Adam Snow

Thread Feature - Minor Diameter is Wrong, or am I Wrong?

Discussion created by Adam Snow on Mar 29, 2016
Latest reply on Sep 8, 2016 by Scott Rypstra

The short version of this post: The Minor Diameter of this 2" thread does not fall between the allowances.

 

My goal is a 2" - 4.5 UNC class 2, external (A) thread. I usually make threads manually, but tried the Thread tool tonight.

Thread Sil.png

Before invoking the thread feature, I sized the Outside Diameter of my part to fall between the allowed tolerances of 1.9971" max / 1.9751" min

The thread tool is easy enough to use, and I selected the following options: Inch Die, 2.0" - 4.5, Cut Thread

Based on my selected cylindrical edge, SW determined the OD is 1.9861" (the midpoint between the OD allowances above)

Now the final Minor Diameter of the thread comes to 1.7455". The allowances for this size thread are 1.7325" max - 1.6865" min.

 

Am I doing something wrong?

Is there a way to control the Minor Diameter on this thread?

Is there a "trick" to edit the sketch used for the Thread feature? I get that it is a library feature, but it would be nice to have some control over it (like a hole wizard sketch).

I tried the Override Diameter button, but I can only increase the value. Making it smaller prevents the thread from forming (as it would be "inside" the part).

As there is no option to pick class 1, 2 or 3 threads, I thought I'd be able to change the Major or Minor Diameter somehow. Yes? No?

I'm just reading the warning thread Lee Brown posted back in 2015 about inaccuracies in the Thread feature, but those are fixed, right?

 

On a side note, I noticed the entire series of 9/16" threads are missing. Is this on purpose, or an oversight?

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