![]() Extrusion parameters must match reality! Screwing it in place shows that it’s slightly too long (I trimmed the length in the source code): Broom handle installed It seems to work reasonably well, though, and is certainly less conspicuous than the screws I’d use. The dimples on the side duplicate the method that secured the original plastic piece: four dents punched into the metal handle lock the plastic in place. ![]() I intended to use a hex bolt, but found a carriage bolt that was exactly the right length and had a head exactly the same diameter as the shaft, so I heated it with a propane torch and mushed its square shank into the top of the hexagonal bolt hole (the source code now includes a square recess): Broom handle screw plug – in handle The hole down the middle accommodates a 1/4-20 bolt that applies enough clamping force to keep the shaft in compression, which ought to prevent it from breaking in normal use. The cylindrical thread form doesn’t have much overhang and the threads came out fine I think the correct straight-sided form would have more problems. The skirt thread was 0.25 to 0.30 mm thick, so the first-layer height tweak and packing density adjustments worked fine and all the dimensions came out perfectly. With the shaft diameter set to the “root diameter” of the thread and the other dimensions roughly matching the broken plastic bits, this emerged an hour later: Broom handle screw plug – as built Fortunately, it turned out to be unnecessary, but it’s there if you want it. ![]() The OpenSCAD source code has a commented-out section that removes a similar shape from the shaft between the raised thread, but that brought the rendering to its knees. Broom Handle Screw – thread model closeup The former obviously weren’t appropriate and the latter produced far too many facets, so I conjured up a simpler shape: 32 slightly overlapping cylinders per turn, sunk halfway in the shaft at their midpoint, and tilted at the thread’s helix angle. But, I didn’t know that at the time a simple half-cylinder 2.5 mm wide and 1.25 mm tall was a pretty close match to what I saw on the broken plastic part.Īlthough OpenSCAD’s MCAD library has some screw forms, they’re either machine screws with V threads or ball screws with spheres. I measured a 5.0 mm pitch (which should be 5.08 mm = 0.2 inch exactly) and a crest-to-root depth of 1.4 mm = 0.055 inch, which makes them look like 3/4-5 Stub Acme threads. For a 5 TPI thread = 0.2 inch pitch, that’s GP = 0.1 inch vs. Machinery’s Handbook has 13 pages of data for various Acme screw threads, making a distinction between General Purpose Acme threads and Stub Acme Threads: GP thread depth = 0.5 × pitch, Stub = 0.3 × pitch. Some after-the-fact search-fu revealed that the thread found on brooms and paint rollers is a 3/4-5 Acme. Instead, an hour or so of desk work produced this: Broom Handle Screw – solid model – overview My lathe has quick-change gears that can actually cut a 5 TPI thread, but that seems like a lot of work for such a crude fitting. It’s a cylindrical Thing tailor-made for (or, back in the day, by!) a lathe. A few minutes of Quality Shop Time sawed off the end of the handle and unscrewed the stub to produce this array of fragments: Broken broom handle thread Somehow, we wound up with a broom handle and a broom head, the former missing a threaded stub that was firmly lodged in the latter.
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