Worm gears

[MrForbes]

I have a friend who installs garage doors, thus he fixes and replaces openers too. He donated a few used gears to the team, so I got to play with them. The worm gear has two teeth, spur gear has 32, for a ratio of 16:1. Apparently it's not a steep enough ratio to prevent backdriving (he said a garage door with balance spring problems will fall closed when connected to one of the openers that uses these gears).

Still, it's a nice light weight 16:1 gearset that fits 1/2" shafts, and looks relatively easy to make a box to hold the parts.

[Jamie Kalb]

Originally Posted by squirrel

The worm gear has two teeth, spur gear has 32, for a ratio of 16:1.

How does that work? Aren't worm gears only 1 tooth gears? Or does this one have two separate threads?

[MrForbes]

There are two separate threads.

If you study the linear actuator thing in the KOP you'll see a similar screw with more than one thread.

Very strange...but that's how it is.

[Jamie Kalb]

Originally Posted by squirrel

There are two separate threads.

If you study the linear actuator thing in the KOP you'll see a similar screw with more than one thread.

Very strange...but that's how it is.

Thanks! That makes sense.

Yeah, that lead screw in the kit is just weird! I've always wondered why it has more than one thread. This year's has six, and last year's only had three (I counted ).

[Edoc'sil]

and the year before that it was 4 threads. Odd that they change it... any Ideas of were someone could obtain a cheap gear system like this that doesn't backdrive?

[MrForbes]

McMaster Carr sells a hand powered worm drive winch, perhaps you could find what company makes it and see if you can get spare parts for it? just the gears?

Some circular saws us a worm drive, for example the Skill model 77. might be some adaptable parts in that?

I've been trying to think of other things....