Concrete ashtray mold

You'll need a printer, filament, and sandpaper. Use these to make the mold. Now you'll need some hard technical grease, a brush, and 700 grams of concrete. Grease the inside of the tub like you would a cake tin with butter. Press the molded parts into the grease and remove the excess grease with a brush. I've included a 0.3 mm gap in the mold in case your printer is inaccurate. If your printer is properly calibrated, a small gap will appear which you can fill with grease using the brush.