Cutting thick leather with complex, tight shapes is difficult with a hand knife. Check out this tool that greatly improves the ability and time it takes to do interior cut outs like on Helmet Shields and many other projects.
Amazon Associate Moto Saw Link:
https://amzn.to/4gYbWgR
Phone Holding Table Mount Light:
https://amzn.to/3WjjqTl
www.leonidasleatherworks.com