Imperfect lumber is just part of woodworking. Sometimes the boards we bring home are warped, sometimes they’re only surfaced on two sides, and sometimes the edges are nowhere near straight enough for a clean glue-up.

A jointer can fix that, of course. That’s exactly what a jointer is made for. But a lot of woodworkers don’t have one. I don’t have one either.

Fortunately, a table saw can straighten a board very well if you use the right setup. The catch is that you can’t just run a crooked board against the regular fence and expect a straight edge. If the edge against the fence isn’t straight, the cut edge won’t be straight either.

That’s where this jig comes in.

Why You Need a Straightening Jig

The purpose of this jig is simple: it gives the board a straight reference surface while it passes through the saw.

Instead of relying on the crooked edge of the board against the fence, the board gets clamped to a flat sled. The sled rides in the miter slot, keeping everything moving straight through the blade.

Once the board is secured to the sled, the table saw can trim one edge perfectly straight. After that, you can use that newly straightened edge against the fence to rip the other side if needed.

Sled Size and Board Capacity

For this jig, I’m using a baseboard that is 36 inches long and 12 inches wide.

I made it 3 feet long because that allows me to straighten boards up to about 3 feet long. If I wanted to straighten longer boards, I’d need a longer sled. For example, if I were making a table and needed to straighten 6-foot boards, the sled would need to be about 6 feet long.

That matters because the sled has to support the board through the cut and keep the high points controlled as it moves past the blade.

Building the Miter Slot Runner

Since the sled rides in the miter slot, the runner has to fit properly.

My runner is 3/4 inch wide and sized to match the depth of my saw’s miter slot. Most standard T-tracks are about 3/8 inch deep, but mine is closer to 5/16 inch, so I had to make the runner specifically for this saw.

Because my sled is longer than the table saw top, I also needed the runner to catch in the T-slot and keep the sled from lifting or wobbling. To do that, I added a thin piece of aluminum into the runner. The aluminum is 1/16 inch thick and is epoxied into a slot cut into the wood.

That gives the runner a little lip that catches under the T portion of the miter slot.

Why the Runner Fit Matters

The runner needs to slide smoothly, but it can’t be loose.

If there’s wobble in the runner, that wobble transfers to the sled. And if the sled wobbles, the edge you cut won’t be as straight or as square as it should be.

After cutting the runner close to size, I checked the fit in the miter slot and then fine-tuned the thickness with a thickness sander. That let me bring it down just enough so it fit properly without sitting too high.

The aluminum insert is positioned toward the far end of the sled, away from me. That way, it still holds the sled down when part of the jig is hanging off the front of the table saw.

Setting Up the Clamp Support

The board being straightened will be clamped to the base of the sled. Since the edge of the sled will ride right next to the saw blade, I’ll trim the sled to its final width after the runner is mounted. That way, the edge of the sled becomes an exact reference line for the blade.

To make the clamps work, I need a raised support on the opposite side of the sled. That support gives the clamps something solid to bear against while holding the workpiece down.

I also want that support to be adjustable, so I’ll cut slots for the T-bolts. I’ll also cut matching slots in the sled so the support can move back and forth depending on the width of the board I’m straightening.

The next step is to cut those adjustment slots with the router, then mount the support so the jig can hold different board sizes securely.

Attaching the Rail

With the slots cut into the sled base, the next step is to glue on the rail.

The rail I used had a slight warp in it, but that wasn’t a problem here. Once it was glued and pinned in place with brad nails, it straightened out.

I didn’t want to overdo the glue because I didn’t want a lot of squeeze-out. This was also one of those “measure twice, attach once” moments. Since the sled had been flipped over and turned around during the process, I had to make sure the rail went on the correct side and that the metal guide was positioned toward the front.

I used short 5/8-inch brad nails to hold the rail in place while the glue dried.

Adding a Handle for Safety

I also decided to add a handle to the sled.

This makes the jig easier to push through the saw, but the bigger reason is safety. I don’t want my hand behind the workpiece or anywhere near the blade path while making the cut.

The handle sits off to the side, near the runner, so my hand stays well away from the blade.

To make it, I cut two small wood blocks, about 2 1/2 inches by 3 1/2 inches, rounded one end, and drilled a hole through each block for a 3/4-inch dowel.

I glued and nailed the blocks in place, then added the dowel between them. The dowel was slightly undersized, which is fairly common, but it didn’t create a real problem. There won’t be much stress on this handle, and a little glue with a brad nail is enough to keep it from moving.

After that, I clamped the handle assembly and let the glue dry.

Adjusting the Handle Placement

If you’ve watched me for any length of time, you’ve probably heard me say I rarely get through a project without making some kind of mistake. This jig was no exception.

My original plan was to mount the handle directly over the runner. That seemed like the best location at first, but once I started assembling the rest of the jig, I realized it interfered with the adjustable support bar and clamps.

So I moved the handle closer to the outside edge, away from the saw blade.

That still keeps my hand in a safe position, and it gives the clamp support enough room to move.

Installing the Adjustable Clamp Support

The support piece on this jig is not really a fence. It’s there to give the clamps something solid to bear against while holding the workpiece.

Because different boards will need different clamp positions, the support has to be adjustable. I cut slots in both the sled and the support piece so it can move back and forth as needed.

The clamp pads also slide in their own slots, which gives the jig more flexibility for different board widths and different cuts.

The slots in the support are slightly off-center on purpose. That leaves more material on the side where the clamp pads sit, which gives them better support.

Once the clamp hardware was assembled, I installed the support bar using bolts through the sled slots. Now the support can move forward or backward depending on the board I’m cutting.

This jig is mainly for straightening boards on the table saw, but because of the adjustable setup, it can also work as a tapering jig.

Trimming the Zero-Clearance Edge

Before using the jig, there’s one final step: trimming the edge of the sled with the table saw blade.

I intentionally made the sled a little oversized. Once the runner is installed and riding in the miter slot, I can run the sled through the saw and trim the edge. That creates an exact zero-clearance reference edge.

From that point on, I’ll know exactly where the blade will cut when a board is clamped to the sled.

With that edge trimmed, the jig is ready to use.

Using the Jig at the Table Saw

Once the jig is assembled, the first thing to do at the table saw is remove the fence.

There’s a natural temptation to think this kind of sled should ride against the fence, but it doesn’t. This jig rides in the right miter slot. That’s why the runner and metal tab matter so much. They keep the sled aligned and prevent it from tipping, even when part of the sled is hanging off the edge of the table.

Before using it on a board, I trimmed the edge of the sled with the saw blade. I only needed to remove about 1/16 inch, but that cut creates the zero-clearance edge. From then on, the edge of the jig shows exactly where the blade will cut.

After that first cut, I noticed the sled had a slight tendency to bind against the riving knife. A little beeswax on the freshly cut edge fixed that. I wax my table saw sleds and jigs anyway because it helps them slide smoothly, and this was one place where it clearly helped.

Straightening a Bowed Board

To use the jig as a jointer, the board gets clamped to the sled with the bowed edge positioned so the blade removes the high area.

Not every board is worth trying to save. If a piece is warped in multiple directions, there may be no safe or practical way to clamp it well enough. By the time you cut away the bad parts, there may not be much board left.

But a board that’s bowed in one direction is a good candidate.

The important thing is to line up the board with the zero-clearance edge of the jig. In this case, I positioned the ends close to the edge and let the middle bow out slightly past it. That way, the saw removes material from the middle and creates one straight edge.

The adjustable support bar is only there to support the clamps. It is not a fence. Keep it far enough away from the blade path so there’s no risk of the clamps or support getting into the cut.

After the cut, the waste piece showed exactly what happened. It tapered from almost nothing at the ends to a wider strip in the middle, which is what you’d expect when removing a bow.

Once the board came out of the jig, one edge was straight. From there, I could put that straightened edge against the table saw fence and rip the opposite side parallel.

Using It as a Tapering Jig

This jig also works well as a tapering jig.

For example, if I’m making tapered legs for a table, I can mark the taper directly on the workpiece and line those marks up with the zero-clearance edge of the sled.

In this example, I left the top 4 inches untapered because that’s where the table skirt would attach. From there, the leg tapers down by about 3/4 inch.

Once the marks are aligned with the edge of the jig, I clamp the piece down and make the cut. Just like before, the adjustable support is only there for the clamps. It should not be treated like a fence.

After the cut, the offcut clearly shows the taper, and the leg has one clean tapered face. From there, I could repeat the same process on the other side or taper all four sides if I wanted a square tapered leg.

Why I Made Mine 3 Feet Long

I made this sled 36 inches long because that fits the kind of work I usually do.

If I were straightening long boards for a tabletop, I’d build a longer sled, probably 6 or 7 feet. But most of the pieces I work with are shorter, and a 3-foot sled gives me a lot of versatility without becoming awkward to handle.

It can straighten anything from small pieces up to about 3 feet long.

If you’re working with a warped long board, it’s often better to rough cut it to length first, then straighten the smaller pieces. Don’t finish cut them yet. Just break the board down close to the sizes you need, straighten those pieces, and then make your final cuts.

That usually creates less waste than trying to straighten one long warped board first, especially when you’re working with expensive hardwood.

Final Thoughts

This jig turned out to be a very useful addition to the table saw.

It lets me take lumber that might otherwise end up in the scrap pile and turn it into usable material. It can straighten a bowed edge, help prep boards for ripping, and even double as a tapering jig.

Some boards still won’t be worth saving. If a piece is badly warped in several directions, it may be safer to cut it into smaller parts or scrap it altogether. But for boards with a manageable bow, this jig works very well.

It’s not a complicated build, and it’s a great companion to the other table saw sleds in the shop. If you don’t have a jointer, this is one simple way to make your table saw do some of that work.