Tips for Quality Printing

Layer Thickness and Fine Details

So what makes a good design that can be printed on a 3D printer? The answer is tied to the capabilities of the printer. The print nozzle on the Replicator has a diameter of 0.4 mm, so the plastic layer that it puts down is made of strings of plastic 0.4 mm wide. Usually an outer surface (and an inner surface if there is one) is made of at least two passes of the print head. So if you are making a vase, make sure the wall thickness is at least 0.4 mm x 4 = 1.6 mm thick. Fine details and features also may not come out very well if they have a width of less than 0.8 mm. (In the previous discussion, substitute 0.5 mm in place of 0.4 mm when using the BFB-3000 printer.)

The same thing can be said for small features in the vertical direction. The printer uses layers of plastic that are usually about 0.25 mm thick. (The thickness is set in Makerware when you set it to Low, Standard, or High quality before creating the print file.) Details in the vertical direction that are thinner (top to bottom) than 0.5 mm may not come out perfectly.

Printing Holes

If you are printing holes in your object (like holes for bolts and screws), you may need to increase the size of the holes a little bit in your design. When the print head curves around to make the perimeter of the hole, the plastic builds up a little bit on the inside of the curve (think about laying down a piece of ribbon in a circle) and the diameter of the hold becomes a little smaller than planned. Sometimes this isn’t a bad thing, as it gives screw threads a little more holding power when they cut into the plastic. But if you want a threaded screw or bolt to move freely, upsize the hole a little bit. Try practicing by printing a small test block with the right size hole to get a feel for it before printing your important part.

Overhangs and Things That go "Droop" in the Night

Another thing to look out for are “overhangs”. Think of a model of a person standing upright with one arm held out horizontally. The model can be printed pretty easily except for the one arm. It sticks out over open air. When the printer tries to print it, there is nothing underneath the liquid plastic to hold it where it needs to be, so it will fall down to the build plate. What to do? Well there are two things you can try. First, try to reorient the object so there are no overhangs. For the example of the person with one arm held out, try rotating the model so the person is on his or her back and the arm then lays on the build platform. Voila, no overhang! If that doesn’t work (like say there are multiple overhangs on all sides), then when preparing the S3G file or BFB file try turning on “support”. This will build (hopefully) easy to remove support structures under the overhangs so that they can be printed. It works pretty well, although you may have to clean up your object with a craft knife to get the last little bits of support material off of it.

Not Enough Strength or Layers That Don't Bond

This is usually due to the plastic needing a higher print temperature. It's common for colorful ABS to need a little higher temperature than the more usual "natural" (white) ABS. The blue filament is known to need a little higher temperature - maybe 5 or 10 degrees higher. A similar effect can be encountered when printing PLA on the BFB-3000 printer.

Teeny Tiny Prints

The plastic has to be hot when it's laid down, but you want it to be solid when the next layer is printed on top of it. Unfortunately, a fast printer means that for very small things one layer may not cool and solidify before the next layer is extruded on top it. This can lead to droopy, saggy prints with a loss of most of the detail. What to do? Well, the first thing is to try slowing down the print speed (it's set in the gcode generator, i.e. replicatorG, Makerware, AXON, or KISSlicer). The goal is to have each layer take at least 6 to 10 seconds to print. Some third-party gcode generators have an option to set a minimum layer print time, but the freeware gcode generators we use don't. But you can always do a test print and "count Mississippi's" to get a resonable estimate of layer print times.

A second thing you can try is to reduce the print temperature a little bit. I don't recommend this as the first thing to try because it can lead to a loss of strength in your printed part (see the previous section on this page).