Lessons learned from printing the drain screen

I had to modify the drain screen - the arms weren't long enough to hold it securely. I lengthened the arms of the previous design, printed a new copy, and it's up on the roof - we'll see how it does.

Building these taught me a few lessons about designing parts for the Makerbot:

* SketchUp might not make it easy to add cosmetic curves, but it's really easy to grab particular edges and pull them to get smoother shapes. I extruded one of the sides out an extra 1/8 inch, then moved the top in so the whole face slanted, and got a more interesting design.

* There's a few magic numbers to know about your Makerbot. Smaller (1/16" wide) features often get fabricated with only the two extruded lines along each edge. (The Skeinforge Carve setting "Perimeter Width over Thickness" sets the thickness of the perimeter.) Pieces that are wide enough for four extruded lines will appear solid; pieces that are 4.5 lines wide will have a hollow in the center. This was a big deal when I was printing the HO model strip mall parts because I needed the face of each part to be smooth.

Building smaller features with perimiter lines only was a good thing for the drain screen; the spanning horizontal pieces were sized 1/16" wide so the extruder bridged the gap quite well. When I widened the face, the edges of the bridge were fine, but all the fill between the lines just fell out because there was no support below.

* Printed parts are stronger in the x/y direction than in the Z direction. I had problems with adhesion between layers for parts that took stress (such as the drain arms.) Printing these separately and flat might be a better idea. I also had adhesion layers in the vertical sections, probably because the horizontal strands bridging the gaps would pull on both the pieces supporting it. I don't have a good solution for this.

* I did try building a piece with unneeded solid connections between the legs to cut the amount of loose filaments. This worked well, but probably isn't good for keeping the drain clear.

Making Practical Things

Our flat-roofed 1960's modernist tract house may have really cool lines, but it requires a bit more maintenance than a normal house. Leaves and other debris fall on the roof and clog the downspouts, resulting in cold and annoying maintenance as well as potential long-term problems. It doesn't help that the tree that shades the house and keeps us cool in the summer drops nasty, sharp seed pods that are almost the same size as the drain openings.

Unfortunately, our drains aren't standard - the openings are a bit less than two inches wide, which means those seed pods can block a downspot and give us a miniature lake on our roof. Much of the drain hardware we find at the store either is intended for commercial buildings, or for the typical gutters that most houses use, so I've never found a good solution for keeping the drains clear. I'd found some wire "baskets" that fit in the drain opening, but these were designed for 3 inch openings, so I'd spend an hour of work unweaving them to fit a smaller opening.

Luckily, I've now got a Makerbot, so as long as I could design a basket, I could protect the drains. These two drain screens have prongs which fit into the drain pipe to hold it in place, but otherwise sit flush against the roof. I designed the openings so they were smaller than the round seed pods from the Liquidambar tree. I'm assuming they'll also keep the leaves out, but let some of the smaller debris into the drainpipe and away from the house.

This is the most practical use of the Makerbot I've found so far. I haven't been able to find suitable drain screens commercially, but I've got a reasonable idea of what will work. I also need multiple pieces; Makerbot sometimes seems like a lot of work for a one-off piece, but if I need duplicates, it's great!

On the negative side, I'm not sure how the white/natural styrene is going to survive life on the roof. I've had problems with white styrene sheet warping from direct sunlight, and the roof's liable to be hotter than any place I normally use styrene. Painting might help (or I could just buy the black styrene rod on the assumption the black pigment will ward off the UV.) We'll see how it does.

I designed these over a few hours in SketchUp. Each is 3.5 inches across and 1 inch high, with the drain arms being 2.75 inches tall. Each drain screen prints
upside down with the flat top printed first. The arms that press against the sides of the drain are springy enough to fit in a slightly smaller hole. Note how horizontal pieces bridge space; even without support material, the extruded plastic will cool and tighten horizontally to bridge short (1 inch) gaps. Each piece took around 90 minutes to print. As usual, objects printed flat have great detail and sharp edges. The multiple small outlines for each of the legs prints less nice, and the extruder's jumps between legs left a lot of filaments and rough edges on each vertical piece. If I were doing this again, I might try to have wider or connected legs so that the extruder can extrude several areas on one path. I also considered printing the drain arms separately and flat so they printed cleaner, then attaching them to the main assembly with a snap-fit. I decided in the end it wasn't worth the trouble; maybe I'll do that on my next project.

I'd originally planned these to be round and have interesting curved lines, but SketchUp's extruder tool works better on flat faces than on curved faces. I'm also disappointed that adding in cosmetic curves in SketchUp isn't so easy. Gratuitous curves might not be needed for function, but printing curves in Makerbot is so easy that I feel guilty if I don't add some in.

If these two fit the openings on the roof when I test tomorrow, I'll print several more for the rest of the downspouts. They're also the largest things I've successfully print, so I'm feeling like this has already been a successful project.

Both printed pieces had problems when I was doing cleanup. On the first, the slimmer arms broke, and on the second, part of one side delaminated. Superglue works great for repairs; liquid cement (aka MEK and acetone) doesn't seem to melt the extruded plastic as well as it melts regular styrene sheet, though it'll eventually soften and weld the break.

There's a Skeinforge Setting for That...

I'll share a couple bits of wisdom from trying to do a 3d print of a HO scale model building. (BTW, the prettier pictures are here.)

Keith's Electronics Blog reminded me that if there's a printing problem, there's usually a Skeinforge setting to fix it. The picture shows the front face for the store. I've inset this behind my nice arches, so I didn't think it would be as visible as the main building facade. So, I tried seeing whether I could print an adequate building part without spending a couple hours on gesso, spackle, or other fillers.

The top blank shows the initial attempt. Note the diagonal striping from the fill, and also note that it has a strong washboard texture. This doesn't look so hot (even from a distance), and if I was seriously building this model, I'd be scratchbuilding the building face from plastic strip.

The diagonal stripes are the worst part, but I remembered that Skeinforge has a setting to specify the fill pattern - the angle of the initial fill lines, and the amount to rotate the fill on each layer. Making the stripes either vertical or horizontal would help make the piece look more realistic, because then it might be passed off as the outlines of wood. I tried changing the initial fill angle to 0 (then to 90 degrees when I realized the stripes came out horizontally.) The vertical strips look better; they might be wood detail, but the curves at the end of each fill pass spoil the illusion.

On the third one, I made two changes: first, Keith's blog suggested playing with the Carve setting's "Extrusion Width over Thickness". This controls the thickness of each layer, and determines how much the stream of plastic get squished into place. By changing this value from 1.9 to 1.5, the occasional gaps between the extruded plastic disappears, and the surface starts looking more like a flat surface with board texture. Second, I added some "trim pieces" to the top and bottom to cover where the fill path curved back. This final piece looks much more realistic (except that the "trim" over the window has a gap because it's 4.5 extrusions wide; reducing that size a bit would get rid of that gap.

The third building face still isn't suitable for close-up viewing, but it looks decent at a distance and in shadow. With this print, I'm starting to believe I could use the Makerbot to build HO buildings.

Now it's getting hard to figure out where to put the entries. The post had more on the model, so check my railroad blog for details on printing a model of a 1920's drive-in market, and more photos of my progress.

I Trust My Makerbot / Making Model Buildings

Makerbot's much more fun when you trust it enough to leave it alone for 30 minutes.

Last weekend's experimentation made a huge difference; with the cable to the extruder replaced, I'm having every print work fine. The Brio train track was one of the first things I tried, and I was amazed that the first print went perfectly. The Brio track's also interesting because it uses a lattice structure on the lower layers to minimize warping. When there aren't lots of uninterrupted threads of plastic, shrinkage won't cause the part to curl.

With such good luck, I moved on to one of the projects I'd bought the Makerbot for: could I use it to build model buildings for my model railroad? Specifically, I wanted to print out Spanish Revival style building facades. The curves and layers would be difficult to do by hand, and much harder to do repeatedly, but easy to do with the Makerbot.

Here's a quick look at my first print. The print is 90mm (3.5 inches) across and 70 mm (2.75 inches) deep, and was intended to be around 3 mm thick. It's getting close to the maximum width for the Makerbot; the stock build platform is 100 mm square, but the raft for this print - the crosshatched layers of plastic put down first to hold the model to the surface - is 102 mm. I found my machine could move 110 mm, so I cut a new build platform out of Plexiglas to do larger objects. My first two prints for the building facade failed quickly; the pieces warped horribly within a few layers, and usually bumped the nozzle as they moved around. Bad.

But the Brio track hadn't warped. I wondered if I could break up the long side pieces so that the top layer couldn't pull across the piece to cause the warp. Back in SketchUp, I made the piece twice as deep, and cut some wedges out of the thickened back side perpendicular to the warping.


The new design printed perfectly - no warping, and very little problem with the print. I even managed to print four more over the next couple days. Each print took around 35 minutes, and used 10cc of plastic (or about 20c worth). Best of all, these were the first prints I'd done on the Makerbot where I felt like I could walk away for several minutes without worrying if the printer had stalled and was spewing out hot plastic at one spot.


Warping parts is a big deal in the Makerbot community. The warping occurs because the styrene plastic shrinks about 2% as it cools, pulling at the lower levels and causing the part to cup and pull away from the build surface and first "raft" of plastic laid down. In the best case, the parts end up with a rounded base; the lower levels warp, but later levels get affected less by the warping and build up new flat surfaces. In the worst case, the part curls enough to foul the machine. There have been lots of potential solutions. Some think that changing the plastic used will help. Others are experimenting with heating the build platforms to 60 degrees Celsius so less shrinkage and warping occur. My experiences make me wonder if some simple tweaks to the design might be enough.

My printed building fronts are for a 1920's drive-in market. These weren't the drive-your-car-in markets of the fifties, but the predecessors of modern strip malls - inexpensive buildings put up on corner lots along the new roads leading out to the suburbs. The markets had a pretty standard format: one market, one greengrocer, one butcher, a baker. Each was an independent business with an individual space, but together they were just the place to stop for groceries on the way home. Like many 1920's and 1930's buildings, they often used some extra architectural detail to draw in drivers, and Spanish Revival was a popular style back then. Longstreth's book shows pictures of drive-in markets around Los Angeles, but they appeared elsewhere in the U.S., and were certainly seen in the San Francisco and San Jose area that I model. (The old photo, in fact, is of a drive-in market on Telegraph Ave. in Berkeley, CA. It's long-gone, or at least remodeled.)

I'm planning to glue the building fronts together to make an "L" shape to fit the lot space, and my usual model building supplies for the back walls. The Makerbot surfaces are still pretty rough, so I'm planning on using spackle to fill in the rough spots and simular plaster. Some of the detail, such as the sawtooth row above the arch, will stay to simulate some of the details found on the actual buildings.

Better Luck

I spent the day trying to figure out what might be causing my hangs during printing. I started by trying to print a simple object - a leg for the Makerbot. Like the maker of these legs, my power supply had a fan pointing down, so I needed to raise the Makerbot up a bit to get air to the power supply. My legs are shorter than pattywac's; I didn't want the Makerbot raised up so high.

I ended up trying to print 13 legs, and 8 were usable. My first four prints went great, then things went downhill from there. The two conditions I tested were (1) turning off the fluorescent lights above the workbench, and (2) using a real Ethernet cable for the motherboard-to-extruder cable, rather then the home-crimped cable I had been using. I also routed the extruder cable away from the USB line and the Z stepper motor wires.

Results: with the lights off and the cable replaced, I had three of four prints go fine, with the fourth hanging at the 13 minute mark just as the piece finished printing. When I switched back to the old extruder cable, I got an immediate failure, then two successes. Turning on the fluorescent lights caused a couple of immediate failures, but things didn't improve after the cable and light were replaced. I wondered if something was overheating after several prints, but couldn't find any unusually hot pieces.

Still, I had pretty good luck today. Here's pictures of my Makerbot legs, sitting on their own. I modeled these in SketchUp Pro, then used Blender and skeinforge to convert them to a printable form.

I also tried printing building fronts as a model railroad project. The Makerbot did a great job with the curved lines of a Spanish Revival building, but the piece warped pretty quickly and eventually jammed the extruder nozzle. I even tried printing on a piece of 0.060 inch sheet styrene, but the extruded plastic only stuck a bit better than on the acrylic.