Repair or replace?

All cutting tools eventually wear or break. It is up to end users as to how much tool life they are going to get before a cutter is gone for good. Resharpening cutting tools is a well-established practice, but when does it make sense to regrind instead of buying new? That’s a question any user of carbide and HSS rotary tools should consider. There are many variables in the equation: the tool’s geometry, substrate, coating, wear, damage and application all play a part in the decision to resharpen a tool.

Most companies, large and small, have their cutting tools resharpened, whether they do it in-house or outsource it to the OEM or, more commonly, a tool resharpener.

“Many of our customers are larger manufacturers,” said Jamie Dunneback, product manager of solid-carbide tools and gundrills for Star SU LLC, Farmington Hills, Mich. “Many smaller shops handle tool resharpening on a small cutter grinder, although they might use a local source, depending on the complexity of the tool.”

Courtesy of US Tool

Customers send in boxes of dull tools (above and below) and US Tool, after determining what is economical to resharpen and what is not, resharpens and packages them to be sent back. Customers ship from 30 lbs. up to 3,000 lbs. of tools per week to US Tool.

Although a tool resharpening house tends to resharpen all brands, most OEMs only accept their own and may even limit resharpening to certain product lines.

The determining factor when deciding to resharpen is cost-effectiveness.

“You can save from 35 to 80 percent on the cost of a new cutting tool by having it resharpened,” said Bruce Williams, president of US Tool Group, Farmington, Mo., with a savings of about 50 percent being the most common. With 400 employees, US Tool reconditions more than 500,000 cutting tools per week. Customers ship 30 lbs. to 3,000 lbs. of a variety of tools per week to US Tool.

Williams pointed out that even a 5 percent savings on some isolated cutting tools still makes resharpening worthwhile because the customer already owns the tools. “There is no procurement process, no purchase order needed for that specific tool,” he said.

Customers generally let the tool resharpener determine what tools are cost-effective to resharpen. “The customer sends in a whole box of dull tools—drills, endmills, custom tools, everything—and asks us to evaluate what is economical to resharpen and what is not,” said Jonathan Wilkof, manufacturing engineer, Stark Industrial LLC, North Canton, Ohio. In addition to operating as a job shop, Stark makes and resharpens cutting tools.

The main reason tools are not resharpened is because they have been resharpened enough times that there is no more value in them, according to Williams. “Either they are too short or too small in diameter.”

The second reason a tool might not be resharpened is damage, such as broken edges, structural problems or extensive margin wear. However, many broken or excessively worn drills are salvaged. The damaged section is cut off and the drill point is reestablished.

Have a Plan

If a tool is “pulled” before there is any chipping or significant wear, only a minimal amount of material is removed during regrinding, enhancing the economic gain. “We spend a lot of time educating our customers about tool wear, and most are knowledgeable, but we still get tools in all the time that are too far gone and not economical to resharpen,” Wilkof said.

Depending on the complexity of the tool geometries, Star SU works with customers to determine maximum tool life and when the tool should be taken out to maximize the number of regrinds and maintain part print tolerances, Dunneback noted.

The number of times a cutting tool can be resharpened depends on tool type and condition, but three to six times is typical. For instance, a general-purpose drill might be resharpened five or six times before being discarded, but a drill for making tight-tolerance holes might only be reground three times, according to cutting tool resharpeners.

Custom Benefits

Most types of round cutting tools are resharpened, with the majority being specials. “About 70 percent of our work involves custom tools, meaning the customer has a specific print and we recondition to that print, and about 30 percent are standards,” US Tool’s Williams said.

Courtesy of Specialty Tools

Before (above) and after (below) images show a worn solid-carbide drill resharpened by Specialty Tools.

Gear hobs and cutters, because of their high cost, are almost universally reconditioned. “Most gear cutters are designed for resharpening and reconditioning, where the tool user has an expectation of how much life the tool can provide and, therefore, has a systematic method of running the tool, pulling it out to resharpen and recoat, and then reinstalling it,” said Tom Bell, vice president of sales for cutting tools at Star SU’s facility in Hoffman Estates, Ill.

In general, the bigger the tool, the more economical it is to resharpen. “For example, a ½ “-dia., through-coolant drill that goes 10 diameters deep might cost $170 and can be resharpened for $25 to $30,” said Jerry Plummer, president of Specialty Tools Inc., Beloit, Wis., which specializes in solid-carbide high-performance drills. But Specialty Tools generally draws the line at solid-carbide drills 1⁄4 ” in diameter and smaller for sharpening because it is not as economical.

However, for large manufacturers that consume hundreds if not thousands of cutting tools monthly, it can still be economical to sharpen tools no matter the size. “Because US Tool processes 500,000 cutting tools per week, setup and operational costs are amortized,” Williams said. “Even twist drills costing less than $1 can be economically resharpened for heavy users of twist drills.” Carbide drills down to 1⁄16 ” in diameter are routinely resharpened, he added.

Whittling Down

It is inevitable that resharpening reduces tool diameter and length. Resharpening a drill or other tool that cuts on its tip affects its diameter less than other tools because only the end is resharpened, so the drill essentially remains the same nominal size. All drills have back taper, meaning they are larger in diameter at the end, so only a minute amount of diameter is lost, Williams noted.

When resharpening an endmill, however, the material removed from the cutting edges does decrease the diameter.

CNC machine tools have adjustable offsets, making it possible to apply resharpened tools. “CNC machines are programmed to compensate for the actual diameter and length of each tool and recalculate the toolpath to maintain the finished workpiece geometry,” Williams said. “More cost-effective and cost- conscious companies use cutter compensation effectively so they can use their tools multiple times.” (It is common practice for most tool sharpening services to label the tool package with the new diameter.)

When Stark Industrial designs cutting tools, it prefers to use cam relief for its endmills, Wilkof noted. “The benefit of cam relief is that when you resharpen the tool, you only have to resharpen the flute face, right at the cutting edge. If you have a primary and secondary relief, then you have to essentially resharpen the form itself and add back the primary and secondary relief, which takes more time and costs more.

“In the past 10 years there has been an explosion in tool geometries, with things like variable helixes and differential helixes,” he continued. “The first thing we do before resharpening is probe the helix to find the helix angle. We have to probe each flute because they are often different on some high-performance tools.”

The Last Coat