Saturday, June 17, 2017

Secretary Desk: Gettin' Jiggy With It

One of the many items of furniture we have that doesn't hold enough is a cheap, unfinished wood secretary desk, which we've had for somewhere between 15 and 20 years. It's not bad as such things go, but it is too small. So certain persons to whom I am married suggested that I could build a bigger one. And so I did. I pulled out all the technology for this project, since I am a terrible carpenter if left to my own devices.

Peg Jig

I wanted to used dowels rather than screws to hold the structure together. So how do I get all of those peg holes lined up? 3d printer to the rescue. I worked up a little t-shaped piece the same width as the thickness of my boards and evenly spaced 1/16" holes in it. With that in place, I could drill pilot holes in the edges of the upright boards and matching holes down through the thickness of the horizontal ones. Those were followed by a 1/4" bit and then matching dowels.

Adjustable Router Template

I decided to cut dado joints for the internal shelves in the lower cabinet. But how? That requires absolutely straight grooves cut at exactly the same height across the boards for both sides. I started by clamping the boards together side-by-side and penciling lines where I wanted the shelves to slide in. Now, if you're a competent carpenter, you just need to set a fence in the appropriate spot and use that to semi-freehand a groove with your router.

I am not a competent carpenter. Back to the 3d printer, but for something more elaborate. I've got router guides and I've used router templates with some success in the past, but how to make that work for what I'm doing? And here's where I decided to make a multi-purpose device. I modified the design for a set of micrometer calipers with "feet." Then I ripped a four-foot piece of quarter-inch plywood into strips about six inches across. By screwing the calipers to the ends of the plywood strips, I could very precisely adjust the separation of the strips, which were thin enough to make a very good template for the router. In this case, the gap needed to be no wider than the template guide, but I could adjust the gap to rout out a much larger area if need be.

(And fortunately, this worked out in practice about as well as predicted in theory.)

Roll Top

The really fancy part of this is a roll top for the top section. In theory, it's pretty easy. For the opening top, you get a bunch of thin slats of wood (which was a piece of thin plywood run through the table saw a quarter inch at a time) and glue them to a piece of fabric. Not too difficult. But then I need to cut mirror-image curves for the top part of the cabinet and parallel mirror-image grooves inside their radius for the flexible front cover to move through. Yeah, no way I'm doing that. CNC work.

The black lines cut all the way through. The gray lines are grooves a half-inch deep in the 3/4" lumber. The top curve is for the roll top, the horizontal bit in the middle is to keep cubbyholes in place. A little trimming the ends of the slats and sanding the inside of the groove and it fits together surprisingly well.

So Finally

Assembly (with 3d printed elephant heads as hardware to open the roll top), some stain, and a zillion coats of shellac later, it looks like this.

But the important thing is that it contains about 50% more than the old one.

Saturday, June 3, 2017

Dice Trebuchet

I blame John Kovalic.

(Go read the strip now before I ruin the joke any farther. Back now? OK.)

I've got a few dice towers, but a dice trebuchet? Not so much. So clearly, I needed to make one.

The frame, made from 3/4" birch plywood, is easy. A little CNC work for the supports, routing out spaces for 22mm bearings at the top, cutting through all the way in the center to make room for the axle to move freely, and some sockets in the base for the uprights. A little sanding and it all fits together nicely

The other wooden parts are mostly made from standard stock. At the center of everything is a short section of solid 3/4" square birch. It has 5/16" holes bored at the ends and all the way through the middle. Why 5/16"? Because that's almost exactly the diameter of the 8mm holes in the centers of the bearings. A 5/16" dowel for an axle fits very snugly. Since I've got it around, more dowel forms the throwing arm and the counterweight arm. I'm increasingly using the 3d printer to create jigs and other placement aids, and this project was no exception. All drilling was performed with the use of a jig with a 5/16" bore and a small frame allowing it to be centered on a 3/4" width.

Then it's off to more 3d printing. The basket at the end of the throwing arm is 3d-printed and presents a vastly easier solution than cobbling together a more realistic but teeny sling and release mechanism. It's big enough to accommodate 3d6 for any reasonably sized dice if you're playing GURPS. I assume it'll hold die for other games, but why would you want to play those?

The counterweight is, appropriately, a small dice bag, so it can serve as an ammunition supply as well. There's a small hook on the counterweight end of the arm to hang it off of, but it can be taken off to add or remove dice, changing the force of the projectile. If dice aren't heavy enough (and, to be honest, they probably aren't), those little glass stones can be used which double as level markers for games like Munchkin. 

And how effective is it? It's not bad:

That's a fairly standard d6 being propelled across the length of a fairly standard dining table. With a bit of a backstop and/or a smaller counterweight (this was using a stone icosahedron), the trebuchet could actually be used to roll dice. Or to destroy your enemies.

UPDATE: For the benefit of those with CNC machines, I've published the Easel design on Inventables, so you can make your own.