Quincunx - Cast acrylic milling

[bergerud]

This time of year I make math demos for the math students at the college where I teach. (Professional development!) I just finished making two quincunxes. These are models which demonstrate binomial distributions and probability. The 3/16 brass ball bearings flow down over the hexagons and produce the binomial distribution at the bottom. Ok, sorry, this is not meant to be a lesson in math for you guys. It is, however, a demonstration of some milling. Each one was a three hour mill job. Look at the mpc and select all to see all of the paths. Each path was cut twice with a 1/8 cutting bit to get a depth of 0.2.

Milling seems to be mostly ignored by CW users. I think there is a fear of breaking that 1/8 bit! I have had bad experiences milling as I know others have had. If you mill in a single cut, I think the cutting forces are too large and things slip. Things slip and bits break or projects are ruined. As long one stays under the rollers (all about the brass roller really), and makes multiple shallow cuts, it really does work well.

[lawrence]

that is an awesome little milling-- I saw one of those made of legos once and was amazed at the math involved (lightbulbs went off) Thanks for sharing your pics and once again, as soon as I catch up a bit, making a bit dust shroud like yours is very much on my short list.

Lawrence

[ktjwilliams]

Very Interesting Dan

[DickB]

I tried cutting some 1/8" or 3/16" plexiglass with the 1/8" cutting bit, basically cutting out 1" diameter "washers". The first dozen or so were fine, but there must have been a bit of melting that gradually accumulated on the bit and resulted in poor cuts. I was concerned that the bit would break. The last washers were unusable. So I haven't done any more work with that material. I think it would be cool to make one of my clocks with acrylic rather than Baltic birch gears, but I would need to solve this problem. Curious exactly what material and bits you used.

[bergerud]

This is cast acrylic, not the cheaper, common, extruded acrylic which just melts and makes a mess. (The same stuff I made the dust cap out of.) I have no problems at all machining it. I just use the normal carving and cutting bits. (Better to use new sharp ones.) Dust collection is very important lest the sticky shavings get under the truck rollers. It would make very nice clock parts. My pictures do not do the material justice. When painted from behind, it is really quite beautiful. The stuff I use is called Chemcast GP, cell-cast acrylic sheet. It comes in many colors and tints. I strongly recommend everyone who has not tried it to go to your nearest plastic supply, pick up a scrap piece and give it a try.