flattening live edge slabs

Flattening a live edge slab is a relatively simple process if you have access to the right equipment. We use Wood-Mizer’s SlabMizer slab flattener, which is basically a large router attached to a moving head that glides across the slab and removes fractions of an inch with each pass. After you surface across the entire slab, you simply lower the head of the router to do the next pass. Once the entire slab is flat, you’re good to do the other side.

In the video below, we show what a few passes looks like on our Wood-Mizer SlabMizer slab flattener.

Why Flattening Your Slabs Is A Must

Flattening should always be done when working with live edge slabs. Since slabs typically take 2-3 years to properly dry, they can warp with time as they dry at different rates on different parts of the wood.

Slabs are commonly used for dining tables and other furniture and nobody wants a table that isn’t level. Flattening ensures the entire slab is the same width throughout and that it will sit flat on a base. If a large slab is twisted even as little as 1 inch, it will be tough to mount to a base.

Another reason flattening is essential is because slabs are typically rough cut using a chainsaw mill. Flattening the slab will remove the rough chainsaw marks and reveal the grain pattern of your slab. Live edge slabs are expensive, but without flattening to reveal their beauty, they just look like a dirty piece of wood. Don’t take my word for it, check out the images below of a walnut slab before, during, and after flattening.

How Much Do You Lose On Thickness From Flattening?

This is one of the trickiest questions we get from customers, as it varies with each and every slab based on how warped the slab is. If the slab is already relatively flat, a few passes on our flattener usually does the trick. This results in 1/4″ or less being removed from the thickness. With large slabs, 1/4″ being removed is usually about the minimum you’ll see. On large slabs that are more warped, we’ve had to remove more than 1″ at times to get the slabs flat.

Generally speaking, when cutting your slabs, you’ll want to go at least half inch to one inch thicker than what you want your finished slab to be. Then you won’t remove from the thickness you need when you flatten your piece.

Getting The Maximum Thickness From Your Slabs

It’s worth noting that when you flatten a live edge slab, the opposite corners are typically the high and low spots. For example, the back right and front left could be the high spots on the slab, and the back left and front right could be the low spots. The larger of the slab you’re working with, the more you’ll have to remove to get to the low spots. For slabs with a lot of warping, it often makes sense to cut them to size before flattening, or down the middle. The less surface area you have to flatten means the thicker your slab will be once it’s completely flat.

Another trick you can do is use shims on the low spots of a slab (which are typically opposite corners) to remove less on the first side you flatten. Do not use shims on the second side, or your slab won’t be flat. However, using them on the first side puts your slab as level as possible, resulting in less waste.

What If I Don’t Have a Flattener?

If you don’t have a slab flattener, your best bet is to ask your slab supplier. Most businesses that sell live edge slabs will have a flattener in their woodshop. We offer flattening services for $80/hr. Although this results typically in $80-$160 of additional spend on each large slab, it saves our customers time and money from the other option.

The other option is building a flattener by making a sled and using a router. This option isn’t usually ideal, as you’ll have hours of labor wrapped up in this alone. You’ll also spend a few hundred dollars to build the sled, especially if you don’t already own the router. If this is a route you’d like to consider, feel free to do a Google search to get more information. This isn’t a method I’ve ever used, so I cannot speak for it’s effectiveness outside of what I’ve seen online.

Questions About Flattening?

If you have any questions about flattening, I’m happy to help. Simply drop your questions in the comment box at the bottom of the page. If you would like to inquire about buying live edge slabs that are already flattened, simply contact us online.

2 Comments

  1. Jackson on January 6, 2021 at 7:07 am

    How long would it take to flatten a slab that’s 16″ x 60″?

    • Nolan Barger on January 6, 2021 at 7:16 am

      Less than an hour. Typically to flatten both sides it would take about 30-40 minutes, but that would vary based on how flat the slab is to begin with.

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