Straight Router Bit for Spline Grooves, 1/4 in Shank

A frame for pressed cane needs a groove for the spline, and this bit cuts it. It is a carbide straight bit with a 1/4 in shank that plunges straight down into the face of the frame, in three widths that match the three most common spline sizes:

• 1/8 in groove for #7 spline
• 3/16 in groove for #8 spline
• 1/4 in groove for #9 spline

Because it cuts down into the face, it works on new frames and on assembled ones: a chair seat, a stool or a cabinet door that never had a groove. Nothing has to come apart.

Guide the router in one of two ways. For curves, round seats and grooves that run all the way round, make a template from hardboard or MDF and follow it with a template guide bushing (not included). Along straight sides, the router's edge guide running on a straight edge is enough.

Find the depth on scrap of the same wood first. Soak a short piece of spline, tap it into the test groove over a scrap of cane, and adjust until it goes in snug and sits flush. Then cut the real groove in several shallow passes instead of one deep one. The groove comes out cleaner and the bit runs cooler.

A chair that already has a groove does not need this bit. The old groove only needs cleaning, which a caning chisel does without changing its width.

Safety, every time:

• Unplug the router before you change or adjust the bit.
• Keep the guards in place and wear eye protection; hearing protection is wise too.
• Clamp the work and the template, and keep both hands on the router.
• Let the router reach full speed before the bit touches the wood.

Decide on the spline first, then pick the bit to match it: #7 spline needs the 1/8 in bit, #8 the 3/16 in and #9 the 1/4 in. If the new groove should look like the grooves on furniture you already own, measure one of those and use the same size.

Check your router before you order. The bit has a 1/4 in shank, so the router needs a 1/4 in collet. A plunge router makes it easiest to start the cut in the middle of a frame. If you will follow a template, the router base must take a guide bushing, and the hole in the bushing must be large enough for the bit to pass through without touching.