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Tool holder extensions

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Tools for Success by Scott Burton
Scott Burton is the sales and marketing manager for Royce//Ayr Cutting Tools. For more info email:

The emergence of advanced mass timber machinery and new applications in the industry have created a demand for extend length tooling and holder systems to achieve great depth of cut.
Router tools are often required to machine in applications over 12-inch depth and drill bits can exceed 20 inches in some situations. Angled drilling and routing operations are becoming more common as building designs evolve and new joinery designs emerge. Although mass timber machinery designs have greater capacity to hold longer tools, traditional mechanical collet systems are no longer a viable option to ensure optimal machine performance and safety. Tool extenders can still be purchased with a mechanical collet system, and easily assembled with the cutting tool, but there are several concerns, which must be considered.
Precision tool holding systems have emerged to provide safer and more accurate performance when extending tool length. Large robust 5-axis mass timber machinery does allow more tool length flexibility, but any machine is only as rigid as the system holding the tool, so careful consideration of tool and holder technology is critical. Before engaging in any project to extend holder and tools, it is imperative to have consultation with your machine and tool and manufacturer. Tool extensions on CNC routers can be a very helpful strategy to perform applications not possible with traditional CNC machinery, but precision tool holding systems must be utilized.

Hydraulic tool holder extensions
Image 1
shows a large hydro tool extension used to allow maximum tool reach in routing and drilling applications. This allows the tool to project far enough away from the spindle to prevent collisions with the part. ETP Sweden has designed these holders for specific drilling and routing applications to achieve depths of cut up to 14 inches. Hydro-clamping holder technology has existed for many years in metal working industries, but has not been available for mass timber machinery due to variation in tool holder interfaces. Many mass timber machines require HSK 63E and HSK 80 or HSK 100, which were not available until recently. Hydraulic tool holders are designed to eliminate run out and drastically increase clamping force compared to ER collets.  Hydro holders can be pressurized to provide over 1,300 newton-meters of clamping force, which is applied equally to the tool shank resulting in superior performance over mechanical collets. Hydraulic tool holding systems have a proven record of improving cut quality and optimizing tool performance on CNC machines and are now available in extending length format. The result is an extended tool system, which can perform long reach applications, with far greater accuracy and safety compared to ER mechanical collets. 

Shrink fit extensions
Image 2
shows a shrink fit tool holder with extended length solid carbide router tools. These tool holders utilize the basic principles of expansion and contraction clamp the cutting tool in the holder. They are simple in design and involve not moving parts once the holder is heated and cooled after a tool is inserted. Shrink fit designs provide clamping force very comparable to hydraulic holders, but do require special machinery to remove and insert the tool into holder. This machinery can be expensive, but provides value in performance and safe operation is not possible with mechanical collets. The slender design, which is much smaller in diameter than collet nuts, provides a critical advantage in deep machining and extended reach applications.

Integrated tool extensions
The third and most simple design to improve tool holding is manufactured with no connection between the tool and holder.  Tooling manufacturers machine the tool body directly on the HSK holder and use carbide insert or diamond tips for the final cutting edges. This tool format provides maximum tool rigidity and ability to maintain balance, as there are not moving parts or tolerance between tool and holder. 
Image 3 shows an integrated style insert tool for extended reach applications. This type of design can also be manufactured with diamond cutting edges to dramatically extend tool longevity and provide greater cut quality consistency

Routing & drilling applications
The two primary challenges for extended drilling applications are maximum depth of hole and angled holes, which both need to be done without spindle collision. In many deep-drilling applications, the drilling and routing operations often need to be integrated to achieve the required depth and hole diameter. In mass timber products the hole diameters tend to be larger diameters, which are not achievable with drill bits. For example, 3- or 4-inch diameter holes can normally be machined using hole saw style drills or other boring style bits.  However, these holes are often required to be 8 to 12 inches deep, which makes chip evacuation very difficult and traditional style large diameter drills are not adequate for extreme depth drilling. In this scenario it may be necessary to pre-drill with a smaller drill at 1-to-2-inch diameter, and use extended length router tooling to open up the hole to larger diameter using an interpolation tool path. Modest machine parameters and minimal depth per pass must be programmed to ensure safe operation of machine and tool in these demanding applications. Maximum tool clamping force is critical to prevent tool run out in these situations. Therefore, mechanical collets are NOT recommended and hydro, shrink fit or integrated holding solutions must be utilized. Low RPM drilling applications with shorter drills under 10 inches can be done using collet; however, extending length drill bits do require a more accurate holding system to ensure hole accuracy, optimal cut quality and safe operation of machinery. Router tool holding is of the utmost importance because RPM is always higher than drills and tools run in a lateral motion which applies more force especially when using the bottom portion of a 10- to 12-inch-long router tool.
Angle drilling operations are normally designed with smaller hole diameters, so a drill and rout operation may NOT be required. However, an extended length tool held on an angle does apply far greater pressure on the holding systems. As length and diameter of the tool is increased, greater force is applied resulting in greater tool run out. Therefore, precision tool holding systems provide an advantage when machining angels. Whatever extension method is chosen it is clear both provide far superior clamping force and accuracy, resulting in superior cut quality and optimal machine performance. Mechanical collets really have no place in these complex applications and should NOT be considered an option. Mechanical collets cannot provide adequate clamping force or accuracy to perform safely in full production. Mechanical collet extensions are still sold and may work in short-term production situations at specific machine parameters, but they are not a logical solution for modern CNC machinery or high-volume machining.
Before engaging in any project to extend holder and tools, it is imperative to have consultation with your machine and tool and manufacturer. Tool extensions on CNC routers can be a very helpful strategy to perform applications not possible with traditional tool holders. Routing and drilling and detailed machining can be done to produce accurate products not normally possible on CNC routers.

Machine parameters
In any CNC router applications, drills tend to run at lower RPM (3,000 to 4,000) compared to router tooling, which can be run at a wide range of machine parameters depending on tool size, specific machining operations, and material density. Router tooling is generally rated for a specific RPM based on diameter and weight, but must comply with weight restrictions of machine spindle. Recommend RPMs range from 6,000 to 18,000 depending on the size of tool and machine horsepower considerations. Exact RPM and feed rates are normally determined through a chip load calculation based on material type. However, many online chip load calculators do not consider tool extension beyond the holder or tool length in general, which is a critical factor especially when using tools in excess of eight inches in length.
It is impossible to determine exact machine parameters without all the variables, but consultation with your tooling and machinery technical team is the best place to start. Obviously feed rate must be reduced when machining at extreme depths, but RPM must also be adjusted accordingly. If feed rates are reduced without reducing RPM, excessive heat generation will occur, resulting in premature cutting-edge failure.  This will add additional pressure to the cutting tool and ultimately exaggerate the problem. The first step is to eliminate variables such as tool holder inaccuracy, so a decision to use precision tool holding systems in combination with proper machine parameters will yield the best results.
As the industry demands more complex parts and material continue to evolve, it is critical to have a safe effective solution for extended length drilling and routing applications. Hydraulic, shrink fit and integrated tool holders provide the highest level of rigidity and accuracy when machining at extended lengths. Special attention must be paid to machine parameters and tool path strategies to ensure optimal machine performance and safety. If precision tool holding systems are utilized properly and combined with precision tooling solutions, applications can be performed which are not possible with traditional mechanical collets.

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