.I don't have any usage nor time for 20# bows.
Wrong. That's how you learn. Nothing is harder than making a perfectly tillered 20lb bow. Making 100lb bows is easy, subtle wood removal makes very little difference and you have lots of room for error. Plus it's much harder to tell if a 100lb bow isn't perfectly balanced on the release or twists subtly in the hand or has excessive hand shock due to uneven tiller. If you scrape the wrong area with a 20lb bow then it becomes a useless stick before you can blink.
Unless you're a week away from losing your hands and vision and can literally only make one more bow, you've always got time for a learning experience. If you wanna throw it away when it's done that's fine, but get it done. I know far too many bowyers who can make a 140lb self bow but fail miserably if they're asked to make a bow for a kid.