Intended as an alternative to the original clip-in core for the 3DTomorrow MasterCore system - see: [https://3dtomorrow.com/product/mastercore-uk-pla/](https://3dtomorrow.com/product/mastercore-uk-pla/) - which I tried, but in my case found that it didn't hold the spool faces on tightly enough.

Compared to the original design, the advantages are:

• No chance of the spool coming apart.
• Fits cardboard spool widths from between ~ 56mm to 100mm.
• Customisable OpenSCAD design for use with differently made spools.
• Stronger construction.

The disadvantages are:

• Spool bore diameter is reduced to 40mm.
• Spool width is increased by 7mm in the centre area.
• More material and printing time required.

Variants

MasterCore:  for spools supplied by 3DTomorrow

• Spool width:  70 mm
• Core internal diameter:  88.6 mm
• Spool bore:  54.6 mm

MCPP:  for spools supplied by Mitsubishi Chemical, 3DFilaprint, Ooznest etc.

• Spool widths:  ~56mm (500g), 80mm (1000g)
• Core internal diameter:  101.6 mm
• Spool bore:  56.5 mm

Overture:  TBD

Printing

• Print all four of the .STL models (in one folder) for one spool,
  • OR: If re-using a spool with only one side separated, three parts will do - both screws and one core.
• PLA or PETG both work well.
• For strength, 3 perimeters are recommended.
• 0.4mm and 0.6mm nozzles are both suitable.
• Layers 0.2 - 0.25mm, possibly OK on 0.3mm.

Assembly 

Empty cardboard spools can be dismantled carefully with a sharp knife or chisel. Try not to pull apart forcefully or the cardboard will tear.  Cut off the remaining glue blobs.

Cardboard spools from other suppliers may have different dimensions, so make sure to take inner diameter measurements of the core and side bores and customise the design accordingly.

Full 4-part print

• Push screws through outside spool faces.
• Screw down core supports firmly on the matching screws, with flat faces toward each other.
• Place filament refill over the carboard tube.
• Screw sides together and release zip ties.

Alternate  3-part print

• Push screws through outside spool faces.
• Place filament refill over the side with cardboard tube still attached.
• On the other side, screw down the core support firmly on its matching screw, with flat faces toward each other.
• Screw sides together (not too tightly as side without core may buckle inwards slightly.)

Parametric Design

Each part has its respective .scad file.  The primary parameters are:

• Spool Core:  Internal diameter - to fit core support arms inside carboard tube
• Spool Screw:  Bore diameter - to fit screws into spool centre holes correctly

There are other parameters which can be adjusted for less important changes and small adjustments.  I have tried to script these all as well as I can, but some parameters may ‘break’ the model if pushed too far or cause printing or use problems if not adjusted correctly.

UB.scad is required (public domain file included) - source: [https://github.com/UBaer21/UB.scad](https://github.com/UBaer21/UB.scad)

The newest snapshot of OpenSCAD (with Manifold for multi-core support) is much quicker for rendering. It can be found at: [https://openscad.org/downloads.html#snapshots](https://openscad.org/downloads.html#snapshots)  - make sure to enable manifold in preferences/features.