Watering Can
thermoforming & mold design

May 1, 2015

This watering can project was born from my current Industrial Design course. The only requirement that the watering can had to meet was that it can hold half a gallon of water. I wanted to stick with a round shape to match the organic nature of water. I wanted to focus on the issue of the handle placement due to the pain points that arose from the process analysis of using a watering can. It occurred to me that I always have to strain and bend my wrist when I pour water from the can, this prompted me to look into alternate handle arrangements.

Slowly, the shape of the watering can started to take form. The handle closest to the spout (inlet and outlet point) will allow for the user to carry the device to and from the sink to the garden. The handle further from the spout will aid in the pouring process. As the water gets to a lower lever the user can switch grips and not strain their wrist while pouring.

I knew from the start of this project that I wanted to learn how to vacuum form. I am already fluent with CNC machining, so my plan is to machine a positive interior mold and thermoform a sheet of ABS to my desired shape (black portion). The handles and stabilizing base will be machined from Al 6061-T6 stock.

Figuring out how the aluminum handles fixture to the ABS body is the "fun" part. Since the handles are going to be machined, my plan is to add a flange to the flat portion of the handle and use both halves of the molded body to secure the handles in place. The sketch below show some rough sketches of this ideation process.

Manufacturing

The process of machining the handles can be seen above; the piece took close to 2 and a half hours to machine on our Haas 3-axis MiniMill. Some of the operations from the CAM can be seen below. The toolpaths for the various milling operations are represented by different colored lines. The blue and orange paths are the square-mill roughing passes while the yellow pass is the ball-mill finishing pass.

Once the pieces were machined, I did a few post-ops on the handle using the same fixture plate in a different orientation. I purposefully oriented the fixture holes so that the flat handle face would be perpendicular in this flipped orientation (as shown below). This allowed me to clean-up the surface and drill and tap an 8-32 hole for fixturing to the thermoformed shell later in the process.

In order to create a positive mold for the body of the watering can, I bandsawed a large sheet of MDF into a set of smaller pieces which I stacked together. With the aid of some wood glue, I attached the sheets to one another, forming the stock that I would proceed to machine to create the positive mold for each side of the thermoformed can.

The legs of the watering can were turned on a CNC lathe. I designed the legs to have a cylindrical section that have a nominal diameter. This allowed me to hold the part in a collet and perform a few post-ops so that I could tap a screw into the bottom of the piece, allowing it to be held to the plastic mold for the assembly process.