![]() ![]() 8 Excel spreadsheet for calculating involute gearsįor the calculation of involute gears, the involute tooth flank must first be described mathematically.5 Calculation of the profile shift coefficients.3 Calculation of the circular and the base pitch.1.1 Definition of the involute function. ![]() Again, use with the caveats as above.ĭP=1 (read chart values in inches) or M=1 (values in mm), PRESSURE ANGLE = 30* Here I start at only 10 teeth since 30* pressure angles are usually used because of the small diameters of low tooth-numbered gears. Again, use with the caveats as above.ĭP=1 (read chart values in inches) or M=1 (values in mm), PRESSURE ANGLE = 20* TABLE FOR MAKING AND USING INVOLUTE CUTTER-CUTTERSĭP=1 (read chart values in inches) or M=1 (values in mm), PRESSURE ANGLE = 14.5* These cutter-cutter settings are for theoretically perfect 96% wide teeth. This is especially true for the low end of the table. There seems to be some art to sizing cutters, so for any given tooth count you need, you may have to choose a larger count in the table. Here's 20-100 teeth for pressure angle of 14.5*. Divide the table values by the actual DP you need. To use the tables in English, the table values are in inches (in) for DP=1. Multiply the table values by the actual modulus you need. To use the tables in metric, the table values are in millimeters (mm) for modulus 1.0. Hence, the circular cutter described here is a gear cutter-cutter. The edge will take on the profile of a tooth space and it becomes the gear cutter. To make involute gear cutters, use this chart to make a hardened, relieved circular cutter ("cutter-cutter" dia.) and infeed it on both sides of the edge of a spinning disk or fly cutting blank (between ctrs & infeed). I guess the tooth count cutter you actually should use would deviate even more at 14.5* and starting at even larger tooth counts. Notice there is little deviation for usable cutters at a pressure angle of 30*, but a deviation of theory to practice begins at lower numbers for 20*. I'll post the charts in one of the forums here if someone tells me which one.Ĭlick to expand.NOTE: I am not totally convinced that cutting teeth that are perfectly positioned and shaped to fill 0.48 of the pitch will actually work at lower tooth counts. I don't know how he picked his actual tooth numbers. However, if you want to make custom cutters, you'll have to "slide up" the scale some amount for clearance as Law did for his low numbered gears. I was able to make an entire chart with every tooth count (from 6 to 150) for 20*, 30*, and 14.5*. I did enough math to find his chart values do indeed include this adjustment. The bold values above show that as you get down there, you have to cut bigger and bigger relative spaces-creating thinner and thinner teeth forms-so the teeth have enough room to "turn" in the spaces since the diameters become quite small.Īlso, Law states the tooth should be 0.48 of the circular pitch while the space should be 0.52 to add a little backlash as clearance. Notice that the 20* values start to deviate from ideal as the tooth count goes down. #How to select involute gear cutter fullHere are the full results for Pressure Angle of 30* I did some math that let me look at what theoretically perfect teeth would look like for every tooth count. Law gives the values for making a set of 6 cutters from 17-20 teeth to 135-rack for pressure angle of 20 degrees and a set of 9 cutters from 10-11 teeth to 135-rack for pressure angle of 30 degrees. Basically make a button cutter and use the distance between centers and infeed to make the profile of the gear cutter. #How to select involute gear cutter seriesBuy a set, or make them according to the formulas in Ivan Law's Gear and Gear Cutting (Workshop Practice Series #17). If you want to make an involute gear, you'll need an involute gear cutter. ![]()
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