What mechanical flaw characterized the early, largely alphabetical keyboard designs by Sholes?

Type bars frequently clashed and jammed.

The earliest prototypes of Sholes's writing machine utilized a keyboard layout that was mostly alphabetical across two rows. This seemingly logical arrangement presented a severe mechanical limitation. Every key press activated a type bar, a metal arm holding the character mold, which swung upward to strike an inked ribbon against the paper. When a typist rapidly struck adjacent keys, especially those representing letters commonly appearing together in English words, the type bars would collide before they could reset their position. This collision effectively jammed the machine, rendering it impractical for sustained, rapid typing or correspondence, thereby necessitating a fundamental redesign of the key arrangement.