Dual Extrusion - Problem Solved

Eccentric · Jan 28, 2022

It is so fun to have a home machine shop. You run into an issue, you design a few parts on the computer, go out to the workshop and make those parts, and viola, problem solved.

I have a 3D printer and I like to print using HIP filament as support. That is, I use ABS for the main part, then have a second extruder that prints HIP for the support structure. After the print is complete, the HIP separates easily and you can print most anything that has overhangs or large bridges.

But my dual extruder setup has to have the two extruders exactly the same height off the bed. The extruders alternate laying down ABS, then HIP, but they are both hot. The extruder that is not in use drags through the material the other is printing and this impacts the look of the finished part. Sooooo, I thought why not make a mechanism that lifts the extruder that is not in use while the other prints.

I drew up a design on the computer. I put the dual extruder unit on ball bearings, then use a servo to rotate the print head assembly just a little raising the unused extruder about 2mm. I made some steel standoffs and strategically placed some magnets so the print head "snaps" back and forth into position, locked rock steady.

I 3D printed a couple of parts, made a few on the lathe, then cut a couple aluminum parts out on the mill. This is my proto type and is working surprisingly well. As can be seen there is no interference between the two print heads and the white and orange filaments are being laid down cleanly.

Any two filaments can be used, you could make a part in white, and insert black lettering for example.

If you look closely you can see the servo and the linkage to rotate the print head assembly. The servo is the blue thing with the grey, red and orange wires coming out of it. The servo arm with the linkage attached is just above it.

It is so fun to have a home machine shop. If you can dream it, you have make it.

awake · Feb 9, 2022

I'd love to see more pictures or diagrams. I am not quite getting it from the one picture (though the dual white/orange print is great!).

ddmckee54 · Feb 15, 2022

So if I'm understanding this correctly, both print heads are on a common assembly that you are rotating back and forth? To raise the head that's not in use, and to lower the head that's actually printing? Nice, if that's what you did. That puts the majority of the extrusion forces on the pivot and not so much on the servo.

Did you angle the print heads in the mounting assembly? I would think that the heads would need to be angled slightly, otherwise in the print position they would not be perpendicular to the surface. Or is the angle so small that it doesn't affect the print? Did you have to increase the retraction distance for the head that prints the support? (My printers tend to drool when they are at temperature and not in use - if I don't retract enough.)

Don

Eccentric · Feb 15, 2022

ddmckee54 said:
So if I'm understanding this correctly, both print heads are on a common assembly that you are rotating back and forth? To raise the head that's not in use, and to lower the head that's actually printing? Nice, if that's what you did. That puts the majority of the extrusion forces on the pivot and not so much on the servo.

Did you angle the print heads in the mounting assembly? I would think that the heads would need to be angled slightly, otherwise in the print position they would not be perpendicular to the surface. Or is the angle so small that it doesn't affect the print? Did you have to increase the retraction distance for the head that prints the support? (My printers tend to drool when they are at temperature and not in use - if I don't retract enough.)

Don

My X axis is a linear slide as shown below, a 1/8" aluminum plate is screwed to this with four screws, two of which are on tall steel stand offs (shown in magenta). There is an upside down "T" shaped aluminum piece that the print head screws to and moves on a pivot.

Below is the view of the assembly from the rear showing the ball bearing holder and the ball bearings that the T mount turns on. There is a magnet holder with two small magnets screwed to the arm of the T mount. the T mount snaps back and forth with the magnets holding it securely in place. The servo moves the arm back and forth and is not responsible for securing the T mount to the two positions, just moving it from one to the other. The magnets do the holding work.

The rotational movement is pretty small, but more than enough to raise the unused print head up and out of the way. The slight sideways angle of the selected print head is so small that no noticeable difference is seen in the print quality.

I use a macro that switches from one print head to the other which also, as you noted, retracts the filament not is use quite a bit.

Hope this clairifys the design a bit.

ajoeiam · Feb 16, 2022

Eccentric said:
My X axis is a linear slide as shown below, a 1/8" aluminum plate is screwed to this with four screws, two of which are on tall steel stand offs (shown in magenta). There is an upside down "T" shaped aluminum piece that the print head screws to and moves on a pivot.
View attachment 134161

Below is the view of the assembly from the rear showing the ball bearing holder and the ball bearings that the T mount turns on. There is a magnet holder with two small magnets screwed to the arm of the T mount. the T mount snaps back and forth with the magnets holding it securely in place. The servo moves the arm back and forth and is not responsible for securing the T mount to the two positions, just moving it from one to the other. The magnets do the holding work.
View attachment 134162

The rotational movement is pretty small, but more than enough to raise the unused print head up and out of the way. The slight sideways angle of the selected print head is so small that no noticeable difference is seen in the print quality.

I use a macro that switches from one print head to the other which also, as you noted, retracts the filament not is use quite a bit.

View attachment 134163
Hope this clairifys the design a bit.

Interesting (I usually snip the pics but not this time!!) - - - what are you using for CAD - please?