VFD spindle control safety

[Clive S]

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

[magicniner]

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.

[m_c]

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

This.
Unless you have a spindle with lots of torque (I.e. milling machine/lathe spindle that's been geared down from a multiple KW motor), then holding the spindle with your hand will be enough to stop it from spinning up.

Plus most VFD manufacturers advise against regularly power cycling VFDs.


If you were worried about damage, I'd put the risk of crush injuries on any reasonably sized/powered CNC, far higher than a spindle starting up when you've got your hands near it.

[Neale]

If you were worried about damage, I'd put the risk of crush injuries on any reasonably sized/powered CNC, far higher than a spindle starting up when you've got your hands near it.

Probably right. Thinking about it, I've stalled my 2.2KW spindle by trying to push it too fast/deep through steel - with a 4mm cutter. That was at around 5K RPM - no torque worth talking about. A spanner on a spindle would easily hold it.

[routercnc]

I’m in the minority here and I start and stop my spindle manually through large push buttons on the control box main panel. These are linked back into the VFD inside the control cabinet through the built in terminals under the front cover.
Same goes for the speed control which is a potentiometer on the control box main panel linked back to the VFD.

Some jumpers in the VFD have to be set to use external controls.

This means the PC is not in charge of the spindle at all except for an e-stop where it will stop and inhibit the spindle running, again using terminals on the VFD.

I’ve never had the spindle come on when changing tools, and have never forgotten to start the spindle before hitting cycle start. In the same way that I have never tried to drill a hole on a drill press without starting the motor! It’s a preference thing and I just like to use it that way, plus it feels a bit safer.

[Doddy]

I've had my G&T for the night so am feeling somewhat ambivalent. The OP questions safe operation - and he's correct to do so. I hold a view which I think is shared by some that, gauging an acceptable level of personal risk against convenience that I/we are prepared to cut some corners. But, please understand that doesn't make it safe. I wouldn't pretend for a second, or promote that nipping up a cutter in a spindle with your hands/body/spanner anywhere near is "safe" in the event of either hardware or software failure.

Right!, where's that blasted cat?

[Kitwn]

At present I'm following Doddy's principle of taking what I see as an acceptable risk when tool changing but I'm aware my machine has a built in risk which is that the relay that starts the spindle will pulse briefly during power up/down of the controller. I use a cheap Chinese breakout board and LinuxCNC. The relay on the board operates a relay on the wall that activates the spindle and the dust extractor.

Not a problem when it's all switched on but if I wait long enough there'll be a power cut just as I have a firm grip on a tool to pull it out of the (still quite tight) collet and there'll be enough stored charge in the VFD capacitors to modify my finger prints.

It's all a balance of probabilities but reading this thread does remind me I should add some kind of interlock. Perhaps a nice big switch in series with the VFD control relay which includes a back contact for a warning light. I have all the necessary bits in the shed so it's not exactly beyond what is 'reasonably practicable' as the legislation says.

I would never criticise routercnc's KISS approach but know myself well enough to predict the odd oversight, especially towards the end of a tiring day and am therefore in favour of the more automatic control for my own machine.

[ericks]

Been using my new diy machine for a while but must admit i have not completed the safety design...too busy with other stuff:)

I should know better!!