Prusa i3 MK3S+ build guide part 2 y axis

Prusa i3 MK3S+ build guide - Part 2

February 2022
Building the Y-axis

Moving on from the first post where we assembled the 3D printer’s main frame, it’s now time to build and install the Y-axis carriage.

Incidentally, this is where I’ve noticed a difference between this MK3S+ and the earlier MK3S which is the brackets that hold the linear bearings to the underside of the carriage. The MK3S employs zip ties to hold them together!

If you’d like to check out part one of our build guide, click the button below.

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Prusa i3 MK3S+ build guide part 2 y axis

Y-axis carriage during installation

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Gallery - Assembling the Y-axis carriage

Lay out the parts for the Y axis carriage as per the Prusa manual.
Position the linear bearing in the cutout and orientate the lines of ball bearings diagonally. (Not as shown) There are 4 lines of bearings inside the cylinder which should be rotated to make an X pattern.
Repeat for the remaining two bearings.
Find the tube with the steel rods. Use the rods that are medium length or 330mm to be sure.
Insert rods through bearings as shown.
Lay out rod retainer parts.
Insert two M3 square nuts into the holes in the flat edge.
Insert another M3 square nut into the end.
Repeat until you have four assemblies.
Insert the retainers onto the ends of the rods as shown. Note the retainer end with the square nut inserted should face the inside. The longer flat edge of the retainer should be facing upwards in this orientation.
Prusa i3 MK3S+ build guide part 2 y axis
Tighten the rear screws.
Tighten the front screws.
Find your Y belt pulley and make sure the small grub screws are inserted.
Push the pulley onto the Y axis motor and make sure the grub screw is aligned with the flat part of the shaft as shown.
Tighten the screws but not fully. The pulley will need to be aligned later.
Lay out the Y axis belt parts.
Use the part with the shorter extrusion and insert one of the M3 nuts. This part is the belt retainer.
To insert the nyloc nut first push the long M3 screw through the part and screw the nut to it lightly.
Pull the screw back through the part.
Pull the screw until the nut is seated.
Nyloc nut in place.
Fold one end of the belt over one of the M3x10 screws as shown. The belt teeth should be on the inside.
Push the belt and screw into the part opening as shown.
Tighten the screw into the nut.
Turning the frame assembly on its side, screw the belt retainer onto the underside of the carriage in the orientation shown.
Pull the belt through the idler and then back around the motor pulley as shown.
Make sure the belt can move freely through the cutout section in the frame.
Insert one M3 nut into the second belt retainer as per the first part, then fold the other end of the belt around a M3x10 screw and push into the second belt retainer as shown. Insert another M3x10 screw.
Tighten the M3x10 screw to the carriage but not completely.
Insert the M3x30 screw through the second belt retainer.
Screw into the nyloc nut in the first belt retainer.
Screw until the belt is properly tensioned. The belt should not be able to sag but not be so tight as to damage the machine..
The screw should protrude through the nyloc nut.
The Y axis is complete!
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