Nancy LT Hamilton

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Some Uses for Cup Burs

• Rounding prong tips
• Rounding ear wire ends
• Rounding the ends of earring posts
• Cleaning up granulation

Types of Cup Burs

    Busch’s Twin-Cut Burs are much more efficient and don’t clog, but they are aggressive so take care!

    The teeth with traditional burs tend to get clogged – especially the smaller gauges.  You can use a toothbrush or a small brass brush (on Amazon) to clean the fines (tiny pieces of metal) from the teeth.  Otto Frei sells a small scratch brush too.

    Always lubricate your burs.  Always!  It extends their life and, in the case of the traditional bur, helps to keep it from getting clogged.  I love PepeTools Blade Butter as a lubricant.  Not messy like the solid lubricant, nor does it leave an oily mess like liquid lubricants and oils.

Determining Which Bur to Use With Which Gauge – Opinions

• Eternal Tools say:  “The size of the cup bur you choose should be just a hair larger than the wire you plan to use it on. For example, if you use 21-gauge (…0.723mm in diameter) to make ear wires, …you would want to use a cup bur of 0.8mm, or 1.00mm.”
• Rio Grande Jewelry Supply recommends choosing a bur .4 mm larger or slightly larger than your wire.
• Others recommend one slightly larger than the gauge.
• I’m with the “slightly larger than your wire” group.

How to Know if You’re Using the Wrong Bur

• If you see overlapping grooves, and the shape looks somewhat conical, the cup bur is too small.
• If the cut is wobbly and not uniform, it’s too big.

Tips for Using the Cup Bur

• Before using the cup bur, file down the prong tip with a barrette file, gently shaping it.
• Use pumice wheels to clean up the ends of the prongs before rounding.  Pumice wheels have less of a tendency to damage stones.  Stuller carries them. (I use Medium and Fine grits).
• Create the dome with the cup bur before the final setting process.
• Don’t hold the ball bur at a 45° angle as you’ll cut into the top of the prong.
• It’s easy to scratch even a hard stone with a cup bur.  Complete the shaping before pushing the prongs into their final positions!
• If you are nervous about using a cup bur with a motorized tool, you can always mount them in a handle and turn them by hand.  Pre-mounted cup burs are available, but unless you use the same-sized wire gauge all the time, they are limiting.  It’s best to have a variety of bur sizes.  Don’t forget to look at my chart to see what you’ll need!

Using a Cup Bur for Doming Prongs

• After you cut your seat, fit your stone.  Next, push the prongs close to the stone with chain nose pliers or a bezel pusher.  Trim your prongs to almost the size you want. Leave the prongs a little longer than needed, as you’ll remove metal with the ball bur.  Twin-Cut ball burs are very aggressive so go slowly.   Hold the flex shaft, with the ball bur, straight above the prong and cut until you like the finished look.  Don’t cut too much, as your prongs will be too short!  Lubricate!  Check to see if further finishing is needed.  Finish pushing the finished prongs over the stone. Polish the prongs with a pumice wheel. Remove flashing with a small, flat graver.

The Chart

The link to this Google Sheet.  

Busch Twin-Cut Cup Burs

References