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What to do with a 3D Printer: Replace Solar Light Stakes
In rearranging things in the yard, we had these old solar path lights that needed to be moved, and which were due for some refurbishment. We pulled eight of them and discovered that four were without the stake at the bottom. I decided to design and print some new stakes for the lights before redeploying them.
This is an original stake and is what we want to replicate (in function if not form).
Here is an end-view from the rear of the stake where it mates with the tube on the light.
I wanted a print that could be done without support, and which would be sufficiently strong and print reliably. There were a couple of problems with the geometry of the part we're replacing.
If we duplicate this geometry it won't print neatly on its side because the fins keep us from having a flat surface we can orient downwards. We can't easily print this geometry vertically because in its upright orientation there is too little surface area on the point for it to adhere well enough to the bed to print successfully (and even with a raft and skirt the interface would have too little cross section). We also can't print it upside down without support because the fins would be unsupported.
Here's the tube it mates with. It has an inside diameter of 29/32 inches (approximately 23mm).
The possible solutions I saw were to either print it upside down and modify the fins to extend down to the build plate (around the outside of the tube, once installed) so they are well supported, or to just redesign the whole thing so it doesn't need support. I opted for the latter because I wanted an easier print, and one with the traces oriented to give more strength along its length.
To do this I put together a three-finned design that accomplished both of those goals. The two side fins print flat with the third fin vertical - no need for supports. This is a view from the tip of the stake.
Here is a side view. Note the tapered rear, made to more easily insert into the tube for a press fit.
Here is a perspective view. In this picture note the cone at the joint of the fins. Since fillets are rather difficult to do well in OpenSCAD, this feature was meant to serve the same purpose, providing strength for the fins so they can't break quite as easily. While it isn't easy to see in the above picture, this actually replicates a feature in the original stake, though it was much smaller and less pronounced in the original.
In this shot of the rear end of the stake (the top, which mates with the tube) note the offset. This feature isn't concentric with the center of the fins as it was on the original. Again, I wanted this to print well without support, but it needed to have enough of the round cross-section to mate well with the tube. The slight overhang of these edges in the lower layers is not large and is easily handled by most printers with reasonable settings.
You can find the design file (the .scad file) for the replacement solar light stake on Thingiverse.
Printing the Solar Light Stake
With the design in-hand, on to the printing. I'd like to take a moment here to show a brief object lesson on the impact of bed leveling. After the first print to test fit (which was successful) I plated up a print with the other three stakes I needed. Printing the three at once utilized a bit more of the bed and gave me an opportunity to snap some pictures to show one aspect of the impact of an unlevel print bed.
In this first photo, notice the quality of the traces. This print at the rear of the bed had a first layer height that matched fairly well with what Slic3r was anticipating for a first layer height. The traces connect well, but aren't too "mooshed" and there are no jagged features in the surface from over-extrusion. If anything, there might be a little room for this layer to be just a tiny bit lower and give a flatter, smoother surface, but it was certainly good enough to be happy about. This was printed on a Printrbot Simple Metal, in case you're interested.
Now, notice the print in the front. The bed was slightly out of level, making the front of the bed ever-so-slightly higher than the rear. This resulted in an effective over-extrusion for the real layer height, which was now lower than ideal for the amount of plastic being pushed out. The rough surface is due to the plastic flowing up out of the plane of the layer because there isn't enough vertical room for all of the volume being laid down. This didn't have a major impact on the functionality of the print, it just caused some rough edges that take a few layers to smooth out.
These were printed with our Charcoal Black ProSpec PLA.
Here are the final stakes. They were printed with very thick layers both for speed and strength. The very tops are a little bit mooshed around due to several factors including what appears to be just a little bit of overextrusion, a high hotend temperature to facilitate a high print speed, and cooling settings that slowed the print on the topmost layers. This cosmetic defect didn't impact the functionality of the prints, so they were put into service as-is.
Here is a finished stake along side the original stake for comparison.
And the printed stake installed in the solar light - a delightfully well-fitting press-fit.
Finishing the Project
To finish the project off, we replaced the older, worn out (and in some cases dead) batteries with these batteries, which should have a service life measured in decades and an increased capacity so the light extends further into the night.
We also did some cleanup on the lights themselves. In particular we cleaned up the photovoltaic cell on top for increased charging efficiency and cleaned up the plastic that surrounds the light itself so it looks a little nicer and lets a bit more of the light out.
The lights are now ready to deploy!