Adventures with DIY Dual Extrusion

Intro

Everybody wants a 3D printer that can print in multiple colors right?

For a while I’ve been fascinated by the idea of dual extrusion. You could always switch the filament by the layer, but you couldn’t have two types of filament on the same layer that way. You can try a Y splitter with retraction, but retraction settings are obnoxious and you require a bowden setup.

And so the idea of attaching two extruders was born. I bought two MK8 extruders off ebay, making the mistake of not ordering the dual extruder variant. Those have the advantage of having mirrored extruders, minimizing lost printing space.

3D Modeling

I rigged up a holder with Fusion 360. This is one of my first times actually using Fusion, so it was an interesting experience. I used an STL for the backplane, my printer uses a Prusa style backplate anyway so it was easy to find one.

The first thing I did was to make a plate that the extruder can attach to securely, and without any wiggle room. If the extruder can move at all then the prints will be ruined, as it’ll change it’s X/Y coordinates. To do this we print a plate, measure, adjust, and print the plate again. We only print the single plate to save plastic.

Next we copy the plate and put them next to each other. Then we add the backplane, and reinforce everything. If things move, bend, or wiggle at all then it will cause print defects.

Some interesting things:

  • I filleted the bottom screws, so the screw can be flush
  • Because of the height required to contain the motor, it interfered with the screws on the backplane. To fix this I cheved the back part, which cleared the space for the screws while still securing the motor.
  • Because my extruders aren’t mirrored, they’re almost 70mm from each other.
  • Special attention was paid to the area near the hotend. I currently only have PLA on hand, and with it’s incredibly low glass transition temperature it wants to sag under heat.

Assembly

Time to put everything together! Look at that awful pink though! Because of an order mistake I have 2kg of this horrible stuff… May as well use it for the prototype.

Everything went into their spots perfectly. The screws are flush, extruders snug in their spots, even the backplane’s screws works great! Because of complications, I couldn’t use the bearings from my old extruder and had to temporarily use some with a SC8UU I printed off thingiverse. Not perfect but it’ll due for testing.

One of the biggest pains is leveling the extruders. The nozzles must be level or one will drag in the print, or print off the platform, etc. This means turning the whole thing which is incredibly terrible and imprecise. It’s also hard to do once the cables are sleeved. The wires from the heat block also interfere with the cooling that I’ve implemented later too.

The wire connectors are twelve volts, and this lets me connect the fans and lights quickly without running more wires through the crowded cable guide. I’m just keeping the cooling fans on 100% because they make little noise.

Results and what’s next

You can see the results of one of my first prints. Note that this is the advanced marvin, so it has many more shapes in it. Some of the things I’ve done to improve the quality further were:

  • Further calibration of the offsets of the extruders.
  • Added some GCode to S3D so the nozzle moves up before switching extruders.
  • More releveling.
  • Added cooling ducts to both extruders.

I’m having issues with under extrusion just after switching layers, and over extrusion at the actual layer change. The leveling is still an issue as well. My test prints have been small, so the second nozzle doesn’t go over the print much. I’ve had only minor issues with ooze, but that’s likely to change with any large print.

For the future: A new design with screws for changing the elevation of the nozzles, closer spacing, and holes allowing further X movement. Stay tuned!

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