How To Align Jointer Tables That Are Not Coplanar?

Does your jointer leave boards with a slight curve instead of a flat edge? The problem might not be your blades. It could be your tables.

Jointer tables need to sit on the same flat plane. When they don’t, woodworkers call this being non-coplanar. Even a tiny gap can throw off your entire project.

This issue frustrates many woodworkers. You feed a board through, expect a straight edge, and get a curved one instead. The fix often has nothing to do with sharpening knives.

In this guide, we will show you how to check your jointer tables for coplanar alignment. You will learn to use a straightedge to spot problems across width, length, and diagonals.

In a Nutshell

• Raise both tables above the cutter head first. This gives you clear access to check the surfaces properly.
• Grab a straightedge and check across width, length, front, back, and both diagonals. This tool is your best friend for spotting gaps.
• Shim where needed between the bed and side castings. Small shims can fix big alignment problems.
• Tighten jibs snugly, but not too tight. You still need enough play to adjust the outfeed table later.
• Never skip the diagonal checks. Many woodworkers miss this step and end up with tables that look flat but aren’t truly coplanar.
• Adjust knives only after the tables sit level. Doing this step out of order wastes time and effort.

What Does Coplanar Mean for Jointer Tables?

Coplanar means your jointer tables sit on the same flat plane. Think of it like two sheets of glass placed edge to edge with no gap or step between them.

Your jointer has two main tables: the infeed table and the outfeed table. These tables sandwich the cutter head in the middle. When they are coplanar, a board slides smoothly across both surfaces without dipping or rising. The cutter head then removes wood evenly.

When tables are not coplanar, one table sits higher or lower than the other. A board might dip into a valley between the tables or bump over a ridge. This creates uneven cuts, curved edges, and frustration.

Why coplanar matters is simple. The cutter head can only remove a fixed amount of wood. If your tables are not level with each other, the board’s path changes height. The blade then cuts deeper in some spots and shallower in others. You get boards that are not flat.

Coplanar alignment is different from knife height. Your knives sit at a specific height relative to the outfeed table. But that only works if both tables are already on the same plane. Adjusting knife height on misaligned tables just masks the real problem.

The key point is this: coplanar tables are the foundation. Without them, no knife adjustment will give you flat boards. You must fix table alignment first. Then you adjust knife height. This order matters because one depends on the other.

Many woodworkers skip the coplanar check and jump straight to blade adjustment. This wastes time and creates poor results. Spending 30 minutes to verify coplanar alignment saves hours of troubleshooting later.

Signs Your Jointer Tables Are Out of Alignment

Your jointer shows clear warning signs when tables drift out of alignment. Learning to spot these signs saves you time and prevents wasted wood.

Uneven board surfaces are the first clue. You feed a board through, and one end comes out flat while the other has a slight curve or taper. This happens because the infeed and outfeed tables sit at different heights. The board follows the lower table, creating an inconsistent cut.

Watch for inconsistent planing depth. Your jointer should remove the same amount of material across the entire board width. If one side cuts deeper than the other, your tables likely lean sideways. The cutter head stays fixed, but misaligned tables approach it at different angles.

Snipe marks are another red flag. Snipe occurs when the board tips up or down at the end of the cut. This usually means your outfeed table sits too low. The board drops slightly as it leaves the infeed table, and the knives catch the trailing edge.

Listen for unusual sounds or vibration. Misaligned tables force the board to rock slightly as it passes over the cutter head. This creates rattling or a choppy cutting sound.

Test your tables with a straightedge across multiple points. Place it lengthwise, widthwise, and diagonally across both tables. Rock the straightedge gently. If gaps appear under the straightedge at different points, your tables are not coplanar.

Visible gaps between the straightedge and table surface confirm misalignment. Mark where gaps appear. These spots show exactly where shimming is needed.

Tools You Need to Check and Adjust Table Alignment

You need specific tools to check and fix table alignment properly. The most important tool is a straightedge. This simple tool reveals gaps between your tables and shows exactly where misalignment happens. A quality straightedge stays flat and doesn’t bend under its own weight.

Get a straightedge long enough to span your jointer’s width. Most woodworkers use straightedges that measure 24 to 48 inches. Lay it across different points on your tables to check alignment.

You also need shims to raise tables where they sit too low. Shims are thin wedges made from metal or plastic. They slide between the bed and side castings to adjust height. Keep several shim thicknesses available so you can make fine adjustments.

A level helps verify that tables sit horizontally. Place it on the infeed table, then the outfeed table. Check both the length and width of each table. This confirms your tables don’t tilt side to side or front to back.

Gather a wrench set to loosen and tighten the jibs that hold your tables. You’ll adjust these repeatedly during alignment. Loosen them enough to slide shims into place, but keep them snug enough to prevent movement.

Consider having a feeler gauge on hand. This tool measures the exact gap between your straightedge and table surface. Small gaps become visible this way, helping you determine shim thickness needed.

Keep these tools together in one spot. Organization saves time during the alignment process. Having everything ready prevents frustration and helps you work through adjustments systematically.

Step-By-Step: Checking Tables With a Straightedge

A straightedge is your primary diagnostic tool for finding table misalignment. Place it across your jointer tables and look for gaps between the metal and the straightedge itself.

Start by raising both the infeed and outfeed tables slightly above the cutter head. This position gives you clear access and prevents the knives from interfering with your measurements.

Check the straightedge across the full width of both tables. Set it perpendicular to the length of the jointer. Any visible gap means one table sits lower than the other at that point.

Next, run the straightedge along the entire length of both tables. Move it from the front edge toward the back. Note where gaps appear because these spots need shimming.

Test the front edge of both tables together. Place the straightedge so it touches both the infeed and outfeed table surfaces. A gap here indicates a step between them.

Check the back edge the same way. Many jointers develop misalignment at the rear first, so this check matters greatly.

Now perform the diagonal checks. Set your straightedge from the front left corner to the back right corner. Then check from front right to back left. Diagonal measurements catch twisting or rocking that length and width checks might miss.

Mark every location where you see gaps. Use a pencil to note the gap size if possible. Larger gaps need more shimming than smaller ones.

This systematic approach reveals exactly where your tables sit out of plane. Once you identify all problem areas, you can shim strategically and recheck until your tables sit perfectly flat and coplanar.

Step-By-Step: Shimming and Adjusting for Coplanar Tables

Once you’ve identified where your tables sit out of alignment, shimming becomes your main tool. Shims are thin pieces of material that slip under the table bed to raise it into the correct plane.

Start by loosening the jibs that hold your infeed table to the side castings. Loosen them snugly, not completely. You need enough play to slide shims underneath, but not so much that the table moves around freely.

Slide your shim material between the bed and casting at the low point. Use thin shims first. You can stack multiple shims to reach the exact height you need. Tighten the jib gradually as you add shims. Check your alignment frequently with the straightedge.

Work across the entire width and length of the table. Don’t just fix one spot and assume the rest is correct. Tables often sit unevenly at multiple points.

The outfeed table adjustment follows the same process. Loosen its jibs and add shims where needed. Remember that the outfeed table height matters most because it supports the board as it exits the cutter head.

Tighten all jibs firmly once you’ve achieved coplanar alignment. A snug fit prevents the tables from shifting during use. However, keep enough room to make future adjustments without removing the entire table.

Recheck your work with the straightedge after tightening everything. Run it across the width, length, front, back, and both diagonals. Small gaps may still exist, but they should be minimal and consistent.

This systematic shimming process takes patience. Work slowly and verify your progress at each step. Rushing through adjustments often means repeating the work later.

Adjusting Knives After Tables Are Aligned

Once your tables sit coplanar, knife adjustment becomes straightforward. The knives must sit at the correct height relative to your now aligned tables. This step determines whether your jointer produces flat boards.

Start by raising the outfeed table until it just touches the top of your cutter head knives. Use a wooden block and tap it gently across the table surface. You should feel consistent contact along the entire length. This position serves as your reference point.

Next, adjust your infeed table height. Lower it slightly below the outfeed table. The distance depends on your desired cut depth, typically between 1/32 inch and 1/8 inch. Smaller cuts produce better results on difficult grain.

Check knife sharpness before final adjustments. Dull knives require more pressure and can deflect during cutting, ruining your flat surface work. Sharp knives cut cleanly and maintain consistent depth.

Verify knife alignment by rotating the cutter head by hand. Watch the knives as they pass your reference points. Each knife should reach the same height as your outfeed table. Uneven knives create ridges in your boards.

Make small adjustments to individual knives if needed. Most jointers allow you to adjust each knife independently through set screws or wedges. Loosen the fastener slightly, tap the knife to the correct height, then retighten firmly.

Test your setup on scrap wood before processing valuable boards. Make a light pass and check the surface for flatness. The board should feel smooth with no ridges or waves. Adjust knife height slightly if you see inconsistent results.

Proper knife adjustment transforms coplanar tables into a functional jointer that produces genuinely flat surfaces.

Common Mistakes That Prevent Proper Alignment

Many woodworkers struggle with jointer alignment because they make preventable mistakes during the setup process. Understanding these errors helps you avoid wasting time and frustration.

Over-tightening your jibs is the most common problem. When you clamp those jibs too firmly, you lock your tables in place. This prevents you from making fine adjustments later. Your tables become stuck in whatever position they’re in, even if it’s not coplanar. You need the jibs snug enough to hold alignment but loose enough to allow shimming adjustments.

Another frequent mistake is skipping the diagonal measurements. Many people check only the width and length of their tables. They assume that covers everything. Diagonal checks reveal misalignment that straight measurements miss. Your tables can appear level along the edges but still sit out of plane diagonally. This hidden misalignment ruins your jointer’s performance.

Neglecting straightedge verification after tightening creates problems too. You complete all your shimming work, tighten everything down, and assume you’re finished. But tightening the jibs can shift your tables slightly. You must recheck with your straightedge after final tightening. This final check catches any movement caused by the tightening process.

Some woodworkers also rush through the shimming process itself. They place shims randomly instead of systematically working across the entire width and length. This creates new misalignment problems instead of solving them.

The solution is simple: work slowly and methodically. Check multiple points. Verify your work after each major step. Tighten gradually rather than all at once. These practices prevent most alignment problems before they start.

Troubleshooting Persistent Alignment Issues

When your jointer tables refuse to stay aligned, persistent issues often stem from incomplete diagnosis or incomplete shimming work. The first step is recognizing that coplanar surfaces demand precision across multiple points, not just one or two spots.

Start by examining your measurement technique. Many woodworkers check only the front and back edges, missing critical diagonal points. Use your straightedge across the full width, the complete length, both front and back positions, and then both diagonal directions. This thorough approach reveals hidden gaps that partial checking misses.

If you find ongoing alignment problems after shimming, check your jib tightness. Jibs that are too loose allow tables to shift during use. Jibs that are too tight prevent fine adjustments. You need a balance where they hold position firmly but still allow careful shimming adjustments.

Temperature and humidity changes can also cause persistent misalignment. Wood and metal expand and contract differently. Check your alignment during consistent shop conditions for the most reliable results.

Another common issue is incomplete shim placement. Small gaps between bed and casting create leverage points that throw tables out of plane. Fill all low spots systematically rather than placing shims only at obvious problem areas.

Finally, verify that your straightedge itself is straight. A warped or bent straightedge gives false readings and sends you on endless adjustment loops. Test your straightedge against known flat surfaces before trusting its measurements.

Persistent alignment problems usually indicate incomplete shimming, measurement gaps, or diagnostic tool issues. Address each systematically, and your tables will stay coplanar.

Final Thoughts

Aligning jointer tables takes patience, but the process is simple once you understand it. You level the tables first, then adjust the knives. This order matters, and skipping steps leads to poor results.

Coplanar tables form the foundation of every successful jointer setup. Without this alignment, your boards will never come out truly flat. Take time to get this step right before moving forward.

Your straightedge remains your best friend throughout this project. Check width, length, front, back, and both diagonals every single time. These measurements tell you exactly where problems hide.

Shimming is not a one-time fix. You might need several rounds of adjustment before everything sits correctly. Small changes often require rechecking every measurement point again.

Remember that jib tension affects your results significantly. Tighten jibs enough to hold alignment, but leave room for outfeed table movement. This balance takes practice to master.

Once your tables are coplanar, knife adjustment becomes much easier. The hard work happens during the leveling stage. Everything else builds on that solid foundation.

Test your setup on scrap wood before running valuable lumber through the jointer. This simple step saves materials and prevents frustration. Confidence in your setup matters just as much as technical accuracy.

Jointer alignment is not a one time job. Check your tables periodically, especially after moving the machine or noticing rough cuts. Wood movement and temperature changes can shift things over time.

With practice, this process becomes second nature. Your jointer will reward you with flat, square boards every time you use it. That is the real payoff for taking alignment seriously.

Frequently Asked Questions

What does coplanar mean for jointer tables?

Coplanar means your infeed and outfeed tables sit on the same flat plane. Think of them as two sections of one perfectly level surface. When tables are coplanar, wood slides smoothly across both without dipping or rising. This alignment is essential for producing flat boards.

How do I know if my tables are not coplanar?

Use a straightedge to check. Place it across the width, length, front, back, and both diagonals of your tables. If gaps appear under the straightedge, your tables are not coplanar. You might also notice wood coming out with a slight bow or curve.

What is the first step in fixing non coplanar tables?

Raise both your infeed and outfeed tables above the cutter head. This gives you room to work underneath. Then systematically check alignment using your straightedge across all five measurement points. Document where gaps exist so you know where to shim.

Why do jibs need to be snug but not over tightened?

Tight jibs hold your tables in position. However, over tightening prevents you from making fine adjustments. You need just enough tension to keep tables stable while allowing slight movement for shimming. Think of it as firm but flexible.

Can shimming alone fix all alignment problems?

Shimming is your primary tool, but it works best with patience. You may need several adjustment rounds. After shimming, always recheck with your straightedge. Once tables are coplanar, knife adjustment becomes straightforward.