Tool balance has always been a critical factor in engineering precision tools; however more recently, machine design and application demands have increased the need for balance verification.
CNC moulder and router applications increasingly demand larger more complex tools that must be run at higher RPM and feed speeds. Unbalanced tool mass rotating and higher RPMs can create a costly and potentially dangerous production setting.
Tools running outside of balancing standards will increase vibration levels in the machine, which will negatively impact the performance of the machine. Increased spindle wear, resulting in premature spindle changes can be costly. Imbalance can also negatively affect tool life and finish quality of machined components, and excessive levels of imbalance can be potentially dangerous if they reach levels that compromise the integrity of the tool.
To avoid the negative impacts mentioned above, it is imperative that tool manufacturers possess the necessary equipment, knowledge and expertise to ensure all tooling is properly balanced to meet the demands of modern machinery.
Indentifying unbalanced tools
Excessive vibration and noise is the most obvious sign of imbalance, but other factors such as tool failure or poor cut quality can be indicators as well. Regardless of the scenario, the best way to verify tool balance is through a qualified manufacturer who can provide a formal balancing report. It is critical that tools are manufactured within machine standards for maximum weight, diameter and length. Balancing standards are always based on the mass of the tool body and operating RPM of the machine.
Advanced tool manufacturers should have balancing machinery that ensures tools can be balanced to a G 2.5 specification.
A good indication that your tooling has been balanced is the appearance of ‘minor’ material removal on a specific area of the tool body. However, a ‘large’ amount of holes drilled in the tool may indicate that the tooling manufacturer is not properly equipped to balance the tool properly.
Tool design factors
Properly balanced tools begin with important design decisions that can help reduce weight, increase accuracy and repeatability of tool set up. The need to machine larger wood profiles on CNC routers forces toolmakers to design tools with larger diameters resulting in larger tool masses.
Reduction in tool mass can also be achieved through a secondary milling process on larger steel tools. This process simply involves removing more steel from areas of the cutting tools that do not serve a purpose to the tool performance. Often, this milling process can bring larger tool bodies below maximum weight specified by the machine manufacturer.
As discussed in previous columns, some advanced tool manufacturers have capabilities to produce tooling directly on the tool holder in one solid unit. The ‘integrated tool holder concept’ is the absolute best way to ensure tools are accurately balanced and remains within balance tolerance while in operation.
Strategies to improve tool balance
Like many preventative measures, the act of maintaining proper tool balance is really achieved by attention to simple details provided by your tool manufacturer.
The most obvious factor is tool cleaning, which is the basis for any strategy aimed at consistent tool balance and accuracy. Staff must have sufficient time and resources to keep tools clean. There are various spray-on products that can help prevent the build-up of pitch and resin on tools and tool holders, which can be purchased from your tool supplier.
Ultrasonic technology has become more economical in recent years and should be considered for larger tools or more complex tools that are difficult to clean. An investment in a simple ultrasonic tank can dramatically reduce the labour costs associated with tool cleaning and ensure tools are consistently clean of debris that can prevent accurate tool set up and lead to imbalance.
When purchased, tools should be manufactured within tolerance; however, erosion of tool body, damage from grinding wheels, or general wear and tear can cause tools to become unbalanced over time. If imbalance is evident or suspected, it is important to consult the tool manufacturer and consider returning the tool for balance verification on dynamic balancing equipment.
If all knives and gibs are of equal weight, it is still possible for a tool to become unbalanced through knife ‘movement’ or ‘shifting.’ This problem can be identified visually or through verification equipment on site. Knife movement can be caused by various design limitations; however, the most common reason for knife movement is improper clamping or tool set up.
Manufacturers paperwork should supply proper torque values for all tightening screws, which are best achieved by using a torque wrench to ensure knives are held with proper clamping pressure.
Adjustable cutting tool ‘assemblies’ designed with multiple tool bodies and shims can also cause imbalance if not assembled correctly. When disassembling and reassembling tools, it is imperative that tools remain in the same location as new. There are new innovations in hydraulic clamping that improve accuracy and repeatability of assemblies.
There is no argument against proper balancing and it is a problem that can be easily solved with proper capabilities. It is often inconvenient to take tools out of service and return to the manufacturer, but it is evident that the costs of operating unbalanced tools greatly exceed the costs of returning the tools to verify balance accuracy.
Scott Burton is the Sales and Marketing Manager for Royce//Ayr Cutting Tools.
He can be reached at sburton@royceayr.com
