Thickness Planer vs. Jointer

If you've ever stood in a lumber yard holding a warped board, wondering which machine will solve your problem, you're not alone. The thickness planer and jointer are two of the most essential—and most misunderstood—tools in woodworking. While they might look similar at first glance, these machines serve distinctly different purposes in preparing lumber for your projects.

Understanding when to reach for each tool will transform your woodworking, helping you create perfectly flat, square, and consistently sized boards every time.

The Difference Between Planers and Jointers

The key distinction between these machines lies in their primary functions:

A jointer creates one perfectly flat surface (and can square up edges), while a thickness planer makes boards uniformly thick by creating a surface parallel to the opposite face. Think of the jointer as your foundation tool and the planer as your precision finishing tool.

This difference in purpose means the order of operations matters tremendously. You typically joint first to establish a flat reference surface, then plane to achieve your desired thickness.

How Each Machine Works

Jointers

A jointer consists of two tables—an infeed and outfeed table—with a rotating cutterhead in between. The outfeed table sits exactly at the height of the cutterhead knives at their highest point. As you push your board over the cutterhead, it removes material from the high spots, gradually creating a perfectly flat surface.

• Flattening warped, cupped, or twisted boards
• Creating perfectly straight edges
• Squaring up lumber (making edges 90° to faces)
• Removing mill marks and surface defects

Thickness Planer

A thickness planer feeds boards through rollers past a cutterhead, removing material from the top surface to create uniform thickness. The board rides on the bottom table, and the cutterhead height determines the final thickness.

• Creating consistent thickness across multiple boards
• Producing smooth, finished surfaces
• Sizing lumber to exact specifications
• Making boards parallel on both faces

When to Use Each Tool?

Start with the Jointer When:

• Your lumber is warped, twisted, or cupped. No amount of planing will fix these fundamental problems. The planer will only follow the existing warps, creating boards that are consistently thick but still warped.
• You need perfectly straight edges for glue-ups. Whether you're making a tabletop or bookshelf, clean glue joints require straight, square edges that only a jointer can provide.
• You're working with rough lumber. Most hardwood lumber comes rough-sawn with saw marks and uneven surfaces. The jointer removes these imperfections and creates the flat reference surface you need.
• You need to square up stock. When your project requires 90° angles between faces and edges, the jointer's fence ensures perfect squares.

Move to the Planer When:

• You need consistent thickness. After jointing one face flat, the planer creates a parallel face at exactly the thickness you want.
• You're batch processing multiple pieces. Once you've jointed your boards, the planer excels at bringing multiple pieces to identical dimensions quickly and accurately.
• You want a smooth, ready-to-finish surface. Modern planer knives can produce surfaces so smooth they need minimal sanding.
• You're working with pre-surfaced lumber. If your lumber is already reasonably flat (like most construction-grade boards), you might skip straight to the planer for final sizing.

The Ideal Workflow: Joint First, Then Plane

For most projects, the most effective sequence is:

1. Joint one face flat - This creates your reference surface
2. Joint one edge straight and square - This gives you two perpendicular reference surfaces
3. Rip to rough width (if needed) - Use your table saw, leaving extra material for final sizing
4. Joint the ripped edge - Clean up any saw marks
5. Plane to final thickness - The jointed face rides down on the planer table, ensuring the top face ends up parallel

This sequence ensures every piece starts with a perfect foundation and ends with precise dimensions

Can One Machine Do Both Jobs?

While some combination machines attempt to serve both functions, most woodworkers find that dedicated machines perform better. Here's why:

Thickness planers cannot replace jointers for initial flattening because they reference off the existing surface. Feed a warped board into a planer, and you'll get a warped board that's now uniformly thick.

Jointers have limitations on thickness capacity and aren't designed for the precision thickness work that planers excel at.

If budget constraints mean choosing one machine initially, consider your typical projects:

Understanding the distinct roles of thickness planers and jointers transforms how you approach lumber preparation. The jointer creates the foundation—flat surfaces and straight edges—while the planer adds precision, creating perfectly dimensioned stock ready for your projects.

While both machines working together provide the ultimate lumber prep solution, understanding their individual strengths helps you make informed decisions about which tool to use when. Remember: flat first (jointer), then precise (planer). This sequence will serve you well in every woodworking project, from simple boxes to complex furniture.

Whether you're just starting to build your shop or looking to refine your technique, mastering these two machines will dramatically improve the quality and precision of your woodworking.