Posted by BillS on February 11, 2007 at 22:31:15:
In Reply to: Re: contact length posted by lbmakem on February 10, 2007 at 22:12:29:
Yep - that formula checks out geometrically. It assumes that there is no undercut and line of action extends to the base circle, theoretically. Start of Active Profile (SAP) then is at the base circle. End of Active Profile (EAP) is always at the O.D. as long as there is topland.
Actual root diameter plus root radius left by the cutter tip defines the actual SAP, which is always above the base circle. The formula you quote would always give a maximum possible roll length greater than actual roll length between SAP and EAP, right?
Since roll length is likely used to set up a measurement of profile variations, that probably is the best way to assure you're getting the entire profile within the measurement.
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