Official Luthiers Forum!

Hello,
I've had a K2 3925 machine for several years.
Quick question!
I tend to use it sporadically throughout the day, a short run here and there.
Is is OK to leave the control box on when the machine is not in use? I hear the servos "twitching" as it sits. That's normal. But I'm not sure if I should be powering it down between uses,
when it is not being run for several hours. Am I harming anything if I were to leave it on overnight, for example? Sometimes I like to leave a fixture set up and zeroed instead of powering it down and losing my place.
The computer will go to sleep and I don't worry about that, but I'm worried about harming the box.
Is there a general rule for this?
Thanks for your help!

Saul

I would leave it on just like you do Saul. Are you losing any place when the thing twiddles the motors?

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Ken

Saul, I'm curious, can't you log the coordinates in the machine coordinate system and then return to them after homing the machine which would allow you to shut it down and keep your g54, or does it not have that kind of repeatability? I'm trying to understand what kind of repeatability one can expect from this type of machine.

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Jim Watts
http://jameswattsguitars.com

Thanks for the response!

Ken, No, It doesn't lose anything as it twitches. It's perfect every time- so long as I don't lose power.

Jim, I think your question brings up the real issue: my rookie status on this thing.
I don't work from the home locations and honestly can't remember the last time I "homed" it.
I simply zero it out to whatever I happen to be working with wherever on the table I happen to be working.
If I lose my zero from power outage or for whatever reason it can be tricky to get things back on track. My work-around is to have with almost every part I make some sort of indexing hole or reference point. I run it before the rest of the machine work as a separate procedure and it usually consists of zeroing out the machine in the general vicinity, plunging a hole or two into a spoil board, that's where the parts fit and the rest of my codes contain those points. Since I've re zeroed it, everything is back in sync. Let's say I stall the thing and trip the control box. I simply remove the part, run my index holes again, replace the part on the new holes and pins and continue with the machining with as many steps or procedures it may require. I can stop and start anytime mid job, and if I rezero and run my index holes, everything lines up perfectly in the future.

I'm certain this is not the correct way!

Saul, There's nothing wrong with the way you're doing it but it probably does make for a little more work on your part. Second, I don't know what the power consumption of your control box is when it's idle but obviously it would consume less if it's shut down.

I imagine that the K2 has home switches already but if it doesn't, they're not that hard to add. If you home first thing when you turn on the machine, then zero for your spoil board/fixture holes you should be able to power down the control box and re-find your zero simply by re-homing when you power the control box back up. Jog your machine near the home switches before you power down so that the homing process will be faster. With Mach 3 set up properly re-homing just re-zeros the machine coordinates.

There's other methods of doing it but what I described above will at least let you shut down your control box between jobs. I use a fence more or less permanently attached to my table top that has a repeatable zero - all of my fixtures are referenced to it.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

On my old techno the mechanical home microswitches are fairly accurate and repeatable to a few thou. It is easy to check by using a dial indicator to a face on a fixture or other hard object. Since it is a servo machine (Saul you said you have servos ?) I use a controller feature called INDEX which is intended for ATC machines since they must know where to find the tools to a high degree of accuracy. When an axis is homed it then backs off to the next index pulse location on the little encoder wheel attached to the servo motor and that backed-off-index location becomes home and is repeatable to less than a half-thou. Hall effect home switches are more accurate if you have those on your machine. Saul, the way you and doing relative locating should be really good but a PITA.

I only power down my machine if I am not going to use it for a few months. I do stop the controller program whenever I am not using it which removes power to the servos. It will remember it's zero position when I do this or even if I do power down.

Andy,
RandK,

Thank you! I never knew of this, that Mach remembers my zero, but it makes perfect sense!
This changes everything!

And so it has been with learning to use CNC, learning to draw and learning CAM. I'll figure out just enough info to do work and will operate that way until I stumble upon a new command, a trick, or someone points out a solution or new way, and my world opens. This usually happens with with CAD. I have ways of getting something done and then I'll discover a new command that saves a bunch of steps and my drawings get better and faster.
I'm self taught with the help of videos, books, websites, etc, but most certainly from my friends here on OLF. I learn from every post in the CNC section.
Thanks for all your help and inspiration-

Saul, as you probably know they call this "The School Of Hard Knocks". I agree, the good people here on the OLF sure help soften the blows.

..When you have your controller on, there is current that it is always flowing to the motors. This is why when you turn the machine on, you year the motors "lock." Depending on what type of drivers you have, this current is very small, and the motors will be OK.....but they should not be twitching, that is for sure...

Now with that said, if your computer goes to sleep, there can be surges/spikes/signal that gets send out of the port connected to the controller....it is part of the normal process or bootup process a computer goes through...what this will tend to do, is in "some" cases, cause the motors to twitch or move a bit....hence, loosing your accuracy....

If you are going to leave it on, make sure it all remains on...and the other suggestion I have is to make ABSOLUTELY sure, that you have DISABLED all screensavers, sleep modes, power savings modes etc on your computer! You do not want some background process screwing up your bit stream to the CNC controller....

Go through a homing process or indexing process every time, and all this goes away....

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-CyborgCNC
http://www.cncguitar.com
https://www.facebook.com/CncGuitar

K2's use servos.....

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

We have a 3925G and use the home switches to locate fixtures like Andy said. I've only tested the X switch; it was repeatable <0.001".

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David Malicky

Not sure how the e-stop system works on those, but on a Fadal the e-stop cuts power to the motors and drives but keeps power to the encoders. At the end of the day, I'd just hit the e-stop which meant the only power being used was to keep the control on, and it would never lose position because of the encoders staying active.

Depending on your setup, servos can/will dither all the time. Since there's no load, it's questionable if they're using enough current for the power use to matter, but the drain is there. The electrical noise the motors make goes silent when you kill the power, so there's always at least some juice flowing.

Anyway, having an e-stop setup like the Fadal (or just wiring a switch in to disconnect juice to the motor power supply), would be an ideal solution.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Hi Saul,
I have the 3925 also and mine makes the twitching noise also. It is my understanding that the twitching is the encoder maintaining position on the Z axis as the ball screw needs a sort of brake when turned off to keep it from traveling in the -Z direction, when turned on the servo holds it in position , twitching sound should be super minimal.
Mike