returning to exact starting point

[Ezra]

Is there a way to return the machine to the exact same starting point on a piece of art work after I change the router bit? In order to continue carving an advanced piece without distorting the carving.


Im sure this may seem like a no brainer for you gentlemen but this is my first machine Im in the process of building and am thinking out the cut path and steps in my head..................and just wondering.


Thank You

[quazga]

I shouldn't try to help you out on this cuz I can't remember the exact details of what I used to do as I haven't touched my CNC stuff in over two years. So, from what I can remember, I can give you some basic info until someone who is really in the know shows up. However, keep in mind that everything I say could be subject to error.

As you know your tools come in different sizes and shapes. For each tool, you define the dimensions and type of tool so your CAM software can know what to do with it. As for the tool length, from the tool tip to the end of the tool holder when it's installed in the spindle you can either have you CAM software handle the different sizes or you can have your controller handle this.

In my case I had the CAM software handle the compensation for the different lengths. But one of the things I cannot for the life of me remember was how I went about defining the tool change position! I can't remember if it was defined in the post processor in CAM or a setting in the controller.

I didn't have an automatic tool changer so here is how it worked. In the G code there would be a command for a tool change. This G code is a T followed by the tool number. For example, T6 or T35 etc. When the controller got to the tool change command it would raise the tool up and then move over to a defined spot off to the side and pause for the tool change. I would then do the change and notify the controller that the tool was ready. Then you would see the tool move up or down in the Z axis via a move command in the G code compensating for the difference in length. Once this was done the controller would continue following the instructions of the G code until the next tool change where it would then go back the exact same spot for doing the tool change and then pause and so on.

I believe the technical term you're looking for is tool tip compensation. You get your tools and put each one in its respective holder and measure its length from some reference point. The reference point I used was the bottom of the empty spindle. You then enter the lengths for each tool and corresponding holder in either your CAM software or your controller. That way, either the controller or the CAM software can have a way to know where to move each tool so its tip is in alignment with every other tool that you may use.

Hope that helps until someone with more exact knowledge comes along.