machine... there is little threat of crushing. (If you have a mammoth machine, you NEED breaks and a back-out ability that can be operated manually.)

Again, you can't "trust" that the software will ever safely stop/reverse/operate as intended, if it just failed and needed to be stopped in the first place.

Breaks are not hard. But I admit that it is a luxury item. A simple lever pushing on a turning axle is all you need. it is not hard to mount a pivot close to the spindle, on the spindle-mount, with a simple spring-retraction to pull it into the spinning axle. Remember, it is not a powered-stop, so there is only momentum you are stopping on the router/spindle. You don't need breaks on the axis, though you could also implement them.

I am sorry, but I don't know any stepper that will "coast" without power. The coasting you see is due to the programmed deceleration-coasting. No power results in instant stopping on a stepper, due to the fact that they have a permanent magnet which acts as a break. Routers are AC powered, and have no magnets, normally. They will coast until the bearing resistance slows them down.

If you have ball-screws with a small TPI number like 1-8, you can simply push the steppers out of the way. Not quite possible with an ACME or an all-thread that has 6-20 TPI.

Having a program stop is good only for when the program runs too far, and it does not have a deceleration-coast. (Again, I am talking about an "emergency stop". Not just an, "oops, it went to far stop".) You should not be using an emergency-stop for normal operation. Its purpose is for critical, life-threatening, stopping, in the event of an emergency. Program stops are for "oops, too far" interruptions, and might be used often.

[hemsworthlad]

I am sorry, but I don't know any stepper that will "coast" without power. The coasting you see is due to the programmed deceleration-coasting. No power results in instant stopping on a stepper, due to the fact that they have a permanent magnet which acts as a break. Routers are AC powered, and have no magnets, normally. They will coast until the bearing resistance slows them down.

If you have ball-screws with a small TPI number like 1-8, you can simply push the steppers out of the way. Not quite possible with an ACME or an all-thread that has 6-20 TPI.

While I agree with some off what you say. . . In an emergency stop situation with a moving gantry then a stepper will coast even without power and depending on how it's driven and the speed traveling at the time it can be considerable, certainly enough to trap you if it was at full rapids.
Proof of coasting even while going resonably slow feeds can be seen when you hit the Estop button by how far off from original position due to missed steps caused by inertia.
Anybody who's been cutting at speed and hit BIG RED will vouch for just how far it keeps traveling and when it's 3/4 way thru a 6hr job it feels like it's never going to stop.!
Also My machine is medium sized no way mamoth but I can tell you this for sure, If it grabs ya or you happen to put your arm or hand in the wrong place it's going to rip it off or snap it like a carrot and you wont simple push my 5mm pitch ballscrews out the way when you get trapped.!

[RomanLini]

If you get an Estop with multiple contact blocks, just add one for the Estop input to Mach3. Then, while killing power, it'll also stop the step pulses, as well as stop your g-code from continuing on while the machine is stopped..

Excellent idea! That is basically what happens on my machine when I kill the power switch.

Helmsworthlad-

Erm . . But that mean your steppers are still under software control which isn't a safe state to be in.?

Not with my machine (as the brains on board is powered down too) so no stepper pulses can be made. By killing the power the brains dies in maybe 0.2 seconds and stops making step pulses, the stepper drivers are powered for maybe 1-2 seconds until the big caps discharge which is long enough to brake the machine, then after that it freewheels with no power to anything. And I have handwheels on the stepper motors to let me extract vital body parts from between the cutting tool and the job.

JD_Mortal-

Coasting without power is safer than holding position, while it pins-down your hand, and needs to be programmed back-out. Without power, unless you have a mammoth-machine... there is little threat of crushing.

I get your point, but to me anyway the best way to get the machine to stop moving in a crash is the quickest way. That might be the difference between wrecking the job (or one part of a batch job) or bending the tool, wrecking the whole job and maybe the machine.

But your machine and your needs are probably very different to mine, I do a lot of small delicate type machining, so if I stop the machine dead it just chews a little chunk out of that one part, but if the machine "coasted" it would mash a $50 precision miniature endmill through a 1" solid slab of plastic.