Ring gear

[micro222]

I recently made a small CNC mill and I've been having a lot of fun with it. So for my next challenge, I want to make a model of the planetary gearsets that can be found in a typical 4 speed automatic transmission. I can make *almost* all of the parts. I can use CAMBAM to draw the gears that have the teeth on the outside, but I need 1 gear that has the teeth on the inside.

So I'm wondering if some kind soul out there that has the appropriate software could sent me a drawing of the gear I need in dxf format.

The specs are:
72 teeth
diametral pitch: 12
6" in diameter
20 degree pressure angle
teeth are facing toward the center of the gear
teeth are straight (not helical)

Thanks,
Micro

[RICHARD ZASTROW]

Remember, "Tooth spaces of an internal gear are not the same shape as tooth spaces of external gearing having the same pitch and number of teeth. This is due to the fact that an internal gear is a spur gear "turned inside out"". (Gear Design Simplified)

The flank shape of an internal gear is a concave v. convex involute of an external gear.

Dick Z

[torrey.smith]

This is my first post!

Can you tell me what gears you are using inside the internal gear? (how many teeth)

I will model those, too, and make sure my tooth thickness is appropriate.

[torrey.smith]

OK, Here are the first images.

Let me know what radius (cutting tool) you want for the clearance (not sure if it's addendum or dedendum in an internal gear) on the internal gear, and I will incorporate that and post a DXF.

[micro222]

This could get tricky....
There is an 18 tooth planet that meshes with the ring gear, a 36 tooth sun, and a second 18 tooth planet. That second planet meshes with a 30 tooth sun.

[micro222]

Those gears look great.

I'm using an endmill that is 0.094" in diameter.

http://web.ncf.ca/fp927/cnc/gears-12-18-1.5-20.jpg

[torrey.smith]

OK! I will submit the .dxf in the morning, based on your .094" cutting tool.

I will make sure to model the 18 tooth gear, just to make sure that it meshes right.

The arc-thickness of the gear teeth is the one variable I am still setting independently.

Nice gears!

[torrey.smith]

OK, here is the .dxf file with the .094" tool accounted for.

It looks good so far with the 24 tooth gears I have modeled it with, but I can check with the others later.

Let me know how it goes!

EDIT: Here is the .094" tool relief:

[micro222]

Thanks, it looks like it will do the job. I just have to find a piece of Lexan that's big enough and I'll give it a shot. I'll let you know how it goes.

Micro

[torrey.smith]

I just joined TechShop and used the laser cutter to make this out of 1/8" acrylic.

I used the 6 inch 72 tooth 12 pitch 20 deg internal gear, plus 8 1 inchers orbiting a 4 incher.

I did some test cuts so that next time I can offset by half my kerf width at those settings on that machine.

[micro222]

Since you have access to a laser cutter, you may want to try the gear arrangement I'm working on(if you're looking for things to do). These are the parts that go inside the ring gear.



The yellow gear meshes with the ring gear. The orange and yellow gears are mounted on the blue carrier. The ring gear is the output.

Here's how it operates:

1st gear: hold the blue carrier to keep it from turning. Turn the red gear. The ring gear will turn at less than half the speed.

2nd gear: hold the green gear and turn the red gear. The ring gear will turn at a reduced speed, but not as slow as 1st gear.

3rd gear(direct drive): Turn the red and green gears together. The ring gear will turn at the same speed.

4th gear(overdrive): Hold the green gear and turn the blue carrier. The ring gear will turn 50% faster.

Reverse: hold the blue carrier and turn the green gear. The ring gear will turn at a reduced speed in the opposite direction.

Neutral: Don't turn anything

I'll attach the red, green and blue parts to shafts to make them easier to handle.

Micro

[torrey.smith]

I had some fun today