Wednesday, April 04, 2007



I did a three layer print of the perimeter of the cube with no real problems. I then decided to go for a 10 layer of the perimeter to see what would go wrong.

Several things did, but none that were really troubling. First off, I got the thickness of my layer just a bit too big. For the first 5 layers or so there was no real problems, but by the 6th layer the additive errors got to the point where the extrusion thread began to dribble onto the previous layer instead of being laid down properly. You can see that at the upper right of the foreground perimeter. I should be able to diminish the layer depth and get that problem to go away.

I also observed warping at the corners of the perimeter. I'd seen that before and Vik has reported the same with polycapralactone. I'm wondering if that can be cured by cutting back on the extruder flow as I approach the corners.

Finally, I finally began to get some backlash problems with the y-axis after a while. You can see that happening on the left and right perimeter margins. I noted this before and will attempt to cure that by shimming the sliding joint on the y-axis.

One thing that has always puzzled me about the project is how does the machine deposit exactly the right amount of filament? It can count the turns of the extruder thread, but the filament diameter must have a tolerance of at least a few percent. If the amount is slightly wrong then doesn't the error accumulate the more you print until the shape fails?
Right now I have the extruder running at a fixed rate regardless of the speed at which the tool head is moving. I plan to coordinate the rate and traverse rate before too long.

From looking at Stratasys prints you get voids within a printed object if your deposition rate is off slightly. I think that that is why FDM printers go to a lot of trouble to print perimeters.
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Am I worrying about something that is not a problem or is it asking for a closed loop feedback system. Perhaps we need to build the object on top of an electronic weighing scale.
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