Creating m4x0.7 screw thread using helix+sweep

hello,

I'm sure I must be about the zillionth person to post a question regarding creating screw threads in 3d, but I can't find an answer on this forum that fits my problem.

I'm trying to create an M4x0.7 bolt with a 15mm long thread.

I've used a helix around a 2.939mm diameter cylinder and have created a profile of the thread as per the wikipedia guide to ISO threads. I tried creating a 4mm clinder and subtracting the thread profile, but that didn't work either.

When I try to sweep the thread profile around the helix, the profile is rotated through 90 degrees. If I selected "Alignment: No" in the Sweep options, I just get the message "Unable to sweep 1 selected objects."

I can't see what the problem is and AutoCAD isn't giving up the reason for the failure. The thread-height is 0.7mm and the thread profile object is 0.7mm long, so I'm pretty sure it's not some sort of self-intersecting object problem.

Does anybody know how to get AutoCAD to give more information about why a sweep etc has failed? If I knew what the problem was, I could probably do something about it...

Thanks for any help

Maybe this tutorial by forum member J.D.Mather may help solve your dilemma.

http://home.pct.edu/~jmather/content/CAD238/AutoCAD%202007%20Tutorial%204.pdf

It may be that your profile is not self-intersecting but perhaps the points of the profile you are sweeping are co-pointular (heh, I just made that word up) so when they touch it could cause the problem. Try using .695 mm for your profile dimension.

Have you tried EXTRUDE?

Many thanks for your quick help - using your suggestions and a combination of trial and error, I managed to get it to work, so thanks very much for that - much swearing had been done up to that point!

I think it was a combination of:

a) the start angle of the helix

b) the length of the swept object being the same as the thread height

c) the orientation of the UCS

I set the UCS so that the z-plane was "along" the swept path of the helix (rather than 90 degrees to it for when I created the helix), oriented the helix so that it started perpendicular to the x/y axes and reduced the length of the swept object by 0.001mm and that seemed to fix it.

I haven't tried EXTRUDE but I'll look into it and see if it's easier to use - I have more threads to generate and I'm not looking forward to it

Thanks very much for your help

once you've got got a working process down it'll be easy-peasy.

...famous last words

Having created my m4 bolt and nut, I then 3d printed them and (probably no surprise) they didn't fit together - the tolerances were too tight.

I also decided that m4 was just going to be too small, so I've redrawn an m8 bolt and nut profile and am attempting to sweep them around a suitably sized helix, exactly as before.

However... whilst the nut profile sweeps fine, the bolt profile throws the error, "The min radius of curvature is less than profile length." ...what?!

The helix turn-height this time is 1.25mm and the profile length is 1.24mm, so all should be fine - which "min radius of curvature" is it talking about?

As before, many thanks for any sage wisdom proffered

Did you check out the link to JDM's tutorial I provided in post #2?

I did, thanks - it was very helpful, but nobody ever seems to come across the little "oh, it doesn't normally do that" problems I keep coming up against...

I've finally (an hour of deleting and re-drawing later!!) managed to fix it again - in the end it was quite simple, but just the last thing I tried...I resized the helix radius, but that didn't help, I redrew both swept objects, but that didn't help, I tried to sweep both objects seperately and that sort of helped, as one of them worked. I then shortened the swept object that didn't work and that got it working...I'm sure I'd already tried that, but there you go. Then, the other object inexplicably stopped working, so I shortened that one and it started working again (sun-spots, no doubt) - 3d printed it and, damn me, I've managed to print a bolt that screws into a thread...

I'll certainly never look at nuts and bolts the same way in hardware shops again - what complicated little b*ggers they are!

Thanks for reading all my nonsense

Your hard work and determination paid off. Congrats.

Post an image of your creation so we can all admire your handiwork.

I cheat, McMaster-Carr has a library of screws and bolts for down load.