Reportaje de Brocas

En la revista especializada FINE WOODWORKING, aparece un articulo en la que se realiza una prueba para encontrar la respuesta a lo que mas    preocupa    a la gente que utiliza brocas para router. Cual broca resiste por mas tiempo sin perder el filo y   cual    broca    realiza el corte mas limpio.
Para esta prueba, se sometieron 17   marcas    de   brocas    a   una severa prueba. Entre ellas WHITESIDE, AMANA RIDGE CARBIDE/ LIBERTY, OLDHAM VIPER, FREUD, FREUD, MLCS, CMT, BOSCH, WOOTEK, CARB-TECH,   PORTER-CABLE,    JESADA,      EAGLE AMERICA, ROCKLER, etc.
Se eligieron solamente brocas de 1/2"   de    diámetro, con vastago de 1/2", las cuales pensaron serian representativas de la calidad que el      fabricante le imprime a toda su línea de brocas. Se colocaron en un router CNC de control numérico y se procedió a ranurar melamina de 19 mm., a una profundidad de 1/4", por una longitud de 76 metros.
La manera de medir   el    rendimiento    entre   las     brocas es por CPF (Astillas por pie lineal). WHITESIDE resulto ser el ganador de esta    prueba    entre las 17 diferentes marcas de brocas sometidas, confirmando una vez mas su    alta    calidad   y     liderazgo en el mercado mundial

Fishing lures and router bits have a lot in common: There are more varieties to choose from than I'll ever need. Dressed up in slick packaging with exotic names like Trout Teaser or Roman Orgy, new lures and bits ignite dreams of pride and passion. Bigger catches. Sexier moldings. I've amassed an embarrassingly rich collection of both. But when it comes time to attach one to the end of a rod or router, more often than not I pick the ordinary over the exotic.

For tried-and-true router tackle, nothing beats straight bits. These workhorses are good for a host of tasks, and I use them for rabbeting, dadoing, trimming, mortising and even tenoning. I've tried many brands of bits and have a few personal favorites, but I've never been sure if I was spending my money on the best. It's impossible to compare bits when you buy them at different times and use them for operations in dissimilar materials.

I set out to develop an objective, test to compare router bits and to settle the question of which bits are best.
Along the way I learned there are a lot of scientific ways of testing metal and carbide, but most of them require expensive equipment and an even more expensive education to operate.
But with the help of a metallurgical engineer, a mill-shop operator and representatives from router manufacturing companies, I came up with a fairly simple test to measure what woodworkers really care about most: which bits last the longest and cut the cleanest.
To keep the size of the test manageable, I chose only 1/2-in.-dia., 1/2-in. shank, double-fluted carbide-tipped straight bits. This style of bit ought to be indicative of the kind of effort a manufacturer puts into the rest of its line. Most bits had 1-1/2-in.-long tips. I bought the bits through retail outlets and mail-order companies.

I paid anywhere from a scant $7.65 (Carb-Tech from Trendlines) to $23.10 (Jesada), but the cost averaged out to about $14 per bit. Right out of the box there were some notable differences.

Many of the bits under $10 had thinner carbide tips than the more expensive bits. The bits were manufactured in many locales, including Israel, Italy, Taiwan and the United States.

I delivered the bits to Harris Enterprises, a mill shop and retail outlet in Manchester, Conn.
There, a computer numerically controlled (CNC) router ran the bits through 248 lineal ft. of 3/4-in.-thick melamine-coated flakeboard at the same depth (1/4 in.) and speed and under the same load. The flakeboard was purchased from one manufacturer. Flakeboard from the same lot has a pretty consistent density, unlike solid wood, which can vary greatly because of irregularities. The melamine requires a very sharp bit to cut without chipping. As a bit dulls, chipout increases, and the missing chunks of melamine make it easy to see how well a bit is holding up. Depending on many factors, including type of wood, cutting technique and imperfections such as knots, you may get more or less life out of a bit when cutting solid wood.

A note on melamine-coated flakeboard:
The best bit for cutting grooves in this material, according to some, is a down-cut spiral bit, which will minimize chipping of the thin melamine surface. But I wasn't trying to find the best bit for cutting melamine. In the end, some of these bits were right at home with the material and sliced away with surgical precision.
Other bits tore away at the thin skin of melamine like old sharks with blunt teeth.

Making router bits is a labor- intensive undertaking, even in a modern plant. To get an idea of what goes into making bits,

I took a tour of Oldham's new router-bit and sawblade manufacturing plant nestled in the foothills of the Appalachian mountains in West Jefferson, N.C. The plant runs night and day, turning out thousands of Viper-brand router bits and sawblades per week.

Two main ingredients go into making carbide-tipped steel-shank router bits: carbide and steel bar. Steel bars as long as a pickup trick are plunged into a self-feeding turning center, which via computer instructions turns the bit's profile. Each bit takes a few minutes to turn. When done, the machine cuts the blank, ejects it, feeds some more bar stock and begins turning another bit.

Flutes must be cut into the blanks at a milling machine. From there, the bits are carted to a brazing station. Depending on the type of bit and size of run, they go either to an automated brazing machine or to a table where workers braze the carbide tips onto the bits, one by one.

After brazing, the bits are sprayed with polytetrafluoroethylene (PTFE), an antistick coating, and then put in an oven to bake the finish.

After baking, the bits are allowed to cool off. Then they are placed in a centerless grinder, which trues the shank, and then the ends of the bit are shaped. The faces of the carbide tips are ground flat, and the relief angle and outside diameter are ground to their final shapes, all within a few ten thousandths of an inch.

All along the way, sample bits are withdrawn from the assembly line and tested on scraps of wood. Once a lot passes inspection, it's carted off to the packaging center. To make a typical run of 500 bits that are all the same shape, it takes three to four hours from start to finish.

Most router bits are either carbide tipped (with steel bodies) or solid carbide, which stays sharper longer. Industrial users spring for even tougher bits made of diamonds, but they're 10 times more expensive than carbide, not a viable alternative for a small shop.

The carbide used to manufacture router bits is tungsten carbide, a compound made up of carbon, tungsten and other trace metals. In its raw form, the material is a fine powder (particles under 1 micron) that looks much like the dry ink found in copying machines. The properties of a carbide are dependent on many things, including the mix of compounds. Hardness is a critical property.

Trace amounts of other metals such as cobalt act as binders and are added to the carbide. The powder is placed in a form and pressed, then baked in a furnace under high pressure and high temperature, a process known as sintering. On steel-shank tools, carbide tips are attached by brazing.

Carbide must have a balance of two key qualities: wearability and impact strength. Wearability refers to the hardness of the carbide or its ability to stay sharp. Impact strength is just that: the ability to withstand a sudden shock, such as running into a knot.

Very hard carbide is brittle and may shatter upon impact with a knot. Softer carbide can take impact, but the edge won't last as long. Manufacturers settle on a carbide grade that they believe strikes a balance between these two characteristics based on the material that the tool will be used to machine.

Jim Brewer, director of operations for Freud, explained how carbide wears. "Particles of carbide actually break off, exposing fresh particles. Anything that attacks the binder allows more particles to break off because the binder gives up. The binder is ultimately what fails."

The finer the micrograin, the longer a cutting edge will remain sharp.
"The analogy would go like this," explained Brewer.
"Take a handful of sand and a handful of gravel. If you remove a few grains of sand, there's still a lot of sand left over.
But remove a few chunks of gravel, there's not much left."

After the bits were run, I took them and the sheet goods back to the Fine Woodworking shop and pored over the damage. To simplify the data and not turn this into a science-fair project, I counted the number of chips (chipout) per foot on the edges of the grooves. I focused on the first 25 ft., when the bits were fresh, and on the last 25 ft., when most of the bits were near the end of their lives. I relied on my eyes and index finger. If I could see or feel a chip, I counted it. The chips ranged in size from a grain of salt to a chunk of coarsely ground black pepper.

I added the number of chips from the first 25 ft. to the number of chips from the last 25 ft. and came up with an average number. Comparing the overall averages gave me an idea of how a bit did both in quality of cut and in longevity. But a more important rating might be the first number--the number of chips per foot that a bit produced at the beginning of the test run.

Depending on the job or what bits are readily available, it might be more important to have extremely clean cuts and toss out the bit as soon as it shows signs of wear. Decide for yourself.

Chips per foot (CPF) was our way of measuring each bit's performance against the others. We ran 17 double-fluted, carbide-tipped straight bits through 248 ft. of melamine-coated flakeboard at a depth of 1/4 in. using a CNC (computerized) router. The best-performing bits caused the least amount of chipout, measured in CPF. We recorded CPF numbers for the first 25 ft. and the last 25 ft. of the run, and an average was computed. The bits are ranked based on this average. (NA indicates that the bit wore out and produced continuous chipping.)

Using overall average as a measure, the top four finishers were the Whiteside, with an average of 0.2 chips per ft.; the Liberty, with an average of 0.3; the Oldham Viper, which averaged 0.5; and the Freud, which came in at 0.6. These bits cut cleanly at the start and at the end of the test. It's important to note that both the Whiteside and Liberty bits cut chip-free for the first 25 ft.

The next group of bits that stood out included the Amana (1.5 chips per ft.), the Carb-Tech (0.9), the MLCS (1.6) and the CMT (1.8). A third group of bits, including the Bosch, Eagle America, Porter-Cable and Woodworker's Choice, cut very cleanly when new but wore out sooner than the top four finishers.

There appears to be a relationship between the noise a bit makes and the quality of cut it produces. The CNC router operator noted that the cleanest-cutting bits were also the quietest. That means the bits were machined to tight tolerances, with very little runout and hence little vibration.

The Jesada bit snapped about halfway through the test. Problems, however, surfaced right at the start. The router operator noted that the bit was very noisy and cut poorly. I bought a second Jesada bit, and the same thing happened. I called Carlo Venditto, the president of Jesada, who acknowledged that the company's 1-1/2-in.-long bits were improperly engineered, and they were subsequently recalled. Venditto explained that the rake angle was insufficient (causing chipout), and too much material had been machined off the shank (resulting in a weak point). I bought a third bit, which had been reengineered, and although it didn't snap, it also performed relatively poorly.

It's not clear whether there's a relationship between price and quality. One of the cheapest bits, the Grizzly S-Y ($7.95), performed poorly (7.4 chips per ft.). But The Woodworker's Choice bit, which also cost $7.95, did quite well at the outset (0.5) but suffered heavy wear by the test's end. For small jobs, the Woodworker's Choice might be a good value. But better bits generally cost about $15 or more. Ironically, the most expensive bit, the $23.10 Jesada, performed poorly.

The relationship between quality and country of origin is good news for the national pride: The Oldham, Whiteside and Liberty bits, which performed well, are made in the United States. But you can also find good bits imported from Italy (CMT and Freud) and Israel (Amana). Most of the Taiwanese bits (Carb-Tech, Grizzly S-Y, Rockler, Woodline, Woodtek, Woodworker's Choice) didn't perform as well. One exception was the MLCS bit, which did well.

There does seem to be a relationship between carbide thickness and performance. The Taiwanese bits generally use thinner (about 0.03 in. to 0.05 in. thick) carbide tips. The better-performing bits all have 0.06-in.-thick to 0.08-in.-thick carbide tips.

Is it fair to draw conclusions about a company's entire line of bits based on testing one randomly picked straight bit? Yes and no. Sure, every company runs into quality-control problems occasionally. But when I'm in the middle of a project using expensive materials, and the clock is ticking, I don't want excuses. I'll go with the manufacturer whose products worked well for me on the first try. For the time being I'll presume that if a manufacturer's straight bits are good, then I'll be more inclined to invest in its other products as well.