Tips and Tools: PVC Chuck System Celina Clavijo Kashu

Appears in the November 2019 issue of Ceramics Monthly.

Combine a few basic materials to make a handy system for trimming otherwise precarious forms.

I recently accepted an order to make a crane-necked flower vase for an ikebana teacher. Trimming this tall, narrow form was a challenge that required some problem solving. I decided my best option was using a chuck.

Chucks can be thrown on the wheel to any size needed for a particular piece and used when the clay is leather hard, bone dry, or bisque fired. Just like the pieces being trimmed, unfired chucks tend to shrink as they dry out while being used and may need to be carefully re-centered and re-trimmed for each pot. Bisque-fired chucks need to be soaked in water, the rim covered by a pliable clay coil, then centered and secured to the wheel head before trimming a piece—and the whole process must be done each time. 

A chuck should be tall enough so the inverted piece doesn’t touch the wheel head. The interior should be wide enough and its rim angled to fit the round shape of the belly of the piece. The base of the chuck should also be wide enough to provide stability while in use (1).

Assembling the System

Searching for a hassle-free alternative, an idea came to me in a DIY shop when I saw a PVC pipe with the right diameter for my vase. I requested the pipe be cut to length (based on the measurement from the rim of the vase to its shoulder, plus approximately 2 or 3 inches) perfectly perpendicular to its vertical axis. At the same time, I had another shorter piece cut (more or less ¹∕₃ of the first piece’s height). The longer pipe is for trimming the foot and the shorter pipe is for trimming the neck from the rim down to the belly of the vase.

To cushion the piece and keep it securely in place at the opening of the pipe, I use some ordinary plastic tubing (an old garden hose would also work). Be sure that it is flexible enough and smooth along its exterior surface. To buy only the necessary length, just multiply the diameter of the pipe by 3 (circumference=pi×diameter; pi=3.14) plus 2 or 3 inches, just in case. Slice it open lengthwise with a cutter and fit it to the rim of the pipe, cutting off any excess.

The pipe and hose addressed the need to make a large enough chuck for the vase, but I still thought that centering the pipe on the wheel would be bothersome. The narrow interior would not allow easy access to the wheel head, making it difficult to firmly affix the chuck with clay. Tall chucks, more often than not, are very easy to push off center or knock off the wheel entirely.

I found a piece of wood ¾–1 inch thick and a bit wider than the pipe, and traced the inside circumference of the pipe on its surface. Cutting 8 straight sides within this circle made the shape easier to cut, and ensured the points would fit perfectly in the inside of the pipe (2). Next, on the wheel I centered the octagonal block on an old wooden bat repurposed for exclusive use with this system. After finding and marking the center of the bat, I glued the octagonal block in place.

Once the glue has cured, the bat is ready to be centered on the wheel head. Since the block was glued in the center, the pipe does not need to be centered each time it is used. Just slip it over the block (3, 4) and press a clay coil around the bottom edge for extra security.

Using the Chuck

The benefit of this system is the variety of heights and widths of pipe that could be used for a range of forms. The long pipe is used to accommodate trimming the foot and bottom of the vase (5). The neck of the vase fits inside the pipe, and the shoulder of the vase rests on the flexible tubing. To trim the neck of a crane-necked vase, place the piece right side up on the short pipe (6). Usually, one hand handles the trimming kanna or loop tool and the other helps keep the piece in place. Placing a bisque-fired disk (or for a narrow rim, thick cardboard will do) on the rim will protect it from being distorted while pressure is applied to the body and also acts as a place to steadily hold the form. The disk should not be much wider than the rim’s diameter.

This method also works as a chum for bowls, fitting their interiors over the pipe and hose. I have pipes of different diameters and heights (with corresponding bats to secure them to the wheel), and the only limitation is the flexibility of the tubing to fit narrow pipes.

the author Celina Clavijo Kashu studied ceramics at the Kyoto, Kutani, and Shigaraki Ceramic Research Institutes in Japan, as well as in Jingdezhen, China. She has published two books on ceramics.