Sunday, February 7, 2010

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.

Saturday, February 6, 2010

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.