A dice edger are used to shave the edges of the dice. This can be done with the intention to produce dice without razor-sharp edges (which would be a legitimate use for the dice edger) or to produce crooked dice with their edges shaved in a way that favors certain rolls, such as trip dice or whip dice.
A legitimate cube with shaved edges would have to have all 12 edges shaved at a 45º angle, the same amount. But crooked dice have some of the edges shaved at different angles, such as edges that are slanted at 30º against one side, which produces a 60º slant at the adjoining side. It amy seem that this small discrepancy cannot possibly lead to a bid advantage. This may be true if the dice are handled by regular player, but in the hands of a master manipulator (known as a dice mechanic) such dice can work very close to 100%, in certain circumstances.
Following is a photo of one of several dice edgers that were made by legendary crooked gambling equipment maker, Graham, from Chicago. Graham made a number of gaffs for the crooked gambling supply houses, from the 1930, until 1961. His equipment is greatly valued by collectors of gambling paraphernalia. All the equipment made by Graham bears a triangular Graham stamp, oftentimes barely visible.
Graham took great pride in his work and all of his gaffs are known to be perfectly built. Any Graham gaffs are highly collectable and very hard to come by. The dice edger pictured above was listed in my online shop, for about 2 years, for $1,600, which is a bargain for anyone who knows the true value of a Graham product. Amazingly, the gaff never sold and was eventually given to me as a gift.
Although a dice edger may look mechanically complex, the principle is a very simple one. At the top of a dice edger there is a slide with a 90º wedge, where one is able to insert a die and slide it back and forth. Below the slide there is a sharp blade, so when the die slides over the blade the edge of the die is shaved. The slide has several adjustments to set up the distance and angle relative to the blade.
Expertly made whip dice have edges shave so slightly, that it is impossible to see without a magnifying glass, if the edges are 45º or 30º/60º. And in the right hands, these dice can perform miracles.
Below are photos of two more dice edges, slightly different models, also made by Graham.