About this project
A screw-top jar with a matching lid, generated from the inside out. Set the cavity you want and it builds the body, the shoulder, the threaded neck and a lid to fit.
Sizing
The cavity is what you specify — diameter, straight-wall height, and how much of a tapered shoulder to put above it. Everything outside that follows from the wall thickness. The capacity readout accounts for the shoulder as well as the barrel, so the number in the panel is the volume you actually get, not the cylinder alone.
Mouth ratio is the shape decision. A wide mouth is easier to fill and to get a hand into; a narrow one gives the jar a waist and a more traditional profile. The shoulder is what bridges the two, and the inner surface is mitred so the wall stays a constant thickness measured perpendicular — not the cheaper trick of offsetting vertically, which thins the taper.
The thread
A real helical thread, not a printed approximation. Coarse pitches print far better than fine ones, so 3 mm is the default; below 2 mm the crests start to disappear into layer lines.
More starts means fewer turns to close — a two-start thread shuts in half a turn. It also halves the thread engagement, which matters not at all for a jar.
Thread clearance is the number to adjust if the lid binds. It is diametral, so 1 mm of clearance is half a millimetre of gap on radius. The design check keeps it below the thread depth, past which the lid stops engaging at all.
Lid
The skirt takes grip flutes around the outside — count and depth are yours. The design check watches the flutes against the lid circumference so they cannot merge into a scalloped mess, and against the skirt thickness so they cannot cut through.
The lid sits beside the jar in the scene, spaced by the print gap, so what you see is what you slice.
Label
Text engraved into the side, wrapped around the body and driven by a font of your choosing. Position is set as a fraction of the body height, so it stays put when you resize the jar. The engraving depth is checked against the wall so it cannot perforate it.
Printing
Both parts stand on the bed, no supports. The thread prints as a series of overhangs that each start off the layer below, which is why coarse pitches work and fine ones do not. If the lid is tight out of the printer, a quick pass with a brass brush on the threads is usually enough; if it will not start at all, add 0.1 to the clearance and reprint the lid only.