From Napkin Sketch to Reality Overnight

In our case, the “napkin sketch” quickly turns into a Sketch Picture in SOLIDWORKS to start the design. I had a request to create a dolphin model and I decided to make it a case study on going from a 2D sketch to SOLIDWORKS to a 3D print. Being a long-time user of SOLIDWORKS but new to 3D printing, I wanted to pass forward what I already learned to anyone unfamiliar to 3D printing.

First, the top and side profiles were created and brought in as two separate Sketch Pictures which helped to create the Lofted Geometry in the Part Model.

The sketch pictures gave a good frame of reference for the guide curves to control the shape the body. The loft sections tie to the guide curves using pierce relations to lock down the geometry. Separate loft features create the dorsal fin, flippers, nose and tail fins(flukes).

Two configurations are printed and shown here, one has a straight body, one with a flex feature to give it a little bend at the head and neck area.

Loft and Boundaries with guide curves create most of the geometry. Surface fills are used to close the open loft surface sections. The model is fully commented explaining all the steps involved to make it.

STL to “slicer” to gcode.

3D printing is used for rapid prototyping, additive manufacturing and is also used by the general hobbyist. Availability of low cost printers has opened this technology up to the masses. Most libraries now even have 3D printers that can be accessed at no or low cost. My local library charges a cost per gram of print material (15cents per gram), not bad.

From SOLIDWORKS to a “Slicer”

After your model is finished, what do you do next. Take your part or assembly from SOLIDWORKS and export it as a STL format. A separate slicer converts the file into series of layers. There are some free 3D slicers available as well as some with a cost associated with them. Some 3D printers will provide a slicing software with them. The layer information is then formatted into G-code instructions tailored to a specific type of 3D printers Fused deposition modeling (FDM).

Here is the dolphin model in a free version of a slicer. You can see the dolphin geometry along with “support” material.

The support material fills in cavities and holes. With the dolphin not being flat at the bottom, the support material fills in the area below belly from the nose to the tail. When creating the 3D print, we try to look at the layer lines and orient the part so that is stronger in the thinner sections. Usually printing the model so the layer lines go across it horizontally. Of course, support material can be factor for the build time and material cost with different orientations. With one print material only, there is some trial and error involved in trying to get the print right. The extra footprint layer on bottom is a called a “Raft” it helps make the plastic stick to the bed better and is optional, but my printer works much better with the raft added. Issues with getting material to stick to the glass bed are fixed by using hair spray, painters tape or using a special print build surface on top of the glass bed.

Here is the first print at 50% of the actual size.

The top of the part has very good finish.

After the support is taken off the bottom, here is what it looks like.

The bottom surface is rough. I made the wall thickness thicker to allow for sanding and filing but there will be some rough areas remaining that will be shown in a later picture. How can this be avoided?

This shark from Roger-Marie Couture on GRABCAD shows how I split the print into two pieces to get a better finish on the bottom.

Dowels are used very similarly to the way they would be built with a wood material, with the dowels and holes lining up the two pieces. Then a plastic filler, like a wood filler “filled” in the joint line.  You can see the shark finished below before it is to be painted.

Plastic parts will usually need some post processing usually some sanding or filing. In my example some filler might be added at the bottom under the neck, flipper and tail areas. Just know that extra layers of paint can hide some smaller gaps and finish issues. Some of post processing depends on if this a rough prototype or a finished part.

Now back to the dolphin. Here is the dolphin finished with its two-tone paint job.

With more time, I could have maybe found a better orientation to save some material cost and print time. For example, printing the side flippers separately would save a lot of support material. That is the beauty of 3D printing, you can try to balance time, material, strength and finish. More expensive printers offer a larger variety of materials and avoid some of support and finish issue you see with my example. Printing with soluble support material is a big advantage of the two print heads (dual extruders) printers.

Here is view of the belly where you see the finish isn’t quite perfect.

If I really wanted to get the same smooth finish as the top, I might split it up in to two pieces and print it vertically just like the shark model.

One of the other things that was also experimented with was placing a bend in the front of the model. The picture shows the results of the two different configurations being printed at the same time side by side.

Making small sample prints give a faster look at the finished product and saves on material cost. In this case, this is printed at 60% of the actual model size. Once the design is finalized and the print orientation is set, the model can be created at a larger or at full size, if it makes sense. After the first 3D print of the model, the eyes were enlarged, and a blow hole was added as you can above. This is typical example of rapid prototyping on 3D printer, make a 3D print then modify it, make another print, adjust, print, etc… The nice thing is that this iterative process is hours, not days or weeks to make changes. After making the first print, the next day my modifications that were added in SOLIDWORKS were in the next print as you see above.

Print Materials

All my 3D printing experience so far comes from working with PLA (Polylactic Acid, made from sugarcane and cornstarch) which is good for a nice surface finish and is easy to print but it is not as heat and moisture resistant as other materials. I have had 3D printed parts deform in a hot car in direct sunlight. I will next try to print with PETG and at some time later, ABS which both have better temperature resistance but can be more challenging to print than PLA. For example, PETG must be printed at slower speeds than PLA to prevent “stringing” and ABS does need ventilation because it does create fumes during printing.

Sample Models

If you are looking for sample models to print yourself, check out 3dcontentcentral, Grabcad or thingiverse. Try to get a STL file to print direct or if you want to make modifications, first get a SOLIDWORKS part file or a parasolids STP, or IGES. Once done making any modifications, save it out as a STL file. From there it depends if you have direct access to 3D printer, follow the steps above or bring it to the library. Have fun and enjoy the more accessible world of 3D printing.

Download this model to learn more about dolphins, sketch pictures, surfacing modeling and additive manufacturing.