Rattleback

[bergerud]

Here is a curious thing for a weekend project. It is called a rattleback. If you try and spin it, it will wobble and rattle until it changes direction and spins the other way. It will spin fine one way but not the other. (Another one of my student demonstrations.) It is a forgiving double sided carve since the sides do not need to line up exactly. If you have a nice small piece of exotic wood (denser is better), this is the perfect use for it. There are two versions, one nice and smooth and the other a "voodoo" version. (The pictures are of a smooth one made of rose wood and lacquered.) They are very easy to finish and make great little gifts.

This is my own mathematical surface that I created in a math program called Maple. Imported using the STL importer.

http://youtu.be/OHCc22r329Q

[brdad]

I have some of these in plastic, they are interesting. I often wondered how a larger one would work, now I can find out. Easy to see these are much classier in wood. Thanks for sharing.

[aokweld101]

what are the uses for the rattleback, never heard of it. is it just to look at?

[bergerud]

what are the uses for the rattleback, never heard of it. is it just to look at?

It is a 200 year old toy to amuse children. Its strange behavior still intrigues scholars today. Scientific papers are still published as people try to computer model the behavior. Can you explain why it does what it does?

[brdad]

I had some free time tonight so I carved the mask version of this tonight while cleaning up the basement shop. I used a scrap of maple and it came out nice, and I think I'll make a few more, probably the smooth ones but with darker wood and centerline names or windings of some sort. I think I'll also make a simple sled so I can carve them at 90° to cut down on a few minutes of carving time.

I questioned why the feather was not set to 0 to also help with carving time, and was surprised to see it actually estimated a longer carve time with 0 draft. But, carved at 90° setting the draft to 0 decreases the time, I'd guess because there are several passes on each side of the project across the X axis that serve no purpose than to carve the draft.

Anyway, thanks again for putting out this project.

[bergerud]

The feather is just to be easier on the machine. I do not like the bit plunging at the beginning and hitting a wall of wood on each side as it goes.

I like the idea to carve it sideways. I would worry a little about the line up. The x cannot be trusted to be as accurate as the y. Let me know how that goes.

[aokweld101]

Bergerud< [got the spelling right] ..lol...will oak wood work on this project?

[bergerud]

Sure, oak is fine.

[aokweld101]

thanks, I have some oak to try it out.

[brdad]

I've had carver's block since my wife and I got back from our 8000+ mile drive across country and back (so much to see!), so I decided to try these at 90° on a sled yesterday. It worked very well, I was able to carve two at once from a scrap of bubinga. The software estimated 30 minutes carving time on normal with the feather off; I forgot to check the actual time but I think it was close. I also wish I had chosen best or optimal as they did take a bit more sanding than the first one I carved. There was a slight variance with the two sides in the X, but it sanded out easily and might not have been as prominent had I not used the normal setting.

I think my next attempt at these will be the smooth version with a conforming vector design of some sort on them. And I definitely will do them at 90°.