saving tool offsets

[ethanbrush]

Good afternoon, I have been racking my brain to figure this out and was hoping someone could get me squared away. We have a 2002 fadal vmc 15 and I am trying to understand when the machine "knows" or doesnt "know" where the axis are, particularly in relation to powering off, cold starts, e-stop. For example, can I power off the machine, restart it the next morning and still have my coordinates as they were exactly? When the machine boots up it says "press start to initialize" and if i do that it jogs the axes a bit and seems to lose its position. If I skip the initialize, should the coordinate system remain as it was? Why this is important now in particular is we are getting ready for production and are wanting to save are tool height offsets and it is obviously very important that I know when the offsets have changed and when they are on. I have done some tests and it seems like that whenever I align the scribed line for the z-axis and do a cs, my z position and thus my tool offsets stay on, but if I to the cs with the scribed lines a little bit off, then my offsets are no good. Is it just a coincidence that when lining the scribes by eye I got it dead nuts where it was before, or can it somehow pick up its old location as long as you get it close?

Thanks

[scadvice]

The simple answer is the machine must find it's 'machine home' position each time you turn it on. The scribed lines, as you called them, are there to give you a repeatable machine home, thus everything works as you want it to. This 'CS position' is there to make everything repeatable as I said, and it also controls/protects your xyz software limits to about 1/4 inch from the hard travel limits. So...when you shut down at night always do a 'set CS' and 'HO'...the manual tells how to do this.
Steve

[ethanbrush]

thanks for the reply steve,

..But isnt there a serious limitation to how accurate one can visually align the scribed lines? typically my machine doesnt hold its xy coordinates after rebooting and I am not sure what I am doing wrong when its off or right when its on. Say I have the z lines lined up visually (which sets it for the correct height for tool change), to a cs and then set my offsets. Then I do the same thing again - visually line up the lines and cs it. Will cold start z height and thus offsets be the same?

[MBX5]

thanks for the reply steve,

..But isnt there a serious limitation to how accurate one can visually align the scribed lines? typically my machine doesnt hold its xy coordinates after rebooting and I am not sure what I am doing wrong when its off or right when its on. Say I have the z lines lined up visually (which sets it for the correct height for tool change), to a cs and then set my offsets. Then I do the same thing again - visually line up the lines and cs it. Will cold start z height and thus offsets be the same?

I am a noob at this, but in my limited experience if you home it before shutting down, and do a CS when starting up at the exact position it was left, the coordinates should not be off at all... I do not think you should have to re-align the scribe marks every time you power down if you send it to its machine home position, your CS should be right on every time...

When I CS my machine, it seems to jump all axis a bit probably to get a reading from the encoders but it doesn't lose position....There might be something else wrong if your machine is losing position between power up/down...

[vmcchris]

When you do a CS, the machine finds its exact home position through the machines encoders. The machine needs to be at an approximate location, then it will find the exact location. That is why you see the machine move a little. It scans for its home position.

[ethanbrush]

great, thanks that makes sense now

[Neal]

There is only 1 index mark in the encoders. If it misses the correct rotation of the motor it will cold start approximately .400" off its mark under normal circumstances. That is why you can just be close to indicators. The control searches positive and minus looking for the index mark and then locks on to it.

Neal