Thursday, January 14, 2010

Hello slurry World!

Here they are, the first extrusion tests with white baking throwing clay. All in all I am pretty happy with the initial results and the design ideas for rapid prototyped clay products start flowing too :)

The first set shows some prints with a Gcode file that turns the extruder's solenoid on and off for each layer. The benefit of the pressurized extruder should be instant on/off but apparently I have to tune some parameters to get to that. Off was very instant but repressurizing took considerable time. In this example you can see various pressure settings (3,5-5 bar) and as a result the extrusion gets thicker and the restart is quicker. The clay is probably a bit to thick, it didn't work at all straight from the pack so I mixed it with some water by hand. So maybe when it is more fluid, use a smaller orifice (add short a blunt needle), run quicker and higher pressure I could get instant restarts? I am also going to try not to depressurize the syringe by closing the exhaust. I hope that when I can keep some pressure that it will be easier to find a balance.

For the next tests I just removed all the start/stop code for the solenoid in between layers and got pretty good results, I should increase the Z speed to get thinner blobs when going to the next layer. The slightly thicker squashed extrusion (back left) gives much more reliable builds.

Here you see some 'solid' object, this are various stages of a cube with sparse infill and two solid layers  aborted somewhere in the print. The solid layers need some adjusting and I really should learn how to calibrate my machine, something I always run around. For all this tests I just set the layer height in Skeinforge to 1.4 mm and left the rest as is (except the amount of perimeters, infill ratio etc). In the bottom left example you see what happens if you run out of clay... A little air blast. At ths stage I got really enthusiastic about the possibilities for this mashup of old craft and new tech. This types of structures are very hard to do in traditional ceramics and we have some initial ideas with this.

Some less successful examples ;)

Lessons learned and questions unanswered so far:

  • While initially enthusiastic about Zach Hoeken's pressurized syringe tool I am after two days a bit skeptic about how controllable this process is. I had to remove as much distance as possible between compressor and extruder to prevent pressure build up in the tubes. I will try soon with a separate pressure controller that I can mount close to the extruder and that is much more precise than the system build in the compressor. But what worries me more is that the flowrate is dependent on the pressure AND the mixture of the clay and so far it is hard to get that very consistent true different batches. Its a nice test bed but I think I will need to build a stepper driven tool to compare.
  • We-Need-Software... And we plan working on it. Skeinforge is not very useful when you want to build single filament wall objects and when you really want all the control you can get over infill structures etc. For us this is not so much about reconstructing 3d object but about using the very form language of FDM but in different materials. What we want is a tool in which you can draw gcode lines. At the moment we are looking at a Gcode import/export plugin for Illustrator using Scriptographer. Yes, AI is not 'free' but it is what we know best. But we'll trow the plugin out for anyone to use.
  • Rapman is definitely not intended for wet slurries, the design is very open. An air bubble can trow around some mud and dry clay gives lots of dust. Will need to look at a system to cover some parts ore have a closed build area. Thinking about a paper/plastic bellow around the build area.
  • Object stay flexible true the build and hours after so one rapid move from the extruder can deform parts of your object.
  • No idea why objects taper, shrinkage?

Monday, January 11, 2010

Claystruder mounted, ready to test

So I'm moving along with my paste extruder, tomorrow I will do the first wet clay test with the extruder mounted on my Rapman. Today I did a dry test only with pressurized air to see if I could coble together some Gcode to switch the AUX port of my Rapman electronics. My original filament extruder is still connected to the board so I set the temp in Gcode at 100 degrees, RPM at 0 and replaced all extruder start/stops by AUX start/stops. That did work, setting the temp at 0 did not work because rapman would move to the center and do nothing. Removing all set temp and RPM code resulted in random movements. I'll have to test some more on this quick 'n dirty solution. I am looking for a method to skip the whole heat-up phase all together, remove my original filament extruder and use only the AUX. The Rapman firmware is already setup to work with different (future) extruders like a pen tool and a router. You can set a different ID for the extruder with different resistors:

Tool Header
The RapMan identifies the type of tool fitted by checking the voltage dropped across a reference resistor, values as follows:
Description Resistor A/D
976 Ohm resistor for PEN 1K (90)
4.7K Ohm resistor for Extruder 4K7 (320)
9.9K Ohm resistor for Extruder2 10K (500)
22K Ohm resistor for Not Defined 22K (700)
47K to 100K Ohm resistor for Router 47K to 100K (840 to 920)
1M Ohm resistor for No Tool 1M to open circuit(1010 to 1024)

At Ver1.0.5 the Extruder, Pen and Router have been defined in firmware.

Pen and Router would probably be interesting for me but there is not much more info on what they do, I'll  have to test that out and ask around. Then I will need to find a way to make Skeinforge output usable code for this extruder. At the moment I use hand tuned code with a single filament wall. Lets see tomorrow how the code and the clay behaves!