Loading
Mangatar

Worm Drive, Non-Throated

by syvwlch, published

Mangatar
Worm Drive, Non-Throated by syvwlch May 26, 2011

Description

Ok, once you have an involute gear library AND a trapezoid thread library, you can easily make the simplest of worm drives, i.e. the non-throated kind.

Like all worm drives, the gear advances by one tooth for each revolution of the screw but with non-throated ones, there is only a single point of contact at any one time, and so torque and wear capabilities are limited.

UPDATE:
As I pointed out in the comments, AFAIK a trapezoidal profile for the worm screw is all you need to match the worm gear's involute.

To make them mesh, all I did was to make sure that:
1. the pitch is the same (distance from crest to crest),
2. the pressure angle of the gear is equal to the angle of the sides of the screw profile,
3. the distance between screw and gear is equal to the gear's radial pitch plus the screw's mid-profile radius, and
4. the twist on the gear is equal to the gear's pitch radius divided by the screw's mid profile radius, with a sign depending on the screw's handedness.

Recent Comments

view all

Amen!

Nah it's ok I've reverted back to 2010 version.

However printing the screw is now proving very problematic. Specially when using PLA. And switching on Support while also using PLA is a nightmare to clean up.

Time to invent a two headed Cupcake extruder :-D

Yeah, the one on Git I've been bashing on to try to get the throated worm gear to work, so I don't know if if works with this script anymore.

As for the bald gears, that's a bug in the later versions of OpenSCAD that breaks the MCAD involute gears library. That's been an issue for at least two versions of OpenSCAD and no-one is fixing it. I have a kludge/hack version of the involutegear library that sorta works, if you want.

Liked By

view all

License

Public Domain
Worm Drive, Non-Throated by syvwlch is licensed under the Public Domain license.

Give a Shout Out

If you print this Thing and display it in public proudly give attribution by printing and displaying this tag. Print Thing Tag

Instructions

This openSCAD script is a demo of the trapezoid thread library but also uses the MCAD involute gears library. It will only work if both of these are in the same directory or in your libraries directory.

It is ready for animation, and I have added a GIF of the animation in the comments below.

This code is in the same repository as the library:
github.com/syvwlch/Thingiverse-Projects/tree/master/Threaded%20Library

Comments

You must be logged in to post a comment.

johnnyfp on Jun 29, 2011 said:

Can't seem to F6 (Compile and render) this keeps crashing my OpenCad. Is there a trick to this?

syvwlch on Jun 29, 2011 said:

It compiles and renders fine on this machine, but that was one version of OpenSCAD ago... there may have been changes that broke something?

syvwlch on Jun 2, 2011 said:

Ok, it's the right shape but won't export as an stl. Have a couple ideas to try when I have a little time.

syvwlch on May 27, 2011 said:

Here is an animation of the negative space between the worm screw and the worm gear, showing that:

1. there is only a single point of contact, since neither are throated, and

2. an involute gear and a trapezoidal screw mesh just fine.

syvwlch on May 27, 2011 said:

Again, I highly recommend clicking on it to see it in HD, it will stutter a bit while your browser loads it, but after that it's a pretty neat view. :-)

JelleAtProtospace on May 27, 2011 said:

again amazing stuff Syvwlch!

After looking at your animation it struck me: shouldn't the screw have a involute profile too to mesh with the gear? Or does it have that already? Not that it would be practical to buy such leadscrew anywhere...

syvwlch on May 27, 2011 said:

IANAX, but my current understanding is that you do not need a fancy profile on the worm screw to match the involute on the worm gear. A trapezoidal lead-screw works just fine.

All I did was make sure that:
1. the pitch is the same (distance from crest to crest),
2. the pressure angle of the gear is equal to the angle of the sides of the screw profile,
3. the distance between screw and gear is equal to the gear's radial pitch plus the screw's mid-profile radius, and
4.
the twist on the gear is equal to the gear's pitch radius divided by the screw's mid profile radius, with a sign depending on the screw's handedness.

mirk on May 27, 2011 said:

Does anyone have any ideas on how to print the worm well on a makerbot? I tried to print one a while ago, but failed many times and ended up just going with spur gears (my modular gear reducer).

syvwlch on May 27, 2011 said:

If you want to print it rather than use an existing, machined lead screw, I would try what Tunell did with his kibble auger:

http://www.thingiverse.com/thi...

Print it in two halves split along the axis. To guarantee some semblance of strength, you might want to make the radius rather large relative to profile depth, and you might want sandwich a square metal shaft in there as support.

zignig on May 27, 2011 said:

all this stuff is great , a throated worm drive would be great. gearbox-o-rama.....

syvwlch on May 27, 2011 said:

So throating the worm screw should be relatively easy, because the way the thread library is build, changing the radius along the shaft is already built into the lower levels of the code. I just need to figure out how to bring that up to a top-level module with some simple parameters.

To throat the worm gear, I'm thinking we could stack several bevel gears to approximate the curve. Again, the trick is figuring out the math and packaging up the stack into a module with a set of parameters.

WilliamAAdams on May 27, 2011 said:

Well, there you go! More things to play with! Looks great.

syvwlch on May 27, 2011 said:

Libraries are awesome, once you push the complexity down under the covers, you can start building the next level. :-)

syvwlch on May 27, 2011 said:

Here is the animated GIF:

Auzze on May 27, 2011 said:

Outstanding, more great stuff to play with, it just get better and better.

syvwlch on May 27, 2011 said:

I highly recommend clicking on it, to see it in HD. :-)

Top