Expressway to Stopped Flutes

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This article is from Issue 26 of Woodcraft Magazine.

For centuries, furnituremakers have cut parallel round-bottomed grooves, known as flutes, not simply to add visual interest, but as a silent nod to the stone columns of classical architecture. Considering the flute’s popularity, it’s not surprising that this detail has inspired dozens of articles and fancy accessories, all promising straight-as-an-arrow grooves, perfect spacing, and burn-free ends. This simple sled puts even the best to shame.

The best thing about this jig is that it’s stone simple. With just a few pieces of wood and a guide bushing, you can turn your plunge router into a first-class fluter. We’ve designed the sled to mill the delicately fluted stiles for the display case on page 24, but you can easily re-size it for any fluting job. Invest a little extra time testing and tweaking the sled during construction, and you’ll enjoy flawless flutes every time.

Note: The display case’s fluted stiles are a little trickier than most. To allow for the assymetrical top and bottom stop spacing, you’ll need to make a sled with two pairs of of holes. The longer sled automatically controls the flutes’ starting and stopping spots.

As shown shown in Figures 1 and 2, you'll rout flutes 1 and 3, then rotate the sled to rout flutes 2 and 4. If the flutes stopped the same distance from the top and bottom, you’d need only one pair of holes along the sled’s centerline.

Fine-Tuning Your Flutes

Minor measuring or marking errors can cause major spacing problems. Laying out the centerlines of all four flutes takes a few more minutes than marking two, but this extra step can help ensure that your guide holes are exactly where they need to be.

In some cases, you might find that the measuring and marking tools in your shop aren’t accustomed to 1/32" precision. For the sharpest lines, draw out the flutes on your computer or drafting board then affix with spray adhesive that paper template to your jig’s base to serve as a dead-on drilling guide.

Make the sled

Cut the sled and rails to the dimensions in Figures 1 and 2. Now mark two lines 21/4 in from both ends of the base. Because it’s important that the holes are the same distance from each end, scribe a layout line onto both ends as shown in Photo A.

Attach one rail so that it’s flush with one edge of the base. Measuring from the inside edge of your rail, mark out the centerlines of flutes 1 and 3 on one of the scribed lines. Normally, 32nds of an inch aren’t worth worrying about, but this time is different because any error will double when you flip the jig. You may also discover that your eye has the uncanny ability to catch even the smallest spacing irregularity. 

To help place your marks, consider using a self-guiding rule (#125477, $11.99), as shown in Photo B. Carefully outfit your drill press with a fence and stops to ensure that the guide holes are drilled exactly where they need to be.

To complete the sled, place a piece of scrap that’s the same width as the piece you intend to flute against the fixed rail and attach the second rail. The sled should straddle the board snugly, but still slide from end to end.

Set the marking gauge with a etched ruler then scribe the sled to establish two guide lines that are the exact same distance from both ends.
Making a mark that’s accurate to a 32nd inch can be tough for tired eyes, without a little help. The laser-cut holes keep the pencil point right on track.

Using the jig

You’re almost ready for your first flute. Chuck in the fluting bit and add a 1/2" OD guide bushing onto your plunge router’s base. Adjust the bit to rout a 3/32"-deep groove.

To test your jig’s flute spacing on a practice board, secure the board to your bench between two hardwood blocks, like the ones shown in Figure 1 and the opening photo. In addition to protecting the stile from bench dog damage the blocks provide a reference stop for the ends of your sled.

Starting near the center of the board, turn on the router, plunge the bit to full depth, and slide the sled from end to end. After routing your first flute, raise the plunge bit, insert the bushing into the adjacent guide hole and rout the third flute. To rout flutes 2 and 4, simply rotate the jig and repeat.

You can now inspect your machining. Your flutes should be straight, smooth, and perfectly spaced. With some light sanding, they should be ready for a finish coat. 

Don’t get too upset if your flutes are not perfect on the first try. Review the tips in “Fine-Tuning Your Flutes” opposite page, make a new base, and take another practice routing run. 

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