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Re: TIR VS Position
Re: TIR VS Position -- lvw	Post Reply	Top of thread	Forum

Posted by: Kelly Bramble ® 01/30/2007, 14:11:12 Author Profile eMail author Edit

For all practical purposes, TIR is measuring the position of the smaller cylinder relative to the larger datum cylinder or origin. Except, that the TIR (Total Indicator Reading) or Total Runnout is also controlling the cylindricity and straightness. So, if by TIR you realy mean Total Runnout, the tolerance is a little more aggresive or comprehensive than position tolerance used alone. To me, your challenges are that manufacturing one end of the cylinder relative to the other datum end to .016 TIR over twenty inches may not be a reasonable tolerance. Most modern CMM's should be able to measure Total Runnout. An advantage of Total Runnout is that this is simple to measure during an in-process inspection while manufacturing. Another question that should be asked is if Total Runnout is realy required? If the larger diameter datum feature is actually rotating within the target assembly and all of the surface elements of the smaller diameter feature must meet the requirements of runout, than the specification is justified. Position is more of a surface boundary requirement relative to the specified datum.

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