Design Blog #1 – Measure twice, print once

My shower has two controls: a temperature ring and a flow rate knob. The flow rate knob in my shower broke the other day.  Without the knob, you can’t turn the shower on or off, which is kind of crucial for taking a shower.

Each of the above are various solutions or attempts at solutions to the problem of having no on/of knob. The pliers worked in a pinch, and I used them for about a week or so, but they weren’t an elegant (or permanent) solution. I set about designing a new knob. The original knob was held onto a post with a screw. The first centimeter or so of the post had an oval-ish shape; you can see it in the printed designs above, but the shape is essentially a circle, but with two flat, parallel sides. The one key dimension in this case would be the width across the two flat sides. The dimension of the circle isn’t critical so long as it is at least as long as the long dimension of the post (it can be longer; the knob “grabs” with the flat sides). I’m printing in white ABS, at 235/105 (extruder temp/bed temp).

For the first attempt, I had incorrectly recorded the key measurement: I had used 4 mm instead of 6 mm. The knob finished printing, but it didn’t fit. I had also incorrectly oriented the model in the slicing software such that it printed supports and a raft. You can see the remnants of the raft in the picture above. It is the filled in part of the long section

For the second attempt, I used the correct measurements for the keyhole area. It fit, but the keyhole section wasn’t sufficiently deep, again, because I had recorded the wrong measurement. It worked-ish, but wasn’t nice. It was also humorously long and was aesthetically intrusive. As you can see above, I didn’t even bother putting a hole through the keyhole.

For the third attempt, I scaled back the handle part of the knob to a much more reasonable size. I also used a drill press to make a hole for the screw to fit it. I mounted it to my shower and it functioned, but it still looked funny. It was also time (and resource) consuming to print because of the big flat pancake of the top.

For the fourth and final (for now) attempt, I went with a hollow gear shape. First, aesthetically, it fits much better and is much less intrusive compared to the rest of the elements in the shower. Second, avoiding large flat spaces improves printing speed and reduces resource consumption. Third, I included the hole for the screw directly in the printed design so I didn’t have to drill it out after. I’m mostly happy with this design, and it works quite well. I think it could use a bit of flair, but the design itself is clean and prints quickly.

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