I Made a Box!
This is a slippery-slope story about how I made a small box and that lead to making a much larger one.
As readers of my blog may know, I’ve been working on a new book for quite some time. As part of that process I got into making acrylic models of various mechanical devices, which are now available for sale at MechanicalGIFs.com. Now that the book is nearly finished (it will be out in October, but my part is largely done), I’ve gotten back to spending more time on model-making.
In particular, I’ve designed several new model kits, including a one that has the distinction of being my largest (by weight of plastic) kit so far: a combination-lock safe.
It’s a very nice kit, highly recommend, but one particular aspect of it got me thinking that it might be time to expand my plastic part production capacity to the third dimension.
To date all of my kits have used exclusively laser-cut acrylic parts (plus assorted screws, nuts, springs, etc). Laser cutters are great, but fundamentally limited to making 2-dimensional parts. These can be combined to make lovely three-dimensional models (see, for example, this 2-speed transaxle), but still, all the individual parts are flat sheets (of varying thicknesses).
It was this corner joint in the Safe model that made me think it was time to break out of that limit. Typical T-joints many people use to join laser-cut acrylic at right angles are just not very strong, so I designed this connector block made with four separate pieces of laser-cut acrylic plus five nuts and bolts. Now, it is very strong, and I like the look of it, but on the whole, I think the world would be a better place if it could be made of a single symmetrical piece of acrylic plus only three nuts and bolts (one for each panel). That would require three holes, each one going in a different direction, which is fundamentally impossible to make with a laser cutter. But…trivial to make with an injection molding machine.
So I decided to buy a small tabletop injection molding machine. Which is of course useless if you can’t make molds for it so I also needed to get a small CNC milling machine to make the molds. Milling machines are messy: they use a cooling spray and send chips flying in all directions. So if you have one in a relatively small space that needs to stay clean, you need an enclosure to surround it.
So I made a big box!
And when I say I made it, I mean I made every single part of it from flat acrylic stock (except the 830 nuts and bolts that hold it together). It’s designed and made a lot like the kits I sell, just bigger.
The corners are joined with acrylic “angle iron”, by which I mean 6cm wide, L-shaped strips of 3mm acrylic bent at a 90 degree angle (the long way) with laser-cut holes along both sides that match the holes in the panels. Every side (including the top) has hinged doors, so I can access all sides of the machine with minimal obstruction. Even the hinges are laser cut from 12mm (1/2”) acrylic. (They in fact are exactly the same hinges as used in the Safe model I have for sale.)
Below is the whole setup, installed on top of the worktable/acrylic storage shelves I built for the tool suite. From left-to-right we have:
1) Vacuum forming machine with small oven on top. The vacuum forming machine softens sheets of plastic and then sucks them down over a form (made with the milling machine), creating semi-three-dimensional sheets. The oven on top is for drying acrylic for use in the the injection molding machine.
2) The thing that looks a bit like a small drill press is the injection molding machine. It has a pneumatic (compressed air powered) cylinder that drives a piston down into a heated chamber, forcing molten plastic out through a nozzle and into a mold (also made with the milling machine).
3) Next in line is a tiny vacuum forming machine (ca. 10cm x 10cm working area). It’s sold for making “Invisiliner” style transparent plastic dental retainers. I got it because it’s cheap, and because most of the parts I expect to make by vacuum forming will be very small. Every time you use either the large or small machine, you have to use a full-size sheet of plastic, 45 cm x 45 cm (18” x 18”) for the big one. That’s a lot of plastic to waste for testing the shape of a small part. So I figured I can use the small one for testing, and then when the part is right I can make a mold with many copies of it to use in the larger one.
4) Finally on the far right is the CNC mill in its glorious home-made box.