Never been a fan of the glass method. In my opinion, it affects the area around the dent in a bad way if you are not careful. I have always had good luck with the balled up paper towel method and most success with the iron method.. I've just seen to many times where people used the glass method and pushed in the wood around the dented area giving them the illusion that the dent has been removed when really you just pushed the shaft in that area down and made it out of round. Take what you will out of this because I am certainly no expert.

Also try doing a search on here for dents or dings. It has been covered in much details in the past.