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Trimmed, Trimming

Trimmed, Trimming.  Any method of giving final shape to a medallic item. Unless an item is struck within a collar (which gives it its final shape) it must be trimmed, usually after the piece is struck, particularly so for any shape other than circular, an irregular or unusual shape. Thus the die used to make the piece will dictate whether trimming is needed or not – coins and medals struck in collar dies do not need trimming – those struck by open face dies always require trimming. Trimming removes the burrs, the flash, or unwanted excess metal of a struck piece. There are three ways of trimming any medallic piece:  on a lathe, by hand, or by trimming tool.

Lathe trimming.  Large round medals can be trimmed on a lathe, by turning off

the excess metal. This can be done for any medal 2-inch diameter or larger. A form mold is made of one side of the medal (either side may be used, however, the one with the grates relief, usually the obverse, is preferable). The form mold is a jig in effect to hold in place a piece while some work is done on it. Form molds are also called lead form, or lead chuck.

A sample medal is taken, using this as a pattern, a fence is built around it and a form containing a 1-inch shaft is centered over the medal and molten lead is poured into this form. The medal must be discarded because the lead contaminates the surface (however some of these have reached collectors' hands). After the form mold solidifies it is further shaped to fit into the chuck at the head of the lathe.

The form mold is mounted in the lathe and it is itself trimmed to about a hundredth of an inch less than the required diameter of the trimmed medal. Then each medal is placed in position – by finger positioning – up snug against this form mold; the tailstock (with a wooden plug) is brought up against the opposite side of the medal and

its pressure holds the untrimmed medal in place.

The lathe is turned on, a cutting tool is brought into position removing the flash metal. The form mold in effect acts as a template for the required diameter. The turning is done to the edge of the form mold (if the operator cuts into the lead he knows he has gone too far!). In most instances the operator uses a caliper to check the required diameter.

Should an exact diameter be required – say, to fit a porthole in an album – a trimming gauge is prepared in a small piece of flat metal. It is a slot, or a hole, machined to the exact diameter. The operator tests each medal to make sure it fits the aperture in the trimming gauge.

This method of trimming may leave some tool marks on the edge of trimmed medals. These will be very light concentric lines on the edge parallel with the obverse and reverse planes, called annular rings. (These are in contrast to lines across the thickness of a medal from medals struck with segmented collars, called collar gaps.)

Lathe trimming must use this form of jig mounting for position in each medal in trimming, and, of course, is only suitable for large round medals. The jig, can be used over and over again; but a new jig is required for each new medal design.

Hand trimming.  Trimming by hand is usually done with a jigsaw and is not suitable for long production runs. The work is performed at a bench with a hand held jigsaw or a motor driven jigsaw can be used. The operator will trim away by cutting off the excess material. Usually this method is used for short runs of highly silhouetted designs.

While this requires intensive labor, the alternative is to prepare expensive tooling,

thus short runs are necessarily done by hand. The person who does this usually has some experience in chasing; thus while the saw blade does leave some burrs the operator removes the burrs by hand. Since it is all handwork, there may be minute differences in the precise silhouette or shape of each piece.

Trimming by trimming tool.  This is explained by the illustrations and the next entry. A trimming tool allows for trimming to be mechanized and to crate uniformly shaped pieces. The trimming tool is created to the requirements of a particular design (but may be use don more than one design if its internal clearance is great enough – so it does not mash the relief!).

Trimming by this method also requires a press; it can be similar (or the same) as the blanking press. A drop press is satisfactory for small medals (less than 2-inch), otherwise a press with larger capacity is necessary (200 or 400-ton, for example).

Trimming characteristics.  Every trimming method will produce its own type of burrs. Deburring is necessary after every trimming operation. Burrs usually form at the rim/edge juncture and how they are smoothed out and removed will give some shape to the edge.

The shape of a trimming burr is different from a burr formed by coining. Trimming never forms a wire edge, but is usually more irregular, uneven and rougher.

However, some evidence in the trimming – usually file marks – can be observed in finished pieces. We have observed an ocatagon-shaped medal of 1720 with evidence of hand filed edges. (J&J 14:725)

As a final point, trimming cannot be done on proof surface pieces, only on medals that can be deburred and later given a finish and patina. See also topping machine

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators


Roger W. Burdette, Editor

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