![]() ![]() Material Hardness - Hardened materials over 30 HRC can be problematic when form tapping, is this case thread milling is recommended.We often use dedicated tapping fluid when possible vs. It’s just like selecting drill bit sizes for regular drilling, except that tap drill sizes are assigned to match industry standard sized holes for tapping (see more about bolt sizes and charts here). ![]() Cutting oils are generally preferred because of their lubricity compared to water soluble coolants. So what the chart shows you here is the proper tap drill size that you can use to match the bolt or screw you’re cutting threads for. Lubricity - Forming taps require good lubrication.A combination of tap class of fit and pre tap hole size can be experimented with to find the perfect strategy. It is possible to enlarge a hole slightly if tap breakage is an issue, so long as the hole still gauges correctly. Carbide and HSS(-E-PM) Machine Taps HSS(-E) Hand and Serial Taps HSS(-E) Drill-Tap Combination Tools. Select the closest drill size possible for the thread percentage desired. Pre Tap Hole Size - Reaming is always recommended.With form taps, the load is often less upon reversal. With cut taps, the point at which the tap reverses to retract is often the most critical. Consistency - Tool load is consistent throughout the tapping operation.Reaming helps control hole size but is not required. Tool Life - Form taps can last multiple times longer than cut taps with the right recipe, there is simply less wear as the tap does not rely on sharp cutting edges. Straight pipe threads can be form tapped using only a high quality drilled hole.More Consistency - Without random chips smearing or wiping out threads accidently, form taps gauge more uniformly.Tap Strength - Form taps do not have conventional flutes which means the tap has more supporting material and rigidity vs. Tap Chart - UNC/UNF Threads Tap size NF/NC UNF/UNC Threads per inch Basic major dia (inches) Basic effective dia (inches) Basic minor dia of ext.This makes form tapping ideal for blind holes, especially in materials like copper and stainless steel. Chipless Tapping - No chips are created when form tapping, the material is simply displaced into the thread shape. Tap Drill Charts British Standard Pipe Threads BSW BSPP BSPT Pipe Tap Size Pitch (TPI) Drill Size (inch) Pitch (TPI) Drill Size (inch) Pitch (TPI) Drill Size (inch) 1/16 60 0.046 (56) 28 0.261 (G) - 1/8 40 0.098 (40) 28 11/32 28 21/64 1/4 20 0. ![]()
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