VFD spindle control safety

I have bought a CNC machine which has a Huanyang vfd and a spindle pre-wired. At the moment, the vfd is powered up when the control box is switched on so there is no independent control over the power to the vfd. The spindle can be controlled by software so when a tool change is needed the spindle stops.

I would like to be 100% sure that when I am changing the cutter the spindle cannot start and in my inexpert opinion this can only be done by disconnecting the vfd from the power or the spindle from the vfd with a switch. Switching off the vfd (which I cannot do at present but is easily achievable) feels wrong but the manual is very clear that the vfd must never be powered up with the spindle disconnected. If I went down the spindle disconnection route I cannot imagine that I would never accidentally power the vfd without switching the spindle back on.

So, as far as I can work out, the only safe way to do a tool change is to turn off the vfd. Is that what people do?

Quote:

---

Originally Posted by Tangoterrier

So, as far as I can work out, the only safe way to do a tool change is to turn off the vfd.

---

You are correct - as far as providing a completely safe solution you would require to disconnect the supply. The manual does indicate an electromagnetic contactor (relay) but notes that this should not be used as a general on/off control.

Quote:

---

Originally Posted by Tangoterrier

Is that what people do?

---

Nope, life's too short.

No, I never turn off the VFD during tool change. Would probably double tool-change time, waiting for VFD to power down/run up. I'm with Doddy - life's too short...

A little less certain that powering off the VFD, you could incorporate a switch in the control cable from the computer to the VFD preventing it being remotely activated by accident. This doesn't protect you against a control fault in the VFD itself. The danger then is that you forget to switch it back on and dig a non-rotating tool into your workpiece. How you protect against that is up to you.

Kit

I realise that I have to trust some amount of hardware and software. However, I am more concerned about triggering the "start" function by accident, which would move the spindle to the next position and then run up the spindle. So, I would get some warning as the machine would start to move from the tool change position, allowing me to let go the spanners. In addition, my F360-generated gcode seems to need the start button to be hit twice - first moves spindle to tool change position, second moves it to start position before turning it on.

I control the spindle by supplying a signal to the VFD control input, so a loose connection would stop it running rather than start it. There are other possible failure modes, of course, but these seem to be less likely and the associated risk is less.

In addition, I am the only user of a hobby workshop so my approach to risk is different to a commercial workshop. I'm now curious to know how commercial machines address this kind of issue

There will be interlocks on a commercial machine. I was contemplating my little SX2.7 but realised that I'd previously removed the swarf guard from around the spindle - of course its a requirement to move this to change tools and this provided complete isolation from the incoming supply - I expect any commercially available machine will have similar interlocks. God help you within a commercial environment if you defeat such an interlock and the HSE get involved.

Also you can factor in that there is little to no torque on start up of the spindle with these type of spindles .

If the VFD is not of exceptionally poor design you will be able to hard wire an E-Stop switch directly to the VFD data inputs and configure the function in parameters if required, when activated this will over ride any other signal trying to power on the spindle until the E-Stop switch is reset.

I have done the non-rotating tool trick a few times with my previous machine!!

Quote:

---

Originally Posted by Tangoterrier

I have done the non-rotating tool trick a few times with my previous machine!!

---

Haven't we all! My normal process now is to add 8 second delay to the G-code after starting the spindle to make sure it comes up to speed. As the same relay starts the dust extractor I cannot hear the spindle start but keep a wary eye on the VFD display to make sure it doesn't stay at 00000. 8 seconds is enough to realise I've done something stupid and stop the cut before it starts.

Kit