Twin Extruder Carriage

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Twin Extruder Carriage

Postby dave3d » Mon Nov 25, 2013 4:46 pm

I have bowdenized my Wade extruder and jhead (if bowdenized is a word).

Still a few minor problems to sort out but it prints well at higher speeds with less shaking of the printer. The next stage I plan is fitting twin bowden extruders.

Does anyone make a twin extruder carriage? I have not seen one.
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Re: Twin Extruder Carriage

Postby cvoinescu » Mon Nov 25, 2013 10:09 pm

dave3d wrote:(if bowdenized is a word).

It is now. :)

Do you notice a difference in your prints? What tweaks did you have to make to combat oozing and delay, if any?
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Re: Twin Extruder Carriage

Postby dave3d » Tue Nov 26, 2013 11:48 am

I have not altered any settings at all in Marlin. Not sure what is meant by oozing and delay. I am a relative newbie as you know but I do like to experiment and try things out.
I was surprised how much elasticity there is in the ABS filament. If you push the filament into a 1M PTFE tube you can move it backwards and forwards at one end quite a bit without it moving at all at the other. I have therefore kept the bowden tube as short as possible by mounting the extruder directly on the top of the Ord Bot. I turned the handle/controller plate upside down and I have fitted a section of Misumi rail across the top. The length of the PTFE tube is about 18" at the moment but I can probably shorten it back to just 15". I have built two of Bart Drings spool holders that run on roller bearings. I did toy with the idea of mounting the extruders on them but figured the tubes would be too long.
I am using 1.75mm filament and a 4mm od/2mm id PTFE tube with pneumatic fittings. The Gregs Wade extruder pushes the filament easily down the tube. I have printed a mirror image Wade extruder for the second one. It fits better. I had a problem with the filament folding over and jamming in the jhead recess hole in the extruder but I printed a plug from thingiverse which has solved that problem.
Prints seem the same as before ........ when they turn out .....but obviously I have had more failures while sorting out problems. Not sure what oozing is but I am using 1mm retraction.
As well as LCD screen breaking up/Repetier occasionally freezing, I have a problem at higher speeds when the print is sometimes displaced slightly by 1 or 2 mm. I was wondering if the glass has moved very slightly. It does not occur on slower speeds. I am using 6mm glass and I plan to go to 4mm toughened to lighten the Y carriage.
Nobody has answered my question yet about availability of a twin extruder carriage. I must assume nobody does one.
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Re: Twin Extruder Carriage

Postby TLHarrell » Tue Nov 26, 2013 6:51 pm

Oozing is like what happens with a regular hot glue gun. The material in the nozzle leaks out when not being extruded. It should be solved by retract, but not always the case.

Two things affect the amount of "compression" in a Bowden tube. One you have discovered is the overall length of the tube. The other is the difference in ID of the tube to OD of the filament. A larger difference crates a bigger gap, and there's more space for it to pile up before it can be forced forward. This causes a delay when you command the extruder to push filament. This is like "backlash" in a CNC machine. There are settings to take care of that.

If you've mounted the extruder directly to the top of the bot, do you have it on a swivel mount? If not, your tube will bend more as you move up in Z height and cause a lot more force to be required to push the filament.

Displacement of a print at higher speeds may be a sign of dropped steps. If you command a move that it cannot do, due to acceleration, weight, etc, the motors will skip steps. This also happens if you hit a mechanical limit. Solutions are to reduce speed until you don't drop steps anymore, raise current on the drivers, and/or verify no binding on the axis.

I haven't seen a dual Bowden extruder setup before.
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Re: Twin Extruder Carriage

Postby dave3d » Tue Nov 26, 2013 7:43 pm

TLHarrell: I don't seem to get oozing except when the nozzle is up to temp and the printer has been stood stationary for 10 mins or more, but it was like that before the bowden mod. I just remove it with tweezers before starting a print.

Interesting explanation about compression. I don't know what the settings are that you mentioned. Are you talking about Slic3r? I have not altered anything yet.

I also don't have the extruder on a swivel mount. It is just bolted directly on the top of the Ord Bot. The tubing has a short direct route to the hotend so I don't think friction in the tube is an issue. I am using 1.75mm filament and the Wade pushes it backwards and forwards easily. I was generous with the tubing so have avoided sharp bends. It has been a qualified success so far however, I have not done any tall prints.

Early days yet so I need to do more experimenting.
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