You can learn a bunch more from our article on tap drill sizes, but now you know enough to greatly reduce your chances of breaking a tap. That means you’re way less likely to break the tap and you’re sacrificing very little holding strength. Premium tap makers like Guhring actually recommend 60% to 70% percentage of thread for most applications because it significantly lowers the torque force required to tap without giving up much thread strength. That’s conservative from a strength standpoint, but aggressive from the standpoint of over-stressing your tap. The deal with thread percentage is the recommended tap drill sizes you find in most online charts and on the tap packaging are for 75% threads. There is no one perfect size, but you can often do a lot better by considering the thread percentage. The recommended hole size for tapping is usually not the best. Here’s the dirty little secret of tapping:
It’s because of that thread database with the % Thread info. I hate it, but I have largely quit breaking them by using G-Wizard. Of course you want to avoid breaking taps. The thread database includes tapping drill size recommendations with thread percentages for both cutting and form taps. – Tortoise-Hare slider for pinpoint control in difficult materials G-Wizard Tap Feeds and Speeds Calculator… Here’s what G-Wizard’s Tap Speeds and Feeds Calculator looks like: That’s why we make the G-Wizard Calculator, a serious power tool for folks like you. Quick and dirty calculators like the one above are what you see most often on the web, but most machinists and CNC’ers need more than they can offer.
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That’s our Tapping Feed Rate Pro Power Tap Feeds and Speeds Calculator So if we’re going 1000 rpm and cutting a 20 TPI thread, we need to advance 1000/20 = 50 IPM. It’s our spindle rpm divided by our threads per inch (TPI).
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Given the spindle rpm’s the Tapping Feed Rate is just how fast we have to feed to move one full thread per spindle revolution. Tapping Feed Rate & Tapping Feed Rate Formula Given SFM from the table, plus the tap’s diameter, we can calculate rpm with this formula:īTW, that’s from our article on RPM from Surface Speed if you want the details.
We can find the recommended surface speed to tap many materials in this table: For a more sophisticated calculator that will figure that out for you as well as help you find the right TPI value and work in Metric, keep reading! Recommended Surface Speeds (SFM) by Material That depends upon the material you’re trying to tap and the diameter of the tap. Everything starts from Tapping Speeds What Tapping RPM or Tapping Speed Should I Use?
Tapping Feeds and Speeds are pretty easy to calculate because they’re constrained by the thread that is being tapped.