Moai work flow - Print Orientation

When setting up a SLA print, below these are the steps you have to consider.

Here is the work flow:

1 Print Orientation

2 Hollowing

3 Offset from z-axis

4 Support

5 Positioning

 

Print Orientation,

 

This is one of the most important decision when making a print and the first you should consider. We are going to demonstrate this point with this Moai print.

 

Factors:

  1. One continuous build, no islands
  2. Minimize surface area on layers
  3. No Cavity Facing straight into the vat
  4. Keep the tall side of prints close to left part of the vat

 

While you may not be able to do all 4 for a given print, you should try cover as many factors as you can.

Hollowing is a frequently used to save resin that creates cavities. Therefore, when considering

 

We are going to use Peopoly Moai print designed by JohnnieWalker as the example.

Let's first run Meshmixer and load the print file:

 

This file can be print it as straight up as it is shown above. But it does not gives the best results and use too many resins.  The reason why the orientation is suboptimal is that the object is print straight off the plate, making the first few layers susceptible to damages from scrapping. By printing it this way, the layer lines are more visible as well.

Let's first find a better angle to print.

Turning -45 degree looks like it is making it works. Now you have islands (negative over angles highlighted by red circle) that will be impossible to print well. 

 

 Let's try 25-degree turn on X-axis and this looks like more workable. This would also make the support to be at the bottom of the base and the back of the object where the details and finishes are less important.

Next, let's do hollowing. It is a crucial method to save resin and time.  Because it is a solid object, I already decided I want to hollow it and once rotation is set, I can decide the hollowing and the locations of drain holes.

Meshmixer has a nice hollow feature that is the best among free software.  

The default setting works well.  2mm is a bit thick for small object but for this size, it is safer to print thicker.

You cannot do hollow without drain holes and Meshmixer is very intuitive to add drain holes. Simply double click on the spot of the object and it will drill drain holes with enough depth to connect to the hollow portion.

You should have at least two drain holes per hollow portion since this object has one big hollow inside, I select two spots.  One on top of the head and one at the bottom of the base. The top of the head is for the resin to drain out while the one on the base to reduce suction force so that resin can flow out while the object doesn't expect too much downward suction when printing. 

Here is a plane cut to show you the inside is hollowed out.

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Export the model to an STL file.

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Support is another critial step that cannot be considered away from orientation. You need support to print well but too much support ruins the surface of the print and wastes resin. 

 There are many software to generate support. For this instruction, I will use B9Creator software as example based on Evan Morgan's work flow that is favored by many Moai users. 

Once you load B9Creator, open layout and add the STL file you just exported from Meshmixer.  Here is a B9 build platform file made by Evan.

Set Z Position to 5mm to give the model some clearing from the plate. This is needed for support. 

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Now click on Support tab.

I like to print without adding foundation and use manual support features.  I feel the automatic add support features add too much support.

 

Here I use medium support for the base where a grip is an important and light support for the spots on the back to give it some additional help.  Make sure there is support for the lowest part of the model as that is where the print would be starting.

This combination of medium and light supports work well for hollowed object. For solid objects, you may need more and thicker supports.

Export the model STL file.

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Positioning,

Cura is our slicing software of choice for Moai.  Using Cura Moai Edition: we load the previous model file with support.

You could print as it is.  But let's optimize settings based on how Moai separates the model.

The short hand rule of positioning in Cura, is that keep the tallest part of the model up front on the build plate.  This will result in the tallest part of model printed on the left frame side of Moai where separation force is the lowest. 

Such as this.  Now you are ready to slice and print.