Wednesday, 10 April 2013

It's a learning thing: clay gun hollow dies

Some time ago, I bought a clay gun from Top Pots. It's a small, hand held thing, but it's good for small jobs. It came with a set of dies, but none of them were hollow dies. My metal working is not up to scratch, so I had a go with a material I know. Clay.

All of this is very seat of the pants and trying to learn a little each time. This is just my first attempt. Mistakes were made. Successes were had.

My main concern was whether the dies would stand up to the pressure of the plunger. I used Valentine Clays B17C-grogged stoneware because it's what I happened to be using for a different project at the time. I rolled out slabs and marked circles with the end of the clay gun barrel. I cut slightly larger than the mark to account for the shrinkage of the clay.

The inner shape is set back a bit, not flush with the outer ring of the die. The clay has to go around the supports inside and re-join on the other side, so this, I hope, will give it a better chance of doing that.
 I'd just reclaimed some terra cotta that was stored outside in a bin for a few years. Not the nicest of clays, still sporting a few small bits of leylandii. Some of the failures might have been down to that.

 I started to push the handle, and waited for the loud crack. Or the quiet crack. No crack. Just clay coming out in a tube.
 Several tubes, in fact. Not long tubes because this is a clay gun, not a giant motor-driven extruder. It only holds a small amount of clay.
 And lookie there. Intact.
The successful die poses here with its progeny.
 So I tried the square one. Alas, the fit was not so good. It was hard to screw the end cap back onto the barrel and have it stay attached during extrusion. It took some force to wedge the die down into the cap, and the cap blocked the corners a bit. I found that it had shifted a little (in firing no doubt, I couldn't have made it wrong, right?) so that one of the four sides was thinner than the others. Live and learn.
 But it wasn't a total loss. The die was hard to get out again, but it did come out with a little gentle leverage from the front.

 Once removed, the square could be trued up again with minimal effort. The die seems completely unharmed, and taught me some of the things to avoid when I try again.

There is one more die I made, but I'm going to try it another day. Possibly with nicer clay.