Thursday, August 19, 2010

Filling a syringe

Second post today, I'm catching up while sitting next to a humming Rapman printing a batch of ceramics. Unfortunatly I need to keep an eye on the flowrate and correct pressure or printhead speed every few minutes. More on that in another post. Luckily the Rapman has manual controls. turns head-adjusts speed-back to typing. Yesterday I was going through the excellent documentation of the frostruder at Makerbot. All goodies that where not available when I started, looks very usefull for adapting to Rapman. turns head-does not adjust speed-back to typing. On the Frostruder usage page in the wiki I found the following photo's of Zach filling a syringe:

I used this method exactly once :) Its totally unusably for getting a syringe filled with clay and trying to avoid any trapped air. So here's the method we hacked together in a few minutes.

The Syringe Transfer Tool!

The STT is a syringe from which the front is cut of and that is used to suck up material.

You still need a canister or lump of air free material but thats easier than to try and get the material compacted in every syringe individually. turns head-does not adjust speed-back to typing. 
Next step is to fully insert the plunger in the syringe and suck up material. The trick is to pull the plunger while simultaneously pushing the syringe in the material. After 100 times you can do it one handed while taking a picture :)

Now you detach the plastic plunger stick from the silicone plunger cap without letting air in (tricky part). After that you smooth the clay and taper it a bit, I always put little pit in the top to make sure air escapes before the clay reaches the nozzle when transferring the clay in the print syringe.

Onto the magic transfer move.... You make a nice stack of pssst-turns head-perfect print finished. A nice stack of plunger stick - STT - empty syringe and you push the clay out of the STT into the empty syringe, et voila! 

Clay recipe

I get the question often "is this special clay?". I always said that it was fairly standard but since I have been diving deeper into clay it looks more and more like there's a whole other universe in that slurry. Its not pottery, its higher chemistry and I wish I stayed a bit longer in ceramics class :)
At first we tried watering down modeling clay and this works but its hard to get consistent results. Now we always start from clay powder that you can find in the better ceramics supply store. I found out lately by buying a different type of clay that I had been lucky with the first clay that I bought because the last one had a really tough time NOT to collapse during print. The difference? Fat or lean clay, the one I always use is semi-fat (or semi lean, depends on your ideologies) and the one that collapses is lean. I can't find a good explanation in english online but fat clay particles are more plates and have a better cohesion. (if anyone has the explanation somewhere in english?)
So you'll want semi-fat or fat clay for 3d printing with extrusion. Next you need to balance the viscosity so that it extrudes around 4-5 bar (60-70 psi) but has enough strength to support itself as a build object. A water : powder ratio of 1 : 2.2 gives the best results for the clay powder we use here, this may vary for the powder clay you buy in the store but this might be a good starting point.
You could also reinforce your clay with cellulose fibers (paperclay). I have only done a quick test to see if it extrudes but did not build an object with it. I can imagine that it clogs faster.

Next post: how to fill a syringe.