Prusa Core One Gantry Primer - Never Remove a Print Bed Purge Line Again!

Summary

This is a nozzle primer for the Prusa CORE One which mounts to the gantry. This allows for nozzle priming/purging at any point during a print. It removes the need to have any priming or purging directly onto the build plate. The installation is toolless and easily reversable. Never remove another bed primer line/tower for the cost of one bearing, some masking tape, and the 3D printed parts.

See a short video of the priming in action here:

Here is a comparison of the first layer of a 15mm^3 cube using the default bed priming line versus the Gantry Primer priming. Filament is Overature Matte Black PLA with Default PLA settings using a HF 0.4mm Nozzle.

The Gantry Wiper is required to use the Gantry Primer. See it in action here:

Caution: This is a printer modification and should be installed carefully to prevent damaging your printer.

Bill Of Materials

• Gantry Primer 3D Print

• Bearing Axel 3D Print

• 8mm (Inner Diameter) x 22mm (Outer Diameter) x 7mm (Width) Metal Bearing

  • The type of bearing should not matter

  • Example bearing (Amazon, ~$6)

• Masking Tape

• Gantry Wiper 3D Print

• Silicon Nozzle Brush

  • See Nozzle Wiper V2 for links, printing, and installation

FAQ

• What filaments work with the Gantry Primer?

  • I have tested only PLA and Silk PLA. If you try other filaments, please let me know so I can update the tested filaments list

• Does this require the Gantry Wiper?

  • Yes, the Gantry Wiper is required for the Gantry Primer to work

• Why is there no right side mounting version?

  • Partially due to compatibility with the Gantry Wiper and partially due to laziness

• Does this work to replace the primer tower for MMU?

  • I don't have an MMU to try this but theoretically it should work. Let me know if you try it!

• Does this work with the Core One L?

  • I have no idea. Print one and let me know!

• Will this work with Indx?

  • Probably not. Indx extends into the extra space the Gantry Primer uses

• What is Masking Tape used for in this build?

  • This is used to prevent sticking of primer/purge filament to the Primer and Wiper

Printing Settings

0.2mm Structural with Supports will work fine

Orientation

To prevent separation of layer lines during usage, the model must be placed with the door facing side (hooks for the gantry rails) on the print bed. Printing in the upright position can cause the layer lines to split due to the downward force the nozzle has on the Wiper. See the 3mf file for reference on the correct orientation.

Materials

PLA was used for the existing model but it will warp if you print with higher temperature filaments. So far it has worked fine for PLA only printing. If you print higher temperature filaments you probably want to use PC Blend CF, PC, ASA, ABS, etc. which will warp less.

Settings

• Layer Height - 0.2mm

• Nozzle Size - 0.4mm

• Perimeters - 2

• Infill - 10% Gyroid

• Brim - None

• Supports - Required, Rectilinear preferred

Assembly

Three main steps. Make sure to follow the Gantry Wiper Assembly to add the Gantry Wiper before following the Gantry Primer Assembly and Installation steps.

Remove Supports

Remove the supports under and inside of the bearing cavity. Be careful to not bend the thin plate with the axel hole in it when removing supports. Also remove the supports in the cutout at the 90 degree corner bend. This cutout prevents the build plate screws from interfering with the Gantry Primer when the Z position is set to zero.

Attach Masking Tape

Cut out a 8mm x 8mm piece of masking tape or equivalent tape. Stick this on the inside lip of the bearing cavity and bend it around the edge to the outside. Using pliers or tweezers will help with this. The masking tape will prevent any primer filament that makes it around the bearing from sticking to the Gantry Primer.

Attach Bearing

Place the bearing inside of the bearing cavity and line up the hole with the axel hole. Place the axel into the hole with the notched side facing outward. This side allows one to use pliers to remove the axel if needed. The top face of the axel should be flush with the Gantry Primer. If it is not flush, grab the bearing and wiggle it around while putting pressure on the axel. It should slide further into the hole. 

Spin the bearing. It should spin freely and easily with no resistance. If it has resistance, make sure that there are no remnants of supports left inside the bearing cavity and the masking tape isn't rubbing against the bearing.

Installation

The installation is toolless, easily reversible, and should not required any force. Move the print head to the back of the printer to allow for access to the front left belt tensioner block.

Make sure to follow the Gantry Wiper Installation if it's not already installed!

Hook the Wiper Arm

Wrap the rounded hook of the Gantry Wiper under the guide rail of the gantry. The tab above the round hook should be under the sheet metal of the enclosure. The rectangular hook should be over the belts.

Slide on Wiper Arm

Push the Wiper towards the left side belt tensioner block. The rectangular hook of the Gantry Primer should slide onto the belt tensioner block and fit snuggly. Continue to push on the Gantry Primer until it makes contact with the left side guide rail and upper Z axis mount.

Verify Flatness

Push on the Primer around the 90 degree bend to make sure that it is laying flat against the left side guide rail and upper Z axis mount. This flatness ensures the the Primer will be parallel to the build plate. Mounting at an angle may catch on the build plate when it is raised.

Verify Print Bed Clearance

Slowly raise the build plate to make sure the Gantry Primer does not catch on it. There should be a 1-2mm gap between the Gantry Primer and the build plate. After, home all axis to make sure that the gantry X and Y Axis does not interfere with the Gantry Primer.

G-code

The Gantry Primer requires custom g-code. This g-code can replace the default Start G-code priming line, Color Change G-code to allow for priming when changing filaments, or in the Tool Change G-code to replace the prime/purge tower when using the MMU to change filaments.

Start G-code Replacement

To replace the Start g-code, make sure Prusaslicer is on the Advanced mode. Then go into "Printers" -> Customer G-code" -> "Start G-code" and scroll all the way down to the bottom. You should see this g-code at the bottom:

; prepare for purge
M104 S{first_layer_temperature[0]}
G0 X249 Y-2.5 Z15 F4800 ; move away and ready for the purge
M109 S{first_layer_temperature[0]}

G92 E0
M569 S0 E ; set spreadcycle mode for extruder

M591 S0 ; disable stuck detection

;
; Extrude purge line
;
G92 E0 ; reset extruder position
G1 E{(filament_type[0] == "FLEX" ? 4 : 2)} F2400 ; deretraction after the initial one
G0 E5 X235 Z0.2 F500 ; purge
G0 X225 E4 F500 ; purge
G0 X215 E4 F650 ; purge
G0 X205 E4 F800 ; purge
G0 X202 Z0.05 F8000 ; wipe, move close to the bed
G0 X199 Z0.2 F8000 ; wipe, move quickly away from the bed

M591 R ; restore stuck detection

G92 E0
M221 S100 ; set flow to 100%

Replace all of the lines above with the g-code below

; Get Up to Temp
M104 S{first_layer_temperature[0]}

;
; Setup Extruder
;
M107 ; Turn off print fan to prevent primer from moving during extrusion
G92 E0 ; reset extruder position
M569 S0 E ; set spreadcycle mode for extruder
M591 S0 ; disable stuck detection

; Move Nozzle to setup position
G1 Y0 F15000 ; Set initial y position away from bearing
G1 X70 F15000 ; Set initial position away from bearing in x
G1 Y-15 F15000 ; Set initial position away from bearing in y

; Finish Getting Up to Temp
M109 S{first_layer_temperature[0]}

; Purge
G1 E{(filament_type[0] == "FLEX" ? 4 : 2)} F2400 ; deretraction after the initial one
G1 E4 F500 ; slowly start purge
G1 X65 F800 ; Move inward
G1 E8 F650 ; continue purge
G1 X62.5 F800 ; Move inward
G1 E32 F800 ; purge
G1 X152 Y-14 F15000 ; Use wiper to remove any remaining purge
G1 X185 Y-17 F15000 

M591 R ; restore stuck detection

G92 E0
M221 S100 ; set flow to 100%

Color/Tool Changing G-code Replacement

When using the Gantry Primer for Color Changing or Tool Changing Priming with the Gantry Primer, add the slightly different code below. Note that this code is the same as above but removes setting the temperature of the nozzle. If you switch between different filaments with different nozzle temperatures, you may need to add g-code that changes nozzle temperature. Prusaslicer does this automatically for the MMU so I have no way to program this ahead of time.

;
; Setup Extruder
;
M107 ; Turn off print fan to prevent primer from moving during extrusion
G92 E0 ; reset extruder position
M569 S0 E ; set spreadcycle mode for extruder
M591 S0 ; disable stuck detection

; Move Nozzle to setup position
G1 Y0 F15000 ; Set initial y position away from bearing
G1 X70 F15000 ; Set initial position away from bearing in x
G1 Y-15 F15000 ; Set initial position away from bearing in y

; Purge
G1 E{(filament_type[0] == "FLEX" ? 4 : 2)} F2400 ; deretraction after the initial one
G1 E4 F500 ; slowly start purge
G1 X65 F800 ; Move inward
G1 E8 F650 ; continue purge
G1 X62.5 F800 ; Move inward
G1 E32 F800 ; purge
G1 X152 Y-14 F15000 ; Use wiper to remove any remaining purge
G1 X185 Y-17 F15000 

M591 R ; restore stuck detection

See the full priming and wiping process here:

Expected Usage

It is expected that the Gantry Primer will prime the nozzle by creating pressure against the bearing. Priming the nozzle allows filament to come out immediately when printing and removes any bad filament that may be left over in the nozzle from previous usage. The Gantry Primer achieves this by pressing the nozzle against the bearing at an angle so that the filament coming out of the nozzle slides down the bearing and pressurizes the nozzle at the same time.

Appropriate Movement

It is expected that the Gantry Primer will flex in the Z+ and Z- axis when priming due to the nozzle pushing the bearing down. The Gantry Primer should not flex much if at all in the Y+, Y-, X+ or X- axis. The Gantry Primer should never shift positions from its mount if mounted correctly. The bear is expected to rotate when priming but may not depending on the filament used. Instead, the filament may just slide off of the bearing.

Safety

This is a printer modification and should be carefully tested before being used. The printing nozzle should not be able make contact with any part of the Gantry Primer other than the bearing. The print bed should not make any contact with the Gantry Primer.

Tested Filaments

Gantry Wiper Usage

The Gantry Wiper is required to work in conjunction with the Gantry Primer. The Gantry Wiper helps to remove the primer/purge waste from the Gantry Primer by pinching off the excess. Please see the Gantry Wiper for more details on its usage.

Remixing

The Fusion360 (f3d) file is provided for those who want to make modifications. It's not my cleanest model and is not fully parameterized so be cautious about the relative distance between features if you change the model.

Updates

04-11-2026

• Added STEP files

04-10-2026

• Initial Version Uploaded