Cuboro... How would you...

[Eric DeSilva]

Bought my son some cuboro recently (see, e.g., http://www.amazon.com/Cuboro-111-Standard-Marble-Maze/dp/B0002W0RBI/ref=sr_1_1?ie=UTF8&qid=1295546816&sr=8-1). It is a fantastic little Swiss toy. Basically, blocks of birch about 1.5" on a side, fairly tightly machined. They have grooves routed into the tops/bottoms the same diameter as a standard marble, but maybe only 1/4 diameter deep. Some have 90* curves, some straight, some Xs, things like that. You can arrange the cubes and roll marbles down the grooves, so you can set up different paths depending upon the configuration of the blocks.

But here's the thing. They also have holes through them--some straight through, some 90* curves... Allows you, for example, to have a path across the top of some cubes then back through the cubes. Fascinating toy--fun for anyone to play with.

Which brings me to my question. I started thinking about trying to make some of these--the grooves on the top/bottom are easy, just a router and a core bit. But how would you go about making a hole that takes a 90 curve through the middle of a block?

[Brian Vaughn]

I'd just drill in halfway from both sides. Is it a smooth curving 90 or a sharp 90? Creating a smooth turn would be a bit tough, but that would be my start. Trace the drill path on the outside of the block to make sure the slopes will line up (At least for the first one)

[David Thompson 27577]

Which brings me to my question. I started thinking about trying to make some of these--the grooves on the top/bottom are easy, just a router and a core bit. But how would you go about making a hole that takes a 90 curve through the middle of a block?

Seems to me that you could at least try to do it with the same core bit. The difference is that it would be a 100% plunge -- no side-to-side movement. First from one side of the block, and then from one other side.

Where the cuts meet on the "inside" of the curve would indeed be a 90* angle -- but it seems that if you get the depth just right, the outside of the curve would be equal to the sweep of the core bit.

[Eric DeSilva]

Don't think drilling in from each side would work. Its a smooth arc inside the block in order to avoid having the marble slough off too much momentum. I'm beginning to thing they must drill them with some kind of proprietary drill press with a curved quill or something. Just wondering whether I was missing something obvious.

[David Thompson 27577]

Perhaps you're right about losing too much momentum using bored-cove cuts. I can think of two other options.

If you get hole-placement just about perfect, you could probably just drill through the block at a 45* angle. Then maybe use a curved gouge to ease the corners a bit.

And of course, if you slice the blocks open, you could then pattern-route whatever you wanted to route. Then glue the pieces back together.

[Dan Cameron]

I made a bunch of these a while back for our wwing club toy givaway. I pre-drilled from two sides with a 5/8 twist drill and then plunged from two sides with a 3/4 core box bit. After experimenting some, I made the angle slightly greater than 90 degrees so the marble continues even when it hits the corner in a funny way. I have a shop made slot mortiser which was just the ticket, but it should be possible to jig up with a plunge router.