Another factor in deep hole drilling is the hole quality. Straightness especially can be an issue as long drills tend to “wander,” particularly if feed rates are pushed excessively.

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Pilot holes are almost always recommended in deep hole drilling and act as a guide for the long drill that follows. The pilot drills to a ~2xD depth and should be manufactured to a plus tolerance‒ ensuring a slightly larger hole but remaining within the hole tolerance. (Example ø6.02mm pilot for a ø6mm hole)

Whether you need a quote or application suport, our expert engineering team is eager to assist with your custom tool cutting solution.

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Having a solid set-up in both workholding and toolholding, along with a reliable machine tool, is critical to reduce runout (TIR) and ensure hole straightness and concentricity.

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The graph below shows an example of the difference in a peck cycle between a parabolic design (on left) and a conventional flute drill (on right).

The pilot drill point angle should also be greater than, or equal to the drill point that follows. This ensures the corners from the long drill aren’t engaged with the material prematurely, which could result in catastrophic failure.

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Hydraulic chucks are suitable for HSS tools and shrink holders are ideal for carbide. Regardless of the toolholder choice, ensure TIR is minimal.

These deep hole drills are straight-fluted for added strength and feature coolant-through the tool. Gundrills have the largest range of diameters and lengths available. While larger diameters and lengths require special-purpose machine tools to run, smaller diameters can effectively operate on mills and even lathes.

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The PFX HSS-E extra-long series (A976, A977, A978) from Dormer-Pramet offers up to 25xD deep drilling without the typical peck cycle, in most materials, saving valuable cycle time at an economical price.

Peck drilling is usually recommended beyond 5xD to help evacuate the chips, provide hole straightness, and maintain concentricity. Depths and number of pecks are based on the drill diameter and work material. Care is needed to avoid flushing chips back into the hole upon peck retraction, and therefore drills should not fully retract from the hole when pecking.

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The most challenging aspect of drilling deep holes is effective chip formation and evacuation, especially in malleable materials. Chip packing is the most common culprit behind tool breakage in this process.

Sandvik Coromant has placed an emphasis on solid, round tooling in recent years through the introduction of upgraded geometries, substrates, and coatings.

The CoroDrill® 865 has been optimized for deep hole drilling (up to 30xD) in cast iron, steel and aluminum— making it ideal for automotive applications. The design includes a flute profile to improve chip formation, while maintaining strength and produce precise, consistent holes even on an incline.

Deep hole drilling can be a tedious and difficult process, but with the right tooling and technique, it doesn’t have to be.

If performance is your goal and your shop has a reliable, secure set-up, this is the most efficient option for deep hole drilling. Carbide, coolant-through drills run to depths of ~50xD, without pecks and at feed rates 50-100% greater than the other options. These drills are coated and have polished flutes to improve chip flow.

Coolant should be plentiful in these operations and running at a higher concentration to aid in lubricity. In some deep hole operations, oil is recommended.

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Having a knowledgeable and resourceful metalworking distributor can eliminate the challenges that come with deep hole drilling. If you would like to improve your drilling processes, please reach out to the Triumph team today!

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Twist drill manufacturers typically add extra margins to their drills to stabilize the tool, however, excessive contact by the margins can affect surface finish and even work harden some materials.

botek is the world market leader in single-flute gundrills. Their solid-carbide Type 113 series was designed as an alternative to carbide twist drills.

The CoroDrill® 861 is capable of drilling to depths up to 30xD with exceptional chip control due to their unique flute geometry and smooth surface treatment. These drills feature a double offset margin, which stabilizes the drill without disproportionate material contact.

Long, carbide drills feed into ~2xD piloted holes at little-to-no spindle speed (under 500RPM) until the drill point is fully inside. Only at that time is the coolant and spindle increased to the recommended speed and feed. The drill’s speed is again slowed as it retracts from the finished hole.

Walter-Titex is globally recognized as a leader in High-Performance drilling and offers one of the most comprehensive deep hole drilling programs in the market. Dialling-in optimum cutting conditions is straight-forward with their GPS software. Besides detailed cutting data, anticipated tool life— measured in holes, is also provided. It even takes into account regrinds.

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Your shop’s set-up and resources may limit your options for deep hole drilling. Let’s look at the most-common choices for deep hole tooling and their fundamental benefits and limitations:

Worn tools can be retuned for reconditioning where the original manufacturing specifications and coating are applied to the used tool, resulting in “good-as-new” productivity.

While there is no defined depth measurement at which point a hole becomes “deep,” it’s commonly identified at 10 times the diameter of the drill (10XD) and greater.

Beginning with effective chip formation at the cutting edge, drill manufacturers create point geometry to reduce cutting forces and shear the material into manageable pieces. Ideally, the drill point combined with appropriate cutting conditions will create small, tight pieces‒ that with deep, polished flutes and sufficient coolant‒ will evacuate easily.