Coving On The Tablesaw: It’s All About Playing The AnglesComments (0)
When considering a tool to make curves, the tablesaw certainly doesn’t spring to mind. However, there’s one kind of curve this machine is surprisingly good at making: coves. No, you wouldn’t use a tablesaw to produce runs of architectural cove moldings, but it’s great for creating short lengths of waist molding, crown molding, or other transitional elements for furniture. You can also employ the coving process to produce raised panels or even boxes.
Coving on the tablesaw is a relatively simple matter of using an auxiliary fence to guide the stock at an angle over a standard blade, taking very light successive passes. The height of the saw blade determines the depth of the cove, while the angle of the fence determines its width. The more severe the fence angle, the wider the cove.
Coves can be either symmetrical or asymmetrical. The former is made with the blade standing at 90°, while the latter is made with the blade tilted. It’s easy to set up to cut a specific symmetrical cove using a shop-made parallelogram jig designed for the purpose. Asymmetical coves, on the other hand, demand either trial and error or calculations that are too complex to get into here, so we’ll stick with symmetrical coves in this story.
Make a parallelogram jig
The easiest and most accurate way to set up to cut a symmetrical cove of a specific depth and width is by using a parallelogram jig like the one shown in Figure 1. Make it from any straight-grained wood to the approximate sizes shown in the drawing (go with the larger size to maximize use of a 10"-diameter saw blade). The only important criteria are that the legs are straight and of equal thickness and that the pivot holes are equidistant from each other.
The jig will need to lay flat on the saw tabletop, so either countersink for flathead machine screws or counterbore for roundhead screws. Make sure to include lock washers under the wing nuts so the unit will lock securely in use.
Prepare yourstock and fences
It’s important to dress your stock to a consistent thickness and width before coving because an inconsistent width can cause binding between fences.
A fence must be straight, as well as stout enough to resist bowing under pressure. It must be long enough to span your saw table with enough extra length to allow clamping the overhang to your fence guide rails if necessary.
Although you really need only one fence to saw symmetrical coves, a second fence ensures against workpiece wander and prevents possible collapse of a deeply coved piece, as shown in Figure 2.
Setting up the cut
1. Install an appropriate saw blade. In my experience, just about any decent-quality 40- or 50-tooth combination blade works fine. I avoid using thin-kerf blades on the off chance that the sideways pressure involved might distort the blade.
2. Mark the width and depth of your desired cove onto the end of your dressed stock. There’s no reason to draw out the complete shape of the cove; just strike lines on the end of the stock that note the extents.
3. Placing the end of the stock against the blade, set the blade height to match the cove depth (Photo A).
4. Again using the markings on the end of the stock as a gauge, set the inside edges of the parallelogram jig to the width of the cove (Photo B), and then lock the jig tightly at that spacing.
5. Place the parallelogram over the blade, and rotate the jig clockwise until the front and rear teeth just graze the legs at table level.
6. Use a fine-tip marker to draw a line on the table along the inner edge of the right-hand leg at each end, as shown in Photo C. Alternatively, you can align the edge of a short piece of masking tape with the leg at each location.
7. Locate your fence to the right of these marks a distance equal to the width of the cove’s flat shoulder. Now secure this front fence in place, using spacer blocks if necessary to clamp to your fence rails (Photo D).
8. Place your
workpiece against the fence, and then place a secondary “rear” fence against
its opposite edge. Secure the rear fence,
lower the blade below the table, and slide the workpiece full-length between
the fences to make sure it doesn’t bind in its travel. If it pinches anywhere,
adjust the rear fence to create snug, but easy, workpiece travel along the full
length (Photo E). This practice run is important to ensure good tactile
feedback during the cut.
Making the cuts
1. Adjust the blade so its top-dead-center is level with the tabletop. Then raise it so that it projects about 1⁄16" above the table, noting about how much of a handwheel turn that takes.
2. Turn the saw on, and feed the workpiece slowly, holding it down firmly against the table and maintaining pressure against the front fence. To get a feel for the process, feed slowly at first, increasing your feed speed until you feel a consistent, smooth resistance and a steady hum of the blade biting into the wood.
3. For your next pass, raise the blade another 1⁄16", and feed in the same manner, again adjusting your feed rate for consistency in the feel and sound of the cut.
4. After taking a few passes, stop and measure the distance between the edges of the cut and your width markings to make sure your cut is centered. If necessary, adjust the position of your fences to get things back on track.
5. Repeat the process for all successive passes (Photo F). As you cut deeper, you’ll be removing more wood with each pass, so watch your feed speed, slowing it or lowering the blade if necessary. This cutting can raise a lot of dust, especially if your saw isn’t hooked up to a dust collector. If necessary, stop the saw occasionally, and vacuum up the dust.
6. Make the last cut or two very light, feeding very slowly and consistently to produce as clean a surface as possible.
Expect to do some smoothing of the toothed surface. A gooseneck scraper works well for the job, or you can create a complementary sanding block made from stiff packing foam, as shown in Photo G. Also check out the article on page 37 for a variety of commercial products for sanding curves.
Safety At The Saw
· Always unplug the saw when setting up for a cut.
· Wear eye and ear protection as well as a dust mask.
· Always use pushblocks to feed the workpiece while holding it down
firmly against the saw table.
· As with any tablesaw operation, do not stand directly behind the workpiece when feeding; remain off to the side.
· Stay attentive to the sound and feel of feeding. If the operation seems balky, lower the blade and/or decrease your feed speed.
Sawing Half-Coves For Raised Panels
If you don’t have a router table and panel-raising bit, tablesaw coving affords you the opportunity to make raised panels for cabinet doors and other assemblies.
The technique is similar to that for making full coves, except that the setup is a bit different, and you don’t need double fences.
To prepare, first adjust the distance between the inside edges of your parallellogram jig to twice the width of your desired half-cove. Raise the blade to a height that matches the depth of the finished cut, position the jig around the blade, and mark the table as shown in Photo C on page 30.
To determine fence placement, measure over to the left of your marks a distance equal to the full width of your desired half-cove, and draw reference marks there.
Lower the blade below the table, and secure a stout front fence to the table against your lines. Then cut as before. There’s no need for a secondary fence; just maintain consistant pressure against the primary fence.
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