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

[Jonathan]

In LinuxCNC you can specify a tolerance on the G64 command, so the controller sacrifices constant speed to maintain the toolpath within the specified tolerance. e.g. put 'G64 P0.05' at the begining of the G-code and the path will not deviate by more than the P from the true value.

It's not critical and perfectly fine to have differant setting for each axis, Mach will only go fast has the slowest axis anyway when moving 2 axis at same time. Try it.!! . . Double the Speed of Y axis velocity (if machine can do it) and home the machine and jog away good distance and Type G1 X0 Y0 F ( Feed value abobe X axis velocity or same has Y axis velocity) in the MDI box.

You've raised a mildly interesting point there, which I think is worth expanding to show why what you've observed occurs. The velocity of each axis cannot exceed the values in the motor tuning, however the speed of the machine (i.e. the feedrate) can, unless the machine is only moving in one axis. This occurs because when two axes are moving at given velocities, the resultant feedrate is the vector sum of these velocities. One way to visualise it is as a right angled triangle, where (for example) the velocities of X and Y are the sides adjacent to the right angle - the length of the hypotenuse will equal the feedrate.

Example 1:
Suppose you set your maximum velocity settings for X and Y both to 1000mm/min, home the machine (so it's at 0,0) then enter 'G0 X100 Y100'. Mach will move both X and Y as fast as it can (as it's a G0 move), so the feedrate you actually get is ., assuming the machine can accelerate to that feedrate within the specified distance.

The practical upshot of this is you can specify a feedrate higher than the velocity setting, and get that feedrate in some circumstances.

Example 2:
Same as example 1, except we enter 'G1 X100 Y200 F1100'.
The required speed is 1100mm/min, so the following must hold: ., where X and Y are the X and Y axis velocities.
The Y axis must travel twice as fast as X to go in the correct direction (as 200/100=2), so we have .
We also have the condition .,due to the motor tuning settings.
From (2), ., so substitute that into 1:
.
.
.
Whence,
.

(You can also solve this graphically quite easily - which may be more intuitive.)

So the X and Y velocities do not exceed 1000mm/min, yet the machine can in this example cut at 1100mm/min.

In reality, it's probably not a good idea to use this 'feedrate bonus' as it makes the feedrate a function of the direction in which the machine is travelling, so unless you're cutting a single straight line the feedrate you actually get will vary (continuously if an arc move).