Never send a boy to do a mans work, neither use toy tools to cut hard wood. A little 400w Jigsaw intended for home use is no good for cutting 1" thick oak planks with a bevel.
Since I knew that many cuts would be bevelled, I set the blade to 72 degrees, put on the jigsaw fence and tried to cut a straight line parallel to the side of the board.
Not a hope. The blade cut the bevel to within 1 degree, but would not follow a straight line for love nor money.
Primarily I think the problem was trying to get the blade and the base parallel. The blade would always pull the cut to the left. I tried setting the fence on the far side of the plank to prevent this and I ended up overheating the blade and breaking the locking mechanism.
So a cheap jigsaw can cut pine, or thin ply, but forget trying to cut hardwood.
Time to go shopping.