Spool desiccant bag and NFC holder

Recently I was forced to buy another make of filament. My original plan was to always use Bambu Lab filament, so I could benefit from the automatic filament recognition and pre-calculated settings. What I hadn't factored in is that Bambu Labs could be out of stock.

Based on some reading, Sunlu PETG Rapid appears to be a very close match to Bambu PETG HF.

I wanted to add an NFC tag holder to the filament spool. I've already printed out a desiccant holder for my Bambu spools, so my idea was to design one with a place to fit the NFC tags. A quick look on Maker World and it appears that nearly everyone has that idea. 

There are a number of good models on Maker World but, as is typical, my requirements are not quite met by the pre-existing designs. I'd like to thank everyone else that has done similar designs, they have no doubt inspired elements of my version:

My specification:

• Fit a range of filament spool sizes from different brands.
• Fit a 20g (0.75oz) desiccant sachet.
• Position the NFC tag in the same position it would be on a standard Bambu Lab spool.

I prefer silica gel sachets rather than loose desiccant. A 20g bag is very similar in size to the double bags supplied with the Bambu Lab H2D, AMS 2 and the AMS HT.

My design fits spool thicknesses from 50mm (2") up to 75mm (3") and central hub diameters from 50mm (2") up to about 70mm (2-3/4").  Sunlu spools are 60mm thick with a central hub diameter of 60mm. Bambu spools are 67mm thick at the outer edge with a 53mm hub diameter.

The NFC tag is at the same radius it is on a Bambu spool. A tag from an empty Bambu Lab spool can be cut at the bend and it clips in effortlessly. I've modelled in a central undercut to help extract the tag, should that ever be necessary.

As a bonus, this is the first time I've created a thread to 3D print using FreeCAD, so I've learnt a new technique.

Using the Part Design workbench in FreeCAD 1.0, I created a simple 85 deg., thread profile and used the helix function. The depth of the thread is 2.5mm and is offset into the surrounding cylinder by 0.3mm, inside and out, to create the clearance. The helix uses a pitch of 4.5mm. The screw worked perfectly first time. It's quite a loose fit and I could easily reduce the clearance if needed on other models.

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Download:

Spool hub for desiccant with NFC tag STEP and 3mf files (zip)

https://makerworld.com/en/models/1541990-spool-desiccant-bag-and-nfc-holder

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