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So let's design something to print!

October 5, 2017

Well, you finally bought a 3D printer and you're wondering what the heck you're going to make with it!  Even though you're probably having difficulty thinking of something to make right off the bat, the list is almost infinite of what you can make with your new printer.  Limitless, right!?

 

Not quite.  While you can make almost anything, there are some limits to the way things have to be done with a 3D printer.  Well, not just some, a lot of limits and constraints.  You'll need to learn a bit about those before you get started designing something for yourself or you'll end up frustrated that the object you've spent many hours designing won't print properly and may need to be completely redesigned.

 

Support structure

This isn't the building that the 3D printer help staff live in, it has to do with the way a 3D printer lays down the plastic to build your object.  We talked in a previous post about how printers work - they extrude noodles of plastic layer by layer, starting at the bottom and working up to the top of your object.  Immediately, you run in to the first design constraint - support.

 

Look at this object on the print bed.  On the left, you can see that when the printer tries to lay down the plastic for the top of the bracket, the plastic is just going to fall to the bottom.  There's nothing under it to support it.  Remember - Gravity's not just a good idea, IT'S THE LAW!

 

All printer slicing engines have the option to automatically build support structure for you, but for this object, you'd be wasting a ton of plastic as you can see in the picture below with the automatic support structure shown.

A better way to go is to simply re-orient this object with the two arms of the bracket pointing up, as on the right, and this object will print without any support structure. 

 

You'll run into this problem constantly in designing more complex objects, but in almost every case there will be an orientation of the object, or a slight design change that will avoid support structure.  It's not terrible to use support structure, but removing it from the object can leave a rough surface and it can waste a lot of plastic and print time.

 

Build angle

One technique you can use to avoid support structure is by taking advantage of what is called the 'build angle'.  Typically a 3D printer can build out at a 45 degree angle without support structure needed.  So, let's look at a common problem in putting screw holes in a box as an example.

 

On the left, you can see that the plastic under the screw hole will just fall to the bottom.  Adding support structure from the slicing engine would build a column of plastic all the way to the bottom of the box, which, while solving the problem, would be difficult to remove and would leave a blemish on the bottom of the box. 

 

You can use the build angle ability of your printer in a clever way to solve the problem here.  By putting a 45 degree chamfer under the screw hole, the printer will be able to build out from the walls of the box and support the underside of the screw hole so it will print without any support structure required.

 

 

Manual support structure

Using automatic support in an object is great and easy.  But, when you come back to print this object again a month later, you might forget to actually turn on support structure when you print and end up with a mess like this.  I call it a 'birds nest', for obvious reasons!

 

So, I often build support structure directly into my objects.  A common place where I do this is in 'knockouts' in the sides of boxes where I mount rectangular components like switches, plugs etc.

 

To build this knockout into the side of a box, all you have to do is make a rectangle inside a rectangle, basically cutting out a very thin amount of plastic around the knockout.  I find that .01" gap works well and makes it possible to simply push the knockout out with your finger.  Too much of a gap and the knockout may fall out during printing and you'll have a mess.

 

 

 

 

 

 

 

 

 

 

 

Notice the round hole above.  You'll find, that as long as round holes aren't too large, like even up to 1 or 2" in diameter, they'll print fine without support structure, being supported by the 'build angle' concept.  The very top of the circle, although horizontal and unsupported will be handled automatically by 'bridging', something we'll talk about later.

 

Dissolvable support

If you have a dual extruder printer, you can use one of the extruders to create support structure that you can later remove by dissolving it with either water (PVA filament) or limonene (HIPS filament).  This is usually performed quite easily with your slicing engine - just tell it to use the other extruder for support structure.  Then, when you're done with your print, just throw the object into the solvent and wait.  While a good idea for tough designs, it still increases your cost and print time and will leave blemishes on objects where the support structure contacted the surface.  For HIPS support, limonene is difficult to find, expensive and will actually damage the main plastic in many cases.

 

Thinking outside the box

Orienting your 3D print design so it doesn't require support can sometimes involve thinking way outside the box.  The most obvious orientation may not be efficient at all and will require extreme amounts of support with the resulting clean out process being very difficult and often will ruin the object.  Here's an example of a corner bracket to join two pieces of aluminum square tube together. 

The 2 most 'obvious' ways to print this both result in both or at least one end of the bracket getting totally filled with support structure to allow them to print.  So, what can we do?

 

 

 

 

Well, we can use the build angle of the printer to re orient this print in a rather non-obvious way that allows it to print entirely without support.

 

 

 

 

 

 

 

 

 

 

 

 

Summary

Orienting an object in your design is one of the most important factors in being able to successfully print.  Using concepts like build angle and manual support can drastically improve your success.

 

Next, we'll talk about designing your object for maximum strength and then about another important topic - bed adhesion.

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