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ReprapMJ is a highly printable “Prusa Style” Nylon Capable and Easy to Use 3D Printer with Full 200mm Build Size but Small Footprint.

Reprapmj front.jpg

Non heated bed on the left in the background. Alternative 2 hardware extruder on the table on the left. Handbrake on the right.

It is faithful to the reprap philosophy. It is capable of printing itself and it is almost completely printed.

This Wiki will be completed as soon as I can but, for now, the STL files and some additional pictures and documentation can be found on thingiverse:

The Basic Printer Has a total Hardware/Vitamin Count of just one part (the build plate). Only one nema is used for the Z axis and so the electronic parts are also reduced.

The full parts list for the basic printer is:

1x 220mmx220mmx3mm sheet of glass or phenolic board (phenolic for printing nylon).

4x Nema17 (40mm long) motors with wiring.

3x Mechanical endstop switches with wiring.

1x Motherboard (I use the MKS Gen L).

1x Hotend (I use a J7 which comes complete including a fan, bowden tube and wiring).

1x 150w 12v Power Supply.

Everything else is printed (and I do mean everything else!!).

You can add the usual standard options such as Heated Bed, LCD/SD Card and a nylon capable Extruder:

1x 220x220 Heated bed with wiring (I use the Anycubic Ultrabase).

4x Springs for the above.

1x LCD 2004 with SD Card reader (my favourite screen).

An alternative extruder to replace the fully printed one (essential for using nylon) needs:

1x Brass knurled gear.

1x U604 bearing.

Everything else is printed (and I do mean everything else!!).

The basic version is aimed at being almost completely printable and it works amazingly well. The print quality is high and it is capable of making a working version of itself.

The ReprapMJ has a build volume of 200mm on X axis, 210mm on Y axis and 170mm on the Z.

It is very neat and tidy with a small footprint.

Rack and pinions are used for all axis. With no belts, the maintenance and setup is more convenient and easy.

The Z axis uses only one nema motor and a PLA printed counter balance spring to carry the weight of the X carriage. The X carriage can be raised and lowered by hand without needing to use a computer or control interface. The build plate assembly can very simply be removed and swapped for a different bed (I typically swap between a heated Ultrabase for PLA, ABS, PETG etc etc and a non heated plain sheet of Phenolic board for Nylon). The standard J7 hotend works with nylons such as Taulman Bridge or Alloy 910 but there is a version of the J7 available which is rated to 300 degrees if needed. There is a fully printed extruder which works well with PLA. However it does not grip Nylon sufficiently well and so an optional extruder can be used which needs two hardware parts.


The majority of standard 200mm X 200mm PLA printers will be able to print an acceptable quality ReprapMJ.

The majority of parts use standard 0.3 layer settings.

A small number of parts are better with some minor changes.

Only one part needs support (the optional extruder arm).

The fit of “snap together” parts and overall accuracy is much improved if there is little or no elephants foot. Either compensate in your chosen slicer if it has the option or use a loose Z height. I personally use a fairly loose Z height and a good hair lacquer (VP/VA copolymer is the ingredient you need). I keep max print speeds down to 30mm per second and non printing movement to 40mm per second.

Other variations over standard 0.3 layer settings can be found on the thingiverse documents.


Try to print with little or no elephants foot.

In the majority of cases it is only necessary to remove boogers and stringing to make parts ready for assembly.

The less remedial work needed the better.

Some press together parts may be quite tight and a light tap with a wooden or PLA block will work much better than trying to push or squeeze. PLA has a very high sticktion which responds better to a shock than steady pressure.

The bearings and working surfaces such as rack gears are best assembled dry. Then slowly moved through their range of movement tapping where necessary if they get stuck. This will very quickly provide a smooth surface. It must be done slowly otherwise the PLA will heat and start to distort or stick completely. Running the parts in dry is a very good way to provide a smooth movement later. The movement can feel quite stiff with a tendency to stick as the motion stops but this will be fixed when grease is applied.

Use a Silicon/PTFE grease. I use “Technicqll 2206” with 55% PTFE. It is a staggeringly good lubricant for PLA.

Try to avoid the use of grease for assembly joints where possible although in some cases it may help with sliding the Z rails down into the frame.


The ReprapMJ is very much a standard Prusa style 3D printer in terms of use.

The main difference is that the Z rail uses a rack and pinion with only one nema motor. The other end has a spring to counter balance the weight. The nema is not strong enough to lift the whole weight on its own and would skip without the counter balance. Also with no counter balance the x axis will simply fall down to the bed when the nema is turned off. The counter balance is adjusted to hold the Z height static and then the nema only needs to provide movement without carrying the weight. A printed PLA spring is used which will weaken if left under tension and so a parking blank (handbrake) has also been created. When leaving the printer inactive then remove the counter balance spring and fit the handbrake.

When using the printer remove the brake and then lift the x carriage close to the top and fit the spring. Rotate it to provide a small amount of tension at the top of the travel. Push the carriage down and it should then hold its position. The spring holder has ratchet type lugs so tension can be added by clicking the spring holder round. To release tension you need to unlock the lugs (twist slightly and move out).

Raising and lowering the carriage (to work on the hotend etc) is simply done by pushing up or down as needed.

When leaving the printer idle it is also best to remove the extruder filament tension. Both types of extruder have small levers to apply tension. Apply the tension just before the print starts.

The extruder with brass gear and bearing uses standard reprap esteps (92).

The fully printed extruder needs esteps changing to 101 and it may also need the direction changing.

The x, y and z esteps need changing to 64.

Otherwise standard reprap ramps type firmware can be used.

When first operating check the nema motors to make sure they are not getting hot. If they are, then check and reset the voltage on the stepper drivers on the motherboard. They should be close to 0.2 volts. If the extruder motor skips when under tension then increase the voltage slightly but try not to go over 0.25 volts. The nema motors are held by PLA clamps which will soften if the motors get too hot.

Also the nema drive gears are PLA and a press fit. If they get hot they will soften and slack will set in.

Swapping the bed is a pure joy. If its non heated with no LCD then simply pull it forward and off. Job done. If its heated and with an LCD then lift the LCD of its hanger and drop it down. Remove the bed wiring connector and pull it forward and off. Job done. To fit a bed simply slide the new bed on the rails and push it back. Don't push too fast or the extruder movement will back feed the motherboard.

Assembly instructions below the pictures (very poor for now but I will update when I can).

Reprapmj rear x rail.jpg

Reprapmj printed extruder.jpg

Reprapmj left z rack.jpg


General Note.

Print the parts and remove boogers and stringing.

It is better to print with minimal elephants foot but if there is any obvious then it will also need trimming off on mating faces and snap fittings. Try to do as little trimming as possible.

Most parts will simply snap or press together. Many of the dovetail joints have a tension slot in the middle. If you find a loose joint you can adjust the dovetail by heating with a hair-dryer or similar and then gently opening the slot with a knife or blade.

If a joint is tight then a tap with a wooden block or lump of PLA will work better than heavy pressing.

Try not to use any grease on the snap together fitting. However, you may need some grease to help the Z rails slide in.

Frame upright section.

Snap the frame sections all together on a flat surface.

If there is elephants foot the section will not want to lay flat. It is usually not a problem and can be left if so desired. The Z rails and back support will tend to straighten the upright later.

Slide the Z rail spacers all the way down the dovetail joints until they bottom out in the frame lower section. Then slide the main Z rails down until they bottom out on the spacers. If you want to make it easier you can pre fit the spacers into the bottom of the mid section so they are almost in place before snapping the frame together.

The frame upright is now locked together.

Frame rear lower section.

Snap both half's of the rear Y end together.

Press the short cone spacers in the frame upright. Press or tap until they bottom out. The wider arm of the cone faces to the outside of the frame and helps to lock the frame middle and lower sections together.

Put the rear Y end assembly under the other end of the cone spacers and press them in until they bottom out.

Snap the lower supports in place. Make sure the cut out section goes to the bottom so that there will be ground clearance.

Make the upright diagonal supports by snapping an upper and lower section together. Snap on the completed upper diagonal supports.

Frame front lower section

Press the long cone spacers in the frame upright. One long spacer has a shorter cone to avoid the Y nema.

Put the front Y end under the cone spacers and press in until they bottom out.

Snap the lower supports in place with the ground clearance at the bottom.

Try to stand the completed frame section on a surface that is a flat as possible.

Print bed assembly

The base has two bearings which are printed and fixed. The other bearings are fitted in 4 degree angled dovetails so that the rail tension and width between the two rails can be accommodated.

First slide the Y rack gear into the base dovetails until it is roughly in the middle. It can be adjusted later if necessary.

Fit all of the single bearings into the start of the bed dovetails. They only need to be fitted just enough so they will stay in place. Note that they are handed and when in the dovetail the bearing face should be parallel to the rail.

Now slide the bed onto the rails.

Tap in the inner bearings on side opposite the rack until there is little or no play. The correct width of the two rails should now have been set.

Tap each of the outer bearings until they also have little or no play.

Move the bed through its range of movement to start the smoothing process. It will be quite stiff and sticky at first. Don't forget to keep movements slow.

With no grease the movement will never be better than quite sticky and tight.

When happy slide it fully off and get rid of any debris etc. Then grease the rails and bearings.

Slide it back on and it will feel a whole lot better.

Press the drive gear onto the Y nema. It sits slightly higher than flush with the end of the shaft.

Now fit the Y nema to the frame. It locates in a cut out to keep it square but it can slide sideways.

Leave the nut slightly loose and slide the gear to engage on the rack. Check the height and that the gears are lined up. If not remove the nema and tap the gear on or off as necessary.

Grease the retaining nut and thread and refit the Y nema. Slide it over until there is no backlash and tighten the nut. The nut does not need to be too tight. PLA is very sticky.

Run the bed slowly through its range of movement until happy boogers are clear. Then grease the rack and gear.

Then remove the assembly by sliding it straight off the front. Nice and easy ehh!! No need to worry about belts!!

Snap in the bed extensions.

Fit the heated or non heated bed as required.

Put to one side for now.

X rail assembly

Slide/tap a double bearing in each X end.

Fit the X rail T pieces to the ends of the X rail main section. Note they are handed. The slightly longer leg goes towards the X end and the top groove to extend the X travel should also be closest to the X end.

Fit the X ends to the X rail T pieces. The dovetails are longer so that there is room to adjust the width.

Fit the assembly to the Z rails. Locate one double bearing in a Z groove. Then the other double bearing in the other z rail. You may need to flex the rail/frame slightly to get both sets of bearings in the grooves. Now the X end dovetails need adjusting over on the T piece dovetails in order to take the play out of the double bearings up against the Z rails. There are no outer bearings fitted to the X ends yet so you only need to just take out the play.

Move the X rail up a down a few times. It should move up and down staying relatively square and without too much sticking. Some force may be required but it must be done slowly. The movement will soon become less knotchy and sticky. If play has appeared then adjust the X ends on the dovetails again.

When happy slide the outer X end bearings in the dovetail slots. The slots slope in at 4 degrees and the bearings are handed to keep the face parallel to the Z rail. The further in they go the tighter the fit will be. Tapping works best. Tap them in until the rail goes obviously tight and wont move. Then tap them back out slightly until they move but with only slight play. After slowly moving through the range of movement a few times they may need adjusting again.

At this stage with no grease the movement can be quite sticky and slightly stiff.

Tap the single bearings out only and then remove the assembly.

Grease the Z rail grooves and the flat face that the X ends run against. Grease the X end running face and reassemble and adjust the single bearings. It should feel a lot less sticky now.

Z drive assembly

Fit the clamp to the nema and press on the clip.

Fit the drive gear to the nema. This should be a tightish press fit. The depth of the gear on the shaft needs to match the final position of the nema when fully fitted in the dovetails. Offer it up to the dovetails and when they are level with bottomed out, the gear should be lined up with the rack.

Fit the square crossover tube into the nema drive gear. You may need to adjust the depth later.

Fit the Driven gear onto the other end of the cross over tube. Note there are holes in drive and driven gears which need to line up. This will ensure the teeth line up and the X rail will be square.

Offer the assembly up to the Z rack gears and adjust to get the width about right. The gears need to be lined up when the Z rack gears are in the middle of the Z rail faces.

The nema can then be fitted into the dovetails. The gear needs to be engaged on the rack. The rack may need sliding sideways slightly to get the gear engaged and dovetails in. Push the dovetails home until they bottom out.

Make final adjustments to the depth of the drive gear on the nema shaft (tap it to adjust). Then make final adjustments to the width of the cross over tube to get the driven end gear lined up.

Grease the inner tube in the bearing and spring holder. Then fit it over the driven gear shaft and into the dovetails. Press in until fully bottomed into the dovetails.

Both the gears should now be lined up with the center of the Z rails.

The nema and bearing holder have slots by the dovetails which allows them to apply a spring tension to the bearing fit. They may be quite tight and stiff at this point with a lot of pressure on the gears.

Run the rail up a down a few times and any small boogers should be smoothed off the gears. Blow any debris away and then apply grease to the gears. Run up and down to distribute the grease and then recheck the tension. If the bearings are too tight there is an optional shim which can be pushed into the slot to release tension. Fit the handbrake to stop the rail from dropping when weight is applied later.

X carriage assembly

Slide the font plate over the bottom dovetail on the rear plate until it bottoms out.

From underneath slide the pair up onto the X rail. You may need to prise the top open very slightly.

Fit the top bearing into the dovetails and tap it across. The dovetail is on an angle so the bearing will get tighter the further it goes. Tap it across until the carriage goes tight and wont move and then back it off slightly. Run the X carriage through its full range of movement a few times (slowly). You will be able to tension the bearing slightly as the grooves are smoothed off.

When happy remove any debris and then grease the grooves. It should feel a lot better.

Press the drive gear onto the nema shaft until the end is flush with the shaft. It may need adjusting later but that should be very close. Fit the nema into the clamp and press the clip on.

You will need to angle the nema and clamp to pass the gear through to the rack. The dovetail can then be pressed down. There is a tang on the bottom which rests in a location hole when the motor is straight. Tap the dovetails down until the backlash on the gear is removed. Then check the nema gear alignment on the rack. The nema gear can be moved on the nema shaft if necessary.

When the alignment is correct run the x axis through its full range a few times (slowly). Clear away any debris and when happy grease the gear and rack.

Then finally tap the dovetail down to remove any backlash on the gear.

Tap the J head holder clamp into place on the front plate dovetails.

If required fit the 5055 fan holder on the J head clamp dovetail.

Extruder fully printed.

Before assembly run a 2mm drill through the PLA feed and exit holes to make sure they are clear.

Fit the 4 outer drive gears onto the pivots on the arm plate. Apply grease to the shafts very carefully. No grease must get on the grooved bosses which trap the PLA. Slide the reduction drive gear in place and in mesh with the 4 outer drive gears.

Snap the arm plate with all 5 gears onto the arm.

Join the two assemblies by slotting the arm dovetails into the body.

Fit the nema clamp on the nema and secure with clip.

Snap the arm and body assembly onto the nema until the clips snap engaged on the nema clamp.

Press the drive gear onto the nema shaft until the shaft end is level.

Fit the reduction gear spacer underneath the gear. Apply grease to the shafts and then press the camshaft and plate in.

Turn the gears manually a few times to clean off boogers etc.

When happy apply grease to the gears. Be very careful to grease the teeth only and not the PLA grooves.

Extruder 2 component.

Fit the brass gear on the nema shaft with the plain collar to the outside and level with the end of the shaft.

Fit the nema clamp to the nema and secure with a clip.

Snap the tension lever into the hole on the body.

Slide the arm into the body's dovetail slot.

Snap the body and arm over the brass gear and onto the nema and clamp.

Fit the bearing into the slot in the arm and secure it by fitting the pivot. Push both pivot half's in at the same time.


The spool holder riser arm is in two halves and snaps together. When in use it pretty much rests in place and is held by the weight of the filament spool and some locating lugs.

There is a box to hold the motherboard which drops in place between the front rails. It has holes and slots to allow bending so wires can be fed in. The end with a single hole and slot is for the LCD cable and goes toward the front. The lid has lugs that line up with the slots to hold them closed when it is slotted in place. The LCD screen has two holder arms which are slid over the circuit board. The outer cover then slides over the top. The knob simply presses in place.


Personally I like to use the MKS Gen L motherboard.

The extruder with brass gear and bearing uses standard reprap esteps (92).

The fully printed extruder needs esteps changing to 101 and it may also need the direction changing.

The x, y and z esteps need changing to 64.

Otherwise it is pretty much standard Ramps type wiring and firmware.

If using the MKS Gen L then be wary that some older versions are still being supplied. If you find the LCD doesn't work then check the pin assignment and position of locating lug. There are some with the cap fitted backwards. You need to cut the lug of the connector so you can fit it correctly.