If you're going to make pulse, then please learn how to assemble the juicer quick with the least amount of fuss.
If the motor shaft is dirty, use a scratcher pad to clean it. Make sure to oil it now and again with vegetable and preferably olive oil to keep it from rusting.
Now observe the flat inside the cutter and line up with the flat you've observed on the shaft. Push it all the way on until it bumps against motor.
For people that are right-handed, hold the tube like this. You'll find out why shortly
Install the screen onto the tube and hold down the far corner edges (see red arrows) so that you can...
With your right-hand, line up the bracket magnet (in yellow on picture) to point towards the left and line up the grooves (red on picture) on the chute with the notches of the screen and the tube. If you reverse the chute, it won't go on.
Continue to slide on the chute until it fully seats.
Slide the assembled tube onto the motor. Line up the tabs like so.
With the tabs lined up and the tube fully against the motor housing, rotate the tube to make it lock into place.