Hello all, thats my first topic so please be forgiving 
I have problem with printing, all my prints have very visible layer lines. Is it possible to reduce it?
I am using k8200 with all stock parts. Layer height 0.3mm Pic related:
If you hold one of your prints next to the threaded rod driving your Z axis, are the bands the same spacing as the threads on the rod?
Yes! I confess that I assembly printer myself, is something broken?
Your z axis lead screw may be off center, causing the print arm to move back and forth slightly as the print head rises. You should be able to see this happening if you tell the print head to move up a few cm and watch the print head closely.
Some have gone to great lengths to add a second drive on the right hand side of the printer to reduce this. Or a better lead screw may help. But start by tightening everything up and figure out what’s moving.
You`ve got absolute right! Thanks for Your assist
The problem was here:
In my printer nut is lower than hole for it. It was about one milimeter free space and it gave symptoms that You described.
Now I put hexagonal washer in this hole and then comes nut. I have to put spacer under two small screws which hold two plastic parts together, because rod cant move, but after this operations it is quite OK:
There is still small loose, I have to improve it, because nut is smaller than diagonal of hole, but I think it will be good.
If You have any advice I will be pleased to hear it
Do you use a flexible coupler between Z-motor and threaded rod, in stead of the stock rigid one?
The four lineair bearings at the car should do the vertical guiding, not the threaded rod.
No, all parts are stock, only improvement is piece of glass on heated bed.
One bearing can be damaged it move are harder than others, but I dont replace it yet because it still works not so bad.
A flex coupler is a must, I think. It’s easy to replace.
And make sure the top bearing and the plastic nut holder are aligned (in x-direction) I had to put some shims between plastic part and aluminium plate.