rigidity and peak forces lead to breakage, but throughout the entire cutting process. This means more consistent control of thread pitch and tolerance while eliminating re- cutting on exit, even on machines capable of high-speed retractions. The reduction of force also results in significantly less tap chipping that extends tool life, regardless of spiral angle – by a factor of more than two in most cases. Just how much force can a little cushioning in the tapping holder reduce? Using the dynamometer to measure force under the same parameters as detailed previously in our test, but replacing the collet chuck with the MEGA SYNCHRO, the load maxed out at about 13 lb, or more than 10 times less. Today’s shops are fortunate to have machines with specialized coding for this difficult process. Coding is not a cure-all, however. Using the proper holding equipment for tapping operations is the only way to maximize machine tool capabilities and compensate for synchronization errors that are still unavoidable. The next time you think about setting up a tapping operation with a collet chuck the same old way you always have, you may want to think again. CONTRIBUTOR AlanMiller is the Engineering Manager & Product Manager BIG at BIG KAISER Email: alan.miller@us.bigkaiser.com
it’s still a challenge to synchronize depth (especially in blind hole scenarios) and thread pitch with the relatively violent stop/reverse. This brings the quest for more reliable tapping to a key variable outside of the machine itself: tooling. When it comes specifically to holding taps, the majority of shops opt for collet chucks. They’re easy to understand and set up, and they are generally well balanced, with strong runout characteristics. What many shops don’t realize is that another perceived strength of collet chucks, their rigidity, can actually be detrimental in tapping. Rigidity does very little to counteract the dramatic thrust loads imposed on the tap and part, exacerbating the already difficult challenge of weathering the stop/reverse and maintaining synchronization. Using a dynamometer, we measured the load on a spiral tap
held with a collet chuck in aluminum with metrics of 20 m/minute, 1,050 rpm and a depth of 12 mm. At the start of the reversal, the load was approximately 165 lb. It’s the resulting axial pressure that leads directly to breakage, poor tap life and inaccurate threads. If you’ve had to EDM a tap out of a hole, or even scrap a part, you understand the disruption breakage cause. While continuing difficulties with tap life or poor thread quality add up quickly in terms of real cost, you’re still not going to guarantee results or maximize the floor’s capacity if slowing down spindle speed is your solution. Just like machine builders have done their part, I’m here to tell you that we tooling suppliers are doing ours too. There are now tap holders designed specifically to mitigate the load imposed on the tap by essentially absorbing synchronization error. For example, the MEGA SYNCHRO tapping holder is held into the main taper adapter with a cross bolt. The bolt goes through the outside of the cave and through the adapter, locking it in place. The hole in the adapter that houses the bolt has what we call a synchro adapter, an elastomer bushing that cushions the bolt. It’s this relationship between the cushioning and the bolt that allows for the right amount of float. This cushioning is enacted not only at the bottom of the hole during reversal, where
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