Posted by Ron on November 04, 2005 at 23:35:58:
In Reply to: demag crane gears posted by Collin doyle on November 04, 2005 at 20:35:43:
You are working to an old standard for whole depth of 2.157 x Module. For DIN or ISO Module (which an original German part more than likely is) it should be 2.25 x Module. In fact I've never come across the “old standard” for Module before. I assume the gear has 75 teeth. Based on your measurement of the O.D. it has a minus correction of 0.265. This is normal practice. It allows a plus correction to be made to the pinion without changing the center distance. A plus correction, usually made to a pinion with low numbers of teeth is used to help avoid undercut below the involute profile.
I would recommend you not cut these gears on a milling machine. They are being used in a critical safety application. I suggest you get someone to cut them who has a hobber or gear shaper as I don't believe you'll be able to find a form cutter that can replicate the original corrected form accurately enough to suit the application.
The gear will have to be cut based on span measurements taken across certain numbers of teeth from both the original gear and pinion. These measurements can also be taken with a gear tooth vernier or across pins. This will ensure that the original center distance and backlash is maintained. Remember you are working with a corrected gear set.
Should you decide to cut them on a mill, below are some figures to help you, once again they are based on your measurement of the O.D., which I might add, is not really the way it should be done in-case the O.D. has been damaged or incorrectly turned.
Standard O.D. = 154mm
Corrected (measured) O.D. = 152.91mm
Correction factor “X” = -0.265
Corrected Chordal Addendum = 2.016mm
Chordal Tooth Thickness without backlash = 3.141mm
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