Cracked planchet coins are a well known error type. They typically are found on nickel and copper coins, but also on silver coins on occasion, and very rarely on gold coins. We recently acquired an extremely rare and dramatic 1927 Saint Gaudens $20 gold piece, with a large crack extending across the coin from the 8 o'clock position to the center of the coin. The crack is separated about 1/4 inch into the coin (you can even see a little light through the coin if held up to a light source), and then simply extends inwards to the very center of the coin, with a "crack" visible on both sides of the coin to the center of Ms.Liberty.
Although long cracks are actually fairly common on coin series such as Lincoln cents or similar low value coins, it is all but unheard of on U.S. gold coins to have a crack this large. This is because of the high quality standards applied in the manufacture of gold coins. Even the most minute errors resulted in the coin's being rejected and melted down before they were allowed to leave the Mint. Gold coins were typically examined individually by hand, and were weighed individually. This resulted in virtually no errors coming out for gold coins, and this is even more the case with large sized gold coins, such as this 1927 Saint Gaudens double-eagle.
Even today, gold and silver coins are created with extreme care. Anything which effects the metal content or integrity is of utmost importance to the Mint. Gold and silver eagles, for example, never come with cracked planchets (and only very rarely with errors effecting their weight or metal.) As was true in the past is also true today—when the metal content is important, it is vital that the Mint do a near perfect job in manufacturing their precious metal coinage.
When looking back over the last 200 odd years of U.S. Mint coin production, there are remarkably few gold errors. Most of what exists are small strike throughs, slag inclusions or minor laminations. Major errors on gold coins are rare, and the number of cracked planchet coins is minute, with probably no more than a handful known for all gold coin series’. The 1927 Saint Gaudens is the largest planchet crack we have seen so far on any U.S. gold coin. To view images of the coin, here is a link: https://sullivannumismatics.com/coin/ngc-20-1927-saint-gaudens-double-eagle-huge-cracked-planchet-ms64