I talked to to Hugh in New York, forum name “bytewise”, as he is building a Doxford opposed engine
http://www.modelenginemaker.com/index.php/topic,1556.msg23103.html#msg23103 He had to cut some helical gears with same angles as the ones I need. Anyway he told me that there was a formula in Machinery Handbook to figure which gear cutters to use cut the gears. He said you can't go by the ones to cut spur gears.
I looked up Helical gears in my Machinerys' Handbook 28th Editon Large Print on page 2109. It stated that “the cutter for milling the helical gears is not selected with reference to yhe actual number of teeth in the gear,as in spur grearing, but ratherwith reference to a calculated Number N' that takes into account the effect on the tooth profile of lead angle, normal diametrical pitch, and cutter diameter.”
It gave a formula of N' = NK + QK'
K,K' and Q are constants found on pg 2110 in my book.
After much head scratching and moaning
:insane:I was able to figure out how to work the formula.
Math and I go together like oil and water!
N is number of teeth and K and K' are constants from the table on helix angles and Q is from the table on Outside and Pitch Dia. Of Standard Involute milling Cutters. On the same pg.
Any way here is what I came up with.
For the 63* gear the formula is:
N' = (8 x 10.687 ) + ( 53.76 x 3.852 ) = 85.50 + 207.08 = 292.58 say 293 which is a # 1 cutter.
( I round up or down to get to 2 decimal points in the totals)
For the 27* gear it is:
N' = ( 16 x 1.414 ) + ( 53.76 x .260 ) = 22.62 + 13.98 = 36.6 say 37 which is a # 3 cutter.
These are for 32 DP cutters.
Could some one check my math and see if I did it right?
It looks like I'm going to need to buy some cutters. Hopefully I can sell a couple of never used Gas Model Airplane Engines for large scale models I have and will probably never use, to raise the funds for the cutters.
Still haven't heard from Hemmingway yet.
George, did you go thru all this to select the right cutters?
Ron
