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3DPrinting: Striations, Surfaces, Wisps & Fusing


Grelber writes:

Nice article, Bill. It strikes me that you wound up with some interesting textures that might be used for gratings, wickerwork or thatch. Not, of course, what you were going for, but still useful.
Grelber



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Revision Log
24 June 2016page first published

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©1994-2017 Bill Armintrout
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Personal logo Editor in Chief Bill The Editor of TMP Fezian writes:

I was going to write another Workbench article about my latest 3Dprinting efforts, but then I thought that an article on some general principles might be better.

Striations

3Dprinters of the type I have have been called "hot glue guns on steroids." The printer has a nozzle, and from this nozzle emerges molten plastic, the nozzle and the printer bed both move in ways to deposit plastic in places to match a 3D model, and the plastic quickly hardens and fuses to whatever plastic is nearby.

And as I've said before, the 3Dprinter builds an object from the bottom up, one layer at a time – something like a stack of plastic pancakes.

The thickness of those levels is determined by the quality of your printer, and by your printer settings. My printer can be set for levels of 400, 300, 200 and 100 microns.

To help you see these striations, I've printed out a sample object at three different resolutions:

Strations

The sample objects are roughly 50mm by 50mm by 130mm.

Strations

The objects on the right were printed with 400 micron levels, and the striations are clearly visible. The objects on the left were printed with 100 micron levels, the striations are difficult to see, but you can still feel them if you run a fingernail over them. (The objects in the middle were printed at 200 or 300 micron levels, I forget which…)

Textures

Striations affect the vertical surfaces of whatever you are printing. Now let's talk about the horizontal surfaces.

The bottom of your 3D object, the part of the object which rests directly on the bed of your 3Dprinter, will pick up the texture of your printer bed. If you are still using the original glass printer bed, then the bottom will be as flat as your glass. If you are using masking tape to help your model stick to the bed during printing, as many are, then the bottom of your model will have the texture of your masking tape.

Now, if you were printing a simple cube, what texture would the top surface have? Again, that depends on your printer's quality and your printer settings.

Here, I've again printed out three sample objects at three different resolutions. On the printer I am using, the da Vinci Jr. 1.0, there are three quality settings: Normal, Good and Excellent. If you look in the 'advanced' printer settings, you can see that these control resolution between 200, 300 and 400 microns. In the 'advanced' settings, you can also select 100 micron resolution.

Surfaces

The sample object is 1" by 1". The object on the right is at 400 micron resolution, the object in the middle is at 300 micron resolution, and the object on the left is at 100 micron resolution.

As you can see, at least with the 3dprinter I am working with, there is no such thing as a completely flat surface.

Of course, the objects you want to print will probably not have perfectly horizontal or vertical flat surfaces. In these cases, what you will get will be a product of both striations and textures.

Filaments

The outcome of your 3Dprinting also depends on the filament being used.

The 3Dprinter I am using only works with proprietary PLA filament from the manufacturer. It came supplied with a spool of white PLA, a translucent material which I used for the first two samples above. I had a lot of trouble with this filament, including the fact that it did not feed properly and the worm gear was constantly making a loud sound as it slipped on the filament. Tuk-tuk-tuk-tuk! I was ready to throw it against a wall.

The second filament I tried was a spool of black filament. It has no feeding problems, and is much more reliable. I don't know if the improvement is simply due to the filament, or due to improved settings on the chip which comes with the spool.

There are only three PLA filaments currently available from the manufacturer that are not transparent: white, which is translucent and came with my printer; black, which I used in the other test objects above; and neon green, which I have just started working with (fine so far).

On the printer I am using, the filament settings are controlled by the chip which comes with each spool, and cannot be modified by the user. (I understand a previous version of the software allowed the use to adjust nozzle temperature, but that feature has been removed.)

Wisps & Stutters

In a perfect world, the nozzle of a 3Dprinter would just deposit exactly the amount of plastic required, and would shut off immediately when no plastic was required.

In reality, it doesn't always work this way. For example, I found a free model of a fan shroud for the exhaust fan on my 3Dprinter. I thought it would be useful to keep hot air from blowing into my face. It is a simple three-sided object, which I printed in black:

Fan Shroud

Note what has happened. As the printing nozzle prints each level, it goes down one side, the next side, the next side, and then it crosses to the opposite side again. And as it does so, the nozzle does not instantaneously stop extruding plastic.

Fan Shroud detail

Now on a fan shroud, such imperfections really don't matter. If they bother me, they can easily be cut off with a sharp blade. However, if I was printing a soldier model, the same problem is possible wherever the nozzle needs to shut on and off – for instance, moving between the legs of the figure.

And if you were thinking of saving time by printing multiple models in one printing… you're also increasing your chance of getting imperfections as the nozzle moves from model to model.

Fusing

The technology of this type of 3Dprinter depends on the plastic being hot enough to fuse to the plastic that has already been printed. If the plastic is not hot enough, the layers of the object might peel apart, or fail to create a solidly bonded object.

I've discovered that the 3Dprinter I have is unreliable when printing larger objects at faster speeds. For example, here is that fan shroud again, this time printed at Fast (i.e., 400 micron resolution):

Fan Shroud on Fast

Obviously, the nozzle is leaving a lot of wisps and stutters behind!

Fan Shroud on Fast detail

But the bigger problem is that the strands of PLA haven't properly fused together. In places, the shroud is more like a basket of strands than a solid object.

Fan Shroud on Fast detail

My guess is that when the printer is laying down longer strands at faster speeds, the nozzle temperature needs to be higher. (Note that the small sample objects came out fine at Fast speeds.)

However, the somewhat good news is that, as a miniature wargamer, I almost always want to print at the highest resolution on this printer (100 microns). And at that speed and resolution, I've had no fusing/bonding problems.

Final Thoughts

So those are some of the limitations and challenges of 3Dprinting on a low-end 3Dprinter. Next week, we'll experiment with printing out some 28mm figures!