Question about using a router sled for big slabs

Last month I had to flatten a huge walnut slab for a table top, and my usual planer was way too small. I remembered seeing a router sled setup online, so I built one with some scrap plywood and aluminum rails. It took me about two hours to put together, but it saved the whole job. The key was making sure the rails were dead flat across the whole span, about 8 feet. I used a 2 inch flattening bit and went slow, and the surface came out glass smooth. It was a bit dusty, but the result was worth it. Has anyone else tried this method on slabs over 6 feet long? What bit speed did you find worked best?

4 comments

4 Comments

nathankim3mo ago

Whoa hold on, I gotta jump in here. I actually read somewhere that a lot of the chatter about router sleds is that the bit speed thing is way overthought. For a big slab like that, I've heard guys say you want to keep it around 10,000 to 12,000 RPM, not maxed out. Going too fast can actually burn the walnut and make the bit chatter on a long pass. I tried it on a 7 foot maple slab once and slowing it down really helped with the finish. Also, making sure your rails are dead flat like you said is the whole game, I saw a guy on a forum say he spent more time leveling his rails than he did routing and it made all the difference.

mason_reed475mo ago

What router bit did you use?

oliviatorres5mo ago

Oh man, I used a 1/4 inch round over bit for that edge. It gave me a smooth finish without taking off too much material. Worked perfectly for my table project.

sammartinez5mo ago

A 1/4 inch round over bit on a big slab edge? That's wild. I would have been scared to death of tear-out on walnut. I only use those tiny bits for picture frames and small trim. For an 8 foot slab I went straight for a 3/4 inch bearing-guided bit. Can't believe it worked for you.