I a high school student who is new to CNC routing/engraving and was making a plaque for someone at my school when this happened. This was a 1/4" 4 flute carbide chamfer tool in 1/4" polycarb on an EZRouter and the toolpath went from bottom to top and was only supposed to go 1/8" into the stock. It looks like the z height decreased as the toolpath continued and eventually broke through. My first thought was too high of a plunge rate that caused me to lost steps, but I don't think that is the culprit. Any suggestions on what this could be or ways to improve would be appreciated.