More and more woodworkers today are turning to insert tools because they offer an attractive combination of value, versatility and quality. But what exactly is insert tooling?
"The cutting edges are manufactured separately from the tool bodies and joined later," says Mike Serwa of Vortex Tools . "Other types of tooling typically have cutting edges that are permanently attached to the body, usually by a silver solder braze joint." Insert tooling is joined to a tool post by some type of mechanical clamp or screw.
A different grade of carbide can be used for insert tooling, says Mike Staudacher of Guhdo Tools . "The grade of carbide is most often a much better grade, because it's mechanically clamped and doesn't have to be brazed." In brazing, the material used to braze the knives to the tool post attaches to the carbide in the knife, changing the carbide slightly.
With a smaller grain size, less cobalt binder is needed, says Phil Horton, director of special projects for Leuco Tools . "This finer grain also results in a sharper, longer-lasting carbide that typically yields a better cut quality, longer life and more choices of carbide grades to do specific applications well," says Horton.
"Some carbide brazes very well. Some doesn't," says Michael McKenzie of Freud Tools . "With brazing you can't always get the angles you need in machining different types of hard woods, soft woods, composites or whatever. With insert tooling you get a better finish." That allows Freud to do different types of shear and hook angles with the inserts because they're ground outside the tool body, he says.
Insert advantages also extend beyond the cutting edge. Because inserts are attached to tool bodies mechanically, manufacturers can use different, lighter metals for tool bodies, says Mike Alster of Leitz Tooling . "Light-metal tool bodies minimize tool weight when addressing weight-sensitive tool applications."
Insert tooling's biggest advantage is that you can change out the cutting edge and maintain the original cutting specifications, says Linda Wyant, vice president of Her-Saf products.
"Traditional brazed tooling's performance will slowly deteriorate over the tool's life," says Serwa. "The tools' geometry is changing as it is sharpened. The carbide, or other tip material, becomes thinner and the tool diameter smaller with each service.
"Because insert tooling stays the same size, the customer can just change the cutting edges and start back up," says Serwa. "Traditional tooling requires machine adjustments to compensate for the slight differences in each individual (cutter)."
It also helps that the tools can be serviced in-house, says Yves LeMay of Gladu Tools . "If an edge gets chipped, the client can be back up and running in a few minutes, after replacing the knife."
The end-user can also maintain his own tools, says McKenzie. "He doesn't have to have multiple heads, multiple bodies, as in brazed, that he has to send out on a regular basis to get sharpened. He can have a single block or multiple blocks and send out the inserts or replace the inserts."
Being able to change the knives out quickly without adjusting the tool post results in constant cutting diameter and consistent profiles, says Alster.
What about cost?
"Initial cost of the tooling can be higher because the tool bodies typically are more costly to produce, and multiple sets of inserts are required to get them up and running," says Serwa. "In some cases, insert tooling will last longer. Some insert tooling has inserts that are mass produced and therefore inexpensive to use."
Alster says the initial costs of quality insert tooling can be substantially more than brazed tooling. However, a basic cost comparison, including such things as extended service-cycles, reductions in sanding and improved workpiece finish, will typically show substantial cost savings over time.
"Some insert tools can be used for multiple profiles or applications, and the need for multiple cutters is often eliminated because the inserts can be kept in stock and simply changed out when the edges are dull," says Horton.
With profile tools, you can have one tool body, but different inserts within a range. "If a tool costs $100, but you're able to get four profiles for a tool, it's now $25 a profile. Freud can do multiple profiles on a head, within limits, as long as the profile is not radical," says McKenzie.
Freud's profile insert tooling is cost effective because the company guarantees five sharpenings per insert tool, he says, and uses carbide that is 50 percent thicker than the standard. McKenzie says that the face of the insert that Freud makes is recessed, with the screw going below the insert. This allows sharpening of the entire insert, not just the cutting edge.
Maintenance costs must also be considered. Because the majority of inserts are disposable, sharpening costs disappear. Of course, the labor to change the knives has to be taken into consideration as well.
"All costs, including the price of the required tool bodies, sharpening charges and downtime due to tool changes, must be calculated over the expected service life of the tool," says Alster. "The total costs associated with the current tooling option should exceed the cost of an insert tool body, replacement inserts and downtime due to insert change time, over the lifespan of the original tools."
You want to use insert tooling where it's critical to maintain your original cutting specification, says Wyant. "Or if you're going into a project where you know that this material is going to eat up tooling. Insert tooling can reduce tooling costs. With insert tooling there is no brazing and it is hard. It will hold its edge a lot longer."
One disadvantage of inserts is that the tool design has to provide the space and the ability to fasten inserts into the body safely, says Serwa. "This situation will sometimes limit tool performance because design must revolve around factors other than the selection of good cutting geometry."
Another limitation of insert tools is the speed at which they can be run, although there is disagreement about this among manufacturers. Insert tools don't cut that fast, and they're limited in achieving the work loading or the larger chip loads that larger cutter bodies can get at higher speeds, says Staudacher.
There's a huge difference in cost with spirals, but the bottom line is the productivity gain. "A 1/2-inch spiral can run at up to 1,000 ipm. An insert tool can only run at max at 200 ipm. There's a huge productivity difference, especially if they're running larger parts," says Staudacher.
One disadvantage of insert tooling is its size, says Wyant. It takes a bit of dexterity to handle the small carbide pieces to screw in the body. "I feel like I need one more hand whenever I do it," she says.
Insert tools are often not as impact-resistant as their brazed counterparts, says Horton.
There are two types of wear on an insert, says McKenzie. The first is mechanical wear, which is the physical pounding of the tool as it makes contact with the material. The second is chemical wear, where the acids and glue attack the cobalt, which is a binder for the insert.
"We use a 3.5mm-thick carbide. It's rigid. There's more substance there, so it's not prone to failure. Plus we can choose different grades of carbide, harder grades that won't break," says McKenzie. Freud also adds titanium to reduce corrosion and enhance cut quality.
Manufacturers agree that insert tooling can be a cost-saving solution for many applications. V-grooving, parting, rebating, dadoing, tenoning, jointing and planing all require straight knives or standard-type inserts and are economical uses of inserts.
"Micro-grain carbide, the carbide used in inserts, provides the best combination of fine cutting edge quality combined with a relatively long run time in solid wood," says Horton. "Solid wood, characterized by variations in grain, dryness and cutting characteristics, is the most difficult to achieve consistent results in. Insert tools handle that challenge most effectively."
The most cost-effective applications involve tool designs that use standard inserts. "These inserts are usually indexable and are very inexpensive. Edgebanders and spoil board resurfacing cutters are good examples of common applications for which standard tooling can be effectively designed and incorporate standard inserts," says Serwa.
Applications where profile tolerance is important are also good for insert tools, says LeMay.
Alster agrees that the optimal application is long runs of consistent profiles. "A prime example would be the manufacturing of raised panel doors where the cope, stick and panel must fit exactly, and perfect finish quality is paramount," says Alster.
DeHart Tooling says that the stile and rail profile tooling for CNC routers that it offers provides optimum cutting conditions for high-speed machining of critical male and female profiles. Insert knives are available in carbide and alloy grades for all types of materials.
DeHart also offers formed profile abrasive strips, which allow users to change the abrasive in less than one minute and be right back to machining without adjustments. Having matched profiles for insert tooling as well as sanding heads increases total productivity by as much as three or four times.
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