Musings and Experiments on the Art and Science of 3D Printing


Capricorn tubing - not the greatest thing since all-metal hot ends!

By Michael Hackney Sunday, January 6, 2019
I'm continuing to commission and complete the details on my E3D tool changer printer. Over the weekend I calibrated all four tools (hot ends) for Z offset. In the process I printed a small part with each tool. I was aghast at the horrible parts I was observing. On all four tools yet. Something was not right. Was it a slicing issue? A firmware issue? Something wrong in setting up the tools?

The problem looked like typical filament starvation (usually due to an improperly set up extruder or hot end) with visible gaps in the perimeters and missing sections of infill. I know my slicers inside and out so after making sure I wasn't doing anything odd (KISSlicer) I was confident these artifacts weren't due to a slicing issue. I then thought maybe a bad configuration for filament advance in RepRapFirmware might be the culprit. The config.g was provided by E3D and has required some tweaking by us beta testers. But, after going through config.g with a fine tooth comb, I found nothing wrong.

The extruders are Bondtech BMGs and one of them has had some limited service, so I was very confident in it. There is virtually no way to misconfigure a BMG. The tools are E3D V6s. I've worked with E3D all metal hot ends since the v4 days and know how to set one up properly. Even so, maybe I might accidentally mess up one, but all four? Not a chance.

So, I followed my own advice and slowed things down and printed at 20mm/s while I carefully observed. The problem persisted at slow speed and I noticed that the filament "starving" happened at the start of a new segment after a previous one ended - i.e. it might be retract related. Retract was configured to .5mm for these test prints, that shouldn't be an issue. Once going, the filament flowed freely.

I scratched my head on this one. I took a hot end apart and tested by hand pushing filament - it was smooth as silk. I then removed the lever and spring from the Bondtech BMG and pushed filament through it, again smooth. Then I pushed filament through the bondtech up the 800mm of Capricorn tubing. That's when I felt a fair amount of resistance. With nothing else noticeably different, I swapped the Capricorn for normal PTFE tubing and the problem went away! I've done 2 tools now and tried 3 different filaments before and after and the problem IS the Capricorn tubing. Here are some photos.

This part printed with Capricorn was one of the better ones but it had large areas of missing infill and perimeter gaps. The ONLY difference between these two prints is Capricorn vs generic 2mm ID PTFE tubing for the Bowden. So I'm sitting on ~4 meters of Capricorn that is going into the rubbish. Can PTFE be recycled?

6 comments to ''Capricorn tubing - not the greatest thing since all-metal hot ends!"

  1. Hi Michael,

    I haven't had any issues with my Capricorn tubing. I'm not sure how long the bowden tubes are on the E3D tool changer, but maybe that's the difference? Either way, because one man's trash is another man's treasure, I'd be glad to take the Capricorn tubing off your hands. Let me know! Thanks!


    1. Derek, I am going to hang on to it for a little longer to do some force testing pushing and pulling filament through it compared to my standard 1.8mm ID and 2.0mm ID PTFE. If I do "trash it" I will be happy to pass it your way.

  2. Hi Michael, is the filament diameter within a reasonable tolerance of 1.75mm? What extruder steppers are you using, an at what current?

  3. Yes, David the filament mic'd to 1.75mm AND I tried 3 different filaments from 3 different high quality makers. The steppers are the standard Bondtech pancakes at .7A. The steppers were not skipping steps. The issue is the "wind up" within the Capricorn tubing after a retract. I don't know if this is typical with Capricorn as I've only ever used it for short (50mm or so) sections to connect "near direct drive" systems. I've done some googling and found many reports of people adding "extra distance after retract" - presumably to account for this. I am not going to go down that path!

    1. In fact, the stepper on T0 is a 25mm .7A pancake (Bondtech) that I had been using with this BMG extruder for about 6 months. The other 3 were brand new 22mm Bondtech pancakes. But again, there was no evidence of skipped steps.

      Also, several people PM'd me to say that Capricorn does have an issue with tight radius bends. The tool changer CoreXY (the E3d machine) does have a sharper bend than a typical large delta would have, so perhaps that exasperated the issue?

    2. I can see that tight bends could be an issue, because a tight bend will cause the tubing to adopt an oval instead of a circular shape, which would be more of a problem because of the smaller ID of Capricorn tubing. On my Delta the minimum bend radius is about 70mm.