Syringe Pump

Goal: Create a syringe pump to feed material to the Moineau Extruder or the Oogoo Mixer.

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As part of the development of a Moineau Extruder and an Oogoo Mixer for 3D printing, a method of feeding material to be pumped or mixed is needed. A suitable feeder must deliver the material through a flexible tube to the pumping or mixing chamber. While a syringe isn't really suitable as an extruder, it seems perfect for material delivery. However, a standard sized, medical type syringe doesn't seem suitable. The discharge is too small for very viscous material and the volume isn't large enough for a reasonable sized print.

The solution: design a simple syringe that can be made using a 3D printer (since that's the tool I have) and that solves the two problems above.

While there are many syringe pump designs, the ones I have seen all use a standard medical syringe. This design will be for a syringe that has a body made from PVC piping with ends and plunger made of PLA plastic and built with a 3D printer. The design will be done using FreeCAD and all files will be available on Thingiverse, with the latest versions always on github.

The syringe pump will be driven by a NEMA 17 stepper which will turn an 8mm threaded rod to move the plunger. The idea is that this pump will not be mounted on the 3D printer carriage, but will feed material through a tube to the extruder.

Such a supply system is needed by the two extruders I am developing.

  • Action Film as Promised!

    doctek01/30/2015 at 01:51 0 comments

    See the Syringe pushing out peanut butter:

    The stl version of the parts can be found here:

    I'll put the FreeCAD source files up on GitHub.

  • Peanut Butter!

    doctek01/29/2015 at 04:54 0 comments

    Did the big test today: Will the syringe push peanut butter through the tube? Peanut butter is selected since it is pretty viscous and reasonably easy to clean up.

    Short answer: It works!

    I'm making a video showing the peanut butter flowing out of the syringe, but I wanted to make this post first. So it's "film at 11" time - you have to wait.

    "What took so long?" you ask. "I thought all you needed was a few bolts."

    Yeah, well, I also needed to have a stepper motor controller that would run slower than 1 rev/second! So I pulled out a Teensy2 and a Quadstepper and away we go. A bit of work with the AccelStepper library and now I have a controller that will run down to Parade Rest if I want to. Here are a couple of pictures.

    Wait for the video!

  • Securing the outlet tube and a little Welding

    doctek01/17/2015 at 05:58 0 comments

    My plan is to use a length of plastic tubing to deliver the output of the syringe to either the extruder or the mixer. That way, the syringe doesn't have to be mounted on the carriage of the printer. The thing that's always worried me is how to connect the tube securely without a big, ugly fitting. Here's the solution I've come up with. The pictures are truly worth ten thousand words in this case.

    The hose fits in 10mm deep. Then a 3mm setscrew is pushed into the hole and screwed in about 5mm. I made another hole on the other side, but one set screw holds so securely, the second isn't needed. As you can see, this is a very compact way to secure the hose. It grips very strongly and makes only a tiny dent in the hose on the inside of the opening. I'm very eager to try this in operation but I think it'll work great.

    The nut cover needs to be secured to the nut holder (with the 8mm drive nut inside), and the nozzle must be joined to the outlet. I used Multipurpose Plastic Pipe Cement (lots of MEK) to cement the parts and let them dry. Then I used my Dremel to weld the joints as well, as described in a recent HAD item. Very solid!

    You've guessed by now that the syringe is assembled, so here's a look at it. I still need a few 5mm nuts before I can test it; just a trip to the hardware store away. Testing awaits!

  • Design Detail: Coupler

    doctek01/15/2015 at 05:55 0 comments

    Thought I'd have it all done by now, but everything takes longer than you think it will! Let's pause along the way and look at a few design details that might be innovations - maybe even useful innovations!

    The first innovation is in the coupler that will join the drive motor to the 8mm threaded rod that propels the plunger. The end that hooks to the 8mm rod is pretty standard: just three 3mm nuts pocketed into the plastic so screws can be tightened against the rod. Clean out the pockets, drill out the bolt holes and press in the nuts. Done.

    The end that hooks to the motor shaft is perhaps more interesting. I haven't seen this approach used. I cut a length of 6mm round brass tube (5mm id to fit the motor shaft) and coaxed it into a similar length of 1/4" square brass tube. The round tube fits snugly into the square tube. Slight distortion results when the round is pressed into the square, but it's minor. The square tube fits (press fit) into the coupler body and a 3mm clearance hole is drilled through the tubing and threaded. A set screw can now be tightened against the flat on the motor shaft. This provides a very secure, non-slip connection to the motor.

    Next, we'll look at the method of anchoring the delivery hose to the discharge nozzle. What's need is a compact way to secure a plastic hose. Stay tuned.

  • Printing Started

    doctek01/12/2015 at 05:09 0 comments

    With the first parts designed, it's time to fire up the 3D printer and crank out the plastic parts. The outlet I mentioned last time with the black hole was indeed a problem. Although it passed all the checks in the FreeCAD Mesh Workbench, the stl had big problems when fed to netfabb. I had to import the stl into OpenSCAD, subtract the center cylinder, and create another stl. This worked fine and the part printed out OK.

    Had to change plastic in the middle of printing parts. Not uncommonly, this means a few hours characterizing the plastic and resetting parameters in Slic3r. But I got lucky this time, the new plastic uses the same settings as the old and prints perfectly. Here's a shot of some of the new parts.

    Next up is to finish the design of the coupler and the plunger, then put it all together and give it a try.

  • Got the parts!

    doctek01/09/2015 at 06:46 0 comments

    Local hardware store had the parts I needed. The guide rods will be 4mm music wire and the side bolts will be 5mm threaded rods 100mm long. Now that I have the parts, I know what size to make the holes and can complete the design of the components. First designs are done for all the parts except the plunger. I'll print them tomorrow and see how it all fits. Then on to the plunger! I'm planning to use the plastic welding technique recently featured to do some of the assembly, so I'll see how that works also.

    Actually, printing depends on FreeCAD producing the stls correctly. This has not been a problem in the past, but I'm using FreeCAD in ways I haven't tried before, so we'll see what happens. In the mean time, here's the outlet piece. See the black circle in the middle of it? That should just be a hole (like the other holes in the shape). That's the part I'm worried about. Will it mesh correctly? Stay tuned!

  • Off and Running

    doctek01/08/2015 at 06:33 0 comments

    The need for this design became obvious just a few days ago, so the design is still in process. So far, I've chosen 1" PVC for the syringe body and 1/4" plastic tubing for the delivery tube. I've started designing the parts in FreeCAD. The plunger will be driven by an 8mm threaded rod turned by the NEMA 17 motor. I need two smooth guide rods to mount along the sides of the body to guide the motor. I also need two threaded rods to hold the discharge and the drive nut holder in place at the ends of the body. A good sketch will make all this clearer and a trip to the hardware store should provide the precise parts so I can finalize the design and start printing the first version.

    Here's the motor mount. Still pretty rough, no guide holes since I don't have the rails yet.

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MikeM wrote 07/19/2017 at 12:51 point

Check out here - smaller stepper and syringe : 

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doctek wrote 07/19/2017 at 22:46 point

Very cool! Feeding solder paste is a very different application for a syringe, but very useful. Thanks to the pointer to a nice one!

Here's another syringe design using a 20cc medical type syringe:

There's an accompanying valve design for anyone who wants to build a syringe pump for precise metering.

  Are you sure? yes | no

doctek wrote 01/29/2015 at 22:17 point

Thanks for your interest in the Syringe. Great questions! I'll try to respond in the order asked.

The "team". That would be me.

1) quantity to extrude? Since this is my first experiments with this, I'm starting with a fairly small quantity of material. Next time, I will push material through until the delivery tube is full, then refill and insert the plunger. Then I will have the volume in the syringe which should be enough for interesting tests.

2) PTFE tube with snap fittings? An interesting suggestion. I know the type of fittings you mention, but I don't know where to get them. My goal is a reasonably large bore tubing so viscous stuff could move through it without requiring excessive pressure. I also wanted to be able to have a flexible tubing so the syringe can be mounted next to the printer (but not on the carriage with the extruder) and the tubing will move easily without dragging on the extruder movement. PTFE is pretty stiff; in fact, nylon is even too stiff. So the tube mounting itself must hold the flexible tubing in during operation, hence my invention.

3) effect of bubbles? It's still too early to tell if this will be a problem or what to do about it. Since the syringe is intended to deliver material to the actual extruder, there will be opportunity for air to escape - maybe. More experiments will be needed.

4) heating the output? No plan for this yet. I would need to print the parts from something other than PLA.

5) Archimedes screw or positive displacement pump? Yes, this is an important point! This syringe is only intended to deliver material to a Moineau pump (also one of my projects on or to an auger mixer (coming soon). I think that positive displacement is necessary for an extruder for viscous material.

6) pulsating flow? Since this is designed for material delivery only, I'm hoping that an average flow rate will be sufficient and that pulsations will not cause problems. Another area that more experimentation will reveal the answers.

Use of PTFE? Could work well for this, but it is more expensive, stiffer, and I don't have an easy supply of it. If the materials I'm using don't do the job, I'll explore further.

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cluck_market wrote 01/29/2015 at 06:55 point

I should like to ask some questions of the team. (1) Is it desired to extrude more than this quantity or reload the syringe? (2) Have you considered PTFE tubing with high pressure snap connectors for your tubing? -- These are used commercially in commercial coffee makers. (3) have you considered the effect of bubbles in the fluid? (4) is the output going to be heated? (5) Have you considered Archimedes or progressive screws for this job? --- Typically industrial dispensing of such things is done with screws or with small reciprocating pumps. A pair of small medical sized syringes could with a sliding check valve do the job. (6) Is the output intended to be instantaneous with pausing or continual without pauses?

The PTFE tubing for your hoses can be connected with a slide connector similar to used with compressed air. These are relatively easy and inexpensive. The PTFE tubing is nearly as stable as glass for volume and is heat tolerant up to about 450C. It also would make a good barrel and plunger with good lubrication and little risk of wear.

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