"Through face does not intersect path of the tool" while subtracting

[Guga50]

Hi everybody!
I need to subtract a body and get this error: "Through face does not intersect path of the tool"
Look at the part file attached. It's a very simple model.
Everything is fine until you change helix(1) end limit from 40mm to 45mm. Then subtract stops working.
I tried to play with tolerances but with no luck. It makes difference but in quite a random manner.
Can anybody help me to adjust tolerances and explain what I'm doing wrong?
Thank you.

 

[cowski]

Attached is my take on your file. I didn't modify any of the modeling tolerances, instead I took a slightly different approach. I swept the thread profile of your sketch with the "preserve shape" option to keep the corner sharp then I used the "trim body" command to trim the cylindrical body with the swept sheet.

I think the issue with the original file is that the "inside diameter" face of the swept triangle didn't quite match the ID of the cylindrical body (due to the swept being a B-surface approximation). This causes the ID of the tool to not completely extend through the ID face of the cylinder in spots which led to the error you saw.

www.nxjournaling.com

 

[Guga50]

Wow! Thank you very much.
Simple and nice.
Very useful for any kind of unusual threads.

 

[Toost]

I was about to say something smart about you have used a complex way of building this model, but cowski was quicker.
I think Cowski is correct in how the inside face is "almost" identical to the helical "inside" but not exactly and fails to subtract.

The inside face of the extruded body is "cylindrical", i.e a face described by a "analytical" equation. An analytical equation is one which have an exact answer.
- You can at any point on that face get an exact coordinate.
A B-surface is by nature an approximation, the equations are built to be able to handle/produce "any smooth shape"-surface, to do this, there is an approximation and a tolerance involved,
at any point on that surface there is a tiny tolerance , you can get the coordinate within the tolerance.
The tighter you set that tolerance, NX might need to add more patches in the surface to achieve the target tolerance, It most probably will be more like a cylinder in shape but it will take more space to save, more time to compute etc. i.e slower.

This B-surface might "wobble" in and out of the exact shape( the cylinder)within the tolerance and in some situations give the message "Through face does not intersect path of the tool".
The best way to avoid this message is to try use modeling methods where this doesn't occur. The method Cowski used is one such method .


Regards,
Tomas