14 October 2011

Investigating 3mm Filament for the SumPod

I'm thinking of sourcing the parts (initially just the tubing) to use 3mm filament with the SumPod.  The trouble was, I didn't know the exact dimensions of 3mm filament.  Checking the wikis and reading through various blogs, I was none the wiser of the elusive dimension (or my search skills have abandoned me) and hence the required tube size.  Was the filament less than 3mm in diameter?  If so I could use a metric 3mm PTFE tube or was it actually 3mm, and require an imperial 3/16" (3.2mm) inside diameter tube?

Not getting anywhere fast I decided to buy some.  Specifically some PLA filament from Fabadashary.co.uk (no affiliation).

Once before I had dealings with this company, for their 1.75mm rainbow filament kit.  I was happy with the site and the speed of delivery (UK based, so not really surprising).  The real plus and my reason for going back for this application is they offer short lengths of filament (minimum 5m). Utterly perfect for my needs.  For anyone that doesn't know they hold the widest range of coloured filament I have known a comapny to stock.  They were nice enough to include some sample filament along with my original order for some 'mellow yellow'.

Measuring the filament in several places along its length to check consistency,I can happily report a diameter of 2.8mm, with a variation of no more than a 0.04mm.

Now, I am making the massive assumption that 2.80mm is the actual size of nominal 3mm filament.  If I am mistaken and anyone knows any better please, please, please comment below, before I waste money on the incorrect inside diameter tubing.

Now I know the filament diameter, I will source some appropriate PTFE tubing.  When I get a working setup I'll post my findings.  In the meanwhile, if as I suspect others are looking at using 3mm (2.80mm?) filament with their SumPod, due to the lower cost, I am happy to supply lengths of tubing.

SumPod Guinea Pig signing off


  1. I think 2mm and 4mm ID tubes are being used for 1.75mm and 3mm filament respectively. Is the PTFE for lower friction? It's so much more expensive than PVC tubing maybe one should get some and run some experiments. It would help to have a sumpod for that bit though.

  2. 2.85 is normal

    Faberdashery, orbi-Tech, ultimachine, makerbot, grrf, etc will all be under 3.0mm

    Only chinese stuff goes over 3.0 mm now. That can be from 2.6 to 3.5nm not great.

  3. Thanks for the feedback.

    Yes it's for the *much* lower friction

    I'd heard Chinese filament varied considerably and also that it's the variation in diameter that causes feed problems. I imagine any filament that varies considerably would be a disaster for the SumPod, because there is no tensioner on the feeder.

  4. I'm a bit worried about that last bit. The bit about no tensioning. Did you ever get any clarification on the bearing and screw configuration you mentioned in a picture comment?

  5. The clarification I received was it works, my point was it could be much better. As Richard wants to improve the machine he took my points on board and is continuing work on PET and my suggested PTFE pads; in place of the bearing.

    Still this only provides static pressure on the filment, which is fine if it's dimensionally consistent otherwise it's probable feeder problems will occur. Time will tell, but I would prefer some dynamic element to account for any variation.

  6. Thanks for experimenting with out filament- looks fun!

    Our plastic diameter is specified as 2.84 nominal +/- 0.05mm (although many of our lines achieve +/- 0.02mm) to pass through a 3mm hole. For our 1.75mm material, it is actually 1.74 mm nominal (this is standard).

    A problem we have seen is the relatively high stiffness of the PLA to the low stiffness of the 'rigid' bowden tube, makes it necessary to use 1.75mm material. Otherwise, as the Bowden tube gets distorted, you have a very hard time maintaining print quality. The best option is direct drive for 3mm- perhaps this is possible?

    Have you got the hot-end for extruder assembled?

    Keep us posted,

    PS - Minor correction Fabadashary > Faberdashery ;)