Double hobbed extruder

i have problem that my filament get stripped a lot mostly because of fast printing, what do you guys think about a double hobbed extruder like this one [www.thingiverse.com] or this one [www.thingiverse.com]. And there is one called kraken that works with 2 nema 11.
I'm working now on a more ormerodish design but I would love to have some input.

/Joar

I think it will solve one problem and create worse ones! My extruder motor usually stalls before the ABS filament is stripped, and I suspect that a stronger grip will not allow you to print significantly faster before you encounter the same issue. Then, if you were to stop that by increasing the power, I think that you would not get too far along that route before you start experiencing failures with the Bowden tube being pushed out at one end or the other (I have had that happen twice).

Dave
(#106)

How about giving MasonStonehenge/VortyZA's Spring-loaded extruder a try?

RepRap Pro Ormerod Spring-loaded extruder
[www.thingiverse.com]



Erik

I agree that i can get other problems but so far I havent had any big problems except for the first layer with power, here is some sketches

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ormerod168
How about giving MasonStonehenge/VortyZA's Spring-loaded extruder a try?

RepRap Pro Ormerod Spring-loaded extruder
[www.thingiverse.com]

[attachment 33773 RepRapProOrmerodSpring-loadedextruder.JPG]

Erik

I will get this one a try it looks really good/Joar

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Joar107
..I will get this one a try it looks really good/Joar

It's brilliant IMHO, adjustable spring pressure, same force of grip with variating filament diameter yet will not crush the filament as bearing will bottom out on the stepper, easy to service and clean, just swing open and look under the hood

..also make it easier to mount Matt's brilliant herring bone gears, always found it a bit hairy mounting those in one go:



Printed in ABS and sliced with Cura
M140 S110.000000
M109 T0 S240.000000
Layer height: 0.25 Walls: 1.5 Fill: 30






Notice that you will have to print those with support (if Cura, chose "everywhere")



Good thinking, great design, thank you much to MasonStonehenge/VortyZA!

Erik

I do like the look of the hinged extruder. The only problem I can see is that variable diameters of plastic cause different meshing of the gears. It would be better if just the idler was sprung, as in other extruder designs, though this means a general redesign and a more bulky extruder.

Joar - nice work on the double extruder, too! You can reduce a lot of the bulk of the filament input guide. As someone else suggested, you can run the ptfe further up the guide tube, and get rid of the thin walled part on the inside of the guide. It will be interesting to see how it performs.

Ian
RepRapPro tech support

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ormerod168

Good thinking, great design, thank you much to MasonStonehenge/VortyZA!

Erik

It's a pleasure Erik - I like being able to give back to this community! I would be very pleased if you would post those pictures on thingiverse with an 'I made this' - they are great pictures!

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droftarts
I do like the look of the hinged extruder. The only problem I can see is that variable diameters of plastic cause different meshing of the gears. It would be better if just the idler was sprung, as in other extruder designs, though this means a general redesign and a more bulky extruder.

Joar - nice work on the double extruder, too! You can reduce a lot of the bulk of the filament input guide. As someone else suggested, you can run the ptfe further up the guide tube, and get rid of the thin walled part on the inside of the guide. It will be interesting to see how it performs.

Ian
RepRapPro tech support

You're right Ian - there is a slightly different meshing of gears, but that's only with extreme cases of dodgy filament that it changes much during a print - the ratio of the gears remains the same.
I've done a couple of redesigns with a spring-loaded bearing being the only bit that moves, but each time I run into the size of the block becoming unwieldy.

Edited 1 time(s). Last edit at 05/29/2014 07:44AM by VortyZA.

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droftarts
...The only problem I can see is that variable diameters of plastic cause different meshing of the gears. It would be better if just the idler was sprung, as in other extruder designs...
Ian
RepRapPro tech support

..better yes agree, but do the math and you will see it is of no importance whatsoever

another thing I like about this design is that the force of the spring help keeping the bearings in place, one can keep a fairly loose fit and easily index the Hobbed insert to the filament, then mount the spring and it will wrap the printed part around the bearings

but no it ain't perfect, nothing is, always room for improvements, nudge, nudge, wink wink, say no more ;-)




Erik

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ormerod168

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droftarts
...The only problem I can see is that variable diameters of plastic cause different meshing of the gears. It would be better if just the idler was sprung, as in other extruder designs...
Ian
RepRapPro tech support

..better yes agree, but do the math and you will see it is of no importance whatsoever

another thing I like about this design is that the force of the spring help keeping the bearings in place, one can keep a fairly loose fit and easily index the Hobbed insert to the filament, then mount the spring and it will wrap the printed part around the bearings

but no it ain't perfect, nothing is, always room for improvements, nudge, nudge, wink wink, say no more ;-)

Erik

I like your change - so you have a problem with the tab falling out and the Bowden tube running away?

I can make that change permanent if you'd like

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VortyZA
..It's a pleasure Erik - I like being able to give back to this community! I would be very pleased if you would post those pictures on thingiverse with an 'I made this' - they are great pictures!...

Sure thing, will do!

Erik

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VortyZA
...I like your change - so you have a problem with the tab falling out and the Bowden tube running away?

Yes a slight problem, left the printer alone a couple of hours and then....filament all over the place :-)

Not my change, cant model yet - the flap-under-the-gab is actually a part of Mr.Burns pfte-tube extruder mod that I have used up to now

[forums.reprap.org]

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...I can make that change permanent if you'd like

You may not want to ad this, adding the flap makes it a tricky stand alone print as the heat will build up and destroy the flap if the nozzle is not diverted with other printing positions

BTW, did an upgrade from string to steel, so its no biggie :-)



Erik

bad quote day, sorry

Erik

Edited 2 time(s). Last edit at 05/29/2014 11:05AM by ormerod168.

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ormerod168

You may not want to ad this, adding the flap makes it a tricky stand alone print as the heat will build up and destroy the flap if the nozzle is not diverted with other printing positions

Erik

Yes. I find any model that ends with just a small piece just at the top can suffer from this as the layers just take a couple of seconds and the layers don't get a chance to solidify.

I have a number of 'sacrificial' column stls of different heights and a couple of mm in size and I choose a higher one and put one or more of these into the slicer mix a distance away from the top part and this gives a bit of extra time for cooling.

I also added the tongue retaining flap to this excellent extruder design so I'd vote for that being a feature.

I'll take a look when I get a chance. Wasn't there a nice clip replacement someone designed - hooks both in the hole and above?

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VortyZA
I'll take a look when I get a chance. Wasn't there a nice clip replacement someone designed - hooks both in the hole and above?

Correct, iamburnys Replacement Extruder Tube Clip:

"....not one of my best models as it is challenging to print being so small and does required support while printing the over hangs..."

[www.thingiverse.com]

Erik