pneumatic extruder clamp, carriage adapter, and solenoid bracket by nicksears

Last crawled date: 3 years, 1 month ago

Pneumatic extrusion printing is actually very simple on almost any open source 3D printer. All you have to do is make this pneumatic extruder and set up post-processing scripts to turn on an output - this output opens a valve and applies pressurized air to dispense material.
Pressure
The hardest part may be a consistent source of high pressure air. If you have an air compressor/tank or house air at a lab/shop this will work best. I'm also working on an adaptation of a 2L soda bottle, these can hold up to 100 psi! (50psi safely) even still, use at your own risk). You should not need much more than 30 psi, and we will use a 30psi max regulator to the pressure we need (only ~10-15psi). Again the flow is: pressure source/regulator, solenoid to control flow, dispensing syringe.
Electronics
You do not use the existing extruder motor, but you do need an extra output like a controllable fan that can handle ~500mA (some fans are only 20-50mA). Alternatively, you can use the extruder heater output, but you will not be able to heat and control a nozzle tip and you may have to make firmware modifications to make it work. You will have to make sure a safety feature is disabled that kills the printer if the heater is on but an increase in temperature is not detected. This can be dangerous for (hot) plastic printing though, so use at your own risk! Some printers don't have this enabled by default, so for example the Monoprice Mini does not have an extra fan or open source firmware, but can use the extruder with this setup.
Toolpath
To automate the use of these outputs, you will have to install python and point your slicer to scripts that add lines of code (only a semicolon between scripts with the full path). One script turns the solenoid ON AFTER an UNretraction (make sure retraction is >0 in your slic3r) and unretraction should only and always happens when you want to start dispensing. Another script turns the solenoid OFF BEFORE a retraction to stop dispensing (if it stops AFTER the retraction it will leave a blob at the end of a line). A final script may be helpful to give a small pause (100ms) to let the material start extruding or there may be a delay and gap in the line. These scripts will run after slicing a file and insert the respective lines, and the order is critical (pause, on, off).
Extruder
For the physical setup, you will need the printed parts, solenoid valve, and some cheap dispensing syringes/tubing/connectors. The design includes a carriage mount for an anet a8-style printer, but I included the *.step file so you could more easily modify it. I also made a bracket to hold the solenoid so both it and the regulator could be on the top of the frame (pictures to come!) You need to use a 3-way solenoid - if you use a 2-way, the pressure will be trapped in the syringe and ooze, rather than venting.
Calibration
I've included custom calibration scripts that are in coarse, medium, and fine increments. You may need to change some of the coordinates if you printer size is different. First run the coarse calibration - it will begin with a loop tat the average speed that will allow you get a ballpark pressure with the regulator. It will then extrude 5 lines at the lowest speed through the highest. Whichever line is closest to the appropriate width is the correct speed to use with the medium and/or fine calibrations. It's really helpful to have a camera mounted directly to the extruder - the absolute cheapest "6 LED webcam" (~$4!) on ebay or amazon work great for this because they can be manually focused close like we need. You might get 2-3 because they are pretty cheap and you might get one DOA. Additionally, for the exact type linked, you remove the base, tap the stem with m3 thread, and screw into it with the bolt that retains the dispensing syringe. I've included "@pause" commands for use with Repetier Host to simplify taking pictures after printing calibration lines.
Bed Leveling
I highly recommend using auto-bed leveling with a conductive nozzle and metal bed to eliminate variability measuring line width. I may post this as a separate thing with details about how to enable it in the firmware. The physical setup is easy - fix a 3/16" thick 8x8" aluminum sheet from mcmaster-carr to the bed with binder clips. A precision ground surface or extreme flatness is not necessary (you will end up scratching it a bunch anyways). Then connect one alligator clip to the bed and one to the needle, and use those two wires in place of a typical mechanical endstop switch.
The links aren't working, you'll have to copy and paste the text into your browser, sorry!
https://www.amazon.com/dp/B000KKQIZG/ 3/8-18 NPT to 1/8-27 NPT adapterhttps://www.amazon.com/dp/B017VNO33S/ 1/8-27 NPT to 1/8 barbhttps://www.amazon.com/dp/B017VNOMZM/ 1/8 barb to 1/4-18 NPThttps://www.amazon.com/dp/B01BPQDG62/ Precision regulator (3-30 PSI)https://www.amazon.com/dp/B00VU14L4Y/ 3 way solenoid valvehttps://www.amazon.com/dp/B017UXCAQ6/ 1/8-27 NPT thread plughttps://www.amazon.com/dp/B01LH81EC6/ dispensing syringe (set of 5, 10, 30cc)https://www.amazon.com/dp/B003VY4M42/ Generic U19-A Night Vision Webcamhttps://www.mcmaster.com/#89015k239/ 6061 Aluminum Sheet 1/8" Thick, 8x8"https://www.mcmaster.com/#5108k43/ 1/8x1/4 PU tubing (25ft)