One of the first questions new powRgrip owners ask is “How much of my tool shank has to stay inside the collet?” We demonstrate proper use to all our customers, but what makes that demonstration even easier is that we’ve designed our PG collets to answer the question on their own.
PG collets always deliver the proper amount of tool engagement, so long as the tool shank hits the backup screw inside them. We supply our PG collets with backup screws designed to adjust from the minimum to the maximum tool engagement for each specific tool size. Proper engagement is essential in a press-fit toolholding system, and that’s why we take special precautions. We profile set screws so they can’t be interchanged, and these safety measures protect operators from putting too little shank into the collet.
In a press-fit system, the material on the outside of the holder squeezes down on the collet, and we don’t want that collet to deform under the hard edge of the cutting tool. After all, no matter what material we use in our toolholding systems, that piece of carbide will be much harder than the material of the collet. If too little of the shank is engaged when the collet squeezes under the back end of the cutting tool, the tool will deform the material inside the collet and create a step. This essentially ruins that collet because it prevents it from being used to its full depth ever again. A tool cannot go past the step that’s created that way.
Sometimes the length that’s engaged is a bit greater than a customer needs or wants. With a very short cutting tool, the flutes begin to tuck away inside the I.D. of the collet. These customers want to pull the tool up and hold it with the flutes clear of the collet – and to solve their problem, we designed a special PG product range called short-shank collets. These collets incorporate a built-in full-diameter plug built that allows the customer to move the shank up inside the collet without squeezing and damaging it, gaining them three to 10 mm more tool projection than with a standard PG collet. Even with this special design, short-shank collets are fully compatible with our automated and manual press-fit assembly units and all standard toolholders.
On the other end of the spectrum, customers with very long tools want more shank inside the collet, not less, to pull down the projection. For those customers, we designed long-shank collets, which hold between six to 10 mm more of the tool shank than a standard collet.
When you secure less of the tool shank in a toolholder, you inevitably encounter some disadvantages. If your toolholder holds on to less of the tool, it generates less friction and clamping force, depending on the tool size and the amount of engagement. And although it’s not as common, engaging less of the cutting tool also can cause deflection – not of the bending moment during the cut, but of the runout that’s actually ground into the tool itself. This TIR typically only amounts to a few microns, but any small amounts of inaccuracy throughout the entire tool-and-toolholding chain can stack up in the machining process.
Conversely, holding on to more of the tool shank presents few challenges. However, we build our long-shank collets without a set screw for tool adjustment because if you used one in a CAPTO or HSK holder, the screw would interfere with coolant tubes. These long-shank collets literally fill the entire cavity of the toolholder and leave no room at the bottom for a set screw. That makes them a little trickier to preset, but they’re made to fulfill a specific objective.
Why do we see such a plethora of tool lengths? The DIN standard in Europe and the MAS standard in Japan dictate how much round shank a tool must maintain before its grind wash. The U.S. lacks a formal set of rules for tool measurements, and U.S. toolmakers typically create their tools from a blank length that may measure 3″ long or more. Then they grind a carbide profile onto that piece of metal, and toolholders must grab on to whatever length is not part of the cutting surfaces. In fact, some customers who grind their own tools for specific applications are even bigger fans of our long-shank collets because they begin with a long blank and simply grind a series of new profiles on it until it’s all used up.
These special adaptations of our PG collets bring the press-fit precision of powRgrip to customers who might not otherwise be able to use them. We’re always looking for ways to solve toolholding problems, and these collets accommodate the long and short of one of our customers’ biggest requests.