Other advantages include the ability to manufacture large-diameter holes using machines that lack the horsepower or rigidity to drill large holes reliably, and the fact helical interpolation works well in numerous materials.

Jobber DrillBit Set

Also called circular ramping, helical interpolation is commonly done on a 3-axis CNC machine. While helical interpolation has some drawbacks, many industry reps are firmly in favour of using this technique when circumstances allow.

“If making a hole from a solid using indexable tools, you have to choose the correct cutter diameter because indexable tools are not centre cutting like some solid-carbide tools. Cutter diameter ensures that the insert cuts over the centreline of the hole,” said MacNeil. “When you have the right tool, work below the tool’s recommended ramp angle and maximum depth of cut. Ramping adds axial and radial cutting forces. I would rather maximize feed before ramping angle when trying to be productive. For cored holes where you engage less than 25 per cent of the tool, use PVD inserts and maximize chip thinning to prevent rubbing the tool and causing vibration.”

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Industry experts say a 3-axis CNC mill is suitable for performing this machining task. There is disagreement, however, about the usefulness of high-feed milling when it comes to performing helical interpolation.

Jobber Drillbit size chart

Of course, helical interpolation is far from a perfect process. Generally speaking, drilling operations are more productive and can achieve greater depths. Also, additional finishing might be required with helical interpolation.

High-feed milling combines a shallow DOC with a high feed per tooth, which increases metal removal rates. In helical interpolation, using high-feed milling is suitable when making large-diameter holes because it typically eliminates the need for predrilling the hole.

“The majority of helical interpolation operations in the market are being completed using high-feed milling tools,” said Corneil.

The general definition of the term “jobber” is “a person or company that buys from manufacturers and sells to retailers”, most commonly used in the 1850-1950 period. At that time, manufacturers were mostly producing general purpose “for the trade” drill bits, not using specialized machining applications to make specific lengths or designs like today. These drills, were of medium length and suitable for a wide variety of jobs, coining the term “jobber-length”, reflecting the same concept of terms like “general purpose” and “multipurpose”. Today, jobber drill refers to the length of the drill itself.

Mechanicslength drillbits vsjobber

“Most tools that are efficient at ramping have positive tip seats. When ramping into a solid, use CVD-coated inserts to cope with the heat of engaging the whole diameter of the tool. When opening up cored holes, choose PVD inserts and make sure that you are compensating for chip thinning below 25 per cent ae [arc of engagement],” advised Brian MacNeil, milling products and application specialist for Sandvik Coromant Canada.

“I probably wouldn’t recommend [helical interpolation with] aluminum just because it’s a little gummy. But other than that I think I’d recommend it for pretty much anything,” he said.

“Cutter diameter selection is 100 per cent critical during helical interpolation from a solid is being performed. This is an important step for two reasons: clearance on the bottom of the tool when cutting the minimum bore diameter and dealing with a pip if the bore diameter is too large for the tool selected,” said Corneil. “Both of these situations can cause tool failure but can be avoided if the proper calculations are completed in advance.”

What is ajobber drillbit used for

“Helical interpolation is very, very fast and very economical,” said John Mitchell, general manager of Tungaloy Canada. “Take the price of a high-feed milling cutter and compare that to several indexable drills. [Helical interpolation] is much, much cheaper and very, very versatile.”

“Helical interpolation for the purpose of creating a hole from a solid or for opening an existing hole is a very useful and versatile technique. This operation is programmed by adding a Z-axis movement to a simple circular interpolation command. Typically, people are programming this operation using CAM software. Helical interpolation is one of the most reliable holemaking processes in the market, and with proper tool and parameter selection, it’s an excellent weapon to have in your arsenal,” said Jeremy Corneil, milling product manager for Iscar Tools Canada.

Each cutter body diameter and insert geometry can cut a range of hole sizes. Four calculations should be performed to determine the allowable range for each tool.

Because there are two scenarios for helical interpolation – creating a hole from a solid and enlarging existing holes – two different tooling choices must be made.

Patrick Sheppard, national sales manager at Ceratizit USA, which acquired Komet of America last year, takes a slightly different tack.

“Solid carbide is effective if you choose a centre-cutting tool. It makes tool choice less critical, but cost becomes a negative factor in larger diameters,” said MacNeil.

Among the considerations to keep in mind when performing a helical interpolation operation are hole diameter, hole shape, depth, material, tolerances, and surface finish requirements. Photo courtesy of Iscar Tools Canada.

“Helical interpolation has an advantage mainly in the job shop environment where you don’t necessarily want to make a tool change or the production volume isn’t high enough that would constitute using a special drill to do a counterbore. Generally speaking, you can hold the same tolerances with some of our indexable drills as you can with helical interpolation, but the question becomes, Do I need to buy a whole other tool to make this counterbore? Typically, we will use or make a special counterbore if the volume is high enough in a production environment, but for a job shop, they interpolate a lot of holes every day and they want tools that will be able to deliver versatility,” said Sheppard.

Today Jobber Drill Bit are manufactured in a number of different style to tackle a number of different applications. Jobber Drill Bits still remain the most commonly found type of drill bit. A jobber drill bit has a long length compared to its diameter. The length of the flute is between 8-12 or 9-14 times the diameter of the drill, depending on the drill specifications. For example, a 1/2″ diameter jobber drill will be able to drill a 4-1/2″ deep hole because it is 9 times the diameter in length. Jobber drills are measured using a number of different systems:

Jobber length drillbits definition

“For diameters 20 mm and below, I would say definitely solid carbide. Anything above that, you could probably get away with the same productivity out of an indexable-type mill. When you get into larger dimensions where you’re interpolating and your material removal rate has to be much higher, it makes more sense to use an indexable carbide tool,” said Sheppard.

Helical interpolation is an advanced milling technique that can be a handy alternative to drilling when it comes to making holes. As a machining process, helical interpolation involves simultaneous circular movement in the X and Y axes combined with an axial feed (Z axis) at a defined pitch.

“In most materials we prefer to cut with air. This prevents the thermal shock that comes along in milling using coolant. Some materials demand coolant such as ISO N and ISO S and some, but not all, ISO M materials. If you don’t have air and are recutting chips, then yes, use coolant. It is the lesser of the two evils. Make sure you use a tough grade of carbide to deal with the chipping that may occur from thermal cracks,” said MacNeil.

Beyond the slightly contentious issue of feed rate, additional considerations to bear in mind when doing helical interpolation include hole diameter and form, hole depth, the material being cut, tolerances, and surface finish requirements.

Jobber drillvs twistdrill

Cutter diameter selection is paramount during helical interpolation from a solid. Failure to select the proper diameter can lead to tool failure during cutting. Photo courtesy of Tungaloy Canada.

For his part, Mitchell recommends using high-pressure coolant for gummy materials such as aluminum, and through-the-spindle air blasts for steel and iron. The gummy nature of aluminum leaves Mitchell slightly wary about using it with helical interpolation at all.

In a helical interpolation operation, a single tool can cover a range of different hole diameters, which means less tooling in the magazine, according to Rennie Elvin, applications engineer at Vargus USA.

DrillbitlengthChart

“As with all other pocketing operations, chip evacuation is very important. For all steels and cast irons we recommend the use of air to help remove the chips from the hole. For stainless, high-temp alloys, aluminum, and in situations where there is no air blast available, we recommend the use of coolant,” said Corneil.

Helical interpolation is more than just a potential substitute for drilling, he points out. There are bottom-line considerations to bear in mind when deciding to use helical interpolation instead of standard drilling methods to make holes.

Once the proper tool diameter has been selected, you need to determine the optimal DOC for each revolution of the helical interpolation pass, said Corneil.

When you have the right tool, it’s advised to work below the tool’s recommended ramp angle and maximum depth of cut because this adds axial and radial cutting forces. Photo courtesy of Sandvik Coromant Canada.

Jobber lengthmeaning

“High-feed milling is a big buzz word in the industry that blankets a lot of milling applications. But to be honest with you, in the industry we’ve been interpolating holes long before the introduction of high-feed milling. With high-feed mills, you’re really limited to a very small depth of cut at a very high feed rate,” said Sheppard.

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Helical interpolation, also known as circular ramping, for the purpose of creating a hole from a solid or for opening an existing hole is a very useful and versatile technique. Photo courtesy of Iscar Tools Canada.

“I don’t see a need to avoid any specific materials when it comes to helical interpolation. Having the correct grade, geometry, speed, and chip thickness to match the geometry will help you be successful, just as with any machining operation,” said MacNeil.

“There are a lot of really good things about high-feed milling and helically interpolating holes,” said Mitchell. “High-feed milling involves extreme chip thinning, so you can feed very fast, as the name implies.”