Introduction: CoreXY CNC Plotter

Picture of CoreXY CNC Plotter

This instructable describes an A2 plotter made from low cost aluminium extrusion, a piece of particle board, two NEMA17 stepper motors, and a few belts and pulleys.

The plotter is:

    • high resolution (80 steps/mm),
    • fast,
    • low-cost,
    • and scaleable

    The plotter has an on-board interpreter that recognizes the g-code output from "Inkscape" .

    Metal work is simple ... all you need is a hacksaw, three drills, a rat-tail file, and a screwdriver.

    12 October 2017:

    An improved pen-lift is described in instructable

    Step 1: Circuit

    Picture of Circuit

    The wiring diagram for this plotter is shown in photo 1.

    Adjusting the motor current(s)

    Set your CPS-3205 power supply to 12 volts.

    Attach a 12 volt 30 ohm NEMA17 stepping motor to a Big EasyDriver module and apply power to the motor assemby.

    Now adjust the small potentiometer on the Big EasyDriver module for a current reading of 0.4 amps (400mA) on the CPS-3205 power supply.

    Repeat this process for the remaining motor and Big EasyDriver module.

    Disconnect the power.

    Substitute motors

    The plotter also works with 6 volt 8 ohm stepping motors in which case the CPS-3205 power supply should be set to 6 volts and the motor currents set to 0.6 amps (600mA).

    Step 2: Software

    The source code for this plotter is attached.

    Software installation:

    • copy the contents of coreXY_plotter.ino into an arduino sketch.
    • save the file as "coreXY_plotter" (without the quotes).
    • compile and upload the sketch to your arduino

    Step 3: Parts List

    The parts list for either an A4 or A2 coreXY plotter is attached ...

    Wood saws are not required if you ask your timber merchant to cut the particle board and and pine supports to length.

    Step 4: Theory

    The timing belts are arranged in a "coreXY" configuration.

    An excellent explanation of the "coreXY" principle may be found at

    The pen moves:

    • horizontally when the motors rotate in the same direction.
    • vertically when the motors rotate in opposite directions.
    • diagonally if only one motor rotates.

    Step 5: The Mathematics

    This step derives the pen motion equations and may be ignored ...

    If we rotate motor A counter-clockwise by an amount ∆A then the pen carriage will move horizontally to the right by an amount ∆X and vertically upwards by an amount ∆Y. The equation for this is:

    ∆A = ∆X + ∆Y ...................................................... (1)

    If we rotate motor B counter-clockwise by an amount ∆B then the pen carriage will move horizontally to the right by an amount ∆X and vertically down by an amount ∆Y. The equation for this is:

    ∆B = ∆X - ∆Y ....................................................... (2)

    The reason for the ∆Y sign/direction change is that the two timing-belts are moving in opposite directions... the timing-belt for motor A is being fed towards the pen which lets the pen to move upwards, whereas the timing-belt for motor B drags the pen downwards.

    Horizontal motion

    Rearranging equations (1) and (2) we get:

    ∆Y = ∆A - ∆X ....................................................... (3)

    ∆Y = -∆B + ∆X ..................................................... (4)

    Equating equations (3) and (4) we get:

    ∆A - ∆X = -∆B + ∆X ............................................. (5)

    From which:

    ∆X = (∆A + ∆B)/2 ................................................. (6)

    Translating: the pen moves horizontally when both motors rotate in the same direction

    Vertical motion

    Rearranging equations (1) and (2) we get:

    ∆X = ∆A + ∆Y ....................................................... (7)

    ∆X = ∆B - ∆Y ...................................................... (8)

    Equating equations (7) and (8) we get:

    ∆A + ∆Y = ∆B - ∆Y .............................................. (9)

    From which:

    ∆Y = (∆A - ∆B)/2 ..................................................(10)

    Translating: the pen moves vertically when the motors to rotate in opposite directions.

    Collectively equations (6) and (10) infer diagonal movement if only one motor rotates.

    Step 6: Evolution ... a Story of Trial and Error

    Picture of Evolution ... a Story of Trial and Error

    H-Bot design

    My first build comprised a single timing belt arranged in the shape of a letter 'H', or "H-Bot" configuration, as shown in photo1.

    I quickly abandoned this design for three reasons:

    • If both motors rotate in the same direction the tension at opposite ends of the gantry caused unacceptable "wracking" [1].
    • pen wobble was excessive
    • the timing-belt tension spring was not a good idea ... the belt tension needs to be firm.

    CoreXY design

    A few modfications eliminated all of the above problems.

    • The timing belt was cut in half and arranged in a "coreXY" configuration [2]. This arrangement has the advantage that all unbalanced timing-belt tension is in the direction of pen movement as shown by the arrows in photo 2 and photo 3.
    • Pen wobble was eliminated by using an extra guide rail for the pen assembly.
    • Variations in belt tension were eliminated by replacing the spring with cable-ties.

    The design is scalable

    Photo 4 compares the original A4 plotter with the base of a larger A2 plotter described in step 7.

    The gantry and pen carriage dimensions are common to all plotters. The only additional parts required for the larger plotter shown in photo 5 are:

      • a larger base board.
      • longer side rails.
      • longer timing belts


      An H-Bot timing belt pulls the gantry ends in opposite directions whenever the pen moves horizontally (see arrow directions in photo 1). This causes a twisting motion known as "wracking".


      CoreXY requires two full-length timing-belts. Halving the original H-bot timing belt allowed the coreXY concept to be tested before longer timing belts were ordered. It also accounts for the reduced plot area shown in photo 2.

      Step 7: Construction ... the Base

      Picture of Construction ... the Base

      Decide on your plot area:

      • An A4 plotter requires a 6mm x 600mm x 400mm piece of particle board.
      • An A3 plotter requires a 6mm x 800mm x 600mm piece of particle board.
      • or larger ... the design is scalable

      Bolt a length of 1.5mm x 20mm x 20mm aluminium "Tee Section" extrusion along opposite sides of the base. Ensure that both rails are parallel.

      The extrusions should be flush with the long edges of the base and positioned under the base such that the edges just protrude (see photo). These extrusions act as railway lines for the overhead gantry.

      Screw 65mm x 18mm timber end supports to the base. The timber supports will need a rebate for the aluminium extrusions ... make a shallow cut then knock a sliver of timber out using a chisel positioned against the end grain.

      Step 8: Adding the Fixed Pulleys and Motors

      Picture of Adding the Fixed Pulleys and Motors

      The two timing-belts are stacked vertically above each other.

      This is achieved as follows:

      • One motor pulley is inverted as shown in photos 1, 2, & 3.
      • The toothed idler pulleys are stacked in sets of two as shown in photos 4 & 5.

      Mounting the motors

      Drill four x 3mm mounting holes, and one spindle clearance hole, for each NEMA17 stepping motor as shown in photos 2 & 3.

      The outside 3mm holes are 25mm from each edge of the base. This distance ensures the the motors avoid the wooden support and the aluminium side rails.

      Mounting the fixed pulleys

      Drill two 4mm holes for the fixed pulleys.

      These holes are located 25mm from the opposite end to the motors and 40.5mm from the side rails. This distance ensures that the pulleys avoid the wooden support. It also ensures that the timing-belts are parallel with the side rails.

      Key points

      • Timing belts stretched between each motor and the associated fixed pulleys MUST be parallel to the side rails.
      • Separate the pulleys with a 4mm washer. The washer prevents the pulley edges from rubbing.

      Step 9: The Gantry

      Picture of The Gantry

      Vertical (Y-axis) motion is provided by a movable gantry that runs along the fixed side-rails attached to the base.

      Horizontal (X-axis) motion is obtained by running a pen carriage-assembly across two rails attached to the gantry end brackets.

      The gantry wheels are fashioned from VZ624ZZ V-groove sewing machine pulleys (photo 3). The V-groove prevents the gantry moving sideways.

      End brackets

      Cut two 60mm x 130mm brackets from a sheet of 18 gauge aluminium using the method described in instructable

      Drill two 3mm holes and four 4mm holes at the locations shown in photo 1.

      Fold a 50mm top for each bracket.

      Mounting the wheels

      Sandwich four "V-groove" pulleys between a 4mm nut and bolt. The nut prevents the sides of the pulleys touching the aluminium.

      Now bolt these wheels through the 4mm diameter holes as shown in photo 2.

      Attaching the end brackets to the base

      Attach a gantry end plate to each side of the plotter.

      To do this:

      • the grooved wheels must straddle the side-rails.
      • elongate the bottom holes as required to eliminate any vertical play in the gantry.

      When correctly adjusted the gantry end-brackets should roll freely when the base is tilted slightly.

      Top rails

      The over-head gantry rails are attached when we attach the pen carriage-assembly ...

      Step 10: The Gantry Pulley Brackets

      Picture of The Gantry Pulley Brackets

      The gantry pulley brackets

      The gantry pulley brackets are cut from 18 gauge aluminium sheet. An approximate [1] drilling template is shown in photo 1.

      Photo 2 shows the pulleys attached to the motor 1 (left-hand) bracket.

      Photo 3 shows the pulleys attached to the motor 2 (right-hand) bracket.

      Key points:

      • The smooth side of the timing belts always sees a smooth pulley.
      • The ribbed side of the timing belts always sees a toothed pulley.
      • One of the double pulleys on each bracket is NOT used ... it simply acts as a spacer.

      Attaching the pulley brackets to the gantry

      Press each pulley bracket against the inside of the gantry bracket such that the bracket is centered and the heads of the pulley bolts are clear of the base.

      Mark these positions by means of a pencil through the two existing holes in each of the gantry brackets.

      Now drill 3mm mounting holes and bolt the bracket pairs together.


      The 4mm hole positions for the idler wheels depend on the sharpness of the upturned folds.

      Fold each pulley bracket then custom position the holes such that:

      • both timing-belts over-lap when viewed from above.
      • the idler wheels used as spacers don't touch any belts.

      Step 11: Pen Support

      Picture of Pen Support

      The pen support is made from 18 gauge aluminium sheet. The dimensions are shown in photo 1

      Custom size the large holes such that your pen slides freely but without any sideways wobble.

      Attach a pen-lift collar to your pen. Mine was made from the brass fitting found inside a radio knob and a circular piece of plastic but anything will do ... so long as the position can be adjusted.

      Step 12: Pen Carriage Assembly

      Picture of Pen Carriage Assembly

      The pen carriage is made from 18 gauge aluminium sheet. A drilling template (not to scale) is shown in photo 1.

      Assemble as follows:

      • drill and fold the metal
      • attach 8 x v-groove pulleys as shown in photo 2. Elongate the lower holes such that there is no vertical play when the aluminium "tee section" rails are fitted.
      • use a cable-tie to attach the SG90 servo as shown in photo 2. Drill the cable-tie holes to suit.
      • use the 3mm holes in the pen-support as a drilling template when attaching the pen.

      Fitting the top gantry rails

      Attaching the rails:

      • Pass two 600mm lengths of aluminium "tee section" between the "V-groove" pulleys as shown in photo 2.
      • Attach each gantry bracket to one of the rails by means of two 3mm nuts and bolts.
      • Position the second rail such that the pen carriage-assembly moves freely. Now drill and bolt the rail to the gantry brackets.

      Step 13: Attaching the Timing Belts

      Picture of Attaching the Timing Belts

      Key points:

      • the plotter has TWO timing belts.
      • each timing belt forms a continuous loop (see photo 2)
      • the timing belts are mounted at different heights ... the pulleys share a common shaft.
      • the timing belts are tensioned using cable-ties.
      • both timing belts are attached to a common 3mm bolt (see photo 3)


      • push the pen carriage-assembly to one side.
      • tape both gantry ends to prevent movement (photo 1).
      • thread the bottom timing belts and fix the ends (photo 2).
      • thread the top timing belt and fix the ends (photo 3).
      • the timing belts should look like this (photo 4)
      • remove the tape.
      • tension the belts such that the carriage-rails are the parallel to the base end.

      Step 14: Attaching the Pen Carriage Assembly

      Picture of Attaching the Pen Carriage Assembly

      Two 25mm long threaded spacers are joined together (by means of a 3mm head-less bolt) to form a solid rod.

      The belts are attached to this rod as shown in photo 1.

      Attach the top of the rod to the center of the pen carriage-assembly using a 3mm bolt.


      The pen should:

      • move to the left when BOTH motors are turned clock-wise.
      • move to the right when BOTH motors are turned counter-clockwise.
      • move diagonally if only one motor is rotated.

      Step 15: The Menu

      Picture of The Menu

      Upload coreXY_plotter.ino to your arduino if you haven't already done so. Instructions for this are given in step 2.

      Connect a USB cable to your arduino and left-click "Tools|Serial Monitor" ... a menu similar to photo 1 should appear.

      Apply 12 volts power to your motors and your plotter is ready to use.

      The menu is not case sensitive. Typing:

      • MENU brings up the menu
      • G00 allows you to send the pen to a specific XY co-ordinate with the pen raised.
      • G01 allows you to send the pen to a specific XY co-ordinate with the pen lowered.
      • T1 allows you to position your pen over your 0,0 co-ordinate. Type 'E' to exit.
      • T2 allows you to scale your drawiing. For example "T2 S2.5" will scale your drawing 250%. The default scale is 100%.All pen moves use the drawing scale last set using this menu option
      • T3 and T4 allow you to raise or lower the pen.
      • T5 draws an "ABC" test pattern.
      • T6 draws a "target".
      • T7 draws a set of radial lines

      The internal wiring of some motor brands are reversed. If your motor directions are reversed then use the alternate code in the step_motors() function.

      Step 16: Creating and Sending Gcode Files to Your Plotter

      This plotter assumes that co-ordinate (0,0) is at the lower-left corner of your paper. As such it is 100% Inkscape compatible.

      Instructions for creating gcode files are given in the following instructables:

      Instructions for sending your gcode file to this plotter are given in instructable:


      ondadiluce (author)2017-10-20

      Another question: is 16 gauge aluminium sheet going to be enough? I'm having a hard time finding the 18 gauge.

      lingib (author)ondadiluce2017-10-20

      16 gauge aluminium should be fine.

      I only used 18 gauge aluminium because it was available.

      cjohn6 (author)2017-10-14

      hi, please help I’m having trouble running the stepper motors ...whatever command I sent through universal Goode sender both the x and y axis steppers rotate , when I press y axis both of them rotate in same direction and when x axis is pressed both rotate in opposite direction.... I’ve been trying to sort out this issue, I tried using rabbit code sender, changed a4988 stepper drivers, cleared eeprom , flashed Grbl multiple times , tried changing the comport,tried different baud rate, nothing seems to work ..I’m stuck with this problem and when I stream a Gcode file both motors struggle due to multiple commands like when x axis code is running y axis also rotates ,at the same time if Yaxis command is given motor struggles making grinding noise... please provide a solution . What could have possibly went wrong ,should I change Arduino or CNCinfusion shield v3 ?

      My setup:

      Arduino Uno

      Nema 17 4.2kg/cm

      A4988 stepper driver

      Arduino CNC shied v3

      Tower pro mini servo

      Power supply: 19v 4.7 A

      Grbl 0.9i

      lingib (author)cjohn62017-10-18

      On re-reading your question I see some potential issues:

      1 - my plotter does not use a motor shield.

      2 - my software is self-contained ... 3rd party libraries are not required.

      It would appear that some of the pins to your motor shield are incorrectly mapped or your motor connections are swapped as HORIZONTAL motion requires both motors to turn in the same direction and VERTICAL motion requires that both motors rotate in opposite directions.

      The logic I have used when stepping the motors assumes that each motor controller has a "direction" pin and a "step" pin. The logic level for each direction pin is set then both motors are SIMULTANEOUSLY stepped.

      You may have to remap the "direction" and step "pins" to match your motor shield. These pins are defined in the arduino header.

      lingib (author)cjohn62017-10-17

      Is your plotter a CoreXY Plotter ... I ask this because you mention items not in this article such as GRBL and Universal Gcode Sender?

      The good news ... your motors appear to be working correctly.

      Horizontal movement occurs when BOTH motors rotate in the same direction. Vertical movement occurs when BOTH motors rotate in opposite directions.

      You may try loosening the belts ... the motors can stall and produce a growling noise if the belts are over-tightened.

      Try talking directly to your arduino using the serial monitor in your arduino IDE. Only move to GRBL and Gcode sender when you have each function on the test menu working.


      ondadiluce (author)2017-10-16

      Hi! Awesome project! I have a question for you: what is the bore I need to select for the 2GT Idler Pulley? I can select 3, 4 or 5 mm, and I can't find the correct bore size in the description. Thanks!

      lingib (author)ondadiluce2017-10-17

      All idler pulleys have a bore size of 4mm.

      All stepper pulleys have a bore size of 5mm.

      Bramma nantham (author)2017-10-09

      thanks for ur efforts... its awesome ;-)

      lingib (author)Bramma nantham2017-10-10

      You're welcome. Thank you for commenting :)

      celiosantos (author)2017-10-10

      WOW! Thanks! what a good instructable! zeroed my doubts about this design, i was looking at the MASLOW cnc but this one i presume is more suitable to the litle format that i´m looking up. Please keep sharing your experiences.

      lingib (author)celiosantos2017-10-10

      Unable to comment as I don't know your required format ;)

      The MASLOW is a "beefed up" hanging plotter able to winch bricks and CNC routers with ease. As such it is able to cut out plywood shapes. The price reflects the cost of parts.

      This plotter uses lighter weight materials. Heavier guide rails would be needed to support the router used in the MASLOW.

      staltung (author)2017-10-09

      nice one…

      here ist the same belt concept but now much more versatile :

      "MaXYposi" started with an plotter too .

      Documentation is in German, because developed by the German Make: magazine…

      here ist the Github-Project:

      maybe some nice details to lea(r)n on ;)

      lingib (author)staltung2017-10-09

      Thank you for the reference :)

      Perhaps I am mistaken but the belt arrangement for your plotter is different.

      Your plotter appears to use a single belt in an H-Bot configuration for movement along the Y-axis (H-bot does not "wrack" in the vertical direction).

      X-axis motion appears to be from a motor mounted on the carriage-assembly itself. (This would eliminate the "wracking" I experienced in step 6).

      staltung (author)lingib2017-10-10

      You´re absolutely right! - My fault, missed it.

      So it´s an other kind beauty and I´ve learned something new again!

      thx :D

      BrownDogGadgets (author)2017-10-08

      Have you ever thought about using an Adafruit Motor Shield?

      lingib (author)BrownDogGadgets2017-10-08

      Thank you for your suggestion :)

      I opted for my method as the parts were on hand from other projects.

      BrownDogGadgets (author)lingib2017-10-09

      I figured that was the case. We built a Core XY drawbot a couple of years ago, worked with the open source Makelangelo software. Nice, but nothing we could sell. I recently posted everything to GitHub. It may be worth checking out. We used a laser cut design, but never got the pen lift right.

      lingib (author)BrownDogGadgets2017-10-09

      Thanks for your reference ... will check it out :)

      Regarding pen-lifts I have found them to be a major source of error. The tiniest mechanical error is magnified by the length of the pen. About about to try a new idea ... will publish it if it works.

      You may be able to help me here ... I'm looking for simple pattern filling algorithms such as TSP (travelling sales person) that will port to the arduino. I have found a few articles but they seem overly complicated. Any references would be appreciated ... I don't care if the algorithm isn't efficient so long as it works.

      BrownDogGadgets (author)lingib2017-10-09

      Unfortunately I'm not the person to be asking about that kid of thing. You may wish to check out the open source Makelangelo software. It is kind of the "go to" for open source plotting software. Dan, the author, might be able to fill you in on what he did.

      lingib (author)BrownDogGadgets2017-10-09

      Thanks for the lead :)

      Henri.Lacoste (author)2017-10-09

      A very elegant design, nice job!

      I made one a plotter a couple of years ago, would love to have another go one day. I think I could learn a lot from your design :)

      lingib (author)Henri.Lacoste2017-10-09

      Thank you for your comment :)

      wmrhoward (author)2017-10-08

      excellent project. Do you think this would work with a drag knife vs. pen. I need to cut thin vinyl for templates. I only know about drag knives, no experience but they don't seem that they would need much power.

      Thank you

      GeorgeP165 (author)wmrhoward2017-10-09

      If you can manage a vibrator on the draw-knife ( I used a vibrating motor from a dead cellphone) mounted as near the tip as you can. Start out slow and dial it up till you lose accuracy. Mine cuts thin leather no problem.

      lingib (author)wmrhoward2017-10-08

      Have no experience with drag knives but your idea seems plausible ...

      Anshu AR (author)2017-10-08


      lingib (author)Anshu AR2017-10-08


      pgs070947 (author)2017-10-08

      I'll second all the praise.

      A lot of effort has to go into the planning, doing and the presentation.

      Just looking for some spare time to have a crack at something like this

      lingib (author)pgs0709472017-10-08

      Thanks :)

      eternal77 (author)2017-10-07

      great job, good documenting, thanks for sharing.

      lingib (author)eternal772017-10-07

      You're welcome. Thanks for your feedback :)

      Surajit Majumdar (author)2017-10-07

      awesome project :)

      lingib (author)Surajit Majumdar2017-10-07

      Thank you :)

      About This Instructable




      Bio: 55+ years in electronics, computers, and teaching ... now retired.
      More by lingib:CNC Pen and Wash PortraitCNC Pen LiftCoreXY CNC Plotter
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