Prusa Mendel Assembly (iteration 2)

From RepRap
Revision as of 06:45, 20 July 2012 by Mowi (talk | contribs) (Undo revision 61611 by Mowi (Talk))
Jump to: navigation, search

Prusa Mendel Documentation

Before You Begin

Before assembling a Prusa Mendel, make sure you have all the parts necessary. For the bill of materials, see Prusa Mendel.


  • This document is work in progress.
  • These instructions follow making a PLA based Iteration 2, where integrated bushings are included as part of the RP objects. The design officially supports different bearing combinations, including brass bushings, felt, and linear bearings. RP parts that are for different bearing types will look different and require additional steps but the primary assembly remains essentially the same.
  • TODO: Merge contents of Kliments Pastebin:
  • Although most steps are absolutely harmless when done right, you still might want to take precautions for your Health and Safety.
  • In this manual it is assumed that the smooth rods are 405mm each. The resulting threaded rod lengths are:

1x 440mm - low center rod 2x 450mm - top rods 6x 400mm - frame vertex 4x 320mm - lower rods for front and back side 2x 250-300mm - Z smooth rods

Assembly Instructions

Assembling the X-axis

Parts Required

  • 1 RP x-end-motor


  • 1 RP x-end-idler


  • 2 405mm smooth rods (420mm in recent instructions)
  • 3 M3x10 bolts
  • 1 608 bearing
  • 2 M8x30 fender/mudguard washers
  • 1 50mm M8 threaded rod and 1 M8 nut or 1 M8x25 or longer bolt
  • 3 M8 washers
  • 1 M8 nut

Instructions <videoflash>K9bXwOZOXps</videoflash>

  1. Drill out the center hole in the hexagonal section of the x-end-idler and x-end-motor parts to 8mm, if it is not already this size.
  2. Take the x-end-idler part. Check the size of the hole on the flat, thin side surface. If it is 4mm in diameter, enlarge it using a file until it's 8mm in diameter.
  3. Place the x-end-motor and x-end-idler parts 50cm apart, so that the hexagonal sections are facing each other.
  4. Slide the two 420mm smooth rods into the x-end-idler part.
  5. Slide the other ends of the rods into x-end-motor part. The hexagonal sections of the motor and idler parts should still be facing each other.
  6. Make sure the rods are seated as far as they will go into the x-ends.
  7. Thread an M8 nut onto one end of the 50mm threaded rod, if not using a bolt.
  8. Put the following parts in this order onto the free end of the threaded rod (behind the nut) or M8 bolt: 1 fender washer, 1 M8 washer, 1 608 bearing, 1 M8 washer, 1 fender washer.
  9. Thread the free end of the threaded rod into the side of the x-end-idler part. The bearing should be on the outside. Put an M8 washer and an M8 nut on the inside and tighten.

Frame Triangles

This step takes about 15 minutes per triangle, for a total of 30 minutes.

There is a triangle on each side of the Prusa RepRap. You will need to make two of these and then connect them together (in the next steps) to form the Prusa frame. Each side is an equilateral triangle with a frame vertex on each corner. You can use either footed or non-footed vertices to build this. (The footed ones look better, but are not critical.) The instructions assume you are using footed vertices.

Parts Required (per triangle)

  • 2 RP footed frame vertices


  • 1 RP frame vertex (non-footed)


  • 1 RP bar clamp


  • 3 400mm M8 threaded rods
  • 14 M8 nuts
  • 14 M8 washers
  • (Optional but recommended) A piece of threaded rod or wood or any other material with precisely 320mm length. This is your frame jig J1.


  1. Take one of the 400mm threaded rods, and slip an M8 washer onto the middle of it.
  2. Take the RP bar clamp (the U-shaped bit with the two holes) and slide the threaded rod through the two holes until the clamp sits next to the washer.
  3. Slide another washer onto the rod from the other side.
  4. Thread two M8 nuts onto either side of the clamp, until they are next to the washer, but do not tighten them yet.
  5. Thread another two nuts on each side of the rod, followed by washers. See the picture for what it should look like. <flickr>5188262096|thumb|right|m|The bar clamp on the threaded rod.</flickr>
  6. 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.
  7. 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.
  8. Take another 400mm M8 threaded rod and place a nut followed by a washer at each end.
  9. 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.
  10. 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.
  11. Adjust the nuts around the bar clamp (but do not crush the bar clamp together yet) until it's approximately in the middle of the rod. Leave the nuts there loose. See the photo for what you should have at this point.
  12. That's it, that's one of the triangles done. Repeat the entire procedure for the second triangle.
  13. After you have done the second triangle, you need to make sure that both triangles are the same. To make sure the holes line up, you can lay the triangles on top of each other and insert six M8 bolts through the each hole in the vertices. When they all line up, tighten all the bolts.

Next we will connect the two frame triangles to form the Prusa RepRap frame. The easiest way to do this is to thread everything onto the front and rear threaded rods and attach those to the triangles first, and then thread the top rods through. That's the method the instructions below will follow.

Front Threaded Rods

This step takes about 30 minutes.

These two threaded rods are used to connect the front/bottom vertex of each triangle as well as to attach the y stage bars and y motor bracket to the frame.

Parts Required

  • 2 assembled frame vertex triangles
  • 2 RP bar clamps


  • 1 RP y motor bracket


  • 18 M8 nuts (or 16 under the described modification)
  • 19 M8 washers (or 17 under the described modification)
  • 2 M8x30 fender/mudguard washers
  • 1 608 bearing
  • 2 294mm threaded rods

Instructions <videoflash>9ut45Pe9gkw</videoflash>

  1. Thread the bottom rod first. Thread an M8 nut onto the middle of the rod. Slide an M8 washer next to it.
  2. Thread the rod through the bottom hole of the RP y motor bracket. The bottom hole of the bracket is the larger one on the long, straight side.<flickr>5373622677|thumb|right|m|The long, straight side of the RP y motor bracket will be parallel to the ground when you are done.</flickr>
  3. Slide another washer onto the other side of the bracket and add another M8 nut to hold it in place.
  4. Add a nut and washer to each end of the rod.
  5. Now thread the top rod. This is a complicated one, so make sure you get it all done in the right order. From left to right, the rod should have: 1 washer, 2 nuts, 1 washer, 1 bar clamp (threaded through the holes), 1 washer, 2 nuts, 1 washer, the y motor bracket (pointing out towards you), [1 washer, 1 nut, 2 washers,] 1 fender/mudguard washer, 1 washer, 1 608 bearing, 1 washer, 1 fender/mudguard washer, 2 nuts, 1 washer, 1 bar clamp (threaded through the holes), 1 washer, 2 nuts, 1 washer.
  6. When you hold it with the protruding part of the motor bracket pointing towards you, it should look like the picture below. Verify this now. NOTE: This diagram and the text above show three washers and a nut on the top rod immediately to the right of the motor bracket. This is inconsistent with the assembly detailed below in Assembling the Y axis, where they are missing and the fender/mudguard washer contacts the bracket directly. Photos have been found of completed printers featuring both assemblies. It appears that unless you have a motor with a rather long shaft, the current drive pulley requires assembly per the Y axis diagram below. The diagram shown here will not work as the pulley will not align with the bearing. You can verify this for yourself on your build by holding the motor in place on the y motor bracket and considering the position of the pulley when mounted on the motor shaft. In operation, the toothed part of the pulley needs to line up with the bearing. The extra washers and nut mentioned above are a spacer to achieve this, and should be included only if necessary.
  7. You can now attach this setup to the triangle sides. Make sure the protruding part of the motor bracket points OUT of the triangle. Thread the ends of the rods through two of the footed vertices. Put a washer and nut on the end of each threaded rod. It should now look like this:

If you are using a wide belt on your Y axis see Prusa Mendel Wide Belts.

Rear Threaded Rods

This step takes about 20 minutes.

These two threaded rods are used to connect the back/bottom vertex of each triangle as well as to attach the y-stage bars and belt pulley to the frame.

=Parts Required