This boolean subtract with offset is not solving - help!

tom_auger

Hi friends, it's been a while but now I'm back and as always I have questions......

One of my most standard things for making 3D printed parts that fit into each other is to use Boolean Subtract with a small (eg: 0.3 mm) offset to create a bit of gap to account for the tolerances of FDM printing. Typically works a charm. I use it for things like threaded parts or even press-fit parts.

Well, here's my latest very simple threaded part - the inner part ("male") needs to subtract from the outer part to create the relief threading. However, if I apply a positive offset, even a tiny one, the boolean feature doesn't solve. Surprisingly, the opposite (negative offset) does work, but that's precisely the opposite of what I'm looking for.

Screen shot below and then a link to the doc if anyone wants to take a quick gander. As always, so greatly appreciated!



https://cad.onshape.com/documents/510bb745140070d8d7d5ce3a/w/83a9ab501d6696ead04ac9c6/e/4b95368fb7fda514f494f445?configuration=List_IWpyc5fQoT6y5H=Default

tom_auger

I was able to solve the issue using three separate "Move Face" features - one for each "side" of the thread (upper and lower side of the "V") and then I had to offset the top face of the collar (in blue) as the inverse operation on the cap was not solving. Dimensionally I'm not pleased with that last piece but I like knowing that my approach is still more-or-less viable.

But I'll probably remember that thread FS tool next time

alnis

I would take a look at the Thread Creator custom feature here: https://cad.onshape.com/documents/6b640a407d78066bd5e41c7a/

It generally creates pretty well-behaved threads.

Here's how you could modify your design to make use of it (reducing the feature count a lot:
https://cad.onshape.com/documents/1c6c17d4576d0f7553bba4a6/

General tips:

• Fully define your sketches whenever possible--this helps a lot with complex geometry
• Watch out for tiny sliver faces--these make offsets not work as well
• There is generally a custom feature available to automate anything annoying

Hope this helps!

lougallo

After a quick look it seems the valley in the thread when offset is disappearing and the overlap is causing the failure. You might consider using scale on the part but it might take some trial and wrror to match the gap you want. 

tom_auger

alnis_smidchens said:

I would take a look at the Thread Creator custom feature here: https://cad.onshape.com/documents/6b640a407d78066bd5e41c7a/

Thanks for the reminder Alnis! I have it installed but sometimes forget to use it. I also like doing things the "manual" way when I can because I always learn something new!

tom_auger

I was able to solve the issue using three separate "Move Face" features - one for each "side" of the thread (upper and lower side of the "V") and then I had to offset the top face of the collar (in blue) as the inverse operation on the cap was not solving. Dimensionally I'm not pleased with that last piece but I like knowing that my approach is still more-or-less viable.

But I'll probably remember that thread FS tool next time

edgelord

which tool are you using for boolean subtract with offset?

eric_pesty

https://forum.onshape.com/discussion/comment/116437#Comment_116437

Just the regular boolean tool, just check the "offset" box…