RepRap 3D Printer - Prusa i3 - Build Log: Part 2

X-axis and Z-axis Assembly

The x-axis and z-axis are both a part of the same frame and are assembled together. The process is similar to the y-axis in that order of assembly is not critical and test fit everything before tightening.

Assembled x-axis frame


Start by preparing the aluminium x-axis frame by tapping all the holes with M3-0.5 threads. I did this at the same time as I prepared the y-axis carriage earlier in the build.

Next assemble the x-axis belt tensioner. The assembly is similar to the y-axis tensioner which was assembled earlier. Insert a 623ZZ Bearing into the printed bearing guide once again taking care not to crack the bearing guide plastic. Heat may help here.

Next install the tensioning bolt into the printed x-axis tensioner. I used an M4x30mm, but a longer bolt would not go astray. The bolt fixes to a captive nut which is inserted into the printed part. Make sure you ream out the hole which takes the M4. 

Finally fix the bearing guide into the printed x-axis tensioner part with an M3x35mm with washers and a nyloc nut. If you have access to a M3x25mm bolt, this may be more suitable as the 35mm long bolt is a little excessive
623ZZ Bearing inside bearing guide

Fully assembled x-axis tensioner

Now insert three LM8UU bearings into the printed x-carriage. It is worth paying close attention to the locations of the bearings on the printed part, to ensure that no unwanted print errors cause the bearings to foul with unwanted plastic. It is also possible to lock the bearing in place with M3x25mm bolts, but my bearings fitted so tightly (like extremely tightly), that I didn't feel it necessary.

Three LM8UU linear bearings inserted in x-carriage

Insert two LM8UU linear bearings in the printed x-axis motor mount. Again, clean up any unwanted plastic which may foul the bearings. Insert a M5 nut into the printed part - this will screw into the z-axis lead screw at a later stage.

Two LM8UU bearings inserted in x-axis motor mount

Captive M5 nut in x-axis motor mount

Insert two LM8UU linear bearings into the x-axis idler, cleaning up spurious plastic as necessary. Insert a M5 captive nut, as was done for the x-axis motor mount. Next insert the previously assembled x-axis tensioner and lock into place with a M3x20mm bolt with washer and nyloc nut.


Fully assembled x-axis idler.
Now assemble the x-axis idler, x-carriage, and x-axis motor mount together with two M8x370mm smooth rods. Note that all the bearings face the same side.
Assembled x-axis.
Now attach a printed z-axis bottom to each side of the aluminium x-axis frame. Use three M3x15mm. (M3x10mm bolts are a better fit with tapped aluminium, as they sit flush with the back of the aluminium; however, the bolt kit I used didn't have enough M3x10mm bolts so I used M3x15mm instead. If you have enough 10mm bolts use these instead.) Don't install the z-axis top yet.
Z-axis bottom fixed to the x-axis frame. Similar on opposite side. 
Now on both sides install the M8x320mm smooth rod into the z-axis bottom by pushing the M8 into the 8mm hole in the printed part. It should be a snug fit.
Z-axis bottom with M8 smooth rod fitted.
Now slide the fully assembled x-axis down into the M8x320mm smooth rods. The bearings should face the aluminium frame. Fix the top of the M8 smooth rods to the aluminium frame with the printed z-axis top. Fix the z-axis top with two M3x15mm and washers.
Assembled x-axis fitted to the z-axis smooth rods. (Note belt is shown installed here, but installation will be covered at a later stage).
Now the stepper motors need to be installed. One stepper motor is fixed to each printed z-axis bottom with three M3x10mm bolt and washer. Place the motor such that the wiring faces the middle of the aluminium frame. I found the fit to be quite tight, and had success by only partially tightening each bolt to get the positioning correct then progressively tightening each bolt.
Stepper motor installed on z-axis. Similar other side.
To attach the stepper motor to the M5 lead screw I used 5mm internal diameter clear plastic tubing. I found the plastic tubing to be such a tight fit that tube clamps weren't essential, however I installed them regardless. Take a lot of car fitting the tube clamps as I nearly broke one of mine trying to fit it onto the tube. I had success by fitting the tube clamps to the tubing, prior to fitting the tubing to the stepper and M5 lead screw.
Tube clamps fitted around plastic tubing.
Screw the M5 threaded rod into the captive M5 nut in both the x-axis motor mount and x-axis idler. The bottom of the M5 threaded rod should be hard up against the stepper motor. Place the tubing to couple the two together and position the tube clamps as low as possible (to avoid them clashing with the x-axis). Use M3x15mm screws with washers and nuts to fix the clamps in position.

M5 threaded rod installed into x-axis .

Plastic tubing coupler installed between stepper motor and M5 threaded rod

Now fix the remaining GT2 belt pulley to the final unused stepper motor with the grub screws. Then, using three M3x10mm bolts, fix the stepper to the x-axis motor mount.

Stepper motor with GT2 belt pulley fixed to x-axis motor mount.
The final step in the x-axis/z-axis frame assembly is to install the x-axis belt. The belt fits around the GT2 belt pulley on the stepper motor at one end and around the x-axis idler at the other end and is joined to the x-axis carriage in the centre. The attachment of the belt to the carriage is a little unusual and is shown below.

Make sure that the x-axis tensioning bolt in the back of the x-axis tensioner is fully out prior to installing the belt (this will give the maximum amount of tensioning possible). Install one end of the belt first, and then feed the belt through to the other end, this will give the maximum offcut for possible later use. The belt loops through the printed x-axis carriage and zip-ties to itself. Remove the ends after installation.
GT2 belt installation on the x-axis carriage. 
Tighten the x-axis tensioning bolt to fully tension the belt.