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Posted by: belinda63

06/03/2009, 10:54:21

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What is the proper symbol to use in GD&T block for Stub Acme Threads?

We have used Total Runout but was told it can not be measured so now we are using True Position and now being told it also, can not be measured.








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: GD & T of Threads
: GD & T of Threads -- belinda63 Post Reply Top of thread Engineering Forum
Posted by: Kelly Bramble

06/03/2009, 11:09:40

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True, runout (total and circular) are not a practical geometric tolerance for an ACME thread. Additionally, runout (total and circular) are unlikely to provide a tolerance control that is meaningful to the function of the thread though there are exceptions.

Position is the most correct geometric tolerance to locate a threaded feature relative to a datum(s) reference. By default, position, orientation and datum reference of a threaded feature applies to the axis derived from the pitch. This is easily measured by using a thread gage whether one has a CMM or height gage, however in the event that a thread gage is not available alternative methods must be used. Generally, when quality and manufacturing cannot measure a threaded feature defined with a positional tolerance, they normally do not have the proper equipment or training, usually it is the former.

When a thread gage is not available and depending on how the ACME Stub thread was manufactured, you could define the positional tolerance applying to the most accessible feature on the thread. For an external ACME thread this would be the major diameter and for an internal ACME thread that would be the minor diameter.

eMail author me if you have more questions on this topic.







Modified by Kelly Bramble at Wed, Jun 03, 2009, 11:10:04


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