I built this prototype out of MDF. It’s configured to make 1/4” thick box joints in up to 3/4” thickness stock. A 1/4” dowel at the front placed exactly 1/4” away from the router bit serves as a relative spacer between cuts.
If you’re interested to see this machine as it develops, follow along and you’ll get the updates. I have plans to make it a lot more customizable in the future. Thanks for reading, and good luck with your box joints.