Canadian Woodworking

Routing Basics – Part 6: Specialty Bits

Author: Michael Kampen
Published: April May 2008

For jobs that are a bit out of the ordinary, you need a different kind of router bit.

A basic selection of straight, edge profiling, and joinery bits will handle just about all your routing needs. But for jobs that are a bit out of the ordinary, you need a different kind of router bit.

Manufacturers are constantly bringing new special purpose bits to market that make routing tasks easier and our time in the shop more productive. Here are four of my favourite specialty bits.

Slot cut with Lee Valley slot cutters

Edge banding with Woodline V-Groove bit set

Dado routed with Dimar insert bit

Adjustable Slot Cutters

The slot cutter is a versatile bit (see Feb/Mar ’08, Issue #52) that gets a great deal of use in shops that do a lot of casework. It excels at cutting slots for cabinet backs and drawer bottoms, and is safer and more efficient for cutting slots for splines when gluing up panels. In a busy shop, when you are milling a lot of slots, you need to have a lot of slot cutters in different diameters and widths on hand; and changing the slot cutters on the router table takes time. As well, there are times when you need a slot of a specific thickness, which requires you to fuss around with the height, making multiple cuts to get just the right slot width.

Adjustable slot cutters solve this problem by enabling you to easily and quickly adjust the specific slot width without removing the cutter from the router table. Dimar Canada’s ‘D-Slotter’ comes in two formats (

One adjusts to cut slots from 1/8″ to 1/4″ wide (#108R4-3-5.5), and the other from 1/4″ to 1/2″ (#108R4-5.5-10). You simply release the spring loaded nut on the top of the bit and rotate a dial to the new slot width. Each rotation of the dial changes the slot width by .004″. The cutters mill a slot 1/2″ deep, and come only with 1/2″ shanks. The cutter head can be resharpened and replaced. I’ve been really pleased with these two bits – they’re fast and efficient, so the time saved will surely offset the initial higher cost (around $210).

Screw Slots

Wood moves, and whatever we can do to accommodate this movement makes for good workmanship. Whenever I screw cleats, runners, aprons or other solid stock to solid wood panels I use screw slots. The elongated holes allow the panel to expand and contract without the panel splitting or the screws coming loose. For years my method involved using a spiral bit on the router table to cut a stopped slot followed by another larger bit to cut the recess for the screw head. Lee Valley’s Screw Slot bits ( provide a simple and elegant one cutter method to cut these slots. The bits come in two formats. One (#16J11.60) cuts a countersink slot for screws with tapered heads, and the other (#16J11.70) cuts a counterbore slot for flat head screws. Both are sized for the more common #8 screws and come only with 1/2″ shanks.

Edge Banding

In my shop I use plywood for most of my cabinetry work, applying solid wood trim to all the cut edges, whether they will be exposed or not. Previously I used square edge trim, which results in a thick edge with a visible glue line. The V-Groove bit set (# WL1324) from Woodline ( provides a clever alternative to square edge trim. The “V” shape of the cut makes for a thin, almost invisible glue line at the edge, while the interlocking shapes help align and hold the trim in place during glue-up. This set of bits is also an excellent choice when edge gluing longer boards into a larger panel. You will loose some width using these profiles to glue up panels, but the profile of the cut will ensure that the two boards mate evenly and precisely along the entire length. This will help overcome the tendency of boards to slip relative to each other as the clamps are tightened. At $59 you are getting great value.

Replaceable Inserts

While a weekend woodworker might have an investment of several hundred dollars in router bits, it would not be unusual for a full-time woodworker to have a thousand dollars or more invested, and all these bits need to be resharpened or replaced on a regular basis. When you think about it, the only part of the bit that really needs to be changed is the cutting edge. The shank simply provides the mechanism for connecting the bit to the router. That would be like buying an entirely new car when your tires wear out.

Dimar Canada has introduced a line of router bits that feature replaceable carbide inserts. This is nothing new in the woodworking industry – the body of a shaper cutter is much larger, and much more expensive, than a router bit. A flush trim shaper cutter might cost $250 in comparison to a $25 straight edge router bit. The tooling costs are primarily in the shaper cutter body. So manufacturers screw the cutting edges (the inserts) onto the cutter body so they can be easily replaced.

Right now you won’t find too many replaceable insert router bits on the market. Dimar Canada lists 29 models. However, I think that over the coming years you will see a lot more styles available. They significantly reduce the lifetime cost of a router bit as once you purchase the body, you only pay for the replacement inserts. Insert replacement is a snap, and downtime unaffected. Most of the inserts have multiple cutting edges, so when one edge becomes dull you simply rotate it to expose a fresh edge. When all the edges are dull you replace the insert. Dimar’s two flute straight no plunge bit (#7RL8-12-2), features a 1/2″ shank, a 1/2″ cutting diameter and 1-3/16″ cutter length. The bit (with 2 inserts) costs $98, and replacement inserts cost $11 each. While more expensive than a conventional straight bit, in the long run the replacement bit will pay for itself in lower costs, as it is less expensive than resharpening the bit. Other Dimar bits include rabbeting, straight plunge, multi-bevel, round over and flush trim.

Specialty bits like these will likely appeal more to the professional or serious part-time woodworker than weekend woodworkers or DIYers. The up-front costs are high, with the savings coming over the long term.

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