Yet another modification of the K8200 Z-axis to prevent wobble, this time with standard M8 stainless steel rods and anti-backlash system using standard M8 hex nuts for the people who have another stepper motor and flex shaft coupler lying around and want to make as few changes as possible. You don't have to adjust the steps/mm value and all in all I think even though this modification doesn't improve the print quality al that much, it at least prevents the M8 threads from wearing by distributing the weight of the extruder arm (on the original design all its weight is only held by one(!) M8 hex nut, which is not even well-suited for building linear motion systems).
Like the design by floyd871, mine uses the following parts:
Upper Z-Carriage Holder http://www.thingiverse.com/thing:175137
A documentation of all mods that I've made on my K8200 see
Besides the printed parts you will need:
-another M8 stainless steel rod. Its material is harder than that of the steel nut and will cut its way through irregularities.
-am M4 threaded rod for cutting into pieces and mounting the anti-backlash nut box to the arm extension
-8 M4 nuts and washers
-an M5 threaded rod for cutting into pieces for mounting the arm. Then you will also need 8 M5 washers and hex nuts. Alternatively 6 20mm M5 bolts should do as well
-an "M8 spring" you can get in hardware stores. Look at the photo above to see which one I got. Cut a piece of about 3cm and bend the cut end away from the center so that it doesn't get between nut and theraded rod while spinning.
-5 M8 hex nuts (2 to be mounted inside the box, to for fixing the axis on the top printed mount [use washers as well] and 1 optional one for counter tension on the flex shaft coupler.
-4 short countersunk M3 bolts with washers and nuts to assemble the printed motor mount.
-4 short (10mm max.) M3 bolts to mount the motor to the mount
-4 10mm M5 bolts to mount the motor mount to the frame. 2 can be scavenged from the original Lm8UU linear bearing holder at the end of the Z-axis arm.
-a total of 11 square M5 nuts for the extruded profiles (6 for the arm extension, on for the top bearing holder and 4 for the motor
-well, a NEMA 17 motor
-a 5->8mm flex shaft coupler
-a 608z ball bearing for the rod
-lubricant for the rod
Some assembly advice:
Don't make the anti-backlash assembly too tight and make sure it travels smoothely along the entire way before mounting.
Increase the motor current a little. I set the motor voltage to 670mV, that worked well.
Connect the second motor in parallel to the first one. For the motor I had lying around, the following modification worked to have it spin in the right direction:
Flat cable->Motor wires:
Blue -> green
Once everything is assembled you can print and attach the M5 and M4 caps to the naked threaded rod endings.