Threads disappear after offset applied

[tonyAQW8H]

Image A shows what happened after I created a block with three tapped holes with an offset added to the middle hole thread - the thread on the middle hole disappeared. It should also be noted that the 2 remaining threads now have a bad thread form - the thread goes to a point rather than being truncated.

Image B shows what happened when I suppressed the offset feature - all 3 threads are visible and the thread form is correct. 

Image C shows what happened when I suppressed the chamfer feature rather than the offset - all 3 threads are again visible with the correct form but the offset has failed.

After playing around a bit a full solution was found by moving the hole counterbores to after the thread feature, ie thread all of the holes all the way through, apply the offset and then add the counterbores.

Is this a how this is supposed to work?

[TheCADWhisperer]

Can you File>Export your *.f3d file to your local drive and then Attach it here to a Reply?

[tonyAQW8H]

Here is the requested file.

[MRWakefield]

I always add the chamfer after the thread otherwise you get an odd anomaly where the thread doesn't run all the way through, as shown in these screenshots of your file.

I also noticed that your offset is only being applied to 5 faces. This should be 9 faces (see explanation below).

When applying offsets to threads to give more clearance or whatever you need to select the minor, major and just one of the flanks. This will keep the thread profile correct. If you select both flanks it will result in a thinner crest and a wider root.

I've attached a modified file that should be what you're looking to achieve.

Hope this helps.

[MRWakefield]

Here are some more screenshots showing the problem with putting the chamfer before the thread.

Notice how you don't see the thread 'emerge' through the chamfer on your original:

Here's how it should look:

[g-andresen]

Hi,

move chamfer in timeline

günther

[TheCADWhisperer]

@tonyAQW8H 

To expand on what @MRWakefield wrote.

Initially model as cosmetic threads, add the Chamfer, and then toggle to Modeled threads.

[MRWakefield]

Yes, I meant to add that but forgot! Thanks for pointing it out.

[tonyAQW8H]

Thanks for the reply. 

I normally add the chamfer before the thread as it is easier to add it to a plain hole and then I move it to after the thread. For some reason it wouldn't allow me to move it in this model and when the thread just disappeared I didn't get around to sorting that.

I'm surprised it is showing 5 faces selected as I was only applying the offset to the middle hole so I only intended to select 3 faces. If one face in each of the other two holes was also selected I guess that explains why those threads went to a point it still doesn't explain why the thread in the middle disappeared though or have a misunderstood your explanation?

[tonyAQW8H]

Thanks for the tip, that's a good way to do it.

I normally move it in the timeline but it wouldn't move on this model and then the missing thread issue overtook that issue. 

[MRWakefield]

Sorry no, I've no idea why the thread disappeared! Hopefully my posts helped you in some way though.

[g-andresen · Accepted solution]

Hi,

I noticed that I cannot select the unselected face with the "Offset Faces 6" function.
However, this is possible when I create "Offset Faces" (in front of 6.) again.
This indicates a (temporarily) damaged tool.
I have experienced such behavior (rarely), but with different functions. If there are repeated problems with such functions, I redo them.

günther

[MRWakefield]

That's pretty much what I experienced. It really wasn't acting as it should so I too deleted the offset and recreated it.

[tonyAQW8H]

Hi günther

Thanks for the reply.  That is interesting, maybe that's what has happened in this case.

Has anyone loaded the model I posted and seen the same disappearing thread issue? 

EDIT: Just seen Marcus has answered this question so it looks like you are correct.

Thank you everyone for your help and advice

[MRWakefield]

Just a quick note: One caveat to my statement regarding the offsetting is that this only works on 60° threads. Anything other than this will cause errors in the form. In these cases the flank needs to be offset by a different amount to the Major and Minor dias. A better way to do it is to create a thread file with the extra clearance added to or subtracted from the Major, Pitch and Minor dias.