Regardless of the CNC machining industrial focus (i.e., production milling, aerospace, automotive, medical, mold making, etc.), dealing with poor tooling performance and its impact on production and costs is something that can affect every shop.
An important part of CNC milling is the v-flange toolholder, which affects the performance of the cutting tools and the machine itself. A critical factor in toolholder performance is the surface area contact between the large end of the toolholder and the spindle, which is essential for tool rigidity. A higher percentage of taper contact with the spindle at the large end and moving up the taper toward the small end results in improved cutting performance and overall milling results. Less than 75 percent taper contact with the spindle results in poor T.I.R. (runout), poor tool life, poor tolerances, vibration and chatter, poor finishes, and excessive spindle wear and tear.
In an effort to ensure optimal mill productivity and tooling performance, JM Performance Products, Inc., developed its patented Taper Shank Test Fixture to check toolholders and test for taper deformation.
A growing area of concern with the use of modern CNC machines with upwards of 500 tools, is tooling cost containment and optimal tooling performance. Unfortunately, when a standard retention knob is installed into a toolholder, it can expand the small end of the taper of the toolholder. This expansion can reduce toolholder to spindle contact by 70 percent or more, resulting in loose tool situations.
The end result is that it will no longer meet ISO 1947 angular taper tolerance (AT) specifications “AT3 or better” for toolholders. Retention knob expansion prevents toolholders from properly seating within the spindle, which can result in vibration and chatter issues that negatively affect tool life, especially expensive carbide tools. It also affects milling at the actual production level.
JM Performance Products’ Taper Shank Test Fixture quickly checks toolholders for distortion caused by retention knob installation.
Development of the patented product was key to identifying the inherent flaw design in v-flange tooling. This discovery was ultimately the driving force for the creation of its patented High Torque retention knobs that prevent toolholder distortion. The High Torque retention knobs are longer than traditional knobs and feature a precision pilot to increase rigidity, and a relief below the flange that forces threads into a deeper cross section of the toolholder. This eliminates the toolholder expansion responsible for costly and ongoing CNC milling and boring issues.
Proper retention knob installation is crucial to toolholder performance. Overtightening the retention knob may damage and unnecessarily stress the knob leading to premature failure. It also exacerbates the effects of toolholder expansion. A quick, simple test using the Taper Shank Test Fixture can be performed on a toolholder with a retention knob already installed.
Following the manufacturer’s instructions to fit the fixture and zeroing out the indicators for a base reading, and then loosening the knob for a second reading, will return an immediate indication of whether the holder has experienced expansion. The good news is an expanded toolholder does not need to be removed from service and scrapped. Once the retention knob has been removed, the toolholder should return to its original state and can be used with a high torque knob tightened to the correct torque spec. When the toolholder taper is deformed, it prevents the toolholder from properly seating within the spindle.
According to JMPP President John Stoneback, “It’s important to note that all v-flange tooling is designed to fit the spindle taper within tolerances of 29-millionths (0.000029”) of an inch. Tests performed using the Taper Shank Test Fixture revealed a significant advantage for our High Torque retention knobs vs. standard knobs. In fact, most of our clients experience a 20-80 percent performance advantage.”
MORE INFO www.jmperformanceproducts.com
