Posted by Jim Pollock on April 30, 2012 at 17:04:16:
A couple posts below I had asked about hobbing a helical gear on my old Barber Colman #12 hobber that has no differential. My biggest problem was that I didn't know for sure what the helix angle was for the gear that I was trying to copy. I thought that it was 32 degrees so Bill S. sent me the gear setup to hob this gear but I was missing three of the gears that Bill said that I needed. My index gears are 10 dp with an 1 1/4 bore and my feed gears are 12 dp with a 1" bore. I don't have a 10 dp or 12 dp hob that is 14 1/2 degree pressure angle so I really couldn't make my own gears even if I could figure a proper index ratio that would use the other gears that I had. So I made a 75 tooth 10 dp gear on my cnc mill using a 1/8" carbide endmill and programming it with cad/cam. I only made the gear 3/4" wide because a 1/8 endmill gets pretty flimsy if it is much longer. It took about 5 hours to make but it ran all by itself why I was in the house so it was really no big deal. I could have milled the gear on my dividing head but that probably would have taken about as long and I would have had to be there the whole time. The other two gears that I needed were for the feed gears but I did these tooth counts but the bore was too big for my feed gear shafts so I made 2 adapters so that I could use my index gears as feed gears and it worked great.
I made a test gear but my helix angle was off by 3 degrees when held against its mating gear. The angle was a little too great. I wasn't sure but I thought that my feed had to be increased a little so I swapped out a 31 tooth feed driver gear and put a 33 tooth in. I then made another test gear and the angle was still off by 1 degree so I went up one more tooth on my feed driver to a 34 and cut another test gear and it was perfect. I installed it in the transmission and it meshes great. So my first helical was a success although I had to make a few practice ones just because I didn't really know the actual helix angle of the gear that I was trying to copy.
I just wanted to thank everyone that helped me on this.
I posted a picture of the gear that I was trying to make. I made this right on the shaft but the original John Deere gear slipped over the shaft and required the shaft to be so small that it would often break in a pulling tractor with high horsepower.
Here is the
placed photo link here - Ed
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