RepRapPro Mendel frame assembly

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Introduction | Frame assembly | Y axis assembly | X axis assembly | Z axis assembly | Heated bed assembly | Extruder drive assembly | Hot end assembly | Power supply | Wiring | Commissioning | Printing | Multi‑colour/multi‑materials | Colour Printing - Slic3r | Colour Printing - RepRapPro Slicer | Maintenance | Troubleshooting | Improvements

A notice about these instructions!

Since 1st April 2013, the RepRapPro Mendel has been superseded by the RepRapPro Tricolour and Mono Mendel.
If you are building the new machine, use the official, and most up to date, instructions on the RepRapPro wiki here


By the end of this stage, your machine should look like this:

RepRapPro Mendel assembled frame


You will need the following tools

  • M8 (13mm) spanner
  • Adjustable spanner
  • 300mm Rule
  • Lasercut MDF Measuring template (supplied with kit)
  • (optional) Spirit level, cotton and Blu-tack

Step 1: Frame triangles

Item Quantity
370mm M8 rods 6
Printed frame vertex with foot 4
Printed frame vertex 2
Printed U clips 2
M8 nuts 28
M8 lock washers 28

Note that there are three types of printed U clips in your kit:


The ones on the left are the frame clips, the ones in the middle are the Z-drive flexible coupling clips, and the ones on the right are the printed-circuit-board clips. For this step you want the ones on the left.

Split the components into two equal sets, then loosely screw them together into each frame triangle. Make sure you slide a belt clamp along the bottom M8 threaded bars between the frame vertices with feet, with a serrated washer and nut either side. The other nuts should also all have serrated washers under them.


Make the gap between the frame vertices measured face to face next to where the nuts and washers tighten about 290 mm.


Your kit has a template to make it easy to get these measurements right.

Don't tighten anything at this stage.

Step 2: Cross bars

Item Quantity
330mm M8 rods 4
470mm M8 rods 2
Printed U clips 4
M8 mudguard washers 2
8mm bearings 2
M8 lock washers 14 (12)
M8 washers 10 (28)
M8 nuts 28 (46)

The figures in brackets are the numbers if you want to add clamp nuts across the top bars (see below).

Assemble the bars as shown in this picture:


From top to bottom and left to right the sequences are:

  1. Nut, nut.
  2. Nut, nut, lock washer, lock washer, nut, nut.
  3. Nut, nut, lock washer, U, lock washer, nut, nut, mudguard washer, washer, bearing, washer, mudguard washer, nut, nut, lock washer, U, lock washer, nut, nut.
  4. Nut, nut, lock washer, U, lock washer, nut, nut, lock washer, 5 x washer, bearing, washer, lock washer, nut, nut, lock washer, U, lock washer, nut, nut.
  5. Nut, 5x(nut, washer, washer, nut), nut
  6. Nut, 5x(nut, washer, washer, nut), nut

Take care not to confuse lock washers and ordinary washers. If you don't want the clamp nuts leave out the [5x(nut, washer, washer, nut)]s on the bottom two bars.

What, you are asking, are the clamp nuts for? We have plans to add extra devices that will mount between the top two bars. The clamp nuts are there to retain those yet-to-be-designed devices. In all probability they will not be needed - we will almost certainly design the devices with U clamps that will attach directly without the nuts - but we put the nuts on the prototype just in case we might need them. If you want our recommendation: leave them off, and definitely leave them off if you are building the multi-colour/multi-material Mendel.

But if you do leave them off put just one of the nuts on plus a washer and lock washer to its left on each of the two bars (this will be used to retain an extruder drive bracket on some versions of the machine, and won't get in the way if you are building other versions). In this case the two long bars go:

5. Nut, washer, lock washer, nut, nut

6. Nut, washer, lock washer, nut, nut

Step 3: Put them all together

Item Quantity
M8 nuts 12
M8 lock washers 24
Printed XLR panel-plug holder 1

Firstly screw the cross bars into one of the triangles as shown:


This is the moment of what embryologists would call gastrulation: the point at which your RepRap acquires a front, back, top, bottom, left and right - as shown. The x, y, and z coordinate directions of the finished machine are also shown. If you like, use sticky tape to attach small labels to the rods while you are building so you can remember which side and which direction is which.

If you put the small number of nuts on the top bars, the ends with the extra washers are to the left.

On the bottom, and using the numbers of the rods from Step 2:

  • Back top: Rod 4, with the 5 washers together to the left.
  • Back bottom: Rod 2.
  • Front top: Rod 3.
  • Front bottom (yes - we know this is funny...): Rod 1.

And at the top attach the two long Rods: 5 and 6.

Use two locking washers and a nut on each rod.

The XLR bracket attaches back left. The indentations on it go towards the inside of the machine - they accommodate the washers on the frame.

Next screw the second triangle to the other end of the cross bars:


Now go round the frame tightening everything up using two spanners. Tighten the triangles first, then the six bars in the x direction.


Use the template to get the measurements right.

Make the gap between the faces of the vertices on the triangles 290mm, as mentioned above. Make the gap in the x direction between the faces of the vertices 273mm.

Get the two top rods even, with an equal amount projecting each side, then move the back one 5mm to the right and the front one 5mm to the left.

Try to get the measurements accurate. But it is more important to get the lengths equal than to get them precise.

You will find that you can make very fine adjustments when things are almost tight by slightly slackening a nut on one side of a join then tightening the nut on the other side.

Step 4: Z-motor mounts, diagonal, and power connector

Item Quantity
470mm M8 rods 2
Printed Z motor holders 2
Printed U clips 2
M8 nuts 12 (14)
M8 lock washers 10
M8 washers 6
XLR panel plug 1
12mm M3 caps 2
M3 washers 2
M3 nuts 2

The two extra nuts are for the optional lock on the Z bar U clips - see below.


Put the two U clips already on the frame roughly in the middle of their bars, then push one of the 470mm rods through. You may have to twist it, using its thread to move it - it can be quite a snug fit. Use nuts and lock washers to put two more U clips on its ends for the Z smooth rods, as shown. Leave all these lose:


If you want put two extra nuts just inside the ones on the U clips for the Z smooth rods - these will allow you to lock the inside position of the U clips so you can slacken and tighten them later to assemble the machine without losing the vertical adjustment on the Z smooth rods.

Next thread the base diagonal rod through two of the four feet. Put nuts and lock washers on it both inside and outside each foot, but leave them lose.

Put four smooth washers on the top bars, then put the Z motor mounts on as shown. Secure them with two nuts each, with one smooth washer and one lock washer. The smooth washer goes on the clamp that will hold the Z rods. Tighten the other nuts against their lock washers, but leave the Z-rod-clamp nuts lose:


Fit the XLR plug to the printed XLR panel-plug holder using the M3 screws, nuts and washers. The washers go under the nuts. Fit the plug so that the triangle formed by its three pins points upwards.

Step 5: Smooth rods

Item Quantity
400mm smooth rods (Y) 2
350mm smooth rods (Z) 2

If the ends of the rods are sharp from cutting, use a file to smooth off the ends to give a small conical chamfer (0.5 .. 1 mm). Without it, there is a risk of unseating the balls inside linear bearings while inserting the rods.

Adjust the U clips for the Y rods at the front and back of the frame so that the gaps between their outer nuts and the nuts on the frame vertices are about 20mm. Slide the Y rods through. Don't tighten them:


Next place the frame on a flat surface. Wooden furniture, by and large, is not flat. But thick kitchen worktops are very flat.

Chances are that the frame will rock slightly about one or the other diagonal.

Tighten the diagonal bar in such a way as to stop the rock. If the frame rocks about the bar's diagonal, the gap between its nuts needs to be bigger. If the frame rocks about the opposite diagonal, the gap between the diagonal nuts needs to be smaller.

Adjust the U clamps on the left-hand Y rod so that their nuts are 22mm from the nuts on the left frame triangle, and then adjust the right-hand Y rod U clamps so there is 175mm between the rods. Leave the clamps lose.

Aligning the Z Rods

You can now slide the two Z smooth rods into place. Do not over-tighten the clamping nuts on the Z motor mounts. The rods need to be held firm, that is all.

Use a set-square to get the angle of the Z smooth rods correct.


You can now tighten the M8 nuts along the bottom cross bar.

Alternative alignment method

Some people swear by this method, others hate it...

For this you will need the spirit level, two pieces of cotton, and a small blob of Blu-tack.

Build the frame as above, as far as "Aligning the Z Rods".

Place the frame on a flat surface (as just mentioned, 40mm-thick Formica-covered kitchen worktops are remarkably flat).

Put the spirit level across the Y smooth bars, and place folded paper shims under the left or right feet until the frame is level left-right. You will discover that a spirit level is an exquisitely sensitive instrument, and that it can easily detect a couple thicknesses of paper.

Rotate the spirit level through a right angle so it rests between the front and back cross bars, and get the frame level front-back too.

Check the frame is level in both directions.


Now thread two lengths of cotton (red arrow) down through the top bracket and the U clamp on the bottom where the Z axis smooth rods will be. Attach it to the Z-axis-smooth-rod holes at the top with Blu-tack such that it is half-way round the inside of the clamp arc.

Put a small blob of Blu-tack on the bottom of each piece of cotton to act as a plumb weight.

Now, in the Y direction adjust the positions of the threaded rod at the bottom and the Z-axis-smooth-rod U clamps so that the cotton falls freely in the middle of the U-clamp holes.

Tighten the nuts on the main frame holding the threaded rod, making sure that the cotton stays in the middle of the holes where it was.

Now tighten the inner nuts to move the U clamps outwards so that the cotton just kisses the edge of the U holes in exactly the same relative position as it is falling through the clamps at the top of the frame.

Slide the Z-axis rods in, tighten the clamps from the outside, and check with a square as in the section above. If you've done everything carefully there should be little or no discrepancy, but it is more important to have a right angle than to have the Z-rods plumb.

Frame finished

You will now have an assembled RepRapPro Mendel frame (though the smooth Y rods and the bearings will still be lose):

RepRapPro Huxley assembled frame

Next stage

assemble the Y axis.