However, straight bits aren’t the only choice when it comes to flush trimming. Spiral bits offer several features that are particularly attractive to professional woodworkers and avid hobbyist woodworkers. As the name implies, spiral bits have their cutters spiraling around the body of the bit, unlike straight bits, which have their cutters parallel to the body of the bit. This helical design causes the cutter to enter the wood at an angle, producing a shearing cut, rather than having the whole cutter enter the wood at once, as happens with a jointer or planer blade. There’s always some portion of the cutter in continuous contact with the stock, which produces a much smoother cutting action.

As a result, spiral bits run cooler, generate less vibration, are more efficient at ejecting waste, nearly eliminate tearout, and produce a much cleaner finish that straight bits.

Spiral bits can be made of high speed steel or solid carbide, and they come in three styles: up-cut bits, which force waste away from the tip of the bit (resulting in a cleaner bottom edge on stock); down-cut bits, which force the waste toward the tip of the bit (giving a cleaner top edge); and compression bits, which have an up-cut design near the tip of the bit and a down-cut design closer to the shank. The design of a compression bit serves to compress the waste towards the center of the bit, resulting in clean top and bottom edges. Compression bits are widely used in the CNC industry because they can be run at high feed rates and they deliver clean finishes and a long lifetime in abrasive materials.

Until recently there have been few bearing guided spiral router bits available, so that woodworkers have had to use spiral bits with guide bushings. While guide bushings are useful in some routing tasks, including edge trimming operations, they’re awkward to use on a router table. More importantly though, guide bushings aren’t always concentric with the bit.

Whiteside, one of the last remaining router bit manufacturers in North America, have introduced a new line of Ultimate Trim Bits.

These solid micrograin carbide spiral bits feature high shear cutting angles with compression action. The cutting edge closest to the tip has an up-cut design, while the lower cutting edge has a down-cut design. And, of course, the result is no tear out on either the top or bottom edges of your stock.

There are three styles to choose from: an end-bearing flush trim bit, which is ideal for flush trimming with a hand held router (though you can also use it on a router table); a shank-bearing pattern trim bit; and a double-bearing trim bit. Both the pattern and double-bearing bits are excellent for use on a router table. The double bearing bit lets you rout half your stock in one direction against one of the bearings, flip the work piece over, and then rout the other half in the opposite direction against the other bearing, without repositioning your pattern.

I decided to try the pattern trim bit (UDP9112), as I could use it for template routing, and also for plunge routing.

The Whiteside Ultimate Pattern Bit (UDP9112) comes packaged in a durable plastic container that you can use to store the bit, or safely transport it, if needed, to a job site. The container is also handy for protecting the bit if you send it out for re-sharpening. The bit is expensive – $282. Though not expressly endorsed by the manufacturer, it is entirely feasible to re-sharpen the bit at least once. Doing so will reduce the cutter diameter by .005″ to .010″ in relation to the diameter of the bearing – about the thickness of a sheet of printer paper. Having it re-sharpened, even once, makes the cost of ownership much more affordable. Most competent sharpening services can do the job (including Quality Saw & Knife and Carbide Tool Works in Canada), or you can ship the bit back to Whiteside who will do the job at a cost of $12.

The UDP9112 is impressive in size, measuring 3-3/8″ long overall, and weighing almost 6 ounces. It features a 7/8″ diameter, 1-1/8″ long cutter, and is equipped with a 9/32″ x 7/8″ bearing and a stop collar. The cutter is made of industrial-quality solid micrograin carbide. The bit is precision machined and superbly finished, with sharp, polished flutes. Compared to other spiral bits the UDP9112 is simply massive.

As you might expect, this bit has a 1/2″ shank. A larger shank provides a lot more surface area when you’re tightening it in the collet, which makes the bit much less prone to slip out of the collet. Plus, you don’t have to be concerned about the shank breaking under load, as can happen with 1/4″ shanked bits.

What I find particularly impressive about the UDP9112 is the ‘one-two’ punch it offers – a large cutting radius and those opposing aggressive shear angles, two that are angled upwards and two angled downwards. The result is virtually no vibration, no burning, no tearout, and exceptionally clean edges.

When using this bit I set my router speed to between 16,000 and 18,000 RPM. I don’t get too concerned with the feed rate, and probably feed the stock just as fast as when using smaller diameter bits. I haven’t experienced any tearout, even when trimming some fairly knurled grain Ash. If anything, I am somewhat more cautious about too slow a feed rate, which can build up extra heat, and leave burn marks on the edge of stock.

To date I’ve used the UDP9112 bit on about 70 linear feet of hardwood and several dozen linear feet of plywood. I also tried it on medium density fibreboard and melamine. Without exception the UDP9112 is equally adept at producing exceptionally clean cuts on all four materials. And not only on edge grain – it gave consistently smooth cuts on end grain, which can’t be said for straight bits. Along with its clean and smooth cutting action the UDP9112 clears debris very effectively, reducing bit heat, and ultimately prolonging the serviceable edge of the cutters.

Overall, I am very pleased the Whiteside Ultimate Router Pattern Bit. It gives the best finish of any router bit that I’ve used. If you do a lot of pattern work, you can’t go wrong with this bit. Remember that your router is only as good as the bit you use it with.