I have been playing with this website and I wanted to try fast speeds, but it seems like LowRider is not accepting them
https://vector76.github.io/gcode_tpgen/
with these speeds, the squarness test should last 23s (according to Repetier-Host), but it lasts 1minute and 30 seconds. Am I being unreasonable?
Have you updated the firmware? The standard firmware has hard limits set for max speed.
You can also use M203 to adjust the limits without recompiling. M503 to view the current settings, and M500 to save.
so writing “M203 X100 Y100” is going to set speed for 100mm/s without doing anything to firmware?
I have not updated firmware so far. I thought that I got SKR board 3 months ago, so there should not be a need to update. But if you think that I should do so, I will look into it
Yes. It will revert next time you reset the controller unless you also use M500 to save to EEPROM, in which case it will persist.
should i write it like this? both line of code under each other
“E500 X100 Y100”
“M203 X100 Y100”
Sorry, I wasn’t clear. M203 sets the MAX speed so the speed cap is much higher. You generally only do it once. You can do it on the console if you have a console, or at the start of the gcode file if you don’t have a console.
Then everything else in the gcode script is unchanged and it will go up to the max speed you specified. 100 mm/sec is 6000 mm/min so if you want the full 15000 you need to specify a higher value like M203 X300 Y300.
Never seen the ‘E’ command.
Just to be clear, M203 sets the max federate in millimeters per second. It is likely that other federate settings you use will be in millimeters per minute. To save the settings, as Jamie indicates, you need an M500. This writes them to EEPROM so that they are set after you reboot. And, they will also remain when you do a firmware upgrade unless you do a factor reset (M502).
Personally, I changes the max federate when I change to using my laser, but I don’t use an M500 to save the setting. I place the feedrate change in my start g-code for my laser. Thay way my machine will revert back to the lower federate for my router when I cycle the electronics.
Also, you may want to play with the acceleration. It can have a big impact.
Shared a drag race script I use to test Rapid motion limits. Doing a few drag race runs helped me identify a few things to tune and fix, places where cords on and off the gantry would snag, rails/leadscrews to lube, rattling because belts and/or Core bearings need tighten/adjust, need for a mod to keep Vac hose from slapping against the belt, etc…
Ran with NO bit in the router. Running this script with a bit will likely damage the bit/surface.
I don’t configure Rapids this fast for a job, mainly did this to learn the limits, and for fun. It’s ridiculous seeing how quick these things can move.
At what point do the rotational forces of the spindle/collet start interacting/interfering with the lateral forces of the gantry movement? Well, in a meaningful way; they are always interacting, but it’s minimal enough to be inconsequential at the limits of the bits and/or hold-downs…
Just riling up the math/engineering ADHD geeks… 
Thanks to all for suggestions. Right now, I dont have access to LowRider as it is in my college. As soon as I come back, I will look into fast speeds to find the sweet spot I will be using. I will let you know about the progress
“E500 X100 Y100”
“M203 X100 Y100”
I tried these commands and I have to say, that LowRider went much faster. But it behaved little bit weird, I will have to tune and fix, when I come back
I’m not sure our end mills have enough mass to cause their own gravity, no matter how fast they’re spinning.
I mean, I don’t expect my dewalt to spin fast enough to cause a singularity in my shop.
Don’t overlook the Armature spinning those collets. That does have enough mass. 
That was sort of my thought… you’ve got a low-energy (in the grand scale of things) gyroscope that you’re pushing around. When the gantry is exerting force near the center of mass/rotational force of the spindle/armature, it shouldn’t be an issue, but if you are pushing it from the top or bottom, it’s going to want to lean sideways…
Gyroscopes are funny things. One of my favorite magical tech handwaves from Heinlein in Number of the Beast.