Yesterday I put a new factory blade on my Poulon Wild Thing 18" chainsaw. The original blade had been abused when I cut up a few railroad ties so I put on the spare thaty came with the saw. I cut up a dead 6" diameter dogwood into a dozen logs and cut up a couple seasoned oak logs that were maybe 14" in diameter. In total maybe 6 cuts on the oak logs and 12 on the dogwood. Today I went to cut some more 14" oak logs and the blade acted as if it was dull. I got through them but it felt like the blade was struggling. Is this a matter of me just cutting some big, hard logs or did I already wear out the blade? How long should a blade last?