[rjmorel]

I have BC v25 and need to make a 3D solid model for my 3D plastic printer of pop bottle cap threads that can screw onto a 2 liter bottle.
I believe the threads are stubby 8 tpi ,.450 length, I.D. of 1.00".
Anyone have an idea of how to draw these threads? Outside of cap isn't important at this stage, just need to know how to draw the threads for solid modeling. Thanks, RJ

[BurrMan]

Here's a file with some geometry to look at. On the "normal" layer, there is a helix and a profile. This would be a normal way to make a thread solid for "cutting" thereads out of a cylinder. BobCads "sweep" command doesnt handle this well (It needs an option to define the "flat" of the sweep, so you would need to construct it by surfacing.

To see what you would need to do, just look for the green "Cutter" object and make that the only thing visible and active. Then extract it's edges (From Solid)... You will see 2 profiles one on each end and 4 helixes that makeup the wireframe. 2 inner ones that and 2 outer ones. From these you can skin the solid (That you see in green) that you can use to boolean difference from the inside of your cap shape to make internal threads on a cap.

[SeanDa]

Draw the helix for the thread at the depth that you want. The helix function can be found under Other/Spiral. Then draw the profile of the thread. Then use the sweep function to sweep the profile along the helix. I have provided PDFs on the Spiral function along with the Sweep function.

[BurrMan]

Sean,
Have you tried that in BobCad?

Open the example I posted and look on the "normal" layer. Sweep that profile up the helix.

There is an automatic rotation to sweep that occures due to the structure of the helix. In a program that will accomplish this, there needs to be a "set flat" option, which will maintain the profiles "Flatness" throughout the sweep. (The solid in the file I posted)

Maybe you can share this with the geometry guy's to look at updating the sweep command?

Other than that, you will need to skin the wires to make it. (Or use another CAD package that will do a flat sweep)

Or, maybe you could enlighten me on a rotation/placement of the profile and a pick method to acheive a flat sweep up the helix.

[BurrMan]

I was thinking about a bottle cap, and there ARE different kinds, like the little tin ones that break at the bottom when you twist it... Those arent really "internal threads", but are actually shaped like the threaded surface.

Here's another method to get those types. Although I made an exaggerated shape, and also use a spline (I think a true cross section of that type of thread would use straight lines with arcs where the thread is) As long as you use the true profile/cross section of the cap it should produce one of those this way:

Bottle Cap - YouTube