Cove Cutting

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This article is from Issue 103 of Woodcraft Magazine.

How to make sweeping cove mouldings on the table saw.

Dramatic curves from your table saw

Wide, sweeping coves such as those found in crown molding and raised panels are a hallmark of good woodworking. But how do you achieve them without a large-scale molding machine? On the table saw, of course.

Cutting coves on a machine used primarily for ripping, crosscutting, and joinery is unorthodox. But if done correctly, it’s a safe and efficient method. Essentially, you run a workpiece along a fence and diagonally over the blade in a series of shallow passes, to take advantage of the blade’s curvature.

Adjusting the height of the blade and the feed angle of the piece varies the depth and width. While the resulting cut requires a lot of sanding to remove the saw marks, the technique offers more versatility than stock profiles on cutters you’d use in a router or shaper.

While there is no magic in setting up to cut coves, a parallelogram jig simplifies the process. In this article, I’ll demonstrate how to set up and cut coves—and half-coves—first using typical layout tools, then with the jig.

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Sneak peek. After marking the offset and depth, preview your cove by sketching a line to connect the layout marks.

Cove terminology and layout

A cove cut is defined by its width and depth. With wide, shallow coves, the curve is close to being a true arc, but with narrow, deep coves, the shape is more elliptical. The other key dimension is the offset, or distance from the edge of the board to the edge of the cove. 

In the drawings below, the offsets on either side are equal, but they don’t have to be. And if your cove design goes right to the edge of the stock, start with a pieces wide enough to leave a minimum of 1/8" offsets to provide a bearing surface. These small offsets can be trimmed away later if desired. While you don’t need to draw out the curve, it can help you visualize what the cove will look like if you make a sketch on the end of your stock.

Dedicated to coving. While it may appear to be more of an overgrown shaper cutter, this blade from CMT is designed to cut coves on the table saw.

Blades for Coving

For best results, cut coves with clean and sharp full-thickness 40-tooth ATB or 50-tooth combination blades. Adding a stiffener (or two) can reduce vibration. Thin kerf blades don’t stand up well to excessive sideways pressure. If you do a lot of coving, consider investing in a designated coving blade. Several manufacturers offer these chunky 7" (+/-) diameter blades with rounded carbide teeth that leave a much smoother surface than a regular sawblade. Be aware that the smaller diameter does somewhat limit the size of the coves you can make, and (as of this writing) the blades are not compatible with SawStop’s brake technology.




Rough cut. The profile to the right was cut with a 40-tooth ATB blade, the one to the left was cut with a coving blade. Both require sanding, but the marks from the ATB blade are significantly rougher. 

The basic set up

Once you have determined a cove’s size, use those dimensions to place your primary fence. Since the force from the blade will push the workpiece into this fence, make it from a stout length of scrap (I keep a length of 2 × 2 on hand). Your secondary fence can be lighter.

Adjusting the blade height to equal the cove depth, then determine where the blade’s teeth enter and exit the saw table. Drop the blade completely, align the fence as shown, and mark the feed angle on the saw table. Shift the fence away from your marks a distance equal to your desired cove offset, and secure the fence at each end to complete the setup. This can be tricky—you may need to make spacers to clamp to your saw’s fence rail.

Once the primary fence is in place, add a secondary fence to make the set up more secure. Use your workpiece as a spacer to position it.

Set cove depth. Raise the blade to your desired cove depth, measuring to the blade’s highest point. It’s better to err on the low side.
Determine the in and outs. Bridge the throat plate gap with stiff paper, locating it so that a hand-turned blade just grazes the sheets. Tape the paper in place. Then mark the exit point to the left of the teeth, and the entrance point to their right. 
Set cove width. With the blade lowered, position the primary fence so that it intersects the teeth entrance point. Pivot the rear end of the fence until the distance from the fence to the exit point is equal to the width of the desired cove.
Set the offset. After determining the feed angle with the fence, mark its location at the front and rear of the saw table. (Painter’s tape aids visibility.) Shift the fence away from the feed angle line a distance equal to your desired offset, then clamp the fence in place. 

Cutting the cove

Making the cove is a straightforward though repetitive task. (It’s also dusty, so use dust collection and wear a mask!) Due to the forces inherent in feeding stock over the blade diagonally—something the blade isn’t designed to accommodate—make multiple shallow passes. Raise the blade so its highest point is about 1/16" above the table, and feed your workpiece along the fence and over the blade to make the first pass. Use push sticks to keep your fingers safe. Raise the blade another 1/16", and repeat. Continue like this until the cove reaches its full depth. Taking very light cuts (<1/32") for the last two or three passes can reduce the amount of sanding needed. Scrape and sand away the saw marks to finish up. 

A little at a time. A 1⁄2" deep cove will take about ten passes. Raise the blade about 1⁄16" at a time and follow up with two, light finish passes. Listen to the saw. It will sound a little different than a regular cut, but shouldn’t scream in protest. A steady, consistent feed rate yields the best surface.
Off-center? Since your saw arbor pivots to raise the blade, your cove will appear off-center at first. But don’t worry. Any wonkiness will work itself out by the time the blade reaches its full height.

Lotsa clean up. The only drawback to cove cutting is the sanding required. A curved scraper and a convex sanding block will ease some of the task. To make the block match the cove’s curvature, bandsaw it close to shape then finish up by taping coarse sandpaper inside the cove and lapping the block to final shape.

Cutting a half-cove

When making a raised panel, you need to cut half a cove. The setup is similar to making a full cove, except the fence will be clamped atop the blade instead of in front of it.

Set the blade height first, then determine the feed angle for a cut twice the width of your half-cove. For example, if you want a panel with a 2"-wide bevel, determine the feed angle for a 4" wide full cove, by pivoting the fence away from the exit point (p. 29).

Once you have the angle established and the blade lowered, mark the offset, in this case 2", towards the blade, and clamp your fence there. Now as you raise the blade, its front portion will cut partially into the fence, leaving the rear portion to make the cut. Guide your piece along the fence in several shallow passes.

Offset toward the blade. For a half-cove, measure from the initial feed angle towards the rear of the saw. The offset should be equal to the width of the half-cove you’re after.
Cut into the fence. As you raise the blade, it will cut a slot for itself in the fence. Cutting a half-cove on all four edges of a piece produces an elegant raised panel. 

Fast feed-angle setup. With the blade height set to match the cove depth, align the parallelogram jig’s two straightedges with the blade entrance and exit points. Note that you can cut coves from left to right or right to left. The choice is often made by where you find purchase for the clamps.

The parallelogram jig setup

If you find yourself cutting coves frequently, it’s worth the time to make a parallelogram jig. The jig makes determining the feed angle a snap. It consists of two long straightedges connected by two arms. The exact part sizes aren’t critical, just make sure the pivot holes are placed consistently so the straightedges remain parallel as you adjust the space in between. To use the jig, set the distance between the straightedges to match the width of the cove you wish to cut. Set the blade height to match the cove depth and place the jig on the saw table straddling the blade. Pivot the jig so the straightedge in front of the blade intersects the entry point, and the straightedge behind the blade intersects the exit point. This establishes the feed angle. Then set up your primary fence to accommodate the offset as described on p. 29. Remember to locate the primary fence in front of the blade to resist the cutting force.

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