Our machining class needs information on generating single point (fly) cutters with involute geometry to cut spur change gears.
Eyeball grinding of the tool ala Gingery produces entirely useable gears but we are looking for something more exact.
Ivan Law in his book " Gears and Gear Cutting " [seefor details] [another US source for UK workshop practice series of books is ] shows a technique to generate very close circular approximations to the involute curve for both single point and circular form tools by using two circular cutters of specific diameters spaced a given distance apart. The tool blank is then fed to a specific depth between the circular cutters to generate the correct involute form.
Data take from Gears and Gear Cutting by Ivan Law ISBN0-85242-911-8 Data to generate circular approximation of involute curve For 20 degree pressure angle gears Base table for 1" diametrical pitch gears Inch Cutter # Teeth Diameter C/C In Feed Width 1 135-R 51.300 49.600 17.790 4.000 2 55-134 32.150 31.600 11.470 4.000 3 35-54 15.070 15.510 5.870 4.000 4 26-34 10.260 11.030 4.270 4.000 5 21-25 8.550 9.400 3.710 4.000 6 17-20 7.800 8.700 3.440 4.000 dimensions in inches Table for DP gears 25.400 The problem is that both charts show C/C spacing distances LESS than the specified diameter of the two circular cutters for the form tools for larger numbers of teeth.
Has any one used this technique? If so how are the #1 and #2 cutters formed?
We will be making 1.0 m/m module change gears out of 6061 T6 and/or phenolic / micarta, and possibly a 127 tooth metric conversion gear.
Given that it takes some time to hand grind a form cutter and this is a introductory machining class, we would like to minimize tool breakage. Has anyone tried using a slotting saw to remove most of the material and then cleaning up the slot using the form cutter?
Using the advise from these NGs, our first attempts were done using a spin indexer to make a 40T gear with entirely satisfactory results. We just purchased a rotary table to produce the gears the spin indexer can't divide. This is a WT1990-0015 (see at )
Any advise would be appreciated.