Spool Holder : Yet Another Type ...."SHYAT !"

Rationale

Central-axis spool holders are the best for reliability and low friction, however they have a couple of drawbacks compared to rim-roller types:

1. They need adjustment to accept a range of spool bore diameters
2. The brackets add width, as does (sometimes) the bore adjuster. This can be a problem where space is limited, for example inside a fixed-size drybox.

This design aims to offer a substantial bore diameter range, while adding barely more width than needed for the common 608 bearings.
 

Overview

• It accepts spool bore diameters in range Ø 37 - 72 mm. 
   
• Spool widths up to 83 mm can be accommodated with the appropriate component selections.
   
• Up to two spools (depending on width) can fit inside the popular Ikea365 10.6L drybox.
   
• FreeCAD source model included

Features & Operation

• The configurable Bobbin has 3 x Bars that carry the spool's bore. 
   
• Width capacity is set by choice of Bar length :
  If placing only one spool/bobbin on the assembly, it makes sense to print the longest Bars.
  If wanting to place two spools then measure your spools before printing, and work out which ones can fit side-by-side. 
  Bars are made in 5 mm length steps, and the sum total length of Bars should be 136 mm maximum.  This is what the standard 180 mm Rails can accommodate, and which will fit inside the Ikea 10L box.
   
• Spool bore diameter is set by selecting the appropriate assembly hole in the side Disks and also the appropriate orientation index of the Bars.
   
• The Brackets and Rails together build a frame. The Brackets are indexable side-to-side on the Rails, in 5 mm steps, to suit various bobbin widths.
   
• Bearings type 608 for low friction
  The central bearings are fixed in their Bracket, while the outboard ones are attached to the geared Disk of the bobbin, using the small Axle component.
   
• A Retraction feature allows filament to be reeled back in, by inserting a 6 mm Allen key into the optional Pinion component.

Purchased items

608 Bearing  (2x per spool bobbin)

Woodscrews   Ø3.5 x 50 countersunk
                         Ø3.5 x 20 countersunk
                         Ø3.0 x 10 pan / button head  (optional for fixing to drybox lid)

Printing

The Brackets incorporate print-in-place sliders and hinges. As with any such feature it's imperative that the XY offset compensation is set correctly. It's termed the “Horizontal Expansion” parameter in Cura. Even so, the newly-printed items may require attention to work free their mechanisms.

The small Clips and Bearing Axle are best printed on rafts. The Clips should also be printed on their side, for bending strength.

Assembly

Refer to images.

Some of the bobbin parts are quite thin : please assemble with care, using minimum force necessary, applied close to the joint, and wiggling the components together.

On disassembly it may help to gently ease them apart using a long thin blade.

Inserting the self-tapping screws, go slowly with a manual screwdriver and grip the component close by.

The retraction pinion (if fitted) should turn freely, and it can be lubricated simply using a graphite pencil on the interfaces.

When changing spools and removing the bobbin, push the outermost bearing out of its bracket, by pressing through the hole, rather than pulling it out.

Evaluation & Future ideas

I got a good result from this design. 

I'd say the brackets are the strong point of the design.

The bobbin does also work, but it's less robust. It's a bit awkward to change the spool and especially to adjust the diameter for a different spool type. So it's most suited for when you'll expect to keep the same spool dimensions on subsequent reels.

It should be possible to use a screw-type bobbin with my brackets. Some of these are compact and would likely work, with perhaps slight design tweaks. 
As a starting point I'd suggest the following:
- Item  68223  by @bradm10000
- Item 139191  by @Foreverwinter.
These would both lack the retraction function, at least without making a substantial remix.

To shave a few mm off the width, should this be necessary, it may be possible to redesign for a slimmer bearing type. I stuck with 608 for now as it's ubiquitous in this kind of equipment.

If much extra width is required, to accomodate a pair of wide spools, then longer Rail variants could be made. But these would not fit within the usual Ikea365 10L box.

Conversely, if width isn't a constraint for many users, the side Disks could perhaps benefit from thickening somewhat.