I quite fancy the idea of my CNC software turning the spindle off automatically....what I'm not keen on is the concept of it turning on again while I've still got my hands on the collet holder!
So how is this addressed in practice? (I'm sure it's not just me that it alarms!) ...the thought of a simple relay to control the spindle on/off doesn't seem that robust....I'm figuring there needs to be some form of time delay (sustained condition for X seconds) before the spindle can be allowed to start?
If you're really concerned, build in an interlock of some kind, which can be something as simple as just switching of the spindle power when needed.
If doing a tool changes in Job then the M6 tool change macro code stops the G-code and the spindle via switching the relevant output state controlling the spindle relay. It then waits until you press cycle start again often pausing for a second or two so the spindle spins upto speed before continuing on thru the g-code. It's not a time based operation at all.
OR. . . You can manually stop/start the spindle often Via a screen button or thru MDI using M3/M5 G-codes which does the same has screen button and switchs the relay with it's output signal.
If you really don't trust the relay or system then just do like M-C says and put an in-line isolator switch. Doesn't need to be on power lines it can be a simple on/off switch breaking the signal to relay so the NO relay can't be switch state.!
In practice it's not a problem and I've never had a false start or relay switch state.
Last edited by JAZZCNC; 18-12-2012 at 07:27 PM.
I guess ultimately then, it's how much do you trust the relay (or more so, the relay contacts) that controls the spindle startup! (I'd figured there'd be a little more 'conditional' scenarios involved before a spindle could be allowed to start)
The problem with an isolating switch, is forgetting to switch it back to the 'enable' position & then walking off (or forgeting to isolate it in the first place!)....but far better that then having my hands turned to mincemeat by a spindle relay contact closing while my hands are still on the spindle!
It's the control software or more accurate the signal state you can't trust and in extreme case's it's possible it could switch state thru noise interference.!!
You could build into the Macro some conditional checking like checking the state of a input. This could be done by using double throw relay which sets a spare input used has a NOT-READY-NO-GO
This is one of the reasons for using a M6 tool change macro. It's in this macro where you'd put code for things like auto tool changers etc and also for doing safety checks like this if needed.! (could even turn kettle on for you for quick brew between changes. . Lol)
Thats the reason all factory based cnc machines have to be interlocked!
Although I have seen some bypassed but not to be advised though!
Most problems arise from the ID ten T doing the controlling!
If you're worried about not switching something back on, for the interlock, use a switch with an extra contact, or wire in an extra relay, and have it connected to an additional input, then set up the controller to prevent it from restarting until it sees the additional input, and flagging up if the interlock isn't closed.
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