Defining the shoulder diameter of a single profile thread mill

[admin43NL6]

Hello,

TLDR; It is unclear to me how Fusion 360 calculates the diameter of the shoulder/neck of a single profile thread mill, can anyone tell me what the formula is?

First off, I'm not sure what to enter in the thread pitch field, as it is a single profile tool, so that field seems rather meaningless. I have tried entering the max thread pitch supported by the thread mill, but the neck diameter doesn't seem to change. I also tried to calculate what the pitch would be assuming there was another thread profile immediately adjacent to the one present on the cutter (see attached diagram). This also didn't seem to change the neck diameter.

Specific problem I am trying to solve:

I am using this cutter from McMaster and I want to see if it can cut a 1/2-20 OD thread:

https://www.mcmaster.com/4425N17/

The cutter is advertised as enabling 18-48 TPI threads, so it should work, but when I input the cutter parameters into Fusion, the neck of the cutter collides with the boss. I didn't believe this was correct, so I downloaded the CAD file from McMaster, projected the geometry onto a plane and created a form tool, and sure enough it threadmills the boss with plenty of clearance. I went back and tried tweaking various parameters to see how the neck diameter is affected, but you can't even see what the value is that Fusion calculates, only the graphical rendering.

Do I really have to create a form tool for every single profile threadmill that I want to use? I feel like I am much more prone to making errors by creating a form tool than using the threadmill wizard.

[seth.madore]

Single form thread mills and their graphical representation are known to be deficient in some areas, this being one of them. As far as "should I create form tools"? If you know that it's going to clear, you could just ignore the false collisions, but I can see areas where that would bite you (actual real collisions being one of them..)

[mjpdougherty]

Just going through the experience of adding a new thread mill to my tool library.  It does seem impossible to have it accurately modelled, which is frustrating.  I do not like the idea of false collisions due to inaccurate models.  I realize that is where we are, but wanted to add my voice to this.  I would be great if this was addressed.

Thanks.