New and different dual extruder idea

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New and different dual extruder idea

Postby Tim » Fri Oct 23, 2015 2:49 pm

I previously posted an idea I had for a dual extruder modification that would solve the dripping problem by parking the inactive hot-end on a plate. The idea I had, for a rocker mount for the dual extruder, I couldn't get to work in practice because the rocker mount needs to be extremely stable and so would have to be machined out of metal. Also, either the mount plate would need to be redesigned, or else the rocker hinge causes the whole extruder mount to be pushed up vertically, reducing the vertical overhead to the frame to just about nothing.

So I have thought up a new idea on how to redesign the dual extruder to give it the ability to park the unused hot-end. This idea gets rid of the single dual extruder mount and replaces it by two independent single extruder mounts. The drawback of this method (there's always a drawback) is that the method to switch between extruders becomes complicated and takes longer. However, the current method requires retracting filament in one extruder a long way and extruding forward in the other, and that takes some time as well. Here, the time is taken up by motion on the X axis, which is relatively fast.

The idea is that the extruders don't need to be directly bolted to the X axis belt, but instead would be allowed to disconnect from it and reconnect. It's necessary to make sure that the extruders reconnect in exactly the same spot on the belt, because any slop in that measurement is an inaccuracy in the X axis position between layers. So the method involves keeping the existing belt clamp mostly the same, but not bolted to the extruder mount. Instead, it connects to the extruder mount by magnets, strong enough to keep the extruder firmly and precisely connected to the belt clamp during printing, but weak enough for the X-axis stepper motor to overcome the magnetic force and pull the belt clamp off (probably this can be done with some kind of mechanical latching system, but I'm trying to avoid having additional moving parts). Instead of one dual extruder mount, there are two independent single extruders, but only one belt clamp. Each extruder has a "parked" position on the left or right side of the bed plate, and when parked, the nozzle sits on a plate that keeps it from dripping. The nozzle wipes off on a wiper as it comes off of the plate.

dual_v8_0.jpg
Showing all parts of the system


The following two pictures show how the switching between tools works. It is a 2-step process where the active extruder has to move over to the side of the parked extruder, the belt clamp switches between the extruders, then the new active extruder has to push the inactive extruder all the way to the other side to its parking spot before it can start printing. Although that's a lengthy tool-change protocol, I can't think of anything simpler that won't either have serious problems keeping everything in alignment, or require a large amount of additional hardware.

dual_v8_1.jpg
Switching between tools part 1


dual_v8_2.jpg
Switching between tools part 2


To build this, one would need two single-v4 mount plates and an extra rail carriage. There would be additional need to duplicate the extruder and bed fans for each side, and it would need redesign of various brackets, fan ducts, etc. However, there would be no need for additional machined hardware (apart from the mount plates and rail carriage, which are parts that are available). It can be prototyped pretty easily.

Anybody who wants to poke holes in my idea, feel free.
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Re: New and different dual extruder idea

Postby Jules » Fri Oct 23, 2015 3:52 pm

So far beyond my capacity to comment on, it's not even funny. :lol:

But i do have a word of advice.....patent your idea. ;)

(Hey, maybe you could pick up jprochnow's extra machine to build your prototype.)
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Re: New and different dual extruder idea

Postby Tim » Fri Oct 23, 2015 5:14 pm

Jules wrote:So far beyond my capacity to comment on, it's not even funny


Well, the basic idea is supposed to be simple. I know I'm pretty bad at explaining things in layman terms, I think a result of having to write too many journal submissions where I had to compress a year's worth of graduate research into two pages including citations.

But the basic idea here is that instead of one gigantic dual extruder assembly, you have two separate single-extruder assemblies. Both of them slide along the X rail, but neither one is connected directly to the piece that grabs the belt like they usually are. Instead, the piece that grabs the belt is held tight to the belt, but can magnetically connect itself to either extruder (but not both at the same time).

Each extruder "parks" on its own side: The left extruder parks on the left, and the right extruder parks on the right. So if you want to print with only one extruder, you can keep the other one parked and out of the way instead of dragging it all over your print (less mass on the X axis, too). And for dual extrusion, the extruder that isn't printing is both out of the way where it doesn't drip all over the print, and it also has its nozzle physically blocked off by a metal plate, which prevents it from oozing in the first place.

Jules wrote:But i do have a word of advice.....patent your idea.


I don't even want to get into patent issues in 3D printing. There's too much litigation over that already. I prefer to open-source an idea. Then if it's conflicting with an existing patent, the idea is still out there for anybody who wants to personally take the trouble to modify their own machine.
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Re: New and different dual extruder idea

Postby innkeeper » Fri Oct 23, 2015 5:19 pm

Hi Tim...

let me preface this by saying i've not worked with an m2's dual heads, but i've been doing dual head prints since 2012.

i like the idea of having a printer that can be dual and single head...the dragging issue is why i have both but is only an occasional issue.

i'm at an admitted disadvantage as i didn't read the other comments on leaking, so if this is for very leaky materials like petg, then excuse the uninformed comments... and don't know where that thread is.. so i'll comment there on it

Typically when doing a single head print with a two headed machine, the second head is cold. Therefor dosn't leak, though sometimes the second head drags if your over extruding a bit.
if doing two colored prints, and your getting leaking (abs or pla), it causes gaps in extrusions when changing colors in a multi color print.
this needs to be resolved with proper retraction, proper temperatures, and materials and heads that do not exhibit a lot of chamber expansion causing leaking. This is were filament brands do matter.

you can make use of dual colored towers to, in effect, wipe between layers. and depending on how often the colors are used on a print can be very helpful.. in example, if the second color isn't used till near the end of a print, where it is less likely retraction will prevent leaking and that gap issue i talked about.

in general though, i rarely had much issue with leaking, and get very seamless dual color prints (i'll post samples if you wish to see).... aside from the occasional color drags on the surface of a print..providing i had my retraction and heat dialed in, and i wasn't using some filament that had relatively excessive amount of expansion.

sorry if this is a repeat of what others may have commented on on another thread.
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Re: New and different dual extruder idea

Postby nirfriedman » Fri Oct 23, 2015 8:03 pm

Tim,

If you go for two separate heads, why not have them on two separate belts? as far as I can see, you can put two belt drives in parallel (add one behind the current one) and have one carriage with longer extension backward. The price is that you have another motor and need firmware changes. The benefit is that you avoid the headache of reattaching heads which seems to me highly non-trivial.

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Re: New and different dual extruder idea

Postby Tim » Fri Oct 23, 2015 10:03 pm

nirfriedman wrote:If you go for two separate heads, why not have them on two separate belts? as far as I can see, you can put two belt drives in parallel (add one behind the current one) and have one carriage with longer extension backward. The price is that you have another motor and need firmware changes. The benefit is that you avoid the headache of reattaching heads which seems to me highly non-trivial.


I think rewriting the firmware for two separate X steppers is highly non-trivial. There's also the point that very few controller boards support that many motors (the Fastbot bbp1s that was mentioned recently by PcS is one exception, but I don't have one of those). I guess I've concluded that just about any way you do a dual-extruder setup, something is going to end up being non-trivial. The way I'm trying to do it, though, has a pretty low overhead on extra hardware. Although once I've gone halfway through prototyping it, I may very well end up agreeing with you. I won't know until I've tried it.
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Re: New and different dual extruder idea

Postby Tim » Fri Oct 23, 2015 10:20 pm

innkeeper wrote:i'm at an admitted disadvantage as i didn't read the other comments on leaking, so if this is for very leaky materials like petg, then excuse the uninformed comments... and don't know where that thread is.. so i'll comment there on it.


Well, yes, actually, I got to this point while doing dual-color prints in (1) PETg and (2) wood filament. The wood filament is so drippy that not only is it hopeless for dual extrusion, but it's probably hopeless even with my proposed solution. I'm more targeting PETg, but I realized that there would be other benefits such as a lighter extruder assembly, and the ability to leave the other extruder properly mounted and ready to go without worrying about the nozzle running into prints. I usually keep my right nozzle up a millimeter or so when I'm not using it, and while it doesn't take long to reseat it at the right height, it's an extra hassle to deal with whenever I want to do dual extrusion printing.

Plus, I've found this fabulous color combination with a couple of layers the translucent PETg filements over top opaque white. But I have to hover over the printer while it's printing, or the dripping PETg will eventually mess up the whole print.

I know I could get a lot easier prints with PLA (that's been in the dry box). Maybe I just like doing things the hard way. . . But, I think mostly I just like to experiment. The 3D printer isn't a workhorse for me, it's new technology, and I constantly want to push its limits or see what else I can do with it.
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Re: New and different dual extruder idea

Postby innkeeper » Sat Oct 24, 2015 12:25 am

have you tried the tower trick.
print towers on the side of your print, one from each extruder.
the idea is that by the time you get to the next layer, it would have printed on the tower, and cleaned up the next upcoming leak...
keeps both nozzles active throughout the print. as long as its extruding and retracting ... it might prevent the drips.
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Re: New and different dual extruder idea

Postby Tim » Sat Oct 24, 2015 3:10 am

innkeeper wrote:have you tried the tower trick.
print towers on the side of your print, one from each extruder.
the idea is that by the time you get to the next layer, it would have printed on the tower, and cleaned up the next upcoming leak...
keeps both nozzles active throughout the print. as long as its extruding and retracting ... it might prevent the drips.


All right, dang, where were you when we were discussing wipe towers and ooze shields and all that?

Sounds like a good idea, and much better than the wipe tower generated by S3D.

It still doesn't really solve the problem when a piece is large enough that one of the extruders is sitting on the edge of the part while the other one is working on printing the interior. I've found that dual extrusion works best when the part is smaller than the distance between the extruder heads. Then, when an extruder is dripping, it isn't dripping directly onto the print, and is easy to wipe off on a tower or ooze shield. Your tower idea should work well for the two-color polyhedral dice I was printing, because that's a different problem, in which if the part is small, the buildup of drippings can be so much that it becomes higher than the print, and both extruders start to plow into it and make a big mess. Actually, part of that problem is that the slicer keeps approaching the part from the same direction and position on every layer, so all the drippings build up in one or maybe two spots.
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Re: New and different dual extruder idea

Postby innkeeper » Sat Oct 24, 2015 5:39 am

Tim wrote:All right, dang, where were you when we were discussing wipe towers and ooze shields and all that?


oops like i said, i totally missed that thread...or don't remember it...

almost all my prints i've done on a dual head printer are larger then the distance between the heads...and yea.. the second head is an annoyance if your not really needing it. i think the best of both worlds would be if you could easily swap out single and dual extruders depending on your project,

You do get used to printing with dual extruders. it forces you to keep things dialed in well, and stay on top of the filament diameters once you do your all good.
i find if i am dragging heavily with the second extruder,that i am over extruding. i find if i have it dialed in right, its not a problem.

i've thought about perhaps getting a single and/or dual v4 head for the m2, but i've thrown a lot of money at the m2 printer fixing or finding issues that existed from the day it was made so i was in no rush to spend more on it. so all i can do for now is relate my experiences with my replicator 1 ..

For anyone playing at home ... i am not knocking the current version of the m2..please don't take it that way, I just had a mix of what id call bad luck in having some bad parts, and bad experiences in relation to that....
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