Pastamatic Leadscrew for 43mm Sub-spool (⅔ Spool)

This is a custom Pastamatic leadscrew designed for use with 43mm-wide filament sub-spools (2/3 of a Bambu spool). If you use Cernott’s modular spool system, this leadscrew helps evenly distribute filament while respooling, preventing tangles and uneven winding.

Why I Designed This

I initially tried using the Pastamatic Leadscrew for Divided Spools by @AeonJoey, but I found the narrower threads on that leadscrew made my follower tooth bind and prevented smooth operation. I know that model works great for others, but I wanted to make some adjustments for my own needs. I've rearranged and adjusted the threads on the original Pastamatic leadscrew, ensuring the follower tooth properly follows the self-reversing path while maintaining the correct spacing for 43mm-wide sub-spools.

Compatibility Notes

This leadscrew was designed for Cernott’s 2/3 modular spool (2/3 Bambu Spool, ~550g). If anyone tries it with different spools of the same ⅔ Bambu size, let me know!

Recommended Mods for Best Results

While this leadscrew improves filament distribution, proper spindle stabilization is crucial—especially on narrow spools. They are completely optional, but I strongly recommend using these three mods to keep the spindle aligned and prevent shifting. Without them, it may be more difficult to achieve consistent results:

• Pastamatic Axis by @Poli27  Prevents the receiving spindle from shifting away from the drill.
• Pastamatic Target Side Clip by @andythilo  Locks the receiving spindle securely into the gears.
• Pastamatic Spool Shims by @dadhacks  Prevents the receiving spindle from shifting toward the drill.

Using these mods, I was able to achieve consistent, even filament winding. If you have an alternative method for stabilizing the receiving spindle on a stock Pastamatic, I’d love to hear about it!

Print Settings & Assembly

Layer Height: 0.16mm (like the original design) on threads and gear teeth to preserve smooth operation, 0.28mm on all other layers to minimize print time

Walls: 2

Infill: 5% Cross Hatch

Supports: Not needed

Material: PLA or PETG recommended

To install, replace the original Pastamatic leadscrew with this one, fully load a spool with sub-spools, with your target 2/3 size sub-spool on the side closest to the gears, and use the recommended mods to ensure smooth operation.

Other Leadscrew Sizes

I have also designed leadscrews for other modular spool sizes:

• Leadscrew for 23mm Modular Spools (1/3 Bambu Spool)
• Leadscrew for 33mm Modular Spools (1/2 Bambu Spool)

If you need a different size, check those out!

Notes and Tips

Some filament manufacturers like SUNLU sell 250g mini spools in assortment bundles. It's a great way to try out lots of different colors and types of filament, but these tiny spools do not fit in the AMS, making them inconvenient to use. By respooling onto 1/3 size modular spools, you can store them more efficiently and use them directly in the AMS without hassle. If you use those 250g mini-spools, check out the excellent 1/3 sub-spool designs by Cernott and giuliolibrando.

I printed my custom leadscrews in the same color as the matching sub-spools. It makes it easier to grab the right leadscrew when re-spooling.

Thank you @GekoPrime for the Pastamatic Filament Spool Winder, and thank you @Giuliolibrando, @Cernott, @assorted_mess, @AeonJoey, @Poli27, @andythilo, @dadhacks for your designs and inspiration.

Feedback & Future Improvements

If you test this leadscrew with other divided spools, please share your results! I’m open to feedback and improvements to make this as reliable as possible.