Problem with chamfering a tapped hole in Solidworks 5

[AF2023]

Hi everyone,

I'm assembling some parts in SolidWorks. I added some screws for the tapped holes on the pictures attached to this post.

I can't understand why there is a material conflit between the screw and the tapped hole in the case of tapping from the bottom edge of the chamfer (here is a section view):

And here is the corresponding top view.

but the problem doesn't occur when the tapping is shifted beyond the bottom edge of the chamfer (thus in that case the tapping goes beyond both sides of the hole):

See, there is room now for the first threads:

Again, the corresponding top view:

Obviously, that's not what you would except to see when you have a chamfer on a hole. I mean, the threads shouldn't invade the chamfer's zone right ?

Can you help me understand ?

Thanks in advance !

 

[3DDave]

Normally the chamfer is much smaller and is used to eliminate the knife-edge that would remain where the thread is intersecting the entry surface.

Look at the inverse problem - add external helical threads to a cylinder with a cone at the end - the helical thread climbs onto the cone until it reaches the place where the radius of the outer part of the thread intersects the cone.

 

[hendersdc]

Is there a reason you are modeling the threads to begin with vs cylinders at major and pilot hole diameter?

 

[jassco]

Hi, AF2023:

You may want to explain what your ultimate goal is. There may be a better way to achieve what you are trying to do.

Best regards,

Alex

 

[AF2023]

Hi all,

3DDave : I already tried smaller chamfers but the problem is still there. I understand your point with the cylinder and i guess the second picture i posted is the equivalent to what you are saying. The threads should stop when the cone is reached. The problem is that in this case, i see the "material conflict" i was talking about earlier. Also this prolem doesn't occur when i remove the chamfer... so the problem IS the chamfer right ?

hendersdc : Yes, i need the assembly to be as realistic as possible for marketing purposes.

jassco: Well, the goal is to have the most realistic assembly possible

 

[Jboggs]

"but the problem doesn't occur when the tapping is shifted beyond the bottom edge of the chamfer (thus in that case the tapping goes beyond both sides of the hole):"
From the way you describe it, sounds like you are creating a chamfered hole and then trying to start the thread at the bottom of the chamfer. In the real world a machinist would drill & tap the hole first, and then clean it up with a chamfer if needed. So the thread would go all the way to the top surface, and the chamfer would only remove a little of it.

I'm also wondering why you are modeling the threads in the first place. I've been designing machines for decades and can't remember a single instance where actual modeling of threads was beneficial. In most cases it is just a HUGE waste of computer memory and capacity. That's why cosmetic threads are the preferred choice.

 

[AF2023]

Jboggs : "In the real world a machinist would drill & tap the hole first, and then clean it up with a chamfer if needed. So the thread would go all the way to the top surface, and the chamfer would only remove a little of it."

Are you sure about that ? Take a look at this :

https://www.youtube.com/watch?v=kgUmGXuQ14o

I feel like the guy in the video is right because if you machine an already tapped hole, then you might have troubles putting a screw afterward. I tried the opposite once, i cut a stud and then tried to put a nut on it but i couldn't because by cutting it i messed up the threads. I guess the same would happen if you chamfer an already tapped hole ? I know, the guy in the video completly erased the chamfer zone by using a bigger tap size but i also found this article :

"it is just a HUGE waste of computer memory and capacity"
That might explain why my cpu is getting hot haha. Even if i simplify the task by using cosmetic threads as you suggest, i'm still really frustated to not understand what i am seeing on the pictures i attached to the original post. Would this material conflict make the assembly impossible in real life ?

 

[jassco]

Hi, AF2023:

"tapping from the bottom edge of the chamfer" does not make sense. Why did you try to define the tap to begin intercept starting from bottom of the cone?

Best regards,

Alex

 

[ctopher]

Modeling threads in SW is usually a waste of time. I have done lots of marketing stuff, they don't care about the thread details, unless you're in the thread business.
The thread feature isn't 100% accurate. Also, the chamfer looks too big. I wouldn't spend too much time on it. The part won't be CNC programmed/machined from the model threads anyway.

Chris, CSWP
SolidWorks
ctophers home

 

[TheTick]

Modeling threads in SW is usually a waste of time.

 

[TheTick]

Modeling threads in SW is usually a waste of time.

 

[TheTick]

Modeling threads in SW is usually a waste of time.

 

[TheTick]

The only part I disagree with is the "usually". Should read "almost always".

 

[SBaugh]

Unless you are a bolt manufacturer then you should not make actual threads. Use Cosmetic threads for all internal and external threads.

Scott Baugh, CSWP
Mechanical Engineer
Ciholas

https://www.ciholas.com/

"If it's not broke, Don't fix it!"

faq731-376

 

[matthewcsmith]

Your bottom pictures looks about right for an actual tapped hole through a countersink...

 

[ASIT859]

I didn’t see the is questioned elsewhere, but have you checked to make sure the internal and external threads are correctly modelled? In other words, have you confirmed that the major, minor, and thread profiles are correct?

I have had to model threads before for a pressure vessel design since we were using non-standard features and thread diameter-pitch combinations and detailing everything ourselves and I recall needing to make my own thread profile library bc I kept having interference issues even tho we were using the UN thread profiles.