When i animate a mortor 6d part and there a rig animation where the hands goes straight. the Mortor 6D part moves where the hand gets animated and it doesent stay where i want it to stay. Is there a way where i can make it stay there?
What? Can you elaborate a bit more what you want to achieve. the grammar in the post is not the best…
okay so in the video you can see i made the tool go foward and its spinning. and in the middle of the animation i didn’t add any keyframe so the tool went down to follow the hand. Im saying how do i make the tool stay front and not be effect by the rig animation
You would need to animate it to stay and that position, It will always try to follow the hand because of forward kinematics. Only way to make it not follow the hand is to change the hierarchy and parent the boomerang to HumanoidRootPart.
so there no way to make it not follow the hand. 
but is there any way to make it more accurate to make it stay in that position.
You could try instead of animating the boomerang, to script the movement. Use KeyframeReached to detect the keyframe where it should be thrown then run some code with TweenService and bezier curves to make it go in a boomerang shape or whatever shape you need.