hi i like to build a mechanic part where i rotate the BLUE wormthread and then the RED joint rotates.

but i cant bend the wormthread around the RED round joint-part without deforming the thread to much.
can i make a helix along a path and then sweep the TEETH-Shape along this helix?
The inner radius shuld not change the thread. then i like to bool a negative womthread in the RED joint.
i hope someone understand what i mean. :-)

There is a nice picture of a worm gear here: http://www.nd.edu/~manufact/FME%20pdf_files/FME_Ch15.pdf

Why not use Michaels script for a spur gear?

 
Might have to do some math to figure out the module?
http://www.roymech.co.uk/Useful_Tables/Drive/Worm_Gears.html

On the other hand, looks like you might need a helical gear script: ?



Does anyone know if it is possible to get a worm gear mechanism to work using a spur gear. I am just trying to make a small model of a worm gear out of acetal plastic for demonstration purposes only. I am thinking it might work as long as the pitch on the lead screw, is the same or a little larger than the pitch on the spur gear. What do you guys think?

Posted by: randykimball ®


Yeah, you can do it for a demo.. I'd think about having the worm at a slight angle so that the area contacting the spur teeth is actually mostly flush against the tooth. Realize that a true gear to match a worm is derived from a helical gear with the helix angle matching the pitch of the worm.


Pasted from <http://www.engineersedge.com/wwwboard/posts/6110.html>

Hi BlackBird, so yeah check out the PDF that Brian links to above for especially where it shows the worm gear contact area (section titled "Worm Gear Contact") - I think for the red area you would want to have an extrusion for that area rather than actually bending any kind of sweep or helix like shape at all.

The spur gear profile plug-in that is mentioned above is available here (actually I think Petr wrote it, not me):
http://kyticka.webzdarma.cz/3d/moi/#SpurGear

See the attached file for an example - there I created a spur gear profile, scaled it and cut it into half and then used the half piece with boolean difference on your red part to make the bottom part of the shape to have an extruded gear form. The boolean will cut up the red part into multiple pieces and then just delete the pieces you don't want.

This attached example does not have the proper number of teeth but I hope it shows you the general kind of structure that I think you would want to make, with just an extrusion of a gear on your red piece rather trying to have another helical shape around there.

I think you only need one piece with a sweep done on it for making the wormthread, and then basically flat gears (meaning extruded from 2D shapes) for the other part, not another wormthread for the second part.

- Michael

And yes that is normal that if you just bend (by applying a Flow deformation) a shape that areas to the inside of a bending area will be compressed and areas on the outside of the bend area will get expanded, that's basically just how deformation works. Sometimes if you don't want that kind of deformation happening it can work to only bend a path curve and then build new sweep structures around that deformed path rather than deforming whole already built pieces.

But for your case here I don't think you want to be doing any of that stuff at all though, if I understand what you want correctly. I think you just need for the bottom of your red piece to have the shape of an extruded gear.

- Michael

I was thinking to do a loft or sweep, between two copies of the gear profile. Rotate one of them first,
to sort of match the helicalness...

Boston gear has a free book called "Gearology." Download at their site did not work, but it can be downloaded here:
http://www.beknowledge.com/archives/article/gearology-handbook-on-gears-for-mechanical-engineering

MITCalc has a free 30 day trial.

Lots of math...

Hi Brian,

> I was thinking to do a loft or sweep, between two copies of the gear profile. Rotate one of them first,
> to sort of match the helicalness...

Yeah if you do a google image search just for "worm gear", a lot of the images that show up do show the flat gear to have some kind of twist to it. That could be done by Loft like you mention, or also by applying a Twist deformation onto an extrusion.

But I think that you won't want to be trying to bend a second worm thread to make that piece.

Probably if the main worm thread is a bit thicker at its tips it would require some more rotational allowance in the other gear, if it's thin enough maybe a totally flat one will work ok I guess.

- Michael

A wormwheel tooth form is generated from a hob with trapezoidal shaped teeth, which I don't think would be reproduced by simply bending the worm into a circular shape.

See this video of how they are actually made http://pounceatron.dreamhosters.com/shop/hob/hobbing-gear.mp4

I can't think how you would faithfully recreate this in MoI or any other CAD come to that without quite a bit of work.

 

Martin (2).

Here is a way to make a simple helical gear in Catia, starting from a spur gear. Just add the rotation angle psi, to match the worm.
Should be easy to do, in MoI. It is not "single enveloping worm gearing," as the gear does not wrap around an arc of the worm in a semi-circular arc curve.

http://gtrebaol.free.fr/doc/catia/helical_gear.html

The site links to how to make a worm, and how to make a spur gear.

It explains the relatively simple math.

For "double enveloping worm gearing," the worm wraps around an arc of the gear, as well. It is much more mathematically complicated.
An example is the "cone drive."

The mp4 does not play for me, with Real Player. VLC did play it. The avi file worked in Real Player.

Ok thanks guys.
I made it..
I used the Gear-Script. It was the simplest way to do it, and it works!!! :-)

Layerheigh 0.15mm

Here's a gear I made from an old DXF file I had on my computer.
I extruded the outline and then used the Twist tool to make the gear into a helical tooth form and this should be the same as the helix angle of the worm so as to allow the axes of the worm and wheel to be perpendicular to one another.


Martin (2).

Hi BlackBird, that's cool that it's working!

- Michael

Did Flow for the arbitrary enveloping radius, then did the twist.
Finally got it to be a solid.