I’ve followed @DaveR’s video for drawing screw threads, working at 1000x full scale.
I’m using a somewhat unusual thread - one used since the late 19th century for securing porcelain telegraph and telephone pole insulators onto their metal supports, patented by J. H. Cordeaux.
But as the topic title says, I can’t get the flat face at top and bottom of the thread to separate from the rectangle used when I Intersect faces with the thread to cut it to length.
After much googling, I found a specification for this thread. Here’s what I found.
Cordeaux Thread for Telegraph Insulators
Asymmetric thread. Upper flank: F = 29 deg.; Rc = Rr = 0.015 inches. Lower flank: F = 35 deg.; Rc = Rr = 0.022 inches.
Sc = 0.0166 inches; Sr = 0.0331 inches; h = 0.0642 inches (7TPI) or 0.0832 inches (6 TPI).
And I was able to draw the profile at my second attempt. On the first attempt, I couldn’t work out how the radii fitted, and just drew a flat on the inside and outside of the thread.
I thought I’d managed to create one with flats instead of rounded edges on the threads, but then found it wasn’t solid.
Looks like this:
Cordeaux thread 3d.skp (258.9 KB)
So I tried again, and DID manage to make one solid, but then found I’d cut it off (and then bevelled it) at the wrong height - short by a fraction of a turn of the thread, but the correct pitch (6tpi).
So I thought I’d draw it again with rounded tops and bottoms to the thread.
Here’s an image of the revised profile, and the SketchUp drawing of it.
Cordeaux thread profile rounded.skp (52.2 KB)
And here’s where I’ve got to, redrawing the thread, before cutting to length.
Cordeaux thread rounded 3d.skp (1.7 MB)
But when I use Interesect faces with selection, and trim off the surplus, on the bottom it looks like this:
Cordeaux thread profile rounded.skp (52.2 KB) (saved back to v2017 but drawn in SU 2020).
The problem I have is that the bottom face of the screw doesn’t separate from the whole rectangle, and the same happens on the top. I’ve tried redrawing the lines in the plane, but can’t get the face to separate. I’ve zoomed right in on every vertex in the plane, and can’t see any gaps or anything out of plane.
I don’t know why not, and wonder if anyone can see why not, and help me fix it?
The overall thread portion is six turns at 6tpi, so 1" high - scaled up to 1000" between the planes.
Any help to create a clean solid would be helpful.