Ok, it’s come to the time to repay for all the help and information from the community. This part i copy from my contribution at http://www.thingiverse.com/thing:222245
Next improvement for the Velleman K8200 3D-Printer, the Z-axis parallel spindle gear driven by the original motor. When I had noticed that the extension-arm extremly wobbles when the printer quickly changes directions, i realized that the missing Z-guidance on right site is responsible for that. So, the main target is to reduce/eliminate this wobbling.
The upgrade was planned in concern to keep changes to the original as less as possible and to protect my/your purse ;-)) See printed result on the last image!
Instructions
The right steering track rod is replaced by a control rod. Keep in mind, that this new spindle is of the same type like the left one!!
In my case this is a TR8x1,5 precise-control-rod for CNC-engines i replaced formerly but you can use a normal srew rod M8 like the original one. The left side spindel torque is transferd to the right side by a T5 Belt over two idler pulleys. Replace the steering rod holder on the right side with new holder keeping ball bearings for the right spindle. The only challange is to get a closed T5-belt in defined length between 1060 till 1090 millimeters (in my case 1075 mm from this onlineshop). You can remove the lower angle brackets of the top cross bar to avoid loss of printing height. Attention: Check out the new max printing height and update this value in your printing software/firmware!! (In my case i lost only 6 millimeters)
Furter informations can be found in the german section on RepRap-Forum (forums.reprap.org) - search for “K8200”
Time required to print the parts: ~3-4 h
Time required to assembly parts: ~2-3 h
Additional Needs:
400 mm spindle (control rod) with 8mm diameter +
1x spindle-nut (both like left side - see note above!)
11x M3x10 / 4x M5x10 screws wih nut,
2x M8x30 screw with 2x nuts
10x M8 washers
4x 608 ball bearings
1075 mm closed T5-belt 6mm
P.S.: All things were printed with the original hotend. No further upgrades are necessary to get the parts, but your printer should be set well 
And now the best! the result! …no comment
After several weeks of using this new improvment i came to the conclusion, that it was the best i could change on my K8200. Never see any wobbling problems again.
