Sunday, August 03, 2008


Inverting a Basket

This weekend, while I waited for some ABS to arrive (with all of the warping issues I've heard about, I'm going to avoid HDPE for now), I decided to build a filament holder for my RepRap.

The goal was to seamlessly provide material for the extruder without introducing twists or kinks in the supply line.

Vik Oliver wrote about a nice setup last year, one that dangles the spool above the machine from a support structure, protects the material from humidity, and prevents kinking with a swivel. Here is a picture of his suggested structure, borrowed from that page:

Several people have had success with this design, and some elegantly use a basket with a hole in the bottom instead of the strap, but I thought I would try something a little different. I didn't want flimsy support beams jetting out of the top of my RepRap because they would get in my way when reaching around the machine to fix it, and could be aesthetically displeasing. Because my RepRap is supported in mid air with my laundry hamper frame, as opposed to on a table, I had some space underneath to play with, so I decided to adapt the design to hold the filament under the robot.

One important point about designing this for under rather than over the RepRap, is that a basket is not well-suited for the job.

The three support chains get in the way of any filament coming out of the top of the basket, and any coming out of the bottom would probably kink because of the tight turns involved.

I decided that my holder would have to be hung from its center, so that the spool can unwind around the sides. This is like taking the original design and turning it inside out.

I went to my local hardware store and came back with:
I also had laying around
Bolting the L brackets at 120 degree increments around the tin can, and tying everything up to the swivel with the twist ties and key rings, I made the following device:

Two carabiners clip onto the bottom-most diagonal of my RepRap, on either side of the crossing bottom-diagonal, to keep the contraption centered.

Lastly, a pully attached to one of the legs of the stand ensures that the filament is pulled from the side of the spool, rather than persuaded off of the top.

The whole thing spins effortlessly, and the stiffness of the filament keeps any stray rotation from getting out of hand. With a short, 10 minutes of extruding, I could see the holder slowly rotate as more material was needed. Several rotations were observed without any problems. Success!

It is very satisfying to have something (anything) go from concept to functional physical reality in one day. I suspect this satisfaction may become more commonplace once I have a rapid prototyping machine in my apartment. :)

In retrospect, this design does not exhibit a feature that the original had, namely the moisture barrier. I can think of a couple ways to retrofit it with a bag, but I think I'm just going to hope it is not necessary. I have heard that some filaments absorb moisture quite readily, but does ABS? What has been your experience?

Until next time.

~Andy :)

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Very nice idea. Very printable as well... ;)

I think I'll make my RepRap stand 'on its own feet'. I have a washing basked just like yours and its bag tore open. It would also clear quite some space on my desk to have no RepRap there anymore. Plus, it becomes easier to move around the machine if it's not tied to a spot on the desk.
Shiny! I hope you don't mind if I use that idea. :-D

That's great! :) I'm tickled to hear you're going to make a similar setup. Let me know if you like it.


Please DO use the idea. :) I'd love to see pictures.

Does HDPE "really" absorb moisture? They use it for milk jugs and such...hmm. Now I'm gonna have to look!

Nice work. That thing pretty much rocks.


Thank you very much! :) I don't actually know if HDPE or ABS absorb moisture. I was getting my information from, which says "The filament picks up atmospheric moisture in humid conditions." I think they were talking about PLA or CAPA, I'm not sure. I should remove my fuzzy reference to HDPE before I accidentally start a misinformation campaign. :)
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