RepRap: Blog

The Java host software is now set up to handle objects made from any (reasonable) number of materials. If you load an STL file, select it with the mouse, then load another the system keeps the relative position and orientation that the two had when they were created. Thus you can design something in several materials, save each as an STL, and then load them all together.

As you can see, the sectioning software distinguishes between the two and creates the correct outline and hatch patterns for each.

So far I have tested this on an Arduino-controlled RepRap with LEDs in the place of the extruder motor and valve (because I only have one extruder here at the moment). The LEDs all seem to light up and go out at the right times.

This is cheating slightly, as the Arduino only has enough pins for one extruder, but if you have two, one of which just needs a motor like our plastic extruder, and the other of which just needs a valve, like our prototype paste extruder, then you can control both.

Next I'll update the paste extruder design and get that working again, and see what we can make.

Then I'll upgrade the Sanguino (more pins...) software so it can genuinely handle two extruders.

This, of course, will allow us to use different support materials, and also fun stuff like silicone rubber and Field's metal.

Labels: extruders, materials

I have got the paste extruder working on RepRap. It consists of a 500 ml fizzy drink bottle containing a balloon that in turn contains the paste. You pressurize the bottle using a bicycle pump, and the flow is controlled by a latching solenoid that clamps onto a soft silicone tube on the way to the nozzle. The clamp is the red rectangular piece hovering over the tube in the picture below (the solenoid is behind the green support). When the red bit moves backwards the flow is shut off.



Here is a close-up of it laying down a test square. The material is PolyDiMethylSiloxane (PDMS - silicone bathroom sealant). I had the flow set too high and the movement speed too slow, so it's flooding a bit. But that should be easy to fix.

The controller electronics are really simple - just the standard RepRap controller with slightly modified firmware (which I have just posted in the software repository as extruder_1).

The silicone doesn't set if you leave it in the device overnight, except for the bit actually in the silicone tube that forms the valve. I suspect that this is caused by the fact that the materials are the same, and so a little of the catalyst that caused the tube to polymerise when it was originally made is leeching out and setting the working material as well. If I am right, to fix this we just need a soft tube of another material.

When the valve closes, it deposits a splodge of goo as it displaces some material. The tube I used for the valve is 3mm internal diameter, which it doesn't need to be. I'll try and find some of 1mm I.D. That should cut down the closure volume, and hence the problem, dramatically.

This means that we should be able to work with just about any material that is a paste at room temperature. Tomorrow I'll use up another balloon (no expense spared) and try Polyfilla wall-crack filler paste.

Labels: materials, paste extruder