Tips and Tools: Trimming with a Chuck

Tumbler, 4.5 in. (11 cm) wheel-thrown porcelain, glaze, fired to cone 9 in oxidation, 2014.

Trimming with a chuck has many advantages. After learning how to make and use Mike’s version of a chuck, you may never go back to trimming pots directly on the wheel head. Try it out for yourself!

I started trimming pots on a chuck back in graduate school. A fellow graduate student, Joe Davis, introduced me to the technique. Honestly, I hated the process at first. The pot being trimmed needs to be not only centered, but also leveled. The clay has to be the perfect stage of leather hard. If it is too wet, it sticks. And if it is too dry, it pops loose. Also, the pot you are trimming is elevated off the wheel head higher than usual, so there is a different feel to it. The chuck can also leave a scar on the inside of the pot, although a little clean up with a sponge or rib after trimming easily takes care of that problem. The big catch is that the chuck must fit completely inside your pot. For some potters, making a variety of chucks may be necessary. But once you get used to the process, you won’t want to turn back.

The advantages are many. You can trim pots that are not level, whether wavy-rimmed or leaning to the side. The chuck connects to the inside of the pot, which is almost always centered. You are also taking the pressure off the rim of the pot when you trim, which helps prevent cracking and damage to the edge. It is great for trimming lidded pots, because you do not have to disrupt the flange. And it makes trimming tall, narrow forms much easier. Finally, it puts an end to mashing coils of wet clay up against the rim of your pots, which often distorts the form and destroys the surface.

Making the Chuck

I recommend throwing your chuck as a simple form, similar to a spout. It should have a wide, low base for stability, and a narrow neck that is flared at the rim to make attaching wet clay easier (see figure 1). If necessary, trim the chuck when it is leather hard to make the base of the cylinder as narrow as possible (providing more versatility for tall, narrow forms), and trim the edge of the base to make sure that there are no burrs or brittle edges. Dry the chuck slowly, as these forms tend to lean to the side as they dry. After bisque-firing the chuck, store it in a bucket of water, because it has to be completely saturated when you use it.

 

1 Center and stick the saturated, bisque-fired chuck to the wheel head with clay, then and add another coil of clay at the top.

2 Center the coil with water or let it stiffen to leather hard and trim it.

Using the Chuck

Stick the chuck down to a bat as you would any other pot and then add a generous coil of clay to the rim (1). You can center this coil with water or let it stiffen to leather-hard and trim it (2). I do a bit of both. Then air dry or blowtorch the coil until it is leather hard. It is helpful to match the shape of the coil to the inside shape of the pot you are trimming and make sure that the widest part of the coil is also the highest. If the inside edge of the coil is the highest point, your pot will not sit correctly on the chuck. The shape of the coil I add varies from one pottery form to another, and sometimes I trim the coil a little between pots to improve the fit for a given piece. Because of this, I always trim pots with the narrowest opening last. You may need to add a fresh coil or re-soak the chuck if you are trimming for several hours or working in a drafty studio.

Center your pot on the chuck—making sure it is both centered and level might take some practice—and give it a little downward pressure with a subtle twisting motion. Applying pressure will help your pot adhere to the chuck. Then trim your pot as you normally would. Although the pot is stuck to the chuck, it is still important to apply downward pressure as you trim.

3 Place the cup onto the chuck and begin trimming by defining the outside diameter of the foot ring.

4 Trim away about 90% of the excess clay between the foot ring and the waist or belly of the pot before trimming the inside of the foot ring.

I always begin by defining the outside diameter of the foot ring (3). I do not trim inside the foot ring until later, which allows me to push down on the bottom of the pot while I trim and it helps to keep the pot stuck to the chuck. I trim away all of the excess clay between the foot ring and the waist or belly of the pot, focusing more on wall thickness than on the surface of the trimmed area (4). I stop trimming outside the foot ring when I am about 90% done—before doing any detail work. Then I trim inside the foot ring, because these trimmings can easily damage the detail work outside the foot as the scraps fall. Once the foot is how I want it, I finish it by trimming the outside area (5). I like the final trim marks to have a rhythm and gesture that compliment my throwing. Finally, I use a smaller trimming tool around the waist of the pot and the edge of the foot and clear away any trimming scraps with compressed air. I make a single pass over all the edges with a cosmetic sponge so that they retain their crispness but are not sharp to the touch (6).

5 After trimming the inside of the foot ring, finish trimming the outside area until the rhythm and gesture compliments the throwing.

6 Use a smaller trimming tool to clear away any trimming scraps and then use a cosmetic sponge to smooth the foot.

7 Use a sponge on a stick to clean up any scars left from the chuck.

8 The finished cup after trimming. Photos: Eliot Dudik.

When I am done trimming, a little twist helps the piece pop loose from the chuck. I use a sponge on a stick to clean up the scar on the inside of the pot left by the chuck (7). Of course, chucks are only needed for certain forms. Experiment. Solutions for pottery making are rarely one-size-fits-all.

the author Mike Jabbur is currently an assistant professor of ceramics at The College of William and Mary in Williamsburg, Virginia. To learn more, visit www.mikejabbur.com.


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Subscriber Extras: Video and Archive Article

Click here to read the archive article, “Studio Visit: Mike Jabbur, Santa Fe, New Mexico,” by Mike Jabbur, which originally appeared in the June/July/August 2010 issue.

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