The Bowl

Hi All,

The Bowl is our first shaping exercise.

Theory, Russell:

There are not many things you can do to a metal sheet to transform it into a complex shape: you can cut it, you can bend it, you can shrink it and you can stretch it. All of these processes change the overall area of the material you start with. Bending won't change the area much at all (practically speaking you can assume it doesn't add area for the work we are doing), but shrinking and stretching can change the area substantially.

Recalling from last week; if you add area to a sheet of material it has to go somewhere, and if you add the area in the middle of a plane the material surrounding it resists movement in that direction ... only leaving options for the increased area to go up or down. It's easiest to remove area from the edges of your sheet of metal; in this case less area means the material gets thicker. Working separately or together shrinking and stretching create shape (check out the post on Shape vs Form and Arrangement for more detail on this).

The Bowl is made in 3 steps: we will go over the below in class on Wednesday, but the steps are recorded here as a reminder and as an aid to comprehension.

Top tip? Do the least amount of shaping to achieve the result you need. In other words, really think about it before you start going at it with a mallet or hammer. 

Step 1, Laser Cutting, Martin:

Illustrator and Autocad Files: Bowl Template and Female Radius Gauge

Laser cut the Bowl template consisting of a series of concentric rings ... you'll use these to trace around so you have a guide you can cut around for the 230mm disk and use the smaller ones to create guides for your hammering. It'll look like this:

Then ...

Create a female "radius gauge" to help guide and evaluate your progress. A female radius gauge is a concave curve in 2 dimensions that you can rest on your shape as it develops to test how far you have come and how much extra area you have to add. You have 3 curves to choose from; which one you use is up to you.

Once you've cut the disk from the aluminium make sure you file around the edges to "deburr" it (deburring is the act of removing any sharp edges) so you don't cut yourself.

Step 2, Shrinking and Stretching, Daniel:

We won't need to bend the material to make the Bowl, but so you have a complete understanding of the processes available to you the two diagrams below describe the mechanics of a bend.

If you choose a smaller radius to create a deeper bowl you will need to shrink the aluminium around the perimeter of your disk. Use the shrinking "stumps" (which, in our case, are depressions cut into slabs of plywood) and the mallet to create "tucks" in the aluminium sheet which you then hammer down into themselves causing the material to shrink (subtracting area) and thicken. Be careful not to hit yourself in the hand or jamb your hand between the aluminium and the stump below. See below:




Stretching adds area by making the aluminium thinner. You can do this by squeezing the aluminium between two hard objects (a hammer and dolly for example ... or the English wheel that you'll use in the next step) or unsupported over a depression (the depression in your stump for example) or with some support offered by a sand bag. The sand bag option is the best balance between speed and control. See the demo below:  




3. Planishing, Gabe:

While you can use a hammer and dolly to planish (smooth out or flatten) the lumpy shape you've created in steps 2 and 3 above its faster to use the English wheel. As I mentioned last week the English wheel works like a linear hammer ... squeezing the aluminium in lines rather than points. Watch out for pinching your fingers! See below for a demo:


Keep checking the shape with the radius gauge as it develops; your aim is to get the radius gauge to fit as best as possible to your finished bowl.

Regards

Russell