CNC router occasionally makes jarring noise and home jumps when it does this. Help!!

[Neale]

Dare I ask for a bit more clarification? Dangerous ground, here, perhaps! But here goes...

What I'm not quite sure about here is the difference between G0 and G1. So, a few examples to see if I understand. In all cases, we start at (0,0).

G0 X100 Y100
This is a rapid move at max permitted machine speed. If max X and Y speeds are 1000mm/min, then Mach (or LinuxCNC, I presume) will move each axis at max permitted speed which actually moves the cutter at 1414mm/min across the bed (hypotenuse of right-angled triangle).

G1 X100 Y100 F1000
Mach/LCNC calculates the speed needed for each axis to achieve an actual cutting speed of 1000mm/min along the cutting path, which translates to a speed along each axis of 707mm/min, well within max permitted limits. So you could write G1 X100 Y100 F1400 and actually cut at that speed.

What Jonathan has said is that (using these figures) the max cutting speed along either axis is 1000mm/min, but in principle you could ask for higher cutting speeds and if you are cutting along a diagonal, you might achieve them. What is also relevant, maybe, is that it doesn't matter if you have different max speeds along each axis; Mach/LCNC will do the sums needed to make sure you don't exceed either max although this may mean that rapid moves will achieve different speeds over the bed depending on direction.

That all seems pretty straightforward, but it's the difference between G0 and G1 that I'm not quite clear about. G0 takes max speeds for each axis which you have defined for the machine, and will use them for G0 rapid moves and may even achieve speeds over the bed above the max for an axis if you happen to move along a diagonal. G1 needs a speed defined (either by setting it once in the gcode and using it as a default or by setting it in each G1 command) and will use this to calculate actual cutting speed whether along an axis or at some angle (or even around an arc), as long as max speed per axis is not exceeded. I think this means that if I stick a G0 move in at the top of my gcode file with a ridiculously fast F setting, then LinuxCNC will always give me the fastest rapids that preset max X and Y settings permit, but I should make sure that the F setting for g1 cuts is the actual cutting speed that I want. I use LinuxCNC, by the way, so maybe there is also a slight difference of interpretation compared to Mach 3.

As far as the original question is concerned, all this means is that you can look at max speed and accel along each axis independently in order to avoid missing steps and other nastiness, and actual speeds over the bed are just an accident of geometry and don't affect design and tuning parameters. If you are missing steps along X, say, during rapid feeds you might choose to reduce accel or max speed on that axis but you don't necessarily have to change Y if that is working fine with its current settings. However, if you get skipping during cuts, then it's a bit more complicated and you probably need to reduce the F cutting speed parameter just to reduce load as you can't tune this by axis.

And my apologies, guys - I was desperately trying to find an excuse for using nested integral signs and the odd greek symbol from the LaTeX library but just couldn't find a way to fit them in...