thread relief... can someone explain the purpose?

[USAeng]

From what I can gather on the external thread it is so 2 pieces can mate up completely with no interferance from the thread or maybe a radius from the thread making... something like that?

more so, what is the purpose of the internal thread relief... I read that you should make it 2.5 threads in width and .015" min greater in diameter... thanks for any info

 

[hydtools]

Assembly clearance.
Threading tool runout.
Remove stress riser of thread runout.
For internal thread, eliminate the wire edge of the entry thread at the part surface.
Assembly location to the hole before engaging the thread.

Ted

 

[rb1957]

not quite sure which feature you're talking about. both ends of a thread (the peak and the valley) need some radius ('cause you don't want a sharp point, do you ?). the peak radius is usually larger than the valley, so there's some clearence between teh male and female threads. but to me, thread relief would refer to a grove before the thread (something like under the head of the bolt) which tries to reduce the stress concentration at the thread.

 

[USAeng]

is the purpose of the 2.5 threads relief past the last thread and .015 min wider to let the threading tool pass through?
here is a link to what I'm talking about... figure 4 more than the others... do you only need this when using a tap or what?

http://www.pmpa.org/technology/design/threadrelief.htm

 

[CoryPad]

Yes, to allow the threading tool to pass.

 

[USAeng]

is so a tap can go through all the way or is it for some sort of cutting insert on a cnc or will it work for both?
sorry I dont know a ton about machining...

 

[CorBlimeyLimey]

This may 'explain' it better.

http://www.youtube.com/watch?v=0q_q53wsyHU

 

[USAeng]

nice... thanks a lot

 

[berkshire]

Whilst CBL's video is neat, a lot of thread cutting lathes do not stop the spindle at the end of the cut. That groove then becomes essential when the lead screw is disengaged.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor