Tuesday, June 27, 2006


0.5mm Layers and Cooling

I'm back on light duty after a lower back injury, and firing up the experiments. In the picture below, you'll see two 16mm test hexagonal prisms, now being extruded from layers a mere 0.5mm thick. The one on the left was done contiguously, the one on the right was sprayed with freezer spray to completely solidify it between layers:

Unfortunately, the cooled one detatched from the base and tried to impale itself on the nozzle, so I had to halt the experiment. However, you can clearly see that the distortions are drastically reduced when the lower layers are cooled, and fusion is still good. Hopefully, this will lay to rest any concerns that we might have to do the deposition in a heated environment.

I see Simon has already added a reserved output pin to the PIC for driving a fan in the Wiki. Over the weekend I plan to test deposition on sandpaper, and to try and roughen the glass surface with hair spray. I've tried crosshatching the glass with a diamond scriber, but that didn't seem to help as per above.

Vik :v)

That's beginning to look really good, Vik! :-)
Wow, that's a radical improvement by just cooling things down.

It would be interesting to see how much cooling could be provided by a simple 12v computer fan.

I suppose larger parts would have more time to cool down between layers, but then if the RepPap project evolves and becomes faster and faster as has been mentioned...

Also, if someone extruded with higher temp HDPE, even more heat would have to be taken away. How do those commercial machines deal with the heat?

BTW Vic, Glad to hear you are on the mend... (Quick, tell us how if you had a drill press in the first place, you would never have hurt your back, and it's in the bag! ;) )
When we're using support material (cake icing or whatever), that stuff could probably be at ambient temperatures - so it would presumably help to cool the plastic within the layer. Stuff like plaster of paris sets exothermically though - so a lot depends on what you choose.
How about if you had the construction chamber submerged in a pool of circulating water, level with or just below the top layer of the workpiece? Might that improve cooling? Of course, you'd then have to bugger about with level sensors, pumps, etc...
I'm generally against mixing water, electronics and rustable threaded rod...

Vik :v)
You could solve the problem of keeping water out of the electronics and away from the metal parts of the reprap machine if you had to - that's not the biggest problem IMHO.

Doing the deposition in water would prevent you from using something that's soluable in water as the support material. Having a water-soluable support material is a useful option because it's easy to dissolve the stuff in order to get it out of the small crevices of the work-piece.
Might the cooling problem be improved by using higher melting point materials? Assuming atmospheric construction chamber temperatures, higher MP materials should cool down and harden quicker when deposited, with less need for artificially accelerated cooling.
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