Power Drills

Dentists have found that one of their best tools is a high-speed power drill that will quickly and cleanly remove unwanted tooth material. Such a drill is equally effective with fossils. Unwanted matrix disappears quickly before a burr, tiny grinding wheel, or brush mounted in the chuck of a dental drill.

A used dental drill can sometimes be purchased for a moderate sum, but never cheaply. Such a unit hanging above the workbench is a fine addition to fossil-cleaning tools.

For a smaller sum a small unit operating through a flexible shaft will give almost as much versatility and movement as the dental drill. These units usually consist of a motor the size of a soup-can that is hung above the workbench. A flexible shaft several feet long hangs from the motor and ends in a chuck that will accept a wide range of commercial and homemade abrasive tools. These units can be purchased new for about $35 and are handy accessories in jewelry making and fine metal work. The flexible-shaft hobby machines allow absolute control of speed through a foot-operated rheostat. So do the dental drills.

Tiny hardened steel burrs mounted in the chuck will tear away excess matrix and, if handled carefully, will not materially damage fossil parts they might brush against. Tiny silicon carbide grinding wheels or cut-off discs can be used to remove large quantities of excess matrix to improve the appearance of a specimen or to reduce the thickness of matrix overlying the fossil preparatory to use of some other cleaning method.

With a flexible-shaft tool, small brass and steel brushes are particularly useful. These brushes, about one inch in diameter and less than a one-quarter inch thick, will scarcely touch hard fossils, especially pyritized or silicified ones, but will rapidly remove hard shales or limestones, as has been mentioned in the section on cleaning with hand tools.

The brass brush should not be used for soft fossils after it wears to less than half its original width. The bristles are stiffer then and are more likely to cut into the fossil than to bend while going over it.

Bristle and nylon brushes are also available for the flexible shafts. They do what a hand-operated toothbrush can do but in a tenth of the time.

Burrs come attached to a small-diameter shaft. The wheels and brushes can be purchased attached to a shaft or loose for mounting on a threaded shaft. The loose tools are usually less expensive. When using them, it is rarely advisable or necessary to run the flexible-shaft machine at full speed. Low speed allows better cutting, as the bristles dig into the matrix instead of sliding over it, and, of course, control is easier. Too much pressure strains the flexible cable, which is expensive to replace. Too much pressure also bends the small shafts of the tools.

Most fossils can be completely prepared using grinding wheels or burrs to remove excess matrix and brushes to remove the last vestiges of matrix. Good control can be had with power equipment, particularly with power brushes, and the greatly increased speed reduces mistakes that arise from fatigue and impatience with the slow progress with hand tools.

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