The next one, an example for a simple watertight housing, was surprisingly easy. The sealing is just printed into the groove and the small membrane features tiny holes to interlock with the rigid part.
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Nice! I also believe that multi material is way more interesting than multi color
So what's the trick to make flex filament stick to pla?
That's what I would like to talk about 
Right now I'm experimenting with tiny nested structures like the dovetail guides in wood working. With 3d printing, adding these structures to the parts comes more or less for free. And they could be designed in arbitrary ways, way beyond my imagination.
Did you try to add like an overlap? So the flex is like merged into the PLA? Instead of layed against it.
for some strange reason, the picture only shows up in the reply but not in the first post ...
OK, will be a serial then
While the stopper works and looks quite nice I ended up with glueing the flex parts to the PLA ... multi-material printing was more or less useless as parts started to separate mid-print.
I have made a print once with Ninjaflex and PLA, and that seemed to bond really well.
So maybe it is just the Flexifill?
Do you know how these materials are different?
Maybe the way to go is something like embed a line of flexible material and cover it partially with pla with some gaps to connect with the outer part of flexible... i don't know if i'm clear so lets do a quick ugly drawing (yes i have paint skills!)
The red represents flex and the black pla
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Adhesion properties are likely to differ. Ninjaflex is a different polymer, thermoplastic polyurethane they say.
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The toothbrushes use PP over moulded with TPE which are very chemically similar so they bond together well (PP is technically a rubber, just with a high shore hardness), so one way is to find materials that are chemically similar. I've always wondered why they don't make PP reels for the FDM's....anyone know?
The other way as above is to create a mechanical bond as shown above in the paint image, this kind of approach is used a lot in industry, over moulding rubber onto moulded plastic.
This subject is really interesting and gets more so i think when you start looking at conductive filaments so we can embed electronics into the print, whilst having them naturally insulated by the exterior plastic.
foehnstrum - i couldn't make out which machine you are using... are you using an UM or BCN3D?
@wishbone, good that someone reminded me of my incomplete profile.
It's an UMO with my magnetic tool changer. https://ultimaker.com/en/community/10657-a-different-multi-extrusion-approach-um-tool-printhead-changer
Sounds like you have some expert knowledge on this subject.
Speaking of incomplete profiles, @Wishbone, what type of machine do you have? 
Are you also involved in dual extrusion?
You mean reels as in filament right?
Edited by Guest
Regarding the mechanical bond, an interesting fact is that with 3D printing you could almost "blend" one material into the other. The only limitations are nozzle size and layer height.
sandervg, thanks i also updated my profile a bit , I'm using an UM2.
Yes, i meant in terms of filament.....seems strange why there is no PP available as the glass trans temp is lower than ABS. If we can get PP in filament then i think TPE should be possible then they should bond together well. Either way there is actually a lot of info out there about bonding of different plastics to rubbers, just google "overmolding rubber to abs/pp/etc...." most companies give you a nice chart. Could be something worth looking at for developing new materials for UM.
foehnstrum - maybe try and make the mechanical bond work in 2 planes to get a really solid interlock. The parts in your photo have the mech bond in 1 plane, if you can model it so it works in 2 planes then it will be fully interlocked. Its nice because the rubber can start acting as the support material for the PLA within the interlocks you form.
Edited by GuestThis is a another idea of using 2 printheads: https://markforged.com/mark-two/
for making strong parts. Different approach, but interesting..
the first head is used as a normal fdm print, printing a base structure (in nylon) and leaving some open space for the next printhead: carbon fiber, fiber glass or kevlar. But this second printhead doesn't change the size of the filament, it uses the real diameter and just melts this one into the open spaces. This way the characteristics of carbon fiber keep their long/strong shape, the fibers are not 'chopped'.
Their (browser based) software calculates what the best place for the fiber filament is.
Cura has a feature called Alternate extra wall that is used between infill and external walls to give better cohesion. Maybe for dual print there could be a feature to use this in between both parts.
For your tool changer just have one head that squirts glue between the 2 materials 
Ok, wasted one day for a simple insight. Don't use Colorfabb PLA/PHA with flexible filaments based on TPU or TPC. The PHA kills any adhesion, like printing on grease. If you use standard PLA instead:
Soft/rigid handle, yellow = Filaflex, blue = PLA
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Nice. Hmm, didn't know that about PLA/PHA.
@Wishbone, a quick google; what about this filament?
A colleague of mine printed a box with some bolts embedded into the print using the pause feature, which I thought was cool.
But he then used Primalloy as a sealant for the box, similar to what you guys did.
Anyone tried that? Don't think he had a problem sticking it to PLA.
I'll try and get a picture uploaded tomorrow if I remember.
We also used some PLA Flex white to make an e-nable hand. It had a wrist fastening type thing, we used the PLA as a section of it, and then printed the top layer in PLA Flex which allowed the wrist band to bend. Again no issues with it sticking. So just reiterating what Sander said, maybe it's the particular filament you used.
I'm quite sure it's the PHA component.
I tried it once on PHA and indeed in doesn't stick at all... i thought it was because of PLA but as i mostly use colorfabb i didn't try it with regular PLA... good to know!
Edited by GuestThanks man, that looks pretty promising. I haven't tried any dual extrusion yet but its something I would like to get into.
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for some strange reason, the picture only shows up in the reply but not in the first post ...
OK, will be a serial then
While the stopper works and looks quite nice I ended up with glueing the flex parts to the PLA ... multi-material printing was more or less useless as parts started to separate mid-print.
Edited by GuestLink to post
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