Keeping CNC On Good or Bad

[Cartierusm]

So lets say I had to keep an exact setup while I glue up a part. If the CNC is doing nothing, just holding it's position. And the motors are not very hot, barley warm, is there anything wrong with leaving the CNC on doing nothing, for hours?

[Geof]

Originally Posted by Cartierusm .....is there anything wrong with leaving the CNC on doing nothing, for hours?

Let me pose a different question, after making an observation: Some people on this forum do fine engraving or machine injection molds, both of which which take hours to finish. Obviously in these cases the CNC machine is left on for hours...doing something. Why do you need to worry about leaving it on doing nothing?

[Cartierusm]

You never know, maybe there's something I'm overlooking. I run my machine for hours too, but the motors are moving, I just want to be sure that them holding still is not damaging in any way, but I, of course, understand your observation. Maybe the drivers would get too hot. I've never touched mine after they've been on for a while, but I have a fan blowing on them and an exhaust fan pulling the air out. I'll check tomorrow.

[ImanCarrot]

If you're worried about it, jog the tool away from the table an inch and run it cutting air.

I wrote a simple Warmup Cycle for my machine that spins the spindle up, moves X and Y stops the spindle, restarts etc... just keeps everything nice and even temperature wise.

My machine is never turned off. It's on 24/7, but for me temperature differences are more important than the cost of electricity!

[Geof]

Originally Posted by Cartierusm .....Maybe the drivers would get too hot...

If they get hot not moving the axes they will get hot moving them.

When there are separate cooling fans not dependent on motors turning, and cooling fans for the electronics that are always on or which come on automatically there is no reason to expect problems.

[Al_The_Man]

Originally Posted by Cartierusm is there anything wrong with leaving the CNC on doing nothing, for hours?

Stepper motors generally have current to them even when at rest.
Servo's, especially the modern torque mode amplifiers, have zero current at rest, that is if nothing is acting to back feed them, like a non-counterbalance vertical axis.
If the servo is in position at rest and nothing acts on it, then the command should be zero so the current will be zero.
Al.

[Geof]

Originally Posted by Al_The_Man ......If the servo is in position at rest and nothing acts on it, then the command should be zero so the current will be zero. Al.

On my Haas machines the servos seem to always be drawing a little power; the Z is counterbalancing of course so it is at 30 to 60% load depending on the machine, but the X and Y always stay around 2 to 5% load, sometimes more.

Which is not much different to running at a very light cut.

[Al_The_Man]

Depending on the drives type, it could be due to System or drive tuning, for e.g. if the drive has a balance control and it is not really at null or has drifted a bit, the control will always be making a slight effort to keep it in position.
As long at is not excessive it's usually not worth worrying about.
BTW, the % load on the Z when counterbalancing is often how the C.B. is adjusted close to zero load.
Al.

[Cartierusm]

Iman, what kind of machine do you have? Home built or production? Steppers or Servos? If home made what kind of drives? Thanks.Hmmm never turn it off, it's like when I first got into computer in the mid 90's, I turned them off because it was a little unnerving having them on when I slept, it took a while to get used to...now I have 8 computers in my house and shop and the ones I use everyday haven't been turned off ever, maybe a day here and there.

[Al_The_Man]

Personally what i do if not using a machine for several hours, is to engage the E-stop, this usually disables the drives/motors and other heat producing items.
This also prevents having to re-zero etc.
This may be also be preferable with steppers where heat is being produced and run-away is not detected.
Al.

[ImanCarrot]

Cart,

It's a high precision diamond turning lathe. A temperature change of a degree or two will throw my results out so everything is left running. Even my compressor runs 24/7.

Costly in electricity, but worth it in the long run. Any temperature differences can mean that I've made £15K's worth of parts wrong.

Incidentaly, on my turret mill I do what Al does- leave it in E-Stop- this stops the oil dripping down the spindle into the coolant tray- don't know if this is normal, but at least it shows oil is getting to the spindle