by Kip Hanson
These alternatives to drilling can help save time on internal threading
The spot drill, drill, and tap routine is a tried-and-true metalworking process that manufacturers have used to produce millions of threaded holes. For shops willing to spend the extra money on solid carbide drills, the first step in this three-part threading dance can often be eliminated, but the fact remains that drilling the minor diameter is a time-consuming but necessary evil for most internal thread-making operations.
Cutting Costs
Drew Strauchen, executive vice president at GWS Tool Group, has an alternative. It’s called the Cost Cutter, a combined drill and tap designed and manufactured by North American Tools, a division of GWS. It is a premium high-speed steel (HSS) cut tap with a modified split-point drill on the front end. It’s able to drill a hole measuring 75 per cent of the tap diameter and up to twice its depth before engaging the tool’s tapping section. Special lengths and diameters are available, and the company offers a “QC” quick-change version as well.
In a CNC or automated drilling machine, the drilling operation is programmed at the appropriate feedrate and spindle speed for the workpiece material. Once the drill point breaks through, these parameters must be adjusted for the subsequent tapping operation. The Cost Cutter can also be used in drill presses and even a power drill—success here obviously depends on a steady hand—with the operator applying the appropriate pressure at the different drilling and tapping stages.
“For job shops and high production environments, the Cost Cutter eliminates a tool change,” Strauchen says. “For maintenance shops and fabricators, it reduces inventory and saves tapping after drilling a bunch of holes. It also simplifies things for the operator, as there’s no guessing what size tap-drill to use. On die castings, sheet metal, or any tapped through-hole up to 2 x D, it can be a big timesaver.”
Thrilled to Meet You
Emuge Corp. offers a similar threading solution, although it is not yet available to the general market. In late 2019, the company developed an entirely new type of tool—the Emuge Taptor—in collaboration with European automaker Audi. It is a coolant-fed, solid carbide combination drill-tap tool that uses a single threading flute located directly behind the drill tip to cut the thread.
Based on this description, it sounds like any other drill-tap combo tool, albeit one made of carbide. Not so, says Frank Joswig, national sales manager for Canada. “The Taptor drills at a feedrate equal to the thread pitch, so for a 1/4-20 thread, that would mean drilling the hole at 0.05 in. (1.27 mm) per revolution,” he says. “Granted, feeding that fast means you can’t use it in titanium or Inconel, but for short chipping materials like die-cast aluminum, it’s quite impressive. Audi has reduced the cycle time on an engine block operation from 80 seconds to 47 seconds by using a Taptor with one of our Speedsynchro tapping holders.”
As mentioned earlier, tapping is a mature thread-making process, and cutting tools able to drill and tap in a single operation are clearly a timesaver. Yet there’s another alternative, one that should appeal to anyone looking for greater size control and less risk of breakage than taps—in Emuge’s case, it’s called the BGF Thriller, a combination drill, thread mill, and chamfer tool that, as with its cousin the Taptor, is designed for short chipping materials like cast aluminum. “The BGF Thriller is also suitable for cast iron but is limited to shallow holes two or three times the thread diameter in depth,” Joswig says. “Despite this, it’s a very attractive option for certain applications.”
Four ‘fer
Emuge’s not alone. Guhring Inc., for example, offers the DTMC. “It’s a solid carbide, self-centreing drill, thread mill and chamfer tool, so can actually do four operations with one tool, if you were previously using a spot drill,” says threading application specialist Paul Larson. “It’s a niche product and is limited to non-ferrous metals and softer carbon steels, but for the right job, it will save a ton of cycle time.”
The DTMC produces threads through helical interpolation. What’s different is the presence of a drill point at the tool’s business end. It is fed into the workpiece and cuts a 45-degree angle at the top of the hole upon reaching full depth. It’s then programmed to interpolate just as any other thread mill. A “large standard offering” is available, with or without coolant through, and multiple lengths in UNC, UNF, and metric thread sizes.
“We sell a fair amount of them, as well as quite a few specials,” he says. “A lot of customers have specific depths that they’re trying to achieve, or maybe they want to change the bottom diameter to accommodate a tool coming in from the other side, whatever the case may be. When you do a cost-per-hole analysis and you’re looking at the amount of time spent tool changing, positioning, and all that, the DTMC is a real money-maker.”
Give me an A
Pete Gennuso, product engineering manager for OSG USA Inc., points to another money-maker: the AT-2. A member of the company’s A brand line of cutting tools, the AT-2 also drills and thread mills with one tool. But it’s also able to machine hardened steel, and it interpolates the hole as well as the thread at one time. “It utilizes the same Durorey coating that we apply to our end mills and drills, which provides an incredible balance of wear and heat resistance,” he says.
Thread milling is the preferred approach to high-value parts such as molds and aerospace components, where you can’t afford to break a tap, Gennuso added. And because adjusting the thread diameter is a matter of making a simple tool offset, it provides better process control in materials that are typically considered “high wear.” Add to that the shorter cycle time of a combo tool—especially one that interpolates the thread as it drills—and the AT-2 is worth investigating for any shop engaged in this type of work.
Last but not least, OSG has its own version ofa drill-tap combo tool. The DRT series takes a slightly different approach than the others listed here, in that it boasts a longer pilot drill and is therefore able to drill hole depths greater than 2 x D. It is, however, similarly limited to short chipping steels.
“One of the biggest challenges of any drill-tap tool is that you have chips coming from the drill and chips coming from the tap,” Gennuso said. “The question then becomes, how are you going to manage all those chips in the same flute space? Our approach was to make the tool longer. The caveat is that it can only be used for through holes, and you need a fair amount of clearance behind the part in order to drill all the way through. But here again, given the right application, you can cut out a lot of cycle time.” SMT
