Splice Bowden Tubes (yes you can)

[David Janszen @djanszen Ohio]

I found a way of splicing the Bowden tube that does not create a step that the filament catches on. Unfortunately, after a while, it came apart, so please consider the following as just an exploration of possibility. (There is a way of making the Teflon tubing adhere to an adhesive with a sodium etch, but that’s not something anyone is going to want to do at home.)

One thing of immediate value here is that the lower tube can be replaced without the rigamarole in CEL’s published procedure.

What got me started on this was that I ran into a problem with a filament material that becomes embrittled with repeated flexing. This was happening during co-printing of the other material due to the relatively tight radii of the Bowden tubes while the more sensitive material idled in the tube and was subjected to a rolling motion, i.e., the portion of the tube that is tightest moves back and forth as the head traverses. (FYI: material is kept dry and is quite supple before being subjected to repeated flexure.)

I’d like to be able to set the printer to retract the idle filament to the extruder wall, but this is not a feature, at least not yet.

One solution is to use a longer Bowden tube that coils up and thus maintains a more constant bend radius while the head traverses.

The published/recommended procedure for replacing the Bowden tubes is predicated on the supposition that it’s impossible to create a usable splice, which is incorrect. That procedure involves considerable disassembly of the printer, re-termination of the tube with the pneumatic fitting, and is completely unnecessary.

Here’s an unreliable way of splicing the tubes:

 

Materials:

• 5/32″ brass tubing
• Metal tubing cutter (the kind you spin around the tubing, not a saw)
• Razor blade, single edged
• Sturdy but fairly pointy tweezers
• 2mm x 3mm Teflon tubing (example: https://www.amazon.com/gp/product/B0771DM75J/ref=ox_sc_act_title_1?smid=A1ZG6RQRT97ZKU&psc=1)

Procedure:

1. Prepare printer
   1. Retract both filaments
   2. Await cool down
   3. Shut off printer
   4. Disconnect power and USB
   5. Move printer to bench or other convenient work area
2. Pop the right side cover off
3. Remove the printhead
4. Disconnect the power cable connector (two wires, red and black) from the transit by releasing the catch that’s underneath it
5. Release the tube using a sturdy pair of tweezers to push the retaining bushing toward the transit while pulling gently on the tube
6. If you’re extending the lower tube, disconnect its fitting from the extruder wall and remove the entire tube, which makes it easier to deal with
7. Use the razor blade to trim the transit end square to remove the indentation caused by the retention collar – make sure you cut it as squarely as possible
8. Decide how much Teflon tubing to add. If you start too long, it’s easy enough to release it from the transit and trim it shorter, so start longer than you think necessary. I added about 4.5” to the lower tube.
9. Use the razor blade to cut your additional length, and again, make sure you cut it as squarely as possible
10. Cut ½” from the brass tubing to create a sharp edge
11. Cut a ~1” length to use as the splicing sleeve
12. Prepare the brass sleeve
    1. Insert the pointy end of your tweezers into one end of the sleeve you just cut, and gently open it up by twisting the tube against the tweezers
    2. Check whether the Teflon tubing can be inserted
    3. Repeat (a) until you can just barely insert the Teflon tubing
    4. Do the same for the other end of the sleeve
13. Insert the transit end of the original Bowden tube about halfway into the brass tube
14. Insert one end of your additional length of Teflon tubing into the other end of the sleeve until it firmly strikes the original
15. Pull and push each of the two Teflon tubes very slightly in and out until they are butting against one another and also are reluctant to be pulled out. This should happen pretty fast. They will be retained well enough by the sharp edges left in the ends of the brass tube by the tubing cutter.
16. If you’ve disconnected the Bowden tube at the extruder wall, reconnect it
17. Insert the Bowden tube into its transit fitting and arrange it to coil up
18. If it’s too long, detach it again from the transit and trim square
19. Once you’re satisfied, reconnect the power connector
20. Connect printer and load filament
    1. The automatic loading routine will probably not feed the filament far enough to reach the printhead through your now extended tube
    2. Use the GCode Console to complete the loading, repeatedly feeding a small distance until the filament jams up against the printhead, which makes a nasty sound
       1. Lower tube: G0 D100
       2. Upper tube G0 E100
    3. If the filament catches on the splice, then you’ll have to try again to make the cuts square and abut the ends tightly together within the brass sleeve. My splice worked fine on the first shot, and I expect yours will, as well.

 

 

• This topic was modified 3 days, 4 hours ago by  David Janszen.
• This topic was modified 3 days, 4 hours ago by  David Janszen.
• This topic was modified 3 days, 4 hours ago by  David Janszen.
• This topic was modified 3 days, 4 hours ago by  David Janszen.
• This topic was modified 3 days, 2 hours ago by  David Janszen. Reason: Splice unreliable

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[BHudson @bhudson I have both RoboxDual and other Robox versions Arizona, USA]

If you should choose to remove the Bowden tube, CEL highly recommends that you open a support ticket to get the proper reinstallation instructions. There are several reasons that there is a published process for installing Bowden tubes:

1. The Bowden tube is easily crushed. The published solution tells you how to avoid it.
2. The Bowden tube must be fully inserted into the pneumatic fitting, the “transit” in the above post. If it is not fully seated the Bowden tube will pop out of the fitting at some point in the future and will ruin your print.
3. Properly installing the Bowden tube is most easily and safely done by following the instructions CEL has published. The cable chain bracket makes access to the Bowden tube pneumatic fitting very restricted and it is very difficult to get the Bowden tube seated properly.

If one wanted to have a longer Bowden tube, it is much more reliable and probably easier to just install a longer one. You will have to remove the ferrule on the extruder end of the old tube and install it on the new one, but this is just about as much work as the described splicing process and will be much more reliable.

I operate two Betas and four Production Robox.
I am the US/Canada Technical Support engineer for the Robox.
www.hudsondesignlabs.com

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