10 min jar hourglass timer

thingiverse

This is a versatile 10-minute hourglass timer. I use it in my classroom to time snack breaks and activities with ease. You'll need the following materials: 2 pint Mason jars 1 pt fine sand 1 custom 3D printed coupler 2-part epoxy rated for plastic and glass. Print the coupler, then carefully test fit it into the necks of the two jars. If there's a raised spot, sand it down. Never force this into the jars, as that may cause cracking. Fill the bottom jar with fine sand, leaving about 1 cm of headspace between the sand and the neck of the jar. Apply a generous amount of epoxy to the flange of the coupler, ensuring there's no epoxy in the center hole of the coupler.