As I mentioned in the introduction to this series, the sathar destroyer was first model I created. I had just finished working on the Sathar Destroyer Technical Manual and wanted a miniature of the ship. As I have much more of an engineering/draftsman mindset and approach to things, I figured that turning the existing deck plans into a model would be the easiest way to start.
The design of the destroyer in both the technical manual and the final 3D model was based completely on the silhouette of the ship on the little 1/2″ counter that came with Knight Hawks game, shown on the right. In retrospect, as Delta pointed out in his blog post on the sathar ships, this is probably more accurately a silhouette of the heavy cruiser and the picture on the heavy cruiser counter should be the one for the destroyer. But at the time I was going with the image on the counter. In the end, it turned out different enough (as you’ll see in my post on the heavy cruiser model) that there really isn’t any mistaking the two ships. Maybe in the future I’ll make a different destroyer model based on the other image.
Making the Model
The final model is shown in the image on the left. This final version was arrived at after many different print iterations, sixteen all told. This was my first model and I was learning what the printer could and couldn’t do.
The first step in making this particular model was creating the body of the ship. This is the one part of the ship that I couldn’t make with the primitive shapes available in OpenSCAD: spheres, cylinders, and cubes. However, one functionality that it does have is to create an arbitrary polygon and then make a rotational solid from that shape. Or you can read in the polygon stored in the proper format (a .dfx file in this case) and then rotate that.
In order to make this ship I used the ship silhouette that I had created in Inkscape for the technical manual. I just stripped out everything that wasn’t related to the body. Inkscape can save files as DFX format so I just exported the shape which I was then able to import into OpenSCAD. It was completely the wrong size but OpenSCAD’s scale() command took care of that.
This would be a good point at which to talk about scale. Since my plans were all done in meters, and OpenSCAD works in mm, it was easy enough do make the model at 1/1000 scale. This was too big compared to the other miniatures so in the end I applied another factor of 1/3 to the final model for printing. Thus the sathar destroyer model ended up at 1/3000th scale. This made it basically the same size as the sathar frigate model from the miniature sets. I’ve decided to use this scale for all the capital ships miniatures I make. As I’ll talk about in other posts, this makes some of the small ships too small for printing so I’ll have to make them larger
Other major sections
Adding in the spherical head and tail as well as the cylindrical sections connecting them was quite easy as those were primitive shapes available in the program. I just had to tell it where to place them. The laser cannon peaking out the top was also just another cylinder.
Adding in the backs of the shuttles (the spheroids peaking out around the center) was also quite easy. One of the features of OpenSCAD is that it supports for loops. I just made one shape and then added it to a loop that repeated 8 times, each time rotating the shape 45 degrees around the central axis.
The same was done for the engines. In this case I created a single engine and then had it repeated 4 times each with a 90 degree rotation. My initial engines were just the main cylinder, the sphere at the top and the strut connecting it to the main body. I had originally had some of the other engine details but the test prints kept failing and I simplified it down to just the basics as I worked out the printing problems. The image to the right shows the first good print that I got (after about 6-7 tries). There was one earlier print that worked but the struts were too small and broke off.
Adding in details
Once I got the basic body shape working, I added in all the details such as the extra bits on the engines, all the airlocks and bay doors, and the details around the shuttles.
In this case, it wasn’t an issue of adding in more shapes but rather of subtracting of material from the model. OpenSCAD has a difference() command. This basically takes a list of shapes. The first one is the main shape that is to exist and all the others are subtracted off of it. So to make the upper airlock (the small circular feature on the upper sphere in the model image at the beginning of the post) I simply subtracted off a cylinder from the sphere that made the head of the ship. I simply had to position the cylinder in the right place to get the desired cutout. Then I added back in a smaller cylinder to represent the airlock door itself. Thus in the model, there is a small recess around the door. This was done for all the bay doors, airlocks, and around the shuttles.
I found that I needed to make these feature about 0.2 mm in width and at least 0.1 mm deep in order for them to show up in the print. Any smaller and they weren’t visible. Once the details were added I started printing and tweaking things to make the model look a little better when printed and to make the print process run smoother.
A last note on the model. In the model image at the top of the post, there is a cylindrical structure directly below the sphere at the back of the ship where the engines attach. This is a printing support that I added in to the model because of the way the printer works. It is not part of the final model.
As this was my first attempt to 3D print anything, I went through a lot of mistakes and miscues trying to get it to work. For those unfamiliar with 3D printing, the basic process is that the printer lays down plastic everywhere it should exist on one layer, then either moves the build plate down or the print head up (depending on the printer) and lays down the plastic for the next layer. This is repeated until the model is completely done. The model is built up layer by layer.
This has some implications. First, you can’t print on air. There always has to be some material underneath the new material you are laying down in the current layer. This is why there is that little support structure under the ball at the back of the ship. It couldn’t just start printing the ball in mid air. Now there doesn’t have to be material everywhere directly under what you are printing but it has to be within a nozzle diameter. There has to be some overlap.
This has implications on what kind of details and angles you can print without supports. If you look closely at the rings at the base of the engines in the model image above, you’ll notice that they are not just cylinders but rather have a slope to the top and bottom instead of being simply flat. This was to avoid the need for supports (plus I think it looks better anyway). If it had been flat, the software would have wanted to put supports under those little cylinders. By angling the shape, I avoided that need.
As I said earlier, there has to be some overlap between the layers based on the nozzle diameter which is how much material is being pushed out at any one time. In the case of the printer I’m currently using, the nozzle diameter is 0.4mm (which seems to be typical for most 3D printers I’ve looked at), so as long as the features and overhangs are less than that, I can safely print the model without needing supports. Also, since I’m printing at 0.2mm vertical resolution, as long as my angles are greater then about 30 degrees, I can print sloped surfaces without supports as well as there is enough overlap. I’ve pushed that limit in some cases with mixed results as you’ll see in some other posts.
Another feature of the 3D printing is that you typically don’t print fully solid pieces. While you can, it is typically not necessary and just uses more plastic making the part both heavier and more expensive. By default, we typically print at a 10% infill using a honeycomb pattern. What this means is that any large volume will be mostly hollow but with a hexagonal support structure inside for strength. The printer does this by tracing the outline of the piece twice so that the wall is 0.8mm thick. This is adjustable in the software so you can make it thicker if you want. After that, it prints the infill pattern inside the shape for that layer. Typically it prints three layers (for a total of 0.6mm thickness) on top or bottom surfaces.
However, this tracing of the outline has some impact if you’re printing small cylindrical parts like the engines in the ships. A single layer wall, with a 0.4mm diameter nozzle, means that the smallest diameter you can print is 0.8mm. With two thicknesses, that is 1.6mm. In practice I found that if you try printing a single cylinder less than 2.6 mm the printer has problems. I jammed the printer and had several failed print jobs trying to print stuff that small. If you’re printing more than one part of the object (or more than one object at once) you can often get away with slightly smaller diameters. This may be an artifact of my printer but in the end I never made a piece, especially when it was one of the necks of the sathar ships, smaller than 2.66 mm and even then I preferably printed more than one at once to keep the printer from having issues.
This was figured out completely empirically over the course of about half a dozen failed print jobs. It would print five to six layers of the engines and then the printer would jam and stop extruding plastic. Each time I’d make the engines a little larger until I could get it to reliably print. I had to do the same thing on the neck of the destroyer finally settling on a 3mm diameter to get a reliable print.
The only exception to this is the laser cannon on the top of the ship. That is only 1mm in diameter but is only 2 layers tall at the very end of the print and so the printer was able to handle it okay. Plus it is still printing the top of the sphere at that point as well.
On the smaller models like this sathar destroyer, I found that printing more than one model at once helped in the print process, especially on the small narrow cylinders. The reason for this is that it gave the plastic on the lower layer more time to cool slightly before printing the next layer. This allowed it to have a little more structural strength and not flex. On models where there is only one being printed, you can sometimes sees a bit of sagging and distortion in the print layers. Printing multiple copies at once definitely helped out with this.
Painting the models is pretty straightforward and is done as you would any other miniature. This is something I’m completely new at as well and absolutely zero experience so my paint jobs may not be up to the standards of other. Take that as you will.
In the case of the ships, they typically has a main color that most of the ship is painted. Because of this I found it easier to use a spray paint as the base coat. It’s probably not really necessary on the smaller models but it definitely helps on the larger ones.
In my case, I’m just using Testors brand model paints for the most part. (My wife just got me some different metallic paints for Christmas that I’m going to try out on one of the other models.) I have a wide variety of paint colors in both flat and gloss finishes. I’m using the gloss paints on the ships to help represent the reflective hull.
I actually haven’t finished painting any of the final destroyer models but should have one done soon. I’ll post an update with the final one when I do. I did finish painting the prototype model, however, and that is pictured to the right. This one was painted with the gloss red Testors paint on a grey primer base. The spheres on the top of the engines are painted in gold. The gold paint was so reflective that I kept thinking that I had accidentally touched it with the red when I was doing touch-ups as I kept seeing the red reflections on the gold that looked like paint on that part of the model.
Something that the painting brings out that you don’t notice as much in the unpainted models is the layering from the printing. It really stood out when I primed the prototype model and you can see it a little in the final painted one. Actually handling the models makes it more noticeable. The surface of these models is not smooth as the metal miniatures are. There is definitely a layered surface texture. Personally I like it as I think it gives the models some character. As one commenter on Google+ said, it looks like hull plating.
A Colored Model
There are printers out there than can print in multiple colors, or in the case of a couple I’ve now seen, in full color. OpenSCAD has the ability to add color to the parts so I thought it would be fun to make a colored version of the model. You can see it here on the left. This is what the final painted version of the final model will look like when done. Unfortunately, the color information doesn’t seem to be carried on when I translate it into a printable object file so I’ll have to find a different modeling program to use if I ever want to try a full color print.
Tell me what you think
I’d love to hear your thoughts on this process and any specific things you’d like me to cover in future posts. Feel free to leave comments below or contact me on Twitter (@dagorym). I also post updates about the models as I’m working on them in the Star Frontiers Google+ community.