Getting ready to cut these oak stair treads to fit and will need to scribe them against the inside skirt board. Looking at these treads, I don't think my little Craftsman jig saw is going to do the trick and I see this as an opportunity to aquire a new tool. Whats best for the job?
If the scribes aren't straight use your jigsaw to get the cuts within 1/16th of the pencil mark and then use a belt sander to finish them out. If your craftsman jigsaw can't hack it I'd recomend a Bosch. Make sure your jigsaw blade cuts on the up stroke or it will "push" the oak away from the saw and make it "jumpy".