How to make a board flat and square


Starting out with a flat, square, and even board is essential in woodworking. If your board is not square to begin with, then it will not be square as an end result.

In this article, I will discuss ways to flatten a warped board, even out an uneven board, and square an unaligned board.

Directory

  1. Ways to flatten a board
  2. How to flatten wood using a Jointer
  3. How to flatten wood using a planer
  4. How to flatten wood using a Router
  5. How to flatten wood using a table saw
  6. How to check a board for flatness

Ways to flatten a board

There are many ways to flatten a board and in this section I will go over how to flatten a board using a jointer, planer, router, and table saw.

JointerPlanerRouterTable saw
Warp-nessCan support very warped woodSemi-warpedSemi-WarpedSlightly warped
Efficiency★★★★★★★☆☆★☆☆☆☆★★☆☆☆
Set-up time★★★★★★★★☆☆★☆☆☆☆★★☆☆☆
Finished Result★★★★★★★★☆☆★★☆☆☆★☆☆☆☆

How to flatten wood using a Jointer

The only tool that is specialized to flatten wood is a jointer. This tool can flatten very warped boards quickly and result in the a clean, smooth, finish. Jointers are fairly easy to use, but they are a specialty tool that cannot be used for other purposes.

To flatten wood using a jointer you will use the jointer much like a table saw. You will use a push stick to push the wood across the jointer while making sure that you do not apply too much pressure to the wood.

Pros and Cons of using a jointer to flatten wood

ProsCons
Specialized tool for flattening woodTool is not versatile
Very efficient and easy to useExpensive

The drawbacks of a jointer is that this tool is not versatile. A jointer is just good for flattening wood and is not a good thicknesser like a planer. If you have the funds and space, then I would recommend that you get a jointer.

How to flatten wood using a planer

A planer is a tool that is used to get an even thickness along the board. However, if there is a warp in the beginning product, then the finished product will have the same warp.

If you do not have a jointer, you can still use a planer to flatten a board.

If the wood is slightly bowed, then you can use a shims to even the wood before running it through the planer.

Method One: Using Shims

  1. Use a sheet of plywood as a base
    • Gather a sheet of plywood that is long enough to support the wood and thin enough to fit through the planar
  2. Lay the board on the plywood
  3. Measure the board height
    • With the board laying on the plywood, measure how heigh each section of the board is
  4. Add shims to the lower parts of the board
    • Now you will add shims to the bottom of the board where the low parts are. You want to add these shims throughout the board until its even with a consistent height.
  5. Use a method to secure the wood and shims to the plywood base
    • You will want to secure the wood to the board to ensure that it does not shift while being run through the planar.
    • You can either use nails, screws, wood glue, or hot glue
    • I prefer hot glue because it is easy to come off of wood and does not lead to defects like nails, screws, and wood glue.
  6. Run it through the planar
  7. Lay wood on a flat surface to check for flatness

If the wood is cupped, then it will be best to use side runners to flatten the board.

Method Two: Using side runners

  1. Create two thin, even pieces of wood
    • You will create two pieces of wood that are flat to run across the bottom of the planar.
    • These pieces need to be the length of the board and the thickness of the cupped wood
  2. Align it to the sides of your board
    • You will now attach the side runners to the board. You will want the top of the side runners to be where the planar will cut the wood.
  3. Secure the wood
    • Now you will secure the wood either using wood glue, screws, nails, or hot glue
  4. Run it through the planar
  5. Lay wood on a flat surface to check for flatness

Pros and Cons of using a planer to flatten wood

ProsCons
Even, smooth finishLong set-up time
Save money and spaceDifficult to do with larger warps

When flattening wood with a planar, you will still get an even, smooth finish like flattening it with a jointer. In addition, you will save money and space in your shop than if you had a jointer and planer.

However, you can spend more time during the set-up process and it will be difficult to do more complex or larger warps like twists and larger cups.

How to flatten wood using a Router

To flatten wood using a router, you will need to build a specific jig to perform this task.

First, I will teach you how to build the jig and then how to operate the jig.

How to build a Router Jointer Jig

To build a router jig, you will only need 3 pieces of wood.

  1. Cut plywood A 2″ wider than the router base
    • You will want the router to be able to slide across the wood without friction or getting stuck.
  2. Cut plywood A 3-4 ft long
    • Most wood is sold in up to 16 inches wide. However, if you want to flatten an end product that is wider, then you will need a longer base.
    • As a rule of thumb, You will want the base to be at least 4″ longer than the work piece you are planing.
      • If you are planing a workpiece that is 3′ wide, then you will want the jig to be at least 3′ 4″.
      • A piece of plywood that is 3-4 feet should be long enough for most tasks
  3. Cut plywood B & C the same length as plywood A and 3″ wide
    • Plywood B & C will be the side runners of the jig. You will want to cut these pieces the same length as A and 3 inches wide.
  4. Secure plywood B & C to plywood A
    • Now you will secure plywood B & C to plywood A as shown here.
  5. Use the router to route a hole starting 2″ from the end of plywood A
    • Using a straight bit, you will start the router 2 inches from the end of plywood A and route a hole to the other side stopping 2 inches short.

How to flatten wood with a router

To use the router jig, you will need two pieces of even 2 x 4 or 2×6, depending on the wood thickness

  1. Place the 2×4 or 2×6 on the sides of the workpiece
    • You can use 2×4 if using wood 3 inches or thinner, but you should use 2×6 wood if your wood is more than 3 inches.
  2. Place the jig on the spacers
    • Now you will place the jig on the spacers and over the work piece
  3. Align the router bit to the desired depth
    • Now you will align the router to the jig and adjust the router bit to the desired depth.
  4. Make short passes of the router
    • Once at the desired depth, you will start the router and make short passes
  5. Lay wood on a flat surface to check for flatness

Pros and Cons of using a router to flatten wood

ProsCons
Easy to build jigLong set-up time
Use tools already at handMay not have smoothest finish
Not ideal for highly warped wood

Using a router to flatten wood is useful if you do not have a jointer or planer on hand. However, I would not recommend that you buy a router to flatten wood.

A router is good for edge designs and cut outs. If you already have a router, then I would recommend that you build a jig to flatten wood.

The drawbacks of using a router is that you have to create the jointer jig for the router first. Additionally, you may not get the same smooth finish as you would with a planar or jointer. Lastly, this method is not ideal for highly warped or twisted wood.

How to flatten wood using a table saw

To flatten wood using a table saw you will need long shims to use as spacers and a table saw fence to even the wood. This method is similar to the way you flatten wood using a planar

  1. Use a straight sheet of plywood as a base
    • Use a sheet of plywood that is at least the same size as the wood you will be cutting.
    • You do not want the plywood to be more than 5 inches thick because it will be difficult to keep level with the table saw fence
  2. Place warped wood on plywood
    • Placed the warped wood on the plywood and examine where the wood does not touch the plywood.
  3. Add shims to fill in the gaps
  4. Secure the wood to the plywood
    • Either using screws, nails, wood glue, or hot glue, secure the wood, shims, and plywood together to prevent movement
  5. Place plywood against table saw fence
  6. Adjust blade height and fence depth
  7. Cut the wood
  8. Lay wood on a flat surface to check for flatness

Pros and Cons of using a table saw to flatten wood

ProsCons
Semi-smooth finishLonger set-up time
Can use a common woodworking toolNot ideal for highly warped wood
May have to take off more material

When using a table saw to flatten wood, you will likely get a smoother finish than using a router. Using a table saw will, however, take long to set-up and is not ideal for highly warped wood just like the planer and router.

It is more difficult to take off a little bit of material while using a table saw and is beneficial if you want to take off more than 1/4th inches.

Overview

The jointer

The best tool to use for flattening wood is a jointer. Jointers are specialized tools for flattening wood and can flatten more severely warped boards.

The drawbacks to a jointer is that it is a specialty tool that does not have many additional functions. So purchasing a jointer may be impractical to many woodworkers.

The planer

For those who do not have a jointer, a planer is the next best tool for flattening wood. Planers are made to get the wood to an even thickness, but with the help of shims and jigs, you can use it to flatten the board.

The table saw

Table saws can be used to flatten wood, but they are not the best tool for the job. Table saws require more set-up time and are not ideal for shaving off a little wood.

For table saws, it will be best if you take of 1/4th inches of more of wood. Anything thinner can lead to kickback or be difficult to control.

The router

Routers can also be used to flatten wood and are better than table saws when it comes to taking off a little bit of wood. Using routers to flatten wood, however, will likely result in a finish that is not as smooth.

The router does fall a little behind in the table saw in the sense that it takes a lot longer to flatten a work piece.

You can further smooth the wood by using a planer and sander.

How to check a board for flatness

It is good to check your board for flatness before you even purchase the wood.

How to check for warps at the store

You can weed out highly warped wood at the store by using the eyeball method.

  1. Align the board long ways away from you
  2. Align your eye and look for “blurry” spots

How to check for flatness at your shop

You can ensure the board is perfectly flat at your shop if you lay it on a flat surface and run a ruler or straight edge along the top of the board.

If there are any high spot, your ruler will scratch the wood or get stuck.

Conclusion

In this article, we learned how to flatten wood with a jointer, planar, router, and table saw. We discussed th different ways to flatten, along with the pros and cons of each method. Not every method can be used in every scenario, so we discussed when to use which method.

Afterwards, we learned how to check a board for flatness, and what to do before leaving the shop.

Thank you so much for taking the time to read this article and I wish you luck on your woodworking journeys!

Rachel

My name is Rachel Blanding and I am a woodworker. I started woodworking at the beginning of the COVID-19 pandemic. I mainly create and refurbish furniture and create art. In this site I will share with you the knowledge I have gained over the years, and what worked for me and what didn't.

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