COVID-19 Dumbbells (fill with sand, lead shot, cement or water)

thingiverse

Idea is not new, but I've failed to find working designs on Thingiverse. No additional assembly hardware required. With the beginning of COVID-19 quarantine all the gyms got closed. Avid gym-goers wiped off the shelves of sporting goods stores right away. Some people are now trying to make a killing by selling their old rusty weights, others (who noticed the trend earlier) reselling new items on eBay and Craigslist for triple of the original price: https://www.dailymail.co.uk/femail/article-8190431/People-selling-home-gym-gear-OUTRAGEOUS-prices-online-shoppers-stripped-shelves-weights.html This is my answer to them: * The bells are hollow inside. Scale to your weight/size preference; * Print the handle and two bells (CW and CCW-threaded); * Cut the hole at the bottom of the bell thread with a sharp object or kitchen knife (that 0.4mm shell is there for easier overhang print); * Fill bells with sand, concrete mix, or lead shot; * Screw-in the handle and go for your workout! You may even fill them with water (if your prints come out water-tight,) some silicone glue at the end of the handle-thread will help to seal it when screwed-in. Sand is the best option. It's cheap ($4 for 50lb bag at Lowes). A 1kg roll of plastic should be enough for a single full-size dumbbell ($20 at Amazon). Expected weight of full-size if filled with sand is around 32..34 lb. With this economics you get a twice cheaper dumbbell than what you could get in sporting goods stores before COVID-19 quarantine. As of this moment I've only printed early prototype at 72% scale of original size, after filling with sand it came out at around 13 lb per dumbbell. If the thread of the printed handle does not fit - try to reprint the handle with XY-scaling 1% less than the bell (you should not change scale Z-axis, scale for Z should be the same as bell-print to match the pitch of the thread). TPU material: * It might be tempting to print the handle out of TPU to get that rubbery-feel grip; * My first attempt to do that with 72% scale-down parts has failed, way too flexy (thin shells of 0.8 mm and 33% infill). So go for stiffer settings if you decide to do the same, or use the handle with drill inside and insert a steel rod with nuts on the sides; * I have a plan to print full-size TPU bells using 0.8 mm nozzle and 100% infill, but not sure how that will work out, the bell design might require additional internal sub-frame to prevent too much flexing under its own weight. Why there are two STL models for bells? One is regular and another with mirrored thread: * Symmetrical double thread (CW and CCW) was chosen to achieve matching angles of hexagon faces when both bells screwed tight onto the handle; * Using the regular thread direction on both sides would make that impossible achieve whenever parts are printed with non-original scaling across wide variety of dimensional tolerances that can come out of FDM printers.