Prusa Core One+ Magnetic Top Cover Vent Slide and Handle

This vent slide and handle for the Core One+ allows the magnetic cover I designed for the Original Core One to be used with automatic vent operation on the Core One+.  It replaces the vent slide of the original design; all other parts for the magnetic frame (along with frame assembly instructions) are the same, and can be found at: Prusa Core One Magnetic Top Cover with Integrated Vent Handle.  Rather than design a new frame specifically for the Core One+, I decided to keep it the same so that all of the remixes for the original frame (hinges, different magnet sizes, finger tabs, etc.) can still be used.  This vent slide handle is a direct drop-in replacement, making it easier for people who were using the magnetic cover on the Core One to upgrade to the Core One+.

The slide handle is very solid, and being rigidly attached to two of the vent screws (rather than resting on the vent nuts) ensures smooth, non-binding operation when operated by either the automatic tab or the handle.  This is not true for the the original Core One slide handle which was optimized for smooth operation when moved by the handle, and would sometimes bind if the vent was manually moved; this was a compromise to make assembly easier, and is caused by torsional rotation of the handle when the vent is manually moved (if you have the old design, try it yourself).

To make it easy to test automatic vent operation, there are two test gcode print files included (one for opening the vent, and the other for closing it).  They are hacked versions of a print file, but they don’t heat up the nozzle or bed, perform bed leveling, or print anything.  Simply load the files to the Core One+, hit print, and they perform the homing operation, then open or close the vent (depending on which file is printed).

2026-02-04 Update: Per suggestion, added copy-able text for the G-code modifications to avoid the possibility syntax errors.

Design Features:

• No supports required 

• Drop-in replacement for the original Core One vent handle

• Has self-tapping holes, and uses original M3x10mm screws for easy assembly

Printing Notes:

• Print with 0.2mm layer height, structural, 15% infill.

• Supports are not required.

• PETG will work fine since the part is not under stress, and should not warp, even with a chamber temperature of 55C.

• Please DO NOT use the .bgcode file that has been provided (always slice your own files for your specific printer, filament, environment, etc.).  The file was only included to provide a reference for approximate print time.

Assembly Instructions:

IMPORTANT:  The vent on the Core One+ opens when moved to the left, opposite from the Core One (which opened when moved to the right).

Step 1:  If the vent on your Core One+ opens when moved to the left, skip to Step 2.  If the vent on your Core One+ opens when moved to the right, it must be removed and flipped left-to-right.  Remove the three screws holding the vent to the top cover; use a wrench or pliers to hold the nuts while removing the screws.  Only one of the nuts will be reused during assembly, but be careful not to lose the plastic spacers on the screws (all three screws and three spacers will be used during assembly).  Flip the vent, then re-attach the right end using one previously-removed screw, spacer, and nut.  Take care to support the other (left) end of the vent to prevent the single screw from breaking the vent (a piece of tape can help hold it).  Tighten the screw until it is snug, then loosen it approximately 1 turn.  Be careful not to crimp or bend the spacer while tightening (it should seat fully into the slot on the top cover).  Go to Step 3.

Step 2:  If your Core One+ is new or it was recently upgraded, and the vent is already positioned to open when moved to the left, then only the left and center screws need to be removed; use a wrench or pliers to hold the nuts while removing the screws.  Be careful not to lose the plastic spacers on the screws (both screws and spacers will be used during assembly, but the nuts will not be used).  Take care to support the left end of the vent to prevent the single screw on the right from breaking the vent (a piece of tape can help hold it).

Step 3:  Place the slide into the front piece as shown in the picture.  Place the slide cover on top, and press down on the ends of the cover until it clicks into place.  Operate the slide a few times to make sure it is assembled correctly and moves smoothly.  If you need to remove the cover in the future, lift slightly in the center of the cover; this will reduce tension on the locking tabs at the ends of the cover.

Step 4:  Attach the front piece to the top cover as described in the frame assembly instructions.

Step 5:  From the top of the cover, insert one M3x10mm screw and spacer (removed earlier) into the left screw hole of the vent slide.  The hole in the vent slide is self-tapping; do not apply excessive force to prevent stripping the threads.  Tighten the screw until it is snug, then loosen it approximately one turn.  Be careful not to crimp or bend the spacer while tightening (it should seat fully into the slot on the top cover).  Repeat the process for the center screw and spacer.

Step 6:  Operate the slide a few times using both the handle and the automatic tab to ensure that the slide moves freely.  If not, inspect all three spacers to ensure that they are fully seated in the slots and not damaged (bent or crimped during assembly), then check tension on the screws (may need to loosen them slightly…try another 1/2 turn).

Optional Modifications to Custom Start/Stop G-code

If custom modifications are made to the start or stop G-code, it is recommended to create a custom printer profile because the default printer profiles may be overwritten when a configuration update is performed in the slicer.

Start G-code Modification

Apparently the Core One+ firmware only moves the vent when the filament type is changed…or maybe it’s the first print after the filament type has changed (I haven’t completely figured out the behavior).  Some users might prefer to have the vent moved to the proper position at the beginning of each print in case the vent position was moved between prints, or was adjusted to half-open on the prior print.

A quick survey of filament types typically requiring an open vent (PLA and PETG) shows that they have a minimum chamber temperature of zero degrees, and those requiring a closed vent have non-zero minimum chamber temperature.

Conditional code can be added to the “Start G-code” section to set the vent position (via the M870 command) based on the minimum chamber temperature of the filament profile.  Copy the following command, and add it immediately after the G28 home command as shown in the screenshot below.

M870 {if chamber_minimal_temperature[initial_tool] == 0} O {else} C {endif}

End G-code Modification

Some users might also want to change the position of the vent at the end of each print, maybe to open it for cool-down, or close it to keep dust out.  Copy the following command and add it to the “End G-code” immediately before the M104 command, as shown in the screenshot below (the example shown is to close the vent; use “M870 O” to open the vent).

M870 C