Funny, I have been thinking a lot about designing some kind of valve like this lately.
As you say, it seems like the only way of solving the oozing problem permanently.
It might not be as difficult to design a valve like that as one think actually, the pressure it needs to handle is very slight after all.
I wonder how Stratasys solves this problem by the way? Maybe one could sneak in and spy a bit at one of them at work.. :smile:
In time I hope to see great things from a solid dual head setup
I don't know if we'll ever get a really good dual extrusion setup with current technology to be honest. I think we really need some kind of "valve" to quickly and cleanly shut down the flow of plastic. The cooling down of nozzles, ooze shields and stuff like that just feels like a band aid, not a solution.
...at the same time, to get progress, you need to just start somewhere and straighten out the bottlenecks as they appear. Before bottleneck becomes bottleneck, you wouldn't even think of it as one - or even a potential one.
It will be really interesting to see what will be the primary drivers for dual/multi-extrusion... Different colors, flexible/rigid, conductive/non-conductive, transparent/opaque and different diameters have already been mentioned. Some of them probably require quite high precision/reliability to be useful - some of them are less sensitive for technical shortcomings.
It's funny how something can give so many engineers a problem. I believe there is a workable solution that would eliminate dragging and oozing but would add a bit of weight to the hotend thus slowing the max print speed. But the trade off to me would be worth it to have a quality dual head printer.
I believe that the D3D auto lift setup is a good starting point and with the addition of a small cam operated nozel wiper/blocker would be a perfect proof of concept for my idea. It would use the mechanical motion of the head lifting to move the wiper in and out of position.
Time for the "sound like a smartass"-post of the day. I actually had that very same idea the other day but I'm not exactly an engineer so I had no idea if or how it would work. Now I feel a bit smarterer since someone else also had the same idea. The other idea I had was to have a thin rod come in from the side of the nozzle, just slightly above the exit, to block flow but I wasn't sure how to get a perfect seal while still being able to move freely and stand up to the temperature.
I also remember seeing some kind of "just in time" hotend way back. It used a glass hotend with a tiny induction heater at the very tip. No idea what happened there though, I don't think it even made it into a prototype state.
...at the same time, to get progress, you need to just start somewhere
I feel like we've already started with the current type of dual extrusion setup. The RepRap people have played with it for a long time. Makerbot already have it on their printers (or did they abandon it for the latest one? I forget). To me, it just feels like the wrong approach from the get go. But hey, I'm just an internet armchair engineer so what the hell do I know. Wont stop me from rambling though 
came across this video once,
nice idea for the nozzle….
Time for the "sound like a smartass"-post of the day. I actually had that very same idea the other day but I'm not exactly an engineer so I had no idea if or how it would work. Now I feel a bit smarterer since someone else also had the same idea. The other idea I had was to have a thin rod come in from the side of the nozzle, just slightly above the exit, to block flow but I wasn't sure how to get a perfect seal while still being able to move freely and stand up to the temperature.
I also remember seeing some kind of "just in time" hotend way back. It used a glass hotend with a tiny induction heater at the very tip. No idea what happened there though, I don't think it even made it into a prototype state.
I feel like we've already started with the current type of dual extrusion setup. The RepRap people have played with it for a long time. Makerbot already have it on their printers (or did they abandon it for the latest one? I forget). To me, it just feels like the wrong approach from the get go. But hey, I'm just an internet armchair engineer so what the hell do I know. Wont stop me from rambling though
And here is the problem with text format as in no way was I trying to be a smartass but being thats what you got from it. I'll keep my mouth shut from here on out to prevent any further confusion. I said it's funny because an idea from anywhere can become a possible solution to a given problem no matter the backround.
And here is the problem with text format as in no way was I trying to be a smartass but being thats what you got from it I'll keep my mouth shut and ideas to my self from here on out.
No no no! I wasn't calling you a smartass! I was calling MYSELF a smartass for doing a "me too!" post saying I had had the same idea.
Robert, next time use a double colon 
Time for the "sound like a smartass"-post of the day: I had that very same idea the other day
Yeah, I feel real bad about that misunderstanding. I sent him a PM as well, hope I didn't scare him away completely :/
Don't you hate it when humor comes across wrong in text?
Always use the smiley! :cool:
Those "external shield" and "nozzle retract" -solutions look quite well functioning I have to say, but somehow a bit bulky and complex for me to really like them.
What I had in mind is: Did anyone ever consider a valve inside the nozzle?
I am thinking of something with the same operating principle as the thing old diesel engines has inside the fuel injectors.
Of course we are dealing with plastic which even if really hot is much more viscous than diesel.
But if I calculated correctly we would have up to about 70-80 bars of pressure inside the UM2 nozzle (?).
So using a few bars for opening a tiny valve seems reasonable.
It would be a tiny thing and it would make nozzle cleaning more or less impossible though, so I guess Ultimaker would have to adopt the heater block with exchangeable nozzles.
the Robox seen here:
Has needle valves in the nozzles for it dual extruder.
And much more interesting if you could use conductive and non conductive plastic.
For practical uses you would prefer much lower electrical resistance than the plastics you can currently buy, but I think such plastic can be made with the right ingredients.
A while back I made a proof of concept for myself with conductive copper paint combined with ABS print. Basically, you can make tunnels to your model and inject copper paint to them. I know there are drawbacks, but it's good for many applications. Water based copper paint sticks to ABS really nicely.
Wouldn't solder paste (like the stuff you use for SMD) work better?
Look: a dual extrusion printhead on kickstarter, perhaps you can steal some ideas? 
Could someone from the UM team give an update on the progress of the dual extruder?
Just saying you are stuck is also news, just want to know what is happening...
I really would like to use HIPS for dissolvable support structures, and if the UM2 will not give me that I will have to sell the thing and switch to a better 3D printer that supports dual extrusion.
Cheers.
Could someone from the UM team give an update on the progress of the dual extruder?
I think they are told not to comment on this subject. They promised it first quarter 2015 for UM2. It's been available for about a year now on the UMO so consider buying a UMO instead. They made a major breakthrough on it a few months ago.
I would like option too
http://www.ioncoretechnology.com
I have looked at this machine there are a few other makes as well
But is anyone using the dual extruder in the original Ultimaker with great success?
If they've made some major breakthrough, I am really curious what and if that will filter into the existing Ultimaker
With all due respect, I think they should get the kinks worked out to make the UM 2 into a reliable machine first before even thinking to add dual extrusion. When I read about all the problems I am glad I have two well working UM 1 machines.....
What issues are you talking about? I have bought UM2, took it out of the box and it prints great quality objects in PLA. I haven't yet tested ABS prints dough.
main things I would say are;
> the factory feeder is not great, you'll probably get underextrusion someday, print yourself a better feeder, there are many designs, look here;
http://umforum.ultimaker.com/index.php?/topic/4393-ultimaker2-feeder-system-improvements-and-ideas/
> the Hot-end-isolator (the white thing in your hot end) will need replacement sometimes, consider it maintenance. The frequency is highly depending on the temperatures you print with. When you print PLA you should not have a problem soon.
I don't know if anyone has seen this:
http://3dprint.com/26590/dual-parking-extruder/
Looks like an interesting idea
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I don't know if we'll ever get a really good dual extrusion setup with current technology to be honest. I think we really need some kind of "valve" to quickly and cleanly shut down the flow of plastic. The cooling down of nozzles, ooze shields and stuff like that just feels like a band aid, not a solution.
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