What is a rolling mill?
A rolling mill is a tool used to apply pressure to metal to flatten and lengthen it. Each machine has differences, but these are the basics components: a tightening screw, rollers, and a crank. The rollers on jewelry rolling mills may be half flat and half grooved. The flat side is for sheet, the grooved is for wire.
When should a rolling mill be used?
In jewelry, a rolling mill is often used to press an ingot (a bar or block of metal) into a more easily workable sheet or wire. It is also useful in flattening and stretching metal. A third use is as a part of the fusing process between two thin pieces of metal. Other uses for it include roll printing or patterning, and metal distortion in general.
Tips for keeping a rolling mill in good working order.
As with most tools and machines used for metal working, it’s important to keep oils from hands off/ out of the machine as much as possible. Applying a thin layer of oil to the rollers when the machine is not in use is a good idea as this can help protect them from dust and other contaminants. When not in use, it’s also imperative to release the pressure on the rollers. These tips can help your rolling mill have a longer life and your projects to come out better.
How does one use a rolling mill?
Before using the rolling mill, anneal the metal you’ll be working with. Annealing is basically the heating and then cooling (the speed of cooling depends on the metal you’re working with; some need to sit until cool, some may be quenched with water or other solutions) of a piece of metal to improve its toughness and to eliminate its potential brittleness. Before working with your metal, make sure that it is clean of contaminants. This can be done by pickling your metal using an acidic solution (which is often heated), neutralizing the acid by dipping the metal in a base solution, and then rinsing it in clean water and drying it. Try to keep the oils from your hands off your metal as much as possible as this can cause tiny pits to form.
Place the end of your metal piece into the machine (as close to the middle of the rollers as possible so that the pressure will be even) and tighten the mill down until the rollers are snug (but not tight) on the piece. It should be fairly easy to move the crank. If it is very difficult to roll your piece through, the rollers need to be loosened or you will risk damage to both them and your piece.
Roll the metal making sure to take turns rolling right side up, and then upside down. There is some controversy about changing the direction of the roll (end for end). Some say that if you roll in both directions (forward and backward) that it can produce a lower quality end product because of the molecular alignment of metals may be distorted. However, others say that if you roll the metal both forward (all the way through) and then backward (also all the way through) that you can produce a more evenly rolled sheet. Regardless, one should take care to anneal the metal every few passes through the machine (especially when rolling a millimeter or more down in thickness). This helps the metal not to become work hardened.
If the edges or surface of your metal are cracking or flaking, or if you’re rolling a sheet and it bends, you should anneal the metal and try again. If your metal is warped or wavy after rolling, the rollers may be too tight. If the metal piece pulls to one side, your rollers may not be tightened evenly on each end. If you’re rolling wire, keeping the end that has just been rolled pulled tight or the wire may come out distorted or bent.
Special projects one can do with a rolling mill.
Roll printing or patterning can be done with a single piece of metal and a thin piece of something like paper (cut into pieces), textured fabric, thread, feathers, lace, tape, plastic, leaves, and many more. Harder things used to produce patterns (like pieces of metal) are better used between two pieces of metal to protect the rollers. When using two pieces of metal around a patterning piece, it can produce a mirrored pattern effect which is good for earrings or other projects requiring matched pieces. If using a hard patterning object, make sure to use something harder than the metal you will be imprinted with it.
Keep in mind that whatever you are using to make a pattern will leave the reverse of its design on the metal. So, if you are trying to make letters, you’ll need to make sure that they are reversed (as in a mirror).
Before beginning to imprint your metal, make sure the pieces you will be patterning are very clean and have been annealed so that they will be soft enough to take the pattern you want them to have. Any particles trapped between the metal and the patterning object will show up in your finished project.
To gauge how tight the rollers should be, only roll a short way into your pattern to check the pressure. Each patterning project will require a different amount of pressure. Trying to imprint things that are too thick can damage the rollers and your piece. One should be able to roll the entire piece through the mill in one pass. If you stop partway through, it can damage the design by leaving a “smudge” where the metal stopped in the mill. Also, rolling the piece through the mill more than once can cause distortion of the design.
It is very important to clean the rollers after doing an imprint to make sure that no fibers remain.
There are many creative ways to use a rolling mill in jewelry. There are many books including chapters on their uses, but through experimentation, you can find your own way of making beautiful pieces.