I had a problem with my last carving. It was a 1hr 45 min carve, in the last two minutes of the carve I smelled something funny and the bit was not spinning as fast and clean sounding as before. I checked my flex shaft, seems fine then I went to run another small carve just to see if it was me and the bit was turning slow and was "twitchy" (sorry for this technical words; I feel like I am the transmission mechanic Lol). I stopped the project performed the cut motor test with no bit. Same results. Took the flex shaft out and ran just the motor and same "gritty" noise and I seen a spark shoot out of the dust port (no bag was on). Any ideas before I start the nasty. I would hate to get elbow deep in this and find out it was a common problem and you just have to turn a screw or something. Machine has 50 hrs 47 min on motor time and 76 hrs total machine time. If this makes a difference this is the third "long" over 1hr. carve for me I have done. All my other carves/signs are under 50minutes.