This topic contains 8 replies, has 2 voices, and was last updated by 
Charles Jackson 1 year ago.
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I’ve been trying to get Lay A PVA and E3D water soluble support to work in the robox Dual. Have had some success but eventually the filament swells inside the short piece of Bowden Tube in the head to the point it wont feed through the titanium bridge into the nozzle.
So I have a spare DM head that I experiment with and I’m gonna replace the short piece of tube in the head (which can be too short see my previous posts and cause filament jams by the filament swelling between the end of the PTFE tube and the exit of the head) with 1.8mm ID by 4mm OD tube. I believe the OEM Robox tube is 2mm ID?. See if this helps stop the filament swelling in the head.
Anyone else tried this?
Aerospace Engineer with a creative itch being scratched by Robox!
Well ive done it with some other samples of PTFE I mannaged to source from a UK supplier. And its working well so far after one teething issue.
Initially I used 1.76mm inner diameter(ID) by 2.5mm outer diameter(OD) PTFE for the short piece in the head. this is smaller OD than the Robox original so I was worried that the filament would swell as would the PTFE tube when hot and it would jam. And as predicted using PLA filament this happened pretty quickly into a print.. circa 5 mins.
Bummer i thought.. really need 1.76mm ID by 3mm OD but I cant get that. Sudden brain wave.. ill sheath the outer in heat shrink!!. this has a double benefit.. it took up the 0.5mm diammeter gap inside the head casting ( after heating it and shrinking it down) and its putting a bit of a compression force on the PTFE tube to fight a swelling fillament.
Ill put up pics later and am going to try a couple of filaments that notoriously stop feeding after a bit.. namely PVA and the E3D soluble scaffold.
@pete thought this might be useful info for future design if it works?
Aerospace Engineer with a creative itch being scratched by Robox!
If you can make the heatsink more effective or reduce the heat which is causing the PVA to swell in that area of the head you might get better results.
Try a cold bed, you might need a Lokbuild surface or similar.
Also put a fan on your extruder as it gets hot enough to soften the PVA filament.
Your suggestions of reducing the space for the filament might work, it wont leave room for errors in the filament diameter though.
For official support please visit www.cel-robox.com/support/ and create a ticketThanks for the response.All very good points which bit obvious really since you designed the Robox.
Finding so far are that it works fine and I’ve had no issues with PLA swelling to the point that it wont feed forward into the heat block. This is with prints that have rapidly heat cycled the PLA as I been using it as support with ABS (which works very well by the way see my other posts).
I still cant get LayA PVA or E3D Scaffold to feed. Given its a spare head for experimentation I removed the brass nozzle just leaving the needle valve exposed and neither material would feed into the heater block (extruder slips) which i thought very strange. I suspect its to do with the I/D of the titanium heat bridge. But am a bit stumped really? As it will feed in by hand after heating up head and removing.. is there away of temporarily reducing slip detection and just brute force the filament into the head?
Aerospace Engineer with a creative itch being scratched by Robox!
Below are pics of the 1.76mm ID x 2.5mm OD PTFE tube with a Heat Shrink Tube (forget size) around it which effectively takes OD up to point of filling the guide channel recessed into the head.
Out of curiosity,, whats the purpose of the spring, spring clip and brass ring that sleeve of the feed part of the heat sink.. Also I did think of either removing a significant portion of the metal by drilling a lot of holes in it (reducing heat transfer back up the filament feed) or just cutting the mid section say couple of cm out and just have the head bowden tube supported at the entrance to the head and at the point where it goes into the titanium heat bridge. As per the last two pics below. You have any thoughts on this?
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This reply was modified 1 year, 1 month ago by Charles Jackson.
Aerospace Engineer with a creative itch being scratched by Robox!
I asked Chris E about this and he suggested that the problems he saw was damage to the filament caused by the extruder. It is hot enough to soften the PVA filament and after a short period of use the filament leaving the extruder was crinkled by the gears and this distortion was enough to prevent it feeding easily.
The spring on the brass ring is used to keep the heads internal parts pressed against the front of the housing. This removes the need for perfect fit between plastic and metal parts.
Drilling the heat tube may make a difference but it is a little extreme, perhaps put that at the end of the list 🙂
- Add cooling to the extruder. The motors generate heat.
- In the GC0de box type M503 to view the firmware settings. Look for these 2 lines:
M906 will allow you to control the Drive current. Eg M906 E1.280
M907 will allow you to control the Hold current.
Reducing the E or D (depending on the extruder you want to alter) will reduce the heat buildup and the available torque. Reducing Hold current may have positive effects without noticeable negatives. Leave the figures for the other motors alone. The settings you add will remain until you power off the printer, to write them to firmware type M500, they will be overwritten with a firmware update. - Try adding a 24V fan to the head which will push more air through the heatsink.
- 3 cool the actual tubes by sheathing them and pushing air through.
If you want to alter slip detection threshold you can also do this using M503 then M909, default is 10 units. Try m909 s50.0 t4.0
50 is the number we used while testing flex filament. It will ram material into the head for 50 units (risking the seals), but it will eventually give up and pop up the slip error.
For official support please visit www.cel-robox.com/support/ and create a ticketGreat info, excellent I will have a play.. and dont worry wont be sneaking a repair for the head if I break it.. all in the name of progress LOL! I have a unmolested good head for normal printing.
Also, totally different note. Am interested in investing in CEL.. who do I speak to as I saw the advert a while back
Aerospace Engineer with a creative itch being scratched by Robox!
Ill email you about the investment round we are doing.
For official support please visit www.cel-robox.com/support/ and create a ticketTried the extruder slip detection change you suggested but just couldn’t get the material to feed at all and tried many times. Which is weird as I have got it to feed for a few minutes before hitting problems before.
When i thought about it a bit more,, only thing I could think of is that the extruders are hot and softening the filament too much causing slip as you mentioned. Especially given the only time I’ve had any successful prints for a few minutes with PVA or the E3D Scaffold is when the printer has been off for a day or two (very rare!!!) and I’ve tried it from a completely cold printer. Ill try the fan thing onto the extruders next as I think the internal head bowden tube mod is doing its thing. Maybe then ill look at heat pipes to an external heatsink if it works..
Aerospace Engineer with a creative itch being scratched by Robox!
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This reply was modified 1 year, 1 month ago by
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