Ultimate Guide to Slab Flattening Jigs, Router Sleds (Buy or Build)
VEVOR Router Sled, 64 inches /162.6 cm Width, Slab Guide Jig for Woodworking with Locking Function, Portable and Easy to Adjust, Trimming Planing Machine for Wood Flattening, Home DIY - Walmart.com
DIY Router Sled Tutorial: For The Big Ol' Slabs - Lazy Guy DIY