Thanks Fred, my acceleration settings were indeed at the default value. Increasing them helped.

I'm in the process of creating a spoilerboard with T-tracks for clamping. I plan on surfacing it with a 1/2 straight cut bit. Anything in particular I should watch out for ?

BTW, I discovered an android app called : GRBL Controller. It works great as a gcode sender. No need to turn on the PC. I installed it on an old android phone and connected directly with the arduino uno using a usb otg cable . It even uses the new GRBL 1.1 jogging commands ($J) for instant manual movement control and feedback.