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CARP Box Documentation
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Release status: working

CARP Box.jpg
Printer inspired by Prusa i3 metal frame, Wolfy Y axis and Printrbot. All metal design with worm gear extruder for better reliability and precision.
CAD Models
External Link

This page is under construction. Informations may not be complete or correct.


CARP Box is the improvement of original CARP - (C)ompact (A)nd (R)eliable (P)rinter - Y axis single frame printer based on the idea of first Printrbot. While CARP ended up as a assembled but never tested prototype, CARP Box was released in June 2015.



The external dimensions of the CARP Box are 422x396x440mm and print volume 200x200x200mm (WxDxH).

Key features

Original idea of CARP printers was to achieve full print volume of PCB heatbed while mantaining reasonably small size of the printer. All key parts of the printer like electronics, power supply, extruder, filament spool, etc. are attached to the printer so it can be moved easily. The main structure of the printer is made of 3 and 4mm thick laser cut aluminium. Other parts (vitamins) are common in RepRap community and easily accessible for reasonable price. The total price of home build printer is roughly 350 EUR (when most of the vitamins are shipped from China).

Printer was designed with stress on safety, reliability and ease of usage. All vulnerable electronic parts are hidden in the body of the printer. Enclosure is earthed, printer can be switched on and off. Cooling of electronics and stepper motors was added for lengthy prints, without crashes. Autonomous printing is possible too.

Although precision and speed was not the biggest concern of the design, sturdiness of the case may let you achieve speeds above 100mm/s without shaking. 400step motors with 32 microstep drivers can be used to achieve higher precision in X and Y axis (if typical 200step motors with 16microstep drivers won't be enough). In Z axis M5 threaded rod is already giving very high resolution of the print layers. Usage of worm gear extruder with ratio 27:1 is also beneficial for the precision of extrusion (even with 3mm filament) and will let you print very small parts with low speeds around 1mm/s to let the layers cool down.

Mechanical Parts

Aluminium Parts

Most of the parts are made of laser cut aluminum of thickness 3 and 4mm. After cutting they, have to be machined, cut threads for M3 and M4 screws and counter sunk screw heads. All edges have to be sanded eventually rounded (except for LM8UU bearing mount holes) otherwise you may get injured during the construction.

List of parts:

Quantity DXF file Comments Picture
1 Front plate.DXF 100px
3 Back Plate.DXF 100px

This chapter is not finished yet.

Printed Parts

This printer is trying to avoid structural printed parts at all costs. Some additional parts like display mount, fan ducts, fan mounts, cable trays, etc. may by presented in the future.

Other Parts

For complete list of accessories and screws see BoM in building manual.


Controller Electronics

Mounting holes are prepared for Sanguinololu 1.3a and Arduino Mega 2560 with RAMPS 1.4. There may be slight differences between original electronics and chines clones so be ready to adjust installation as per your piece of hardware.

From the two above I would definitely recommend RAMPS as it will allow you to use multiple extrudes, display, SD card, have bigger memory and runs on higher speed. Sanguinololu is there for the sole reason, if you (like me) have at home older RepRap, want to make an upgrade and single extruder is enough for you.

Stepper Drivers

In above mentioned electronics, Pololu drivers or its cones are used. There are two most common drivers.

  • Allegro A4988 based driver - up to 16 microstepping, maximal current 2A, voltage 8-35V.
  • Texas Instruments DRV8825 based drivers - up to 32 microstepping, maximal current 2.5A, voltage up to 45V.

Both needs atleast passive cooler or even a fan for longer prints. Although DRV8825 may look like the best choice, it seems to me that cheep Chines clones cannot reach more than 3.25turn/s without skipping steps. Clones with A4988 were not so limited.

Stepper Motors

All stepper motors are bipolar NEMA17. NEMA16 have same mount holes and can be used too. Unipolar motors can be used only if they do not have phases joined together internally (should not have odd number of wires). Common step is 1.8° (200 steps/turn) although some 0.9° (400steps/turn) may be found too.

For X, Y, Z axis and single worm gear extruder almost any motor with holding torque above 0.3Nm is good enough. They should not be longer than 65mm though, otherwise they won't fit inside and combined power consumption of two Z motors should not be more than can be delivered by the stepper drive (typically 2.0A). With dual worm gear extruder, X axis motor and both motors on extruder should not be longer than 40mm.


As the carriage is made compatible with horizontal Prusa Mendel carriage, for could-end you can use plenty of already available solutions. Case have on both sides also mounting holes for bowden extruders though you may need to drill your own as for such extruders is no typical mount. Still CARP have its own full metal solution based on M12x20 machined hexhead screw and laser cut stainless steel wheel. With 27:1 gear ratio is capable of very high precision of filament movement and as much cheaper and more compact than gearboxes for NEMA17 motors. It runs great with 3mm filament, but have still some issues with 1.75mm. Further development and testing is required before going public.

For hot-end I would recommend E3D or its full metal clones as they cam print all day long. Conditionally J-head for lower extrusion temperatures and shorter prints. Both with ceramic cartridge heater and 100K glass thermistor. Other solutions like K-type thermocouple or PT100 cannot be used with RAMPS right away but may give better results or endurance.

Heated Bed

Heatbed MK2b is recommended, because for this version is adjusted aluminium heatbed plate. Eventually steel plate may be used too in combination with proximity sensors. Glass is not required as it is either prone to crack or expensive in case of borosilicate. You may use thermal insulation from the bottom side of the heat bed, but this model can reach 110-115°C required for ABS even without it.