Shop Doc – Damaged Taps

Today’s Machining World Archives December 2007 Volume 03 Issue 12

Dear Shop Doc,

Our company has been processing a family of parts made from high strength, low alloy, 60 and 80ksi minimum yield steel plate. After laser cutting and Mig welding, we machine a series of holes using conventional drills, spade drills, boring bars and taps. The problem is we keep breaking taps of all different sizes, 5⁄ 16″-18, 3⁄ 8″-16 and even ¾”-10. We have approached a number of industry representatives who keep moving the taps to successively more expensive versions intended for alloy cutting, but they don’t solve the problem. In order to produce a good part right now, we need to destroy the tap that was in the hole, clean the hole out, weld it shut, and re-machine the hole by hand. As you can imagine, this issue is killing delivery performance and profitability.

Flummoxed in Fort Wayne

Dear Flummoxed,

We had a situation that sounds quite similar to yours.

Our local sales reps also offered expensive solutions that didn’t work, so after enough grief, we finally got some advice from some technical directors at Kennametal and Emuge Corporation.

We sent our used taps back to Emuge and their technical director put them under a microscope to analyze their wear patterns and fracture patterns. The real reason our taps were being damaged was because when the tap was inserted, too many chips were collecting in the hole, or “bird nesting.” When the tap was put in reversal mode, the bird nested chips bound up the tap, broke the teeth, and caused the tap to snap off at its shank.

After this discovery, rather than recommending a more expensive tap, Emuge recommended a less expensive tap with a more aggressive chip removal spiral. We’ve been using the new taps for three weeks now. The bird nesting is gone and no taps have been broken yet. I have asked Emuge to send you some of these higher spiral taps for you to try. I understand that you have also provided Emuge with some sample plates that they can use to replicate your processes. I’ll be quite interested to see the results from those tests.

Fort Wayne Fix-It-Team

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One thought on “Shop Doc – Damaged Taps

  1. Gus Madison

    Forming taps would be worth a try. The advantages are many and certainly worth investigating. You end up with a better, stronger, burnished thread as a result. As a rule of thumb, if the material produces a continuous chip when drilling, it’s a good candidate for forming taps.
    While we aren’t provided enough information about your process, machinery, sfm, etc., I still think you should look this direction. You’ll never go back if you apply them in a correct manner.
    Oh, and don’t spare the Moly-Dee if you can use it 😉



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