[RossMosh]

I purchased a used CNCRP4896 machine about 3-4 weeks ago. I've been going through it, learning with it, and cleaning it up. I'm up to limit switches. I bought some NPN Proximity switches and they seem to work, to a point. If I slowly and carefully jog the machine over to the switch, the machine will go into the emergency mode. If I move over with some speed, the proximity switch stops the machine but the machine has already hit the sensor and moved it back a distance. If I kept the sensor behind the hard stop, it would hit the hard stop pretty good. I expected the machine to stop dead (within reason) and this isn't coming close to that. Are my expectations off?

My second question is more of a preference question. When I load some G-code into Mach3, the orientation drives me nuts. I want the display to orient how I look at my machine. The orientation is 90* the other direction. Everything goes the right direction it's just rotated in a way that bugs the hell out of me. I'll get over it if I have no alternatives but I'd love to be able to rotate the way the code loads if possible.

[underthetire]

That's why
1. You mount the switch at 90 deg to axis travel with a switch dog, so you don't bottom out like that.
2. MTBs usually use a mechanical limit switch for overtravel. Something like a SL1A yamatake-Honeywell.

[ahren]

Ross,

Re-orienting X and Y in Mach 3 is not too hard. You do this under Config->Ports and Pins. You will assign the X axis pin settings to the Y axis. You will then need to go to Config->Slave Axis to reconfigure the Y and A axis to be slaved together, instead of the X and A axes that are slaved in your current configuration file. After doing this, make sure to save settings by going to Config->Save Settings.

Of note, whenever you change a slaved axis setup, it's worth dropping the R&P drives away from the machine to confirm that they are spinning the correct direction. The motors need to spin opposite directions, and you can easily change the direction by changing the "LowActive" setting for the direction bit of any given axis.

As for your sensors, if they are inductive, you might try putting some steel on the carriages -- most inductive sensors have significantly more range when detecting steel instead of aluminum. You might also try lowering the debounce settings under the Config->General Config menu.

Hope that helps!

Best regards,

Ahren
CNCRouterParts

[LeeWay]

You can also setup your soft limits to be identical to your Opto's. This way it will have a slow zone when it is approaching any switch. That should take care of hitting the switches for all but a runaway situation. Then ain't nothing going to stop it nicely.

[RossMosh]

Thanks for all the responses. I'm going to move forward with the limit switches as is and spring load them to hopefully ease the brunt of a boo boo if, or should I say when, it happens. I spoke to someone at PMDX (bad with names) and they agreed with LeeWay with the soft limits being the key to this whole scenario. I know the importance of soft limits but I was unsure if these cheapie sensors were doing their job or not. Didn't want to bother wiring them all up if the sensor was flawed from the start. Tomorrow I'll wire them up and setup the homing and soft limits and hopefully I'll be all set in that regard.

Ahren thanks for responding, I just want to make sure we're on the same page. Mach3 and whatever I draw displays things correctly. I'd just like to see everything rotated 90*. If what you described does what is shown in the attached picture, then I'll follow your instructions.

[ahren]

Ross,

Yes, changing the axes per my suggestion will rotate things 90 degrees on your cutting table. Which axis is X versus Y is really just a matter of preference, and is usually driven by where you park your computer and drive your machine from. If you're used to looking at the front rather than the side, this rotation should make more sense for you.

Best regards,

Ahren
CNCRouterParts

[mmoe]

Just to clarify, Ahren's suggestion will rotate the orientation at the machine, not the display. There really isn't a way to rotate the display that I'm aware of, mostly due to the fact that the X/Y coordinate grid is always laid out the way you see it on the screen. When creating any sort of drawing or graph, X is always horizontal and Y is always vertical on the page (not vertical in 3d, just up and down vs. left and right). Changing the axis should effectively do the same thing, but you will have to draw with the narrow dimension on the X axis and the long dimension on the Y axis. I think it is generally traditional that the Gantry is the X axis and the axis the gantry travels on is the Y axis, so changing them around would probably make sense anyways (at least every machine I've had is set up that way).

Also, proximity switches, which is what you are using for the limit switches, are not the ideal choice for limit switches IMHO. Proximity switches are usually used to signal when something is in position to do something, where timing is less critical than just supplying a signal. They get used for things like indicating whether or not a dust collection hood is up or down, or if some moving component (like a tool changer arm) is in position to change the tool or at rest. These signals are not needed to be instant because the controller will just wait until the correct signal is given, and since the component being monitored will likely always end up in one of two spots, there isn't any need to monitor them beyond are they in position or not in position (by the switch either being On or Off). Also, in some cases the state of being open can be used to prevent motion since these parts can often be in the way of the machine moving until they are returned to their resting state, where the proximity sensor would then be closed.

Limit switches are almost always mechanical levers with rollers on the end that can be adjusted to fine tune when they trigger. They are usually triggered by a ramp, which once past the roller holds the switch open (they are usually Normally Closed loops). You should also use the "Enable" output to signal the servo or stepper drives as to whether or not to be active. If the limits are triggered, the servo/stepper drives are immediately shut down via the "Enable" output. I've never had a machine with this type of setup (Mach or otherwise) where it didn't stop on a dime when the limits are triggered.

Someone previously suggested moving the proximity switches 90 degrees from the axis, but that would be even worse IMHO. The problem is that if the gantry or other axis moves too fast past the switch, it will no longer be triggered and the slower signal could have been missed entirely. If you continue to use proximity switches instead of limit switches, you are best off keeping them where they will collide with the axis, which hopefully has a better chance of keeping the switch triggered. My advise would be to invest in some limit switches as soon as possible.