Incorrect Axis Positioning

[oly2brf5]

I've had a bit of a problem with my Tormach yesterday in that twice it has gone to positions that are unrelated to the numbers in the G-code. The machine has been working pretty well so far, 12 hours a day for several weeks. I have had all the usual boo-boos, mostly finger trouble on my part, but this is the first time it doesn't seem to have followed the G-code. I've already successfully made four of the part in question, so I don't think there's anything wrong with the code. The numbers in X, Y, Z boxes on the computer screen seem to agree with where the tool actually is, it just isn't where it should be. I might admit to the fact that I have been running unreferenced. Also, when the machine had the first problem it had been powered up for over 6 hours. A shut down seemed to cure the problem; the second occurence was after another 5 or so hours. When I spoke to Tormach a few days ago on another matter they did suggest if the system was powered up for a long periods it may increase the chance of a software glitch. I should say I'm not using a Tormach supplied computer. How the PC has been reformatted and a minimal XP version installed. The PC only runs Mach3, no IE, no Firefox, no internet or network connections. I don't even store my G-code files on it.

I do have a suspicion that the limit switches are not working correctly as I have recently had one crash where I was a bit surprised that the limit switch didn't stop the motion. First thing to do this morning is to clean and check all the limit switches and reference the machine.

Any other suggestions gratefully received.

Regards,

Andrew

[LeeWay]

I have one computer that runs Vista. Sometimes if it sits idol for awhile, it won't like jumping right into a cycle. I first hit the reset button on the screen to alert the computer that someone is about to fool with it. Then hit reset again and load gcode as normal. This procedure has stopped a few gremlins I had in the past with that particular computer.

[MarkWink]

When it's "off" - is it all axis or just one?

How far is it off (miss steps - or truly gone a muck)?

Jog the machine with a hand on the table - you can feel and hear missed steps.

I leave the machine on all the time without a problem, although the computer needs rebooted once in awhile - "I'm a PC".

[oly2brf5]

Checked the limit switches, voltages in the cabinet and a few wires this morning, everything looks fine. So far the machine seems to be running exactly as expected.

To answer a few questions:

Both the X and Y axes were off

Long way off, 50mm in X and 20mm in Y

Jogging by hand is spot on, very smooth, no unusual noises

Referencing by hand and jogging across the part was within 0.01mm over 300mm

The really odd thing is the thing went too far yesterday; I can think of lots of mechanical reasons for losing steps, but it's more difficult to think of a mechanical reason for gaining steps. I suspect it's a PC or Tormach control or software issue, or finger trouble on my part. The second time I had just had a TTS collet come adrift and had hit STOP; which I now gather is not a good idea. Should have used PAUSE.

Next stage is to run the program in 'air' until it gets to the toolchange it failed at last time and then set the Z so it starts cutting metal again.

Regards,

Andrew

[saabaero]

You mentioned about not referencing your machine. I used to do the same thing but was having issues with my "Y" axis loosing position by (by random amounts) between .005" to .035". After I would run a short program it would consistently be out of position on the "Y" axis only when I returned and re-probed my origin point.

I checked the motor coupling, wiring, rebooted but nothing seemed to help. Then for the heck of it, I referenced the axes. After that the problem seemed to disappear. Coincidence maybe, but it was repetaably out of position prior to that.

My machine is still pretty new and I haven't run a lot of parts since but anymore I reference the axes and haven't seen the problem reoccur.

Yes, I know, it shouldn't have any effect, but...

[philbur]

I'm no expert but my understanding is that the control system needs a machine reference as all the calculations are done according to machine reference not the user defined part reference. Where the machine gets these references from if you don't assign them I don't know. Possibly they are arbitrary. If one of these arbitrary references are within you part reference envelope then the machine will get into negative number calculations, which it may not be very happy with.

The manual makes it very clear that setting machine reference is important although it is not exactly clear why.

Just a thought from a hack
Phil

Originally Posted by oly2brf5 I might admit to the fact that I have been running unreferenced. Regards, Andrew

[LeeWay]

I never use machine coordinates at all. Not yet anyway., When I start having tooling offsets and things like that, then I might have to start using that and home switches.
If you have servo motors, I think it is more important as well, so that you don't tear up a machine or motor. With steppers though, they are perfectly happy hitting a hard stop with no damage. On my mill, the home is always different depending on what kind of part or fixture I am using, so I have no switches on the table or Y axis. Only a limit at the top of Z.

I do understand the reasoning behind the machine coordinates, but if Mach 3 is setup not to use them at all, there should be no issues with it.

[RTP_Burnsville]

Did you by chance happen to use the MACH stop command in the middle of a program and then try to continue? I found that using stop and then attempting to continue results in where the machine thinks vs where it actually is can be greatly different. Using the pause and continue commands generally yields much better reults.

I always reference my machine before starting and have never had the issue other than what I explained above.

[mactec54]

Hi oly2b2f5

I'm not sure the reason you would not reference/HOME the machine before you start
this should always be done (on every start up) or you will crash the machine as you have done, Once the machine has been homed out then the limit switches & soft limits will work as they should (if Tormach is using soft limits it has to homed for them to work)

If you don't home the machine at start up then it will not know were it is at Tormach should of told you this when you were talking to them

Once the machine has been homed then you set your work offset (X0Y0) & then your tool offset then you are ready to cut

[Don Clement]

And why don't you reference your machine? Alway the first thing I do is reference the machine and I don't have the strange problems you are having.

[LeeWay]

If you aren't using machine coordinates, Mach 3 opens up at home. If you have to move around to find your zero's, which I usually do, then once the dro's are zero'ed, thats it. It's home.

[saabaero]

I for one never used machine references because I saw no value to them for me. For one the Tormach doesn't use soft limits since they offer nothing over tripping a limit in the way of stopping speed without loosing position. Two, I don't find the limit switches accurate enough to use for repeating part reference consequently I always reference from the part or workpiece. Three, I don't have a tool changer. But in defense of this last one... Sprutcam adds a goto tool change position command into the toolpaths which shows as an error when the code is loaded without the machine being referenced. also, It is nice if the machine does return to a high enough Z to allow for changing the tool manually so having this command work is a plus.

Despite that, all I know is that is that, referencing the axes cured my issue with the Y axis loosing position. As I mentioned, it may just be coincidence but until someone can explain to me positively why it wouldn't have any effect I will continue to reference the machine for that reason alone.

I have designed and built several multi-axis trimming machines for manufacturing in the past and I have programmed them to automatically reference themselves to a "Home" position on startup and each time a program is changed. They have very accurate home/limit switches so the operator just installs the appropriate holding fixture for a given part and loads the correct program and the machine is ready to cut.

If referencing is important, I am surprised that the Tormach doesn't reference itself as part of the startup procedure. There can be a machine pause (for safety) so that machine motion doesn't start until the operator either accepts of declines the homing/referencing step.