are travel stops required? or are limit switches enough

[multiplex]

the x, y and z axis on the router i'm building are all enclosed, and will not allow the machine to over travel.

however i have been considering using spring loaded stops, to prevent a sudden bind up if the machine over travels.

what have other people done in these situations?

here is a pic of where i was at a couple weeks ago.

[vid1900]

Stepper motors make a lot of noise, but I don't think they will hurt themselves if they run against the stops for a moment.

If you are using rack and pinion, you could have the rack end just before it hits the stops of the machine. Then the motor can spin freely.

You can use some prox sensors to tell the mech to stop:

http://www.syntextech.com.tw/pro6-body.htm


The mech "knows" where it is in the software, so you might never hit a stop anyway after you do your initial set up.

[Switcher]

I do cnc machine calibrations (day job).

Every cnc machine should have at the very least 3 ways to stop.


1) Software Limits (Machine Control Mach3, etc...)

2) Hardware Limit Switch

3) E-Stop


My 2.0 cents.

.

[Cruiser]

Servo's can Fry in less than a hummingbirds heart beat ! Have limit switches set up at each end of travel and use them to set zero and before allowing "auto set to zero" use limits to find extents and settup your Soft limits with something like 3" for the slow zone to start with. Then as long as machine doesn't loose position it will slow down and stop on the limit switch or any distance that you setup from tripping switch. It is a really neat feature so use it. Good luck on your machine build, looks good so far.

[multiplex]

ok thanks for the help. the machine will definitely have limit switches.

i may forget the spring loaded stops on some of the axises though (it would still be able to bottom out against a hard stop) - it seems like the gantry can move pretty fast, but right now the screw is not hooked up, and i'm sure that will slow things down alot.

[vid1900]

Have you guys had any problems with mechanical switches filling with dust and no longer functioning after a year? Even some sealed ones from Cherry seemed to fail (used as homing switches).

The proximity ones seem to be money well spent. Or am I missing an easy, high quality mechanical switch?

[mxtras]

First - you want hard stops. They may never get used but the first time you have a failure that drives your gantry off the rails, you will wish you had tried to put somthing in place. I have seen a gantry driven off the rails on a $1.5M ultrasonic knife cutter during assembly and testing and it's not pretty, nor is it cheap.

Second - if you are going to use cheap switches as limits, you would be better served operating them through a plunger and putting the $2 switch in a small enclosure to keep it from being contaminated. The industrial switches are expensive but survive rediculous abuse because the case and actuator are well constructed. The contacts inside those Heavy Duty, Industrial limit switches are just as frail and prone to damage as your $2 switch but they are very well protected and sealed.

Put some hard stops in place.

Scott

[Greolt]

Originally Posted by multiplex Are travel stops required? Or are limit switches enough the x, y and z axis on the router i'm building are all enclosed, and will not allow the machine to over travel. however i have been considering using spring loaded stops, to prevent a sudden bind up if the machine over travels. what have other people done in these situations?

I have sitting here on my desk a CNC machine that has a home switch, no limits and no estop. Works perfectly. Very safe.

It sprays ink onto paper. It's made by Canon. Made by the millions.

My point is that every machine is different. So to say a CNC must have this or must have that is just presuming all sorts of things.

Ask yourself what will happen if through user error, electrical fault or software error it tries to travel beyond it's envelope. Will it damage me? Will it damage the machine?

There are many small homebuilt type routers that are very happily running without limits.

Others that have home switches and use soft limits very successfully.

I have a router about the same size as yours. I have limits and home. But it is more to do with convenience than safety or machine preservation.

If I hit a hard stop then I go "Bugger!! I lost steps. Need to start again"

That's it..... No damage...... No safety issues.... Just inconvenient.

So figure out if your router needs them to stay in one piece and stay safe. If it does then there is your answer.

If you want convenience then put them on. Or use homes with soft limits. That will work really well.

In answer to your original question. How about placing some rubber buffers between the relevant components to absorb some of the "BANG" if it hits.

Greg

[Geof]

Originally Posted by mxtras First - you want hard stops. They may never get used but the first time you have a failure that drives your gantry off the rails, you will wish you had tried to put somthing in place......Put some hard stops in place. Scott

Allow me to give a slight correction/modification; you need some soft hard stops. If you stop something over a distance of 0.5 inches with a rubber bumper all the components see a lot less stress than if so stop something over 0.05" with a solid stop.

If you have steppers I think that is all you need; a stepper does not mind being stalled.

If you have servoes you need overcurrent protection.

[multiplex]

yeah just to clarify, i'm not considering not having any mechanical stop - agree thats a very bad idea

but was thinking about these, which since i bought them i think i will use. Would allow for a more gradual bottoming out, and will de-accelerate the machine in a more appropriate fashion

[triden]

Just a suggestion, but if you are worried about a switch getting full of debris and dirt...try using a fully sealed reed switch and have a magnet on your device triger it as it drives by. It would be a very simple solution, and never stop working because of dirty contacts.

[Drakkn]

If you have a 3 axis machine do you need 6 limit switches - if so how do you wire them up , my controller board only has one connector for limit switches