Note 3: Value is obtained by linear interpolation/extrapolation of Note 2: Equals drill size decimal equivalent plus expected amount of Parameters table, the effect of drill oversize will be taken into account in tap drill bit selection. Note 1: If the "Include Oversize" checkbox is ticked in Input Roll tappingĭisplaces metal from the hole walls to form the threads so cutting tap drillĮxpected Hole Size (Including oversize) 2 Roll tapping is a method to be applied to relatively ductile metals such as low-carbon steel, leaded steels, austenitic stainless steels, wrought aluminum, magnesium, copper, and ductile copper alloys.įor roll tapping, cutting tap drill sizes should not be used. The threads produced with roll tapping are stronger than cut threads because the grains are continuous and unbroken, and the displaced metal is work hardened. Roll tapping eliminates the problem of chip disposal. Roll tapping is a process which forms a thread in the hole by displacement of the material into the desired size and pitch. Desired thread size and % of full thread are input parameters for the calculator. Calculations are done according to roll form tap drill charts which are given in the Machinery's Handbook. Then I will present it to the world.Roll Form Tap Drill Chart Calculator for calculation of recommended roll form tap drill sizes for Unified threads. Often the available drills will be as much as 2%, 3%, or even 5% different from the desired size. So I added that section at the bottom that allows an exact drill size to be entered to see the exact percentage of thread it will produce. The sheet finds the closest standard drill size. And when a drill is chosen, it may not be the exact value that was calculated. Oh, and it can do it for any thread angle, not just 60 degree. My calculator can find the drills for any percentage of thread with any truncation value and any fill value. But, of course, those tables never offer any drill sizes for other desired thread percentages. I finally settled on 1/8 values (12.5%) for truncation and fill as the ones that seem to be used for the published, 75% tables. I literally had to experiment and compare the results against published, "standard" tap drill tables. I could not find any other sources that were any help. Machinery's Handbook offered little help on this. The reference documents allow a wide range of values there. Is that 75% of a sharp vee thread or 75% of a thread that has truncated peaks and filled valleys? If so, what percentages of truncation and fill were used. I have not discovered any source of information on that point. In creating it I had to do a lot of work to discover exactly what was meant by a 75% thread. I plan to make it available for no charge, at least to the people on the boards that I frequent, like here. I plan to publish it when it is finished. I had some trouble with that and have not gotten back to it yet. There are drill size tables on separate sheets that it is supposed to reference so I can enter a number or letter size drill and it looks up the decimal size. It is a work in progress as the last section at the bottom is not working as I envisioned. I created it when I could not find the type of tap drill calculator that I wanted.
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