How to Flatten Boards With Just a Planer

Intro: How to Flatten Boards With Just a Planer

In woodworking, there are often many routes to reach the same destination.

This is one way to flatten* large boards using primarily an electric thickness planer (without the help of a jointer).

In order to flatten a warped, twisted, or cupped board, a common approach is to first use a jointer to create one perfectly flat face.

Then you run the board through a thickness planer with the flat face downward, and the planer makes the top face parallel to the bottom.

However, for boards or slabs that are too wide for a jointer (but still narrow enough to fit through a thickness planer), the approach demonstrated in this Instructable is one way to perform both steps needed to flatten boards using just a thickness planer, rather than using a jointer AND a planer.

*The term "flatten" as I'm using it here means: make two board faces perfectly parallel to one another by removing warps, twists or cupping.

STEP 1: Lumber and Overview

I picked up a bunch of old oak beams recently, and have been using the wood for various projects.

In order to use the material, I've been splitting the beams in half using my bandsaw.

However, the resulting boards all had twists and/or cupping, so they were flattened using the process shown in this Instructable. I'm not sure what these boards were used for previously, but they have a lot of character!

Here's the gist of this Instructable:

• To flatten a board with just a thickness planer, secure the board to a perfectly flat and rigid support structure (I show how I made mine in the following steps)
• Run it through your planer until the topside of the board is flat
• Remove the board from the support structure
• Run the board through the planer with the now-flat side down

This Instructable is my version of a pretty common board-flattening solution; if you do a bit of search-engine-ing, you'll find several great versions.

STEP 2: Support Sled

I built a support box using baltic birch plywood.

A simple box like this is guaranteed to stay perfectly flat and will not bow or warp, and creates a lightweight rigid sled to attach boards for planing. Alternately, a plain piece of plywood or MDF could be used as long as it stays perfectly flat and becomes sufficiently rigid when the board to be flattened is affixed to it.

Using a table saw, I cut two 60" lengths of 3/8" plywood that were just narrower than the opening of my planer (in my case, the width capacity is 12 1/2", so I made these pieces 12 1/4").

Two 2" wide strips were then cut from 3/4" plywood.

I used glue and pneumatic brads to fasten all these pieces together as shown.

This created a lightweight, but perfectly flat box.

To finish the box, I sprayed it with a few coats of spray lacquer, followed by a light sanding with 220 grit sandpaper. I then waxed the two larger faces with furniture wax (so either side could be used face down, but this is also helpful to remove masking tape that's used as well - which is shown later).

STEP 3: Level the Workpiece

The board to be flattened is placed on the box and made as level as possible using shims to fully support it. I use sample laminate pieces which you can typically get for free from the kitchen section at home centers and hardware stores.

This was all done on top of a few strips of painters masking tape.

Since this board was so beefy, I felt comfortable only supporting it at the ends. For a thinner board where it is likely to flex in the middle under the pressure from the planer's cutter head, you will want to shim and secure the entire length.

The goal is to affix the imperfect board firmly to the support structure so it cannot move or flex at all.

STEP 4: Hot Glue the Board Down

The board is now fastened securely in place using hot glue.

The glue holds the board firmly in place while planing, but is easy to remove once the top face has been planed.

STEP 5: Plane the Top Face

The top face of the board is now planed using the thickness planer.

You only want to remove a tiny fraction at a time. In my case this was especially important because the middle section of the board was not shimmed, so it was still possible that any extra pressure from the cutter head could have made the board bow downward, resulting in an unflat cupped board.

STEP 6: Remove Glue

The hot glue can be removed with the help of a chisel. You can pull the glue off of the taped surface, or just remove the tape and the glue should come with it.

STEP 7: Plane the Other Side

Now place the newly-flat boardface downward, and plane the remaining side.

My boards were all in pretty rough shape as you can see!

STEP 8: Done!

My boards were all brought to the same thickness and then were ready to be used for other projects.

Thanks again for reading!

Comments

[Chuck666]

This leveling platform is a good example of a tension torsion beam. A very good idea.

[onkelhugo]

I don't get why the box is better than just using say a 3/4in MDF or plywood board by itself?

[DennisT33]

A torsion box that is 2" thick is roughly as rigid as a 2" thick board but much lighter. The reason is that almost all of a board's rigidity derives from the surfaces and is increased by the distances between them.

[charlessenf-gm]

Well, I don't have the Engineering answer either. But the torsion box is (pound for pound) more rigid than a solid piece of the same material as a Steel Tube is more rigid than a Steel Rod.

[Wood junkie]

So did you glue the shims to the board being planed?

[Bsewell]

Thanks for this. I had the same idea and went searching for other experiences. This confirms that I don't need to buy any more tools just yet. The torsion box is a better idea than my approach, which was just to use a spare sheet of plywood. Now I just need to buy some more plywood.
Thanks

[TheNottingHammer]

Some great ideas to take away and all well and good if you have a garage full of electric kit. However, you can't beat the feeling of satisfaction you get from preparing a cupped or warped piece of timber with hand planes.

[arcadezyra]

It can be depending on how many boards u need to flatten. Ive had times where i couldnt get everything done that day and next day back to square 1 practically :(

[seamster]

That is true!

Some people derive a lot of satisfaction working with traditional tools :)

[Kinnishian]

Ooh! I have a tip: Try putting isopropyl alchohol on the hot glue when you want to debond it. It's not guarenteed to work on wood (grains and mechanical bonding) but in the past I've found it works like seeming literal magic to delaminate hot glue joints. If it does prove effective on wood you can go more ham on hot glue knowing you can easily remove it with isopropyl alchohol :)

[arcadezyra]

Ya its crazy how effective it is. Ill wet a cotton swab with 90% isopropyl and as soon as it makes contact it its like the hot glue just gives up :D.

[Nilton]

I recently aquired a tghickness planer and,was having dificulty in getting absolutly flat stock. Being new with this tool, I hadn´t realized that the the stock was very slightly thicker in the middle of the lenght of the boards, making either side "rock" to the left or right and never really getting them really flat width-wise. This solution above solves the problem. I´ll just adapt the way the stock will be fixed to pass through the planer as they´re smaller pieces, but the idea is just that!
Very useful and helpful!
Thanks very much and best regards!
Nilton Tavone

[Shel Michaels]

Great! I never before knew how to do this. You explained it perfectly and the method is dirt simple, Thanks!!

[bcrocker1]

Ah! Brilliant! I've been trying for TWO YEARS to figure a way out of buying a planer AND jointer! Saving me some $$$ here. Thank you!

[OKaneDesign]

I have actually tried something similar in the past... this looks like a much easier and more precise method..... Great Idea

[uncletj]

great article thanks for this one

For all of you wanting to just put it on a flat board the longer you need it the more it will flex

We’ve all done this pick up a piece of plywood from the end and it bends like a wet noodle. And the narrower you make it the more it flexes. but put two rails in each side and you’ve just built something you could drive you car on and it won’t flex. Just my opinion.

[Tsu Dho Nimh]

So make her box-beam sled, without the top?

That would let you get thicker material through the planer

[G.1]

How does this technique achieve parallel surfaces? I assume that the gap to the box allows the oak to flex, but how does this help? I seem to be having a simple misunderstanding of the concept.

I need to do this soon, so nice timing!

[seamster]

Good question. The pieces of oak shown here were beefy enough that I was comfortable not shimming along the middle section of the board. If there's any chance the board would flex under the planer's cutter head, that would require full support of the board with shims in order to produce a flat top surface coming out of the planer.

The concept is to support the piece well enough in a fixed position that we can send it through the planer and incrementally remove the high spots from the imperfect top face of the board, to create a top face that is one perfectly flat surface. This step is typically done with a separate machine (a jointer), but for boards that are too wide for your jointer (or if you don't have one), the approach shown here can be used.

Then this new flat face can be placed downward on the planer bed and the planer will do it's job on the remaining face, making two boardfaces that are perfectly parallel.

[edsobo]

Is it completely necessary to shim the board so the whole surface is lifted off of the backing? It seems like if you left part of it touching the support and shimmed the high spots, it would be less likely to flex during planing.