3D Printing: How to Assemble the Prusa i3 Moving Y Axis
Once you have your frame built for your 3D printer, you continue with adding the moving elements to the basic frame above. Here you use linear bearings and smooth rods for the motion of the Y axis.
To assemble the moving Y axis, follow these steps:
Fit the linear bearings to the laser-cut Y axis plate:
Place three LM8UU linear bearings onto the Y axis plate: They should sit into rectangular cutouts in the laser-cut plate.
Secure these bearings with a single tie-wrap.
Fit 20mm M3 bolts and M3 nuts into each corner of the Y axis plate. The bolt head should be on the underside along with the linear bearings.
Assemble the smooth rods and Y belt clamp:
Fit the printed Y belt clamp with 2 x 20mm M3 bolts into the laser-cut plate on the same side as the linear bearings are secured.
Very carefully slide the two 350mm smooth rods into the linear bearings. (One side has a single bearing and the other has two.)
At the end of this, your moving Y axis plate will look like this.
Fit the Y axis motor and Y axis plate to the frame:
Fit a NEMA17 motor onto the printed motor mount that's already been fitted to the frame; use two M3 x 16mm bolts to secure. Slide on a GT2 pulley onto the motor shaft and secure with agrub-screw.
Place the smooth rods and moving axis assembly into the four printed corners. The cut-outs for them to sit into should be obvious. You may need to undo or slacken off the M10 threaded rod frame for them to fit.
Use tie-wraps around each smooth rod end and the printer corners to secure.
Turn the whole carriage over so the bed is facing down.
Wrap the GT2 toothed belt around the idler bearing and along the underside of the frame towards the motor. Then wrap around the motor pulley and back into the middle.
Secure the two ends to the printed belt clamp and fix them together with tie-wraps. Do not fully secure the tie-wraps at this point, as you will align and square up the frame before you tighten the belt.
Align the frame and tighten the frame and the belt:
At this point everything is hand tight and can be slightly adjusted; the first step is to adjust the M10 rods so the smooth rods are securely fitted into their recess on the top of the printed frame corners. Tighten these, but don't tighten too much as you are compressing the printed part. You do not want these to break.
Now align the M8 threaded rods so the smooth rods have a gap between them of 162mm at each end. It's important to get these parallel so the linear bearings can run smoothly along the rods and do not jam.
Align the motor mount to the correct position along the threaded rods. This position varies depending on the style of the printed belt clamp; just make sure the GT2 belt is in-line at both ends.
At the same time as the preceding step, adjust the idler mount position to achieve an in-line belt.
Make sure everything is tight and check again that distances are matching on each side and on the front and back of the lower Y axis frame.