Posted by BillS on January 09, 2008 at 12:33:15:
In Reply to: Re: sprocket wire size posted by Ron V on January 09, 2008 at 06:30:07:
I still wonder why Frank's print shows the OD circle to be the same as for MOW. The MOW over 0.130 pins should be 0.850 as I see it. If MOW were the same as the OD, this would require a different pin size, but that makes no sense. Might as well measure the minor dia (caliper dia) as to measure a MOW over non roller sized pins (well not exactly - a typical caliper would measure over a small chord to the radiused tooth bottoms...).
I think the important thing about using the roller size pin for MOW is this:
Shaper cutting can yield a smaller radius at the bottom that doesn't match the chain's roller radius. Shapers, somewhat like the involute cutters of yore, must be ground to approximate correct sprocket profiles over ranges of teeth, esp. over lower numbers of teeth. This economy of cutters avoids an exact shaper cutter grind for each number of sprocket teeth to cut (are hobs the same way? don't know...). If the sprocket bottom radius is smaller than the roller radius, then the chain would ride higher if cut to "standard" caliper depth, which means the sprocket must be cut deeper to get the chain to wrap. For most applications and small pitches, cutting 0.002/.005 deeper gets the job done.
I know it's "touchy feely" to some, but wrap a new piece of chain if you can get it just to make sure it's cut deep enough :^).
Here are my guesses about the print:
(1) The cutter was ground especially to generate 9-tooth sprockets, and MOW would be correct when OD is correct. Cutter regrinds might void that assumption, though.
(2) Print specs were done to use a radius insection over one pin instead of MOW or caliper measurement (no odd tooth correction needed for that).
(3) The print is mistaken when referencing MOW (MOW over 0.130 pins should be 0.8498 = caliper factor x pitch + roller dia)
Using the charts and formula from Machinist Handbook, the Caliper Diameter should be 0.5898 +0/-.004 (precision) or +0/-.0075 (commercial)
(Caliper diameter = Caliper factor x pitch - roller diameter)
Thanks for the charts, Ron - always appreciated.
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