Assembly

This document will guide you through putting together your Prusa Mendel.  Please read it through briefly before starting your build, and make sure you have everything you need to continue. It's frustrating to be stuck with a half-finished machine because you are missing a part or tool.
---General notes---
The design is standardized around the LM08UU linear bearing. It is possible to use a printed bushing holder instead and equip it with either IGUS bushings or brass bushings, and it is also possible to use a springy PLA bushing instead.
To make a LM08UU equivalent with IGUS bushings, superglue an IGUS bushing into each end of the bushing holders. If there are two linear bearings on the same rod, only one side of each needs a bushing.
The rest of this document will use "linear bearing" throughout. Substitute whichever variant you are using.

Some M8 washers are slightly bent - they have a wide side and a narrow side. If you place them next to a bearing, make sure the narrow side is against the bearing or the bearing will no longer turn when the nuts are tightened.

---Assemble the extruder---
Plastic parts needed:
-Extruder body
-Extruder idler
-Extruder large gear
-Extruder small gear
Other parts needed:
-1 NEMA17 motor
-1 hotend
-1 M3x8 grub screw
-6 M3 nuts
-3 M3x40 bolts
-1 M8x20 grub screw
-1 M8 hobbed bolt
-4 M8 washers
-2 M8 nuts
-3 608 skateboard bearings
-3 M3x10 bolts
(optional) 2 short, stiff springs or silicone pads
Tools needed
-Wrench/spanner to fit M8 (preferably 2)
-Soldering iron
-Drill with 8mm and 3mm bits
-File
-Screwdriver or allen key to fit your M3 bolt heads and the M3 grub screw

Take the extruder body and snap off the small support piece attached to it. It should separate easily. If it leaves a messy surface, clean the surface up.
Use the drill to drill through the 8mm hole in the extruder body, the 3mm holes for the motor bolts, the 2 3mm mounting holes on the bottom and the 3mm hole for the idler (where the support piece was).
Melt two M3 nuts into the nut traps over the mounting holes.
Drill through the filament channel to make sure it's clear.
Place 1 608 bearing on the M8x20 grub screw and push it into the idler. It will only fit if the bearing is on the middle of the grub screw. It will click in place.
Attach the idler to the extruder body and fix it with the M3x40 bolt. Make sure the bolt head is on the FLAT side of the extruder body. You can put a nut on the bolt if you want, but don't tighten it very tightly.
Place an M3 nut in the small gear and fix it in place with the M3x8 grub screw. Slide the gear onto the motor shaft and fix it in place with the grub screw. Do not overtighten, and make sure the motor can turn freely with the gear in place.
Attach the motor to the extruder body with the 3 M3x10 bolts. The bolt heads go on the FLAT side of the extruder body.
Place 2 608 bearings in the recesses in the extruder body.
Place the hobbed bolt in the large gear. If it's too loose, pad it a bit until it sits tight. Place two washers on the opposite (flat) side of the gear and slide the hobbed bolt through the two bearings into the extruder body. The gear teeth will mesh with the small gear already there. If they don't, adjust the position of the motor and/or the gear on the motor shaft until they do. Make sure the bobbing on the bolt aligns with the filament channel. If necessary, add another washer between the gear and the extruder body. Place a washer followed by 2 M8 nuts on the opposite side of the extruder body to fix the bolt in place.
If you are using springs or silicone pads, place those on the remaining two M3x40 bolts. Place two nuts into the nut recesses above the two bearings. Use the M3x40 bolts to fix the idler in place. You will adjust the tension later when you insert filament, so don't worry about that for now.
Assemble your hotend according to your specific hotend's assembly instructions. I am assuming you have a hotend that is matched to your extruder body.
Attach the hotend to the extruder. If your hotend has a flat mounting plate, make sure the holes on it align with the holes on the extruder body so that the filament channel leads into the hotend. Redrill holes as necessary if something does not fit.

---Prepare the x-end-motor and carriage---
Plastic parts needed:
-x-end-motor
-x-carriage
-2 belt clamps
Other parts needed:
-2 405mm 8mm OD smooth rods
-1 NEMA17 motor
-1 pulley to match belt
-1 M3x8 grub screw
-4 M3x20 bolts
-3 M3x10 bolts
-8 M3x20 nuts
-5 linear bearings
-zip ties
Tools needed:
-Screwdriver or hex key to match your M3 bolts and your grub screw
-Solid surface (table or floor)
-Soldering iron
-Round file

Drill through the hexagonal nut trap from the longer side with an 8mm drill.
Push the 2 smooth rods into the sockets in the x-end-motor piece. Press the far end of the rods against a solid surface to make sure they go all the way in. They will be a bit stiff at first. File the entrance a bit if necessary.
Place the pulley on the motor shaft such that the teeth of the pulley are as close to the motor body as possible. Make sure it doesn't touch the motor body however. Fix the pulley to the motor shaft using the grub screw.
Place the linear bearings in the three slots on the carriage. Be careful - while the holders have a bit of flex, they will break if pushed too far.
If necessary, fix the bearings in their holders using zipties. Do the same for the x-end-motor. Use one of your remaining smooth rods to test that everything is sliding smoothly.
Attach the prepared motor to the x-end-motor piece using 3 M3x10 bolts. Place it so that the cables point downwards, toward the flat part of the piece.
Melt four nuts into the nut traps on the carriage with a soldering iron. Place a nut on four M3x20 bolts, all the way to the head of the bolt. Attach the belt clamps to the carriage using these bolts. Make sure their teeth point towards the carriage. Do not tighten these at all yet, just attach them loosely.
Attach the two linear bearings to the x-end-motor. Slide a smooth rod through them to make sure they move smoothly.

---Prepare the x-end-idler---
Plastic parts needed:
-x-end-idler
-bearing guide inner
-bearing guide outer
Other parts needed:
-4 M8 washers
-1 M8 nut
-1 M8x50 bolt
-1 608 bearing.
-2 linear bearings.
Tools needed:
-M8 wrench
-Second M8 wrench or M8 socket wrench or adjustable wrench
-Superglue

Place the two parts of the bearing guide on either side of the bearing. Put glue on the surface between them and press them together. Let the glue dry. Meanwhile, drill through the nut trap from the longer side with an 8mm drill.
Put an M8 washer on the M8x50 bolt. Slide on the bearing with the bearing guide. Make sure the washer does not lock the bearing.
Add another washer, and slide it through the 8mm hole in the x-end-idler. Place another washer and nut on the other side. Tighten and make sure the bearing can spin freely.
Attach the linear bearings to the x-end-idler. Make sure a smooth rod moves through them smoothly.

---Place the carriage on the x axis---
Plastic parts needed:
-x-end-motor assembly
-x-end-idler assembly
-x-carriage assembly
Other parts needed:
-1 900mm belt
Tools needed:
-Screwdriver or hex key to match your M3 bolts
-Solid surface (table or floor)
-(optional) M3 nut key
-Round 8mm file

Slide the carriage onto the two smooth rods attached to the x-end-motor. Make sure it slides on smoothly. Verify that the belt clamps are on the same side as the motor.
Press the two rod ends into the x-end-idler. Push them in all the way, with the edge of the idler against a solid surface. They will have some difficulty entering at first. Keep pushing.
Once the two x-ends are on the rods, try sliding the carriage back and forth. It should be extremely easy to move.
Attach one end of the belt to the carriage. Tighten the belt clamps against the belt, so the teeth on the belt clamp mesh with the belt. Route the belt around the idler bearing, around the motor pulley, and back to the carriage. Place it in the belt clamp, stretch it tight, and tighten the belt clamp down.
Turn the motor gear by hand, the carriage should move smoothly.
(If you have a hall effect Z endstop, now is a good time to attach the magnet that triggers it. Connect a 5V source to the endstop and see which size of the magnet makes the LED on the endstop light up. Then glue the OPPOSITE side to the bottom of the x-end-motor using superglue, near the linear bearing on the motor side. Verify that the LED on the endstop lights up when you bring it near the magnet.)

---Attach Z leadscrews---
Parts needed:
-2 M8 Z leadscrews (the shortest threaded rod pieces you have)
-4 M8 nuts
-2 springs that fit on the leadscrews
Tools needed:
-M8 wrench

Move an M8 nut all the way along the leadscrews from end to end to ensure no dirt is caught in the threads. Repeat if necessary.
Place an M8 nut at the middle of one of the leadscrews. Slide a spring onto the leadscrew next to the nut. Insert the whole assembly, spring first, into the x-end-motor part. Place a nut on the other end. Push the leadscrew into the x-end-motor, compressing the spring to about half its original length. Turn the nut on the other side until it's next to the printed part. Release the leadscrew, and the nut will be pushed into the nut trap in the x-end-motor.
Repeat the same procedure with the x-end-idler.

---Prepare the frame triangles---
Plastic parts needed:
-4 bottom frame vertices
-2 top frame vertices
-1 u-clamp
Other parts needed:
-28 M8 nuts
-28 M8 washers
-6 threaded rods of approximately equal size (370mm)
Tools needed:
-2 M8 wrenches

Take one of the threaded rods and slide the u-clamp onto the middle of it. Put an M8 washer and nut on each side. Do not tighten. This is your bottom rod.
Place a nut and washer on each end of the rod. Slide the rod through the wider bottom (footed) side of two vertices. Make sure the feet point in the same direction, and the bulge on the non-footed sides of the vertices point outwards. Place another washer and nut on the other side of the vertex. Tighten, but not too much. We'll need a bit of flexibility here still. Take another 370mm threaded rod and place a nut followed by a washer at each end.
Place one end of the threaded rod into the one of the two footed frame vertices. It should be in the same plane as the first threaded rod. Fix it in place with a washer and nut. You should now have two sides of the equilateral triangle.
Take the third piece of threaded rod and put a nut and washer on each end. Place it in the other footed vertex and fix it in place with a washer and nut. You should now have a triangle of threaded rods with two footed vertices on two of the corners, nothing in the third corner, and a bar clamp between the two vertices.
Take the third vertex (non-footed) and slide it onto the threaded rods in the final corner of the triangle. Measure the lengths of the two sides that go into the non-footed vertex to make sure they are both the same length, plastic part to plastic part. Adjust the nuts to make sure this is so. Once done, place a washer and nut on each of the two rods at the top of the vertex. Tighten all the outer nuts.
Repeat the process to make another triangle. Do not tighten the nuts on that one yet.

---Match the frame triangles---
Place the triangles next to each other, feet down. Match the length of the bottom of the second triangle to the first one. Tighten the nuts on the bottom rod. Now match the lengths of the two sides of the second triangle to the first one. Fix them, but don't tighten all the way. Flip one of the triangles around and verify the lengths still match. An easy way to do this is to slide something into the vertex holes so that they are aligned, and check if the holes on the other end are also aligned. A piece of smooth rod or spare M8 fasteners are good for this. Once the two triangles match, tighten all nuts, tightening from both sides to make sure they don't shift.

---Prepare the frame crossbars and Y motor---
---Join the frame triangles---
---Prepare Y bed---
---Attach Y bed and belt---
---Adjust frame to match X axis---
---Attach Z motors and couplers---
---Attach endstops---
---Prepare heated bed---
---Attach electronics---
---Adjust motor driver power---
---Prepare and route motor cables---
---Attach extruder and heated bed cables---
---Setup software---
---Test connectivity---
---Test temperature readings---
---Test heater function---
---Test motor movement---
---Test endstop function---
---Test extrusion---
---Prepare print surface---
---Level bed---