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Sunday, July 6, 2014

Improved 3D printer spool

I noticed that 3D printers have a strange (engineering-wise) way of mounting the filament spool. Its hub sits on a curved plastic bracket and rotates by the pull of the extrude heads stepper. There are no bearings just a guide tube the bracket and the spool. The extruder feed mechanism pulls on the spool which is balanced on a bracket (see the white bracket on the left of the printer)

Afinia H-Series 3D Printer
Then after printing for a while I got surprised by the multiple spool hub sizes ... uggh.
I started down the conventional road to printing multiple size spool holders but all the while it just felt WRONG that the spool was not on a hub with a bearing.
I looked at a number of designs on Thingiverse and it seemed that most designers were also trying to get rid of the friction of a bearing-less spool feeder. I also noticed that the conventional approach was to mount the spool vertically on a horizontal axle which meant that changing filament and spools required removing and replacing axles and hubs (for different size spools).
There is one design that I liked which had the spool ride on its circumference on bearings. I built one of these and quickly found out that tracking was a challenge unless everything was aligned and parallel. Loading and unloading spools was easy since there are no axles and no hubs.
From these experiences and ideas I came up with a hybrid design.
In this design the spool lays on its side over a hub that is supported by two bearings which is dropped on a vertical shaft.
The hub has 2 bearings, one on top and one on the bottom.
The shaft is fixed in a 2x4 frame and the hubs bearings slides down over the shaft.
Hub Adapter:
There is a hub adapter (to the right in the picture below) that adapts the hubs smallest size to various other sizes.

Guide Arm
The guide arm keeps the filament under control while feeding although I have printed successfully without it by just using the guide tube. I still wanted a control arm that I could mount a cleaning sponge on, so I kept it in the design. In the proto it is made of 1/4 fiber board since its length would have called for a multiple piece flat 3D printed design. Not everything is best 3D printed especially if you want it longer that 5.5 inches and flat :). Of course the hub adapter and guide are 3D printed.

Filament Guide:
The guide arm hosts a filament guide, also 3D printed, which is bolted loosely to it. The filament guide captures the feed tube holding it a fixed distance from the spool. The filament guide also houses (crudely with hot glue just now) a cleaning sponge.
Note: My research revealed that some believe cleaning the filament before going into the extrude'r helps to eliminate clogging, so I incorporated that into the prototype for testing.
My sponge is currently the conductive foam that IC's come in,I like that it is conductive since rubbing plastic would seem to build up static otherwise.
The spool is loaded on the hub and a filament guide arm slides down on top of the spool.
The filament and guide tube snaps into the slot in the filament guide.
The prototype can be seen in the video below and I have been using it successfully for a few months.
Simplify the Guide Arm with an integrated upper flange on its lower surface (the video is using a previous designs triangular hub. [I originally tried an triangular hub to eliminate the hug adapter but it was not a stable way to hold the spool and it would tilt]).
Add a cavity to slide the cleaning sponge into so that it is more stable and can be easily replaced when dirty.

Here is a video of the prototype operating.. smoothly... on bearings!