[PhilBa]

Kind of a fun project. See the pictures. Cut on a small desktop extruded AL router. Read about it in more detail here.

 

[PhilBa]

I love that! I have wanted to cut internal gears like that for some time now but Fusion 360 doesn't have a wizard like it does for external gearing. How did you draw or lay out the teeth?

David

Thanks! I think you can get planetary gears out of F360 but the gear extension uses standard gearing types and won't let you create big teeth like this. At least, I haven't been able to bend it to my will. yet.

Like I say in the blog, I used Sketchup because I am pretty familiar it and was just coming up to speed on F360. If I was doing it today, I'd use F360, mainly because Sketchup has terrible CAM support. I basically searched for gear outlines, looked at an online gear generator app, read the wikipedia page and so on until I had a set of good examples. Then I drew a single 20 degree tooth by tracing an image and made it an object. From there I used Sketchup's rotate function with copy (ctl held down) using the center point as the pivot and got the planet. I had to play with the number of teeth to get it right. Then I edited the tooth object to add the connecting line (dedendum circle). Then exploded all the teeth and got the gear pattern. Repeated it for the spur gears. When I put them together it was clear everything was too tight so I had to redo the planet adding another tooth and increasing the radius to make it a little bigger but it's not hard to do. A parametric CAD program like F360 would have made it easier though.

 

[PhilBa]

Thanks for the info, Phil. I missed the link in your OP the first time around but saw it tonight and read your description (well written!).

David

you're welcome. I didn't really describe how I designed the actual gears in the blog.

By the way, here's a video of it in action. Not the best I've done but it gets the point across. There is something comforting about it's clacking as you turn it.

 

[PhilBa]

Had to look up that router hoping it was a CNC type because cutting those by hand, while I know is possible, is something I wouldn't consider in this lifetime. Way cool project. Thanks for sharing Phil.

No kiddin'! I was thinking through cutting them by hand. Probably the first 5 or 6 wouldn't be so bad but it would be ugly after 42. I'd probably change the shape of the gears to triangular to make it easier to cut. Thank god for my mindless little slave CBeam machine. Well, actually don't thank god because Mr CBeam is getting benched.

 

[PhilBa]

So what's coming to the shop to replace it? Start a new thread if you're doing a build. Lots of photos, please! :grin:

David

Not sure yet. I just know Mr CBeam is a little too small and I want a real spindle, not a router. Probably an Avid Pro4824 (because of space, I really want a Pro4848 but don't think it will fit). Won't buy the PnP Electronics and Spindle packages as I'm pretty capable in that area. Figure about $5K to $6K all in. About 10X what I paid for my CBeam. Not sure about the controller yet.

For a LOT less money, I could have a Workbee or similar with a slightly smaller work area but I want to be able to mill aluminum and those low end extrusion machines are slow going.

 

[PhilBa]

It's been a year or more since I looked for a way to cut internal or planetary gears in Fusion 360 so I checked the app store again today and found a few out there. I downloaded the free FM Gears and will see how it does. There are a few that are $20 so if FM Gears doesn't do what I want then $20 is a small price to pay.

David

I think it was FM gears I played with. If you figure out how to make it (or any other app) do "big" teeth, let me know. I'd love not to have to design my gears up from scratch.

 

[PhilBa]

ok. what setting did you use?

 

[PhilBa]

Ah, I was using metric - mode had some restrictions. Not sure how you get compatible spur gears to work with that. Will have to spend some time with it.

 

[PhilBa]

If you set it up with the proper “joints” in Fusion 360 you can animate the gear train inside of Fusion 360. I have a model like that somewhere. Use “motion links” not “contact sets”.

Some friends of mine from my CNC group made a bunch of rope twisters for their (and a few other) scout troops. Utilized exact same gear train.

Very cool.

Gears are a gateway drug, once you start you keep making them. Have you seen the huge Spirograph people make for sidewalk chalk?

https://youtu.be/xrlJGkyKVsk

Yeah, definitely.

By the way, that spiro gear would be a lot better with 3 "ball" wheels.

 

[PhilBa]

Bastardize away! Lexan/Polycarbonate is easily machinable with the right bits. Generally, a single flute upcut "O" works well on polycarbonate. To be honest, acrylic would be fine and a LOT cheaper.

 

[PhilBa]

Plexi comes in 6 mm and lexan comes in 12mm . Lexan is a fortune here . Actually I bought a piece of 6mm plexiglass which was about 18” x 24” and it was $35 , and the guy told me it would normally be $70 if he had to cut off a sheet , but it was a piece left over from another cut.

Pretty sure a 4x8 1/2” sheet of Lexan was well over $1000 ten years ago . Hate to see it now

Interesting. Here (Seattle, USA), I can get either in 6 and 12mm (and lots of other) thicknesses. This is from TAP plastics, a west coast USA store chain but I think most major cities have something similar. A piece of 6mm, 12"x18" extruded acrylic (aka plexiglass) is $14.70 USD. $21.60 for cast acrylic (higher quality, better optical clarity), same size, thickness polycarbonate (aka lexan) is $20.85, for comparison. If find extruded acrylic to be perfectly serviceable for small projects. 12mm poly is, gulp 39.30.

Last time I looked, you can find similar deals for smallish pieces on ebay/amazon though you have to shop carefully as there is a very wide range of prices.

One thing that has somewhat spoiled me is that TAP Plastics has an offcut box - each piece is $1. Some of which are fairly big (12x18-ish isn't rare). I've gone in several times to buy a specific sized piece and found something that would work in the bin. Saves $$$. Helps if you have a decent blade for plastic in your table saw so you can trim it down.

Edit: by the way, I used 4.5mm (sold as 3/16", measured thickness is 4.4mm) extruded acrylic in the planetary gear project. cheaper and has plenty of rigidity for this application.