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Monday 17 August 2015

Printed at last

Ever since I printed and assembled the prototype of my Discovery slot car, I have been trying to print another version.


I've made a few changes to make it fit the chassis better and to be able to fit an interior plus a few other minor cosmetic changes like increasing the door gaps.

The main significant visible change was adding the raised air intake.

Every print failed. However after enough fails to convince me it was not entirely the printers fault I took a closer look at the failures.

They had all failed in one of two places.

The first was at window height and the other by far the more common was half way up the doors.
Both faults coincided with changes I have made to the model!

At the window height it looked like it was running out of filament. I concluded that the tiny little blobs of plastic that form the pillars was not enough to keep a good feed flowing.  I added back the window support structure that I had deliberately thinned out to make cleaning up easier.

It's mainly a thin solid sheet as shown in orange in the above image.

The second fault, of which I have at least four stringy messes, was at the height of a little bar I had added to fill the gap between the doors and the interior floor panel that would be glued in.

I had originally included a simple rectangular step, where the blue section is shown in the above image. It only sticks out by about 1mm but I guess that was enough to weaken the model and cause it to split at that point. The model looked like the head had touched the work and broken the bond with the glass bed. From then on, it was all wrong, probably freely sliding about as it printed!

I fixed this in several ways. I changed the rectangular bar to have a long sloped lead in and I reduced the thickness so it only just overlapped with the inner door panel. That last bit was in the hope it would change the path of the head. On the print settings I used a raft, instead of a brim to give it even more adhesion.

The areas in blue in the above image are structural additions. They are bits that are needed to make it in to a slot car or to join the separate parts of the model together.

The parts shown in yellow are supports needed to be able to 3D print it. They have to be trimmed off to complete the finished model. These are in addition to the automatic support structures that can be added by the Ultimaker Cura software.

I used the following printer settings in Cura 15.04:
Layer height = 0.12mm
Border width = 0.8mm
Speed = 40mm/s
Support = From the build plate
Adhesion = Raft

I'm using ColorFabb PLA/PHA filament at a temperature of 210C on my Ultimaker 2 printer.

I am very happy to have another finished print of the Discovery shell.

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