Multi-start Threads in 3D

Hi, I'm having some difficulty in figuring out how to model a multi-start thread model. It's basically a worm gear that has N starts where N will most likely be the number 5. This means that at the bottom of the worm gear, you will see the thread starting in 5 different areas. So far, the best Idea I have come up with is making 5 helix models and maybe trying to union them together some how, but I'm not sure if that's the best way (or if it would even work?).

Has anyone on these forums tried this before? Or maybe have some ideas on how to make it work?

edit: making 5 helixes with 72 degree angles between each start gives me the shape I want. But I still don't know how to model it!

i would create one helix, copy it and rotate each copy 72 degrees in your case then move them all back to the same base point. then use these paths to sweep your thread and cut it from your model

but no ive never done this before

that's what I came up with, but I'm having problems figuring out how to draw each path. I'm pretty new at 3D modeling in autoCAD and so I have issues with some of the basics.

How do you draw on the plane normal to the end of each helix in order to make the sweep profile?

How do you draw on the plane normal to the end of each helix in order to make the sweep profile?

See Step 4 http://home.pct.edu/~jmather/content/CAD238/AutoCAD%202007%20Tutorial%2011.pdf

but in this case I don't think really want to do that. Consider how you would cut the threads on a lathe. The top face of the cutting tool is parallel to the floor. Not perpendicular to the path. At least with a standard thread. I have to think on that a bit with the worm gear.

You should realize that Autodesk Inventor will create a worm and worm wheel automatically by filling some dialog boxes on the specs. I don't think I would use a program as archaic as AutoCAD for work like this.

AutoCAD is all I got :/

I'll check out that step though and report back with what I am able to do.

AutoCAD is all I got :/

Students can download Inventor Professional for free from http://engineersrule.org

There is also the Autodesk Assistance program for displaced workers

http://students3.autodesk.com/?nd=m_assistance_welcome

I'm not a student, nor am I displaced. My company is just cheap!

I'm not a student, nor am I displaced. My company is just cheap!

If they want to save money they could probably save a lot more by shelling out the extra $1300 for a modern 3D CAD program. Should pay for itself on the first job (like this one). All gravy after that.

Good luck on your worm gear. You might check the rest of the turorials in my signature.

just as jd said, the amount of time spent modeling this as compared to say Inventor is huge.

I drew the helix set above in Acad07. i just used the helix command and entered my values following the command line(turns, starting Dia, ending Dia etc). you will then need a closed profile(the tip of your cutting tool) and sweep that along your helix. after you have one done you can create an array.

I can't get the profile to sweep - it turns the profile to some weird angle...

Make sure you turn off Align.

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

step 7. Didn't I recommend going through all of the tutorials?

By the way, that doesn't look like the correct profile for a worm gear?

I actually did go through them all a while back... I'll have to do that again some other time though.

also,

It's basically a worm gear

there are options when sweeping a profile for twist, alignment etc. Your best bet is to align your cross section with you helix before the sweep. This way you know its perpendicular. here is one i drew real quick. i didnt use the sweep to subtract from the cylinder but if i were drawing this for real, i would do it that way like it would actually be produced.

Thanks for the help guys, I got what I needed

dont forget about the thread starts. I would create a profile and revolve it after to chamfer them. what im saying is draw your gear longer so you can cut it down.