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Here's the place for discussions about those 3D creations for Tguage...and lets not forget the trials and tribulations of designing and printing.

Anatomy of a FFF print

Postby dkightley » Sun Jul 19, 2015 10:05 pm

Printing with a 3D printer is quite simple? Well, no, not really. There's a lot I thought I'd run through the print process for a fairly complicated part and show what's going on....and explain a few things on the way.

Lets start with an image of what we're printing.....a viaduct track bed section (for the Ribblehead viaduct):
Capture00.JPG (87.54 KiB) Viewed 845 times

This shape has two small footprints, which you can't see clearly, however you'll see what they're like as the print progresses.

Okay, let's start printing...or should I say simulating the print process....
Capture01.JPG (94.58 KiB) Viewed 845 times

What we see here are two optional things created by the slicer program...a skirt and a raft. The skirt (the dark purple) give the extruder an opportunity to start extruding cleanly..two circuits around the area of the object. The raft serves two purposes, firstly to compensate for the print bed not being 100% level, and to lay down a larger area than the bottom of the object so as to get a good grip on the bed - to stop curling, etc.

A few layers later:
Capture02.JPG (107.35 KiB) Viewed 845 times

The dark blue is the outline of the object and is backed up by the inner perimeters in light blue. I have set this print to only have one additional perimeter. The green is the solid layer that is the bottom of the object, and the gray zig-zags are what is called "support", which is sacrificial print that acts as a support for layers that are yet to be printed...essentially to make sure each layer has something on which to be laid over! Its worth noting here that the layer thickness is 0.1mm and the width of each line is 0.4mm....two of the fixed parameters when printing.

Three or four layers later:
Capture03.JPG (99.52 KiB) Viewed 845 times

The orage is in-fill. To save plastic, the object is made hollow with an in-fill to give it some strength...and something to print the top layers on top of. I've set the in-fill to 50% here.

After a few more layers:
Capture04.JPG (105.85 KiB) Viewed 845 times

Here we have a couple of layers of the main body of the object. The gray "support" will have done its job by giving the bottom something to be extruded onto.

One layer later:
Capture05.JPG (107.62 KiB) Viewed 845 times

The in-fill is now expanded to fill the whole cross-section of the object. The green layers are actually the "bottom layers", and I have set there to be only two.

Two layers later:
Capture06.JPG (105.44 KiB) Viewed 845 times

Top layers have printed for most of the object....just the uprights to go.

Approx six more layers:
Capture07.JPG (103.57 KiB) Viewed 845 times

We now have some more support material. There's obviously some more overhangs. Note how the stonework detail is printing, the sharp angular edges having been smoothed out by the path of the extruder. The little bits of orage are in-fill...I'l come to this in a couple of images.

Several more layers:
Capture09.JPG (99.06 KiB) Viewed 845 times

The centre upright is now completed and there's just the two walls along the edge of the section. Before we take a closer look at what's going on with these walls, Here's the finished object:
Capture10.JPG (92.5 KiB) Viewed 845 times

Finally, lets go back a few layers and take a closer look at the wall section:
Capture11.JPG (47.76 KiB) Viewed 845 times

The two dark blue wavy lines are the outline of the object. In this simulation, the width of the lines is 0.4mm. The little squigly bits of light blue and green are perimeter and in-fill respectively. In this case, there's actually room for thes bits, as the wall is greater than approx two & a half times the filament thickness wide. Note that at this width, there's room for indentations in the vertical surface of the object, however should the wall only be 0.8mm thick, then there wouldn't be any room for any indentations..and they wouldn't show. Thus, this forms one of the main restrictions in FFF printing, the minimum wall thickness - two widths of the extruded filament.

Okay. The print has finished. If this was a real print, the next step is to gently prise the print off the print bed.....and remove the raft and the support material. If the settings are right, both should separate cleanly from the object leaving minimal scarring.

I hope this has given an idea of exactly what goes on in a FFF print ( forgot to say FFF stands for Fused Filament Fabrication)...and helps anyone thinking of taking the plunge and investing in a printer.

Any questions? Do ask...
Doug Kightley
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