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Removing background and undercutting for inlaying gold

When I first started engraving, I would start by cutting the main outlines, and then go back in and recut with the same V graver to make deeper outlines adjacent to the areas that needed to have the background removed   Next, several sized flats were used to recess the surface between the V recuts. 

Later, I started using a dental rotary tool (made by Buffalo Dental) for cutting away background and undercutting. The metal can be removed faster this way, but it takes practice to maintain control to prevent the tool from getting away from you and taking out a border or leaf.  With experience, a person can become steady with the rotary tool, which speeds up the process considerably.  With good control of the rotary tool, it isn't necessary to do recutting with a V before beginning to remove background, or the material for a gold inlay pocket.  This saves time. 

To steady the hand using the rotary tool, hold the handpiece like a pencil.  Place the middle finger of the same hand against the tool toward the point to brace it.  Also, have this finger rest on the work to provide support.  Use the thumb or index finger of the other hand to rest against the handpiece near the point and against the work.  This provides two fingers to brace the tool (one in each direction) and, finally,  the point of the tool in the work makes the third leg of a tripod. 

Make friends with a local dentist and ask him to save some of the carbide friction grip burrs for you.  Dentists go through them quickly, throwing them out long before they are too dull for what engravers require. 

Use the preshaped ones for the larger open areas in the background, or for pocket cutting.  For getting into corners and undercutting, I grind them down to a point on a diamond lap.  With the burr in the rotary tool, hold it against a turning diamond lap and step on the rotary foot pedal. This will quickly grind the burr to a point.  Depending on what is needed, grind it to a narrow or thicker point.  Next, hold one finger on the burr so it can not spin and grind a couple of flats at random on the point.  Try cutting with it and if it doesn't cut well, place another random flat on the point.  Keep doing this until you hit a grind that cuts well.  It may take three or four tries, but since the flats are random, it only takes a few seconds to place another flat on.  Most of the time, the shape that seems to cut best is similar to a tiny flat-head screwdriver.  Make them different sizes as needed,: a wider one for cleaning out corners and squaring up edges, and so forth., and a narrower one to deepen a line for wire inlay and for undercutting. 

 Undercutting with the rotary is quicker  than using a graver for undercutting small wire inlays, especially if there are a lot of spirals, twists and turns. 

For undercutting straight borders, a graver may be quicker than a rotary tool. If you want to make an undercut graver and use this method, make narrow V graver.  A good shape for this is a knife edge profile with a 45 degree face.  Place a small heel on the tip.  I prefer a 17 degree heel.   Put it the single heel straight on, so that the resulting shape is basically a very small flat tip graver.  Make this type of pointed from high speed steel or M-42 cobalt.  Carbide or Carbalt is too brittle for a point this narrow and it would break.

For larger sheet gold inlays, undercut the edges of the pocket, and raise teeth in the center to grip the underside of the inlay and prevent the gold from bowing up in the middle.

I don't know if the Buffalo dental rotary tools are still made.  The one I have is probably 25 years old, and still works well.  I had to make a new spindle for it, but the bearings are still rolling smoothly. 

I now have an NSK Presto rotary tool ($340, available from Brasseler USA, phone 800-841-4522  ex. 4675) and switch back and forth between the two.  An unexpected thing happened when I made the new push-in spindle for the Buffalo.  I accidentally made the spindle hole slightly off center, but discovered this was a benefit with the homemade sharpened burrs.  Since the shank of the burr is slightly off center, I can remove a freshly ground burr, turn it 30 degrees, and push it back it and the point will have a wobble.  The wobble is a benefit because it throws one of the cutting edges out, and most of the time the homemade ground point will cut better.  If it doesn't,  remove the burr, turn it another 20 or 30 degrees and try again.  When it does cut well, the foot pedal speed will affect how wide the point will cut.  At a slow speed it will cut a fine line, and at a higher speed, the point will cut wider (because it is wobbling more), and be more aggressive.  With the NSK rotary, this won't work because they turn truer than this off-center spindle in the Buffalo. 


 

The tiger whiskers in the tiger are .006" 24k wire.  The larger chunk of gold is sheet.  The edges of the pocket were undercut with a wider, homemade-sharpened burr.  I placed hooks in the center of the large inlay to prevent it from bowing up in the middle.  Hooks can be made with a V or a flat graver without a heel.  The absence of a heel allows the graver to dig in quickly, raising a strong hook.  Be careful not to allow the hooks to be higher than the original surface, since there is a possibility that when the gold is sanded down flush to the surface, the hooks could show through as white spots in the gold. 


The leaves in the above inlays are .010" dia. wire and the vines are .006" dia. wire.


This piece was also undercut with the rotary. 

 

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