Aluminum is a wonderful material. It looks nice, it's easy to work with and it's cheap. The only downside in my mind, it the god awful mess that it leaves behind. This mess seems to be tripled when milling it. Since I consider my shop first and foremost a wood shop, I don't like having metal shavings sprinkled around like glitter at a strip joint. I don't like glitter in my shop for that matter.
Wanting to make use of the gorgeous new X-Carve made by Inventables.com, I came up with a method that allows me to create interesting shapes out of aluminum, without the waste and mess associated with milling.
I started with a 10KG bag of off the shelf Plaster Of Paris, and mixed poured it into a simple wooden mould. Being sure that the mould would clear the height limitations of the X-Carve. After it had dried for several weeks under my shop heater, It was time to start the milling.
Aside from making a lot of dust, the plaster mills very easily. I used a standard 5/8" 2 flute straight bit to hog out the majority of the material and a 1/4" spiral upcut bit for the detail work.
I busted out the Foundry Furnace from the garden shed, stole the half full bottle of propane from the BBQ and set out to complete the scary part. I'd never melted this volume of Aluminum and it was slightly nerve racking. Having suppressed my fears for a short while, I was able to cast the liquid aluminum into the mould without any hiccups. Here is how I figured out how much I needed…
Diameter (mm) Squared X .0007854 / 1000 gives you a coefficient (i.e – .06157).
Coefficient X Depth (m) = Volume (m3). Divide that by .001 to get liters
Here’s my example for a 280mm diameter top that’s 20mm deep.
280mm X 280mm = 78,400
78,400 X .0007854/1000 = .061575m3/m
.061575m3/m / .001 = 61.575L/m
Depth – 20mm X .001 = .02m
61.575L/m X .02m = 1.2315L of Aluminum. Since at room temperature the aluminum is a solid, I used weight to determine how much scrap I needed.
1L = 61.0237ci
1.2315L of aluminum X 61.0237ci = 75.15ci of aluminum
Pure Aluminum is 168.48 lbs. per cubic foot and there are 1728 cubic inches per cubic foot.
168.48 / 1728 = .0975 lbs/ci
75.15ci Aluminum X .0975 lbs/ci = 7.33lbs of Aluminum. This is the amount I would need to fill a simple cylinder. Since the detail will reduce the total amount I actually need, my safety factor is already included in this calculation. Sorry for swapping between metric and standard. It’s standard practice in Canada.
The finished piece came out good enough to be usable and I gave myself a B- grade. I am currently looking for additives that would make the plaster of paris more capable of handling the heat.
The legs were cut from 3/4" Baltic Birch Plywood with a 1/4" spiral downcut bit and the edges got a thin strip of walnut to cover up the layers. The leg assembly was glued together with Titebond 3 and given a few coats of Watco Semi Gloss Lacquer.
The bottom of the cast top was smoothed a little with 120 grit sandpaper on a belt grinder and attached to the leg assembly with two part epoxy putty.
I'm really pleased with how this project came together. The possibilites are endless with this method and it would be easy to scale the size up or down to meet your needs.
Be sure to check out the X-Carve at https://www.inventables.com/technologies/x-carve