Tuesday, September 20, 2005


First non-circular object printed

Last night I ran off the first non-cylindrical shape from the Meccano prototype RepRap in EVA. It's shaped a bit like a keyhole and tapers as it goes up. It was done by programming the PICs rather than sending commands from a PC, pending my fixing of the serial control software that I mucked up. Here it is:

This illustrates several useful things:

o We can produce non-circular artifacts!

o EVA Produces fine filliaments on some corners, which are easily brushed off.

o The indexing of the turntable by means of a magnet and reed switch is sufficiently consistent in operation.

o It is possible to produce tapered objects.

All the layers fused beautifully, but the initial base layer was a little patchy possibly due to me depositing on cardboard. The turntable initially located itself under the head automatically, and after checking the EVA feed I created a stable and well-bonded base by running the bottom layer repeatedly without adjusting the height. Then it was just a question of enabling automatic control of the vertical axis and the object formed before my eyes.

Vik :v)

Monday, September 19, 2005


Computer languages

After extensive and detailed technical discussion (me: "How about X?"; other-RepRap-bods: "Seems all right...") we have decided on the computer languages to use in the RepRap project.

We shall use Java for all the software that needs to run on the computer controlling the RepRap machine. Most users will have Linux, Windows, or a Mac, and Java should be pretty platform-independent.

Inside the RepRap machine itself there will be one or more PICs (at the moment we're trying to make them all PIC16F628-P chips). These we will program in C via the SDCC compiler to generate .hex files for downloading. Occasionally we may also need to use PIC assembler.

Saturday, September 10, 2005


Head Design Released

I have (finally...) completed the design of Version 1 of the RepRap Polymorph extruder head. Here's a picture:

The large grid squares on the image are 10 mm across.

A 12v geared electric motor (A) drives a 3 mm diameter rod of the polymer to be extruded (B) by means of a stack of pinch-wheels (C) into a heated nozzle (D). The heated nozzle has a small hole in the bottom end out of which a stream of molten polymer emerges. The electronics for controlling the heater and the motor can be partly seen at (E). Polymorph has a low melting point of 62 oC, but the heater is capable of being controlled to temperatures up to 200 oC. At around 170 oC the Polymorph becomes inviscid enough to extrude easily.

For complete details of the extruder, including downloads of all its design files, see Item 11 in the Reports, results, and documentation page of the RepRap Website, or follow this direct link.


Meccano prototype's first restarted object

We managed to get the new 12V feeder drive controlled by a PIC, and have fitted a "goop shield" the the nozzle to prevent dribbly messes over the turntable.

The top of the turntable has been fitted with an easier to clean cardboard plate. We might raid the local pubs for beermats - hey! There's a good excuse! Our "goop shield" is a spare beer bottle cap - no relation - and we have wrapped the resistors with PTFE tape to stop "goop" dribbling through it.

We've produced two cylinders with a wall width of 1.0mm approx. The second cylinder was stopped (while we popped the EVA stick back into the heater) repositioned (Vik had knocked everything around a bit in the process) and cleanly restarted. This wasn't too difficult and the hardware is proving to be reasonably precise so far.

We have encountered a setback in that the hot-melt glue overflows from the nozzle, no matter how slow we put the feed at. This is not just causing dribble problems; it is also forcing the unmelted glue feed off to the side of the nozzle entry.

We're sure that we will find a solution soon, most likely involving gaffer tape or an old golf club.

Vik :v) and Ash.

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