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The Most Important Factors Influencing Toolholder Selection
A toolholder is the interface between a precision machine spindle and a precision cutting tool.
The toolholder has three base elements; the taper connection, the retaining device and the cutting tool connection.
Which toolholder you choose to select will be specific to the machine spindle’s taper design; as you cannot interchange the toolholder with a machine tool with a different type of spindle taper.
The number following the toolholder type (i.e BT 40) is the spindle size number. The larger the spindle size number, the larger the spindle.
When considering selection of toolholding for higher speeds, these are your most important criteria:
1. Accuracy/Concentricity:
Holders should be selected based on their ability to hold the tool concentric to spindle rotation. ER collet holders lend themselves to universal applications, light milling and drilling. They are the low-cost solution for many SME’s, due to their versatility - and could achieve a 10-micron run out with a precision collet. The Toolholder with the best accuracy are Shrink / Hydraulic holders, which can achieve a higher clamping force for heavier high-speed machining and an accuracy of 3-micron runout.
2. Balance:
As you increase your spindle speeds, it becomes more important to take note of the balance of the holder. ER collets tend to be balanced to 12,000rpm 6.8G and Shrink/ Hydraulic holders 25,000rpm 2.5G. The effect that a lack of balance has on your cutting operation is poor tool life and poor surface finish. Many Cutting tool manufacturers produce cutting tools which are balanced by design - meaning when a tool is put into a Toolholder, the whole unit stays balanced. We see balance as an issue when your RPM of the spindle is over 12,000 rpm. Machining higher than this could result in spindle vibration and damage to your machine spindle with balancing. (Think car tyres… just like a car tyre needs to be balanced, so does a Toolholder). A balancing machine is available to balance your Toolholders.
CNC Tapers
The CNC Toolholder has three sections (taper, flange & Toolholder) divided by the gauge line (the imaginary line marking the portion of the Toolholder that matches the bottom edge of the machine spindle).
The taper section fits into the spindle, helping locate and centralise the tool holder. The flange, depending on design, plays two parts by locating with the spindle drive dogs allowing the machine tool to transfer rotary motion to the tool which is held in the toolholder section, but also used for machines with tool change arms.
Larger Toolholders will be longer and have a greater diameter gauge line.
We’ve covered quite a bit of ground, so in our next blog, we’ll look at the various types of toolholders that sit within these two categories.
If you’re ready to shop Toolholding and want to make the most of your Priority Club 10% discount, head over to Toolholding & Workholding now. Look out for the products labelled with the Gold Priority Club logo!