Monday, May 28, 2012

An STL to Test the Cube - Part 2

After the first version of the STL designed to test the Cube printer when it arrives, I had this feeling that I was treating it like I did my students on the first day of school when I was teaching.  The bulk of the years that I taught was with the 7th - 9th grades.  And, one had to be a bit creative to survive a full year.

I found, as many teachers can attest, that it helps if, on the first day of school, the students come to think their new teacher just might be on the ragged edge of being so deranged that there was always the possibility that something might tip him right over the edge into the mass murderer category!   Pity the poor new teacher that says to their class, "I want to be your friend!"  Count on that person to end most days in utter chaos and bitter tears.  Only by being tough on the first day of school can you ever hope to be able to have real fun with your students over the rest of the year.  It's about clearly establishing limits first.

But, I digress....


The point is that I felt I was being a little TOO hard on the Cube.  The poor Cube didn't have a chance because I'd made a bit of error in trying to create a tough file for it to render.  My measurement was taken at the wrong place. Here is a video that explains....

I want to be tough; but, not downright brutal!!

As promised, I have uploaded the STL file to the Cubify site at the minimum (I believe) allowable cost.  Here is a link to the STL on the Cubify Store.


I've also loaded another STL that you might find interesting,  Knowing a 3D printer's behaviour with both corners and walls at various thicknesses is a good thing to know when we're designing our own objects.  This second STL includes twisted hexagon shapes having wall thicknesses of .25mm, .50mm, .75mm and 1.00mm. 

Twisted Hexagons with varying wall thicknesses

I'm guessing, based on the behaviour of my RepRap that each of these objects may have different levels of smoothness on both the sides and, in particular, at the corners.  Knowing how the Cube behaves should help us design smoother objects in the future simply based on wall thickness.

In addition there is a larger object that demonstrates another interesting behaviour of 3D printers as wall distance narrows.  It is actually two counter rotated shapes with one rotating inside the other creating a single complex object.

Twisted Hexagons with Counter-rotating Stars

Besides being one of those shapes that only a 3D printer can produce in one piece, the inside object will help us test to see how the Cube performs as walls converge.  The inner 4-point star tapers to a modest point.  The outer 4-pointed star also tapers to a modest point.  

Counter-rotating 4-pointed Stars creating a single object.

Each of the star shapes requires both an outline for the wall and a pattern for the fill for each printed layer and a different pattern for the final top layers.  

In my current 3D printer there is a difference in the printer's ability to completely fill the boundary inside the wall contours as the taper becomes thinner.  So, the outer 4-Star shape, having  a relatively wide taper is completely filled and entirely smooth.  However, a completely different behaviour is exhibited when printing the inside star with the narrow taper. At some point, the fill and the contours of the walls fail to meet, creating a gap.

This STL can also be found in the Cubify store.  Again, it's at the lowest cost I think is allowable.  If that drops below $3.00, I will certainly update the price.  

Twisted Hexagon and Star Test on Cubify Store

I want these files to be affordable to everyone because I think they are very, very useful.


How your particular printer handles these issues is important to know as you design your own objects.  That is why I have concentrated on primitives as the first objects I will be printing when my Cube arrives and why they are the first objects that I have uploaded.  Cube materials might be affordable; but, they certainly aren't cheap and we can waste a lot of material if we are not designing FOR and WITH our particular 3D printer's behaviour and characteristics. 

I'll update this entry with images of all of these objects after I've had a chance to print them on my Cube.   And, hopefully, that will be sooner rather than later!

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