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IndustryArena Forum > OpenSource CNC Design Center > OpenSource Software > Initial moves on CNC job varies from time to time
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  1. #1

    Initial moves on CNC job varies from time to time

    I am using GRBL and UGS, and Fusion 360 for CAM, and i am making my very first chips as we speak.

    I have not installed homing switches or Z probe switch yet. I just jog my way to roughly the XY position where i have put my origin in the model and GCODE, then I do the old paper slipping trick for setting the Z height. Afte that, I set all my axes to 0, and press start.

    the funny thing is that sometimes, the spindle moves slightly up and over the workpiece before it moves in XY direction to where it will do its first cuts. This is what i prefer!
    Sometimes though, and more often than not, the spindle start moving directly towards the location for the first cuts, without moving up and over the workpiece at all. It's snapped one of my precious little Proxxon end mills already. i can prepare for it though, because the visualizer in UGS shows me that the first move only involves XY movement.. that's when I zero the Z axis a little higher to avoid crashing. If the stock had any bumps or raised parts though, it would be unavoidable, i believe.

    What i don't understand is what on earth am I doing differently from time to time to "achieve" this, and am I doing it in CAM or UGS, most likely??

    Thanks for any response.

  2. #2
    Join Date
    Nov 2012

    Re: Initial moves on CNC job varies from time to time

    As I try only using open source software I'm not familiar with how Fusion 360 does things, but the "traverse height" (the minimum Z height to which the tool must rise before doing any non-milling movements) is a distinct concept any CAM processor keeps track of and should let you set as you wish. As such, Fusion 360's CAM (g-code output) processor should let you set it, and you should be mindful of what you set it to, for every project. In this particular case, there are pretty much only two possibilities: either you're unaware of this setting and some of your projects get generated with some default traverse height that is too low or zero, OR the UGS sender, for whatever reason, decides to rip the relevant lines from your g-code (not as outlandish as it sounds - senders routinely mess with the g-code before sending it to GRBL eg. to remove comments or replace arcs with many small linear segments etc. although in this case this removal would be a bug). The easiest way to decide where the problem is would be to load your g-code into a simulator BEFORE ever trying it with UGS, to see if the heights are correct or not. There are a number of these available for free (very useful to see what will happen even when bugs are not involved) - just search for "Basic CNC Viewer", "NCSim", "NC Corrector" or "CAMotics"...

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