Friday, September 11, 2015

Filtering Silly Putty

Years ago, probably about 1995 or thereabout, I hosted a 100lb Silly Putty group buy. I wrote a little web page using JSP, Perl, and Firebird, and used it to let dorks like myself sign up to buy Silly Putty in half-pound increments. I think I ended up with about 25 orders ranging from half a pound up to 15 pounds. Once we reached that magic 100lb aggregate, the minimum order quantity for Dow Corning® 3179 Dilatant Compound I had everyone mail me a check, and ordered a box of the stuff.

Not long after the boxes showed up I and one of the guys from the buy, a Cisco engineer from Austin, spent an evening dividing it up according to the order list and packing it into cardboard boxes for shipping. New 3179 Dilatant Compound is tough stuff, dividing it up is a tough forearm workout!

That was so successful I hosted a second buy for unpigmented translucent putty and a kilo of green glow powder to make glowing putty.

So, tl;dr: that's how I ended up with about 8 pounds of coral Silly Putty, several pounds of white putty, and a fist-sized blob of glowing putty.

The problem with Silly Putty is that over the years it collects lint and grit which makes it less fun to play with, and it darkens, especially if you like to use it to pull ink off of newspapers. So I was thinking of ways I could clean it. Picking out lint and grit is too slow to be realistic, but bulk filtering is impossible because it's a putty. But what if I dissolve it first and then filtered it?

I have a new bottle of Ronsonol lighter fluid that I bought as a home lab solvent a while back, so I figured I'd give it a job. I dropped a small blob of putty into a 20mm test tube, threw in a couple of tiny magnets to act as a stir bar, covered it in a few mL of lighter fluid and loaded it up on the stir plate:

I let it run for an hour or so, but the big chunk wasn't dissolving very fast, so I added a hot water bath to encourage it. Eventually, and with a little encouragement from a glass rod, it all dissolved into a clear solution and the coral pigment.

I centrifuged it and transferred the clear solution and the coral mess to evaporation dishes in the vent hood. After driving off the solvent I was left with unpigmented putty base and the coral pigment with it's contaminant load of lint and grit:

However, as you can see, the solids were a gummy mess. This is because I did not rinse the solids with clean solvent before evaporating the solution, which means that some of the putty base was left behind.

So I repeated the process with the gummy mess, this time rinsing, centrifuging, decanting twice more before drying the solids. The result is a very fine coral powder with some contaminants that I've halfheartedly manually separated. 

I don't have a good way to divide the coral powder to show how small the particle size is, but it's talc-like. If I can get it down to fine powder I will be able to run it through a mesh to remove the remaining lint, and then I can incorporate it back into the putty to achieve the original goal, filtered putty (with only a faint smell of lighter fluid). I may try this again with a different solvent, maybe something that smells nicer. I'm sure alcohol will work, and it's easier to evaporate.

Monday, February 16, 2015

Van Overhead Console

I'm building a new overhead console for the '93 B250 conversion van I've recently acquired:

After driving it around a while I decided that it doesn't have enough storage up front, and there isn't a good place to mount my FT-8800 amateur radio transceiver. A good way to fix that is a new overhead center console. Fortunately, all the interior trim is oak, so it's easy to match the existing style.

The roof of the van is 3/16 OSB, or something similar, in two pieces with a gap running down the center. The gap is covered by a third piece which is attached to the ceiling and holds everything up.

 To that center piece I've attached some LED lighting, to brighten up the interior:

One of the problems with this is that the center strip is visible if the rear view mirror is angled upward a bit. This means that in the normal viewing position the night-mode reflection is pointed up at the LEDs, producing a ghostly reflection. The sight-line from the mirror to the rear windows is about four inches below the original center console, which means that if the new one comes down just less than 4 inches I won't be able to see it, but it will block the view of those LEDs.

This is the original upper center console. It's just a 3/4" oak plate.

The first step is to mock up the shape of the new console so I can drop it as low as possible without interfering with the rear view mirror sight-line. Cardboard and packing tape:

That gives me an approximate template. A little sketching and measuring provides the details.

For construction I used a 4'x8"x1/2" oak board. The angled cuts for the side pieces were interested. I don't have a sled for the table saw that will make those safely, so I just carefully cut them with the bandsaw, clamped the planks together and ran it across the jointer a couple of times to clean it up.

For the trapezoidal bits that extend up into the recessed area above the front seats I reused the existing trim pieces.

I ran the old finish pieces through the jointer to take off the old finish and glued them on.

Unfortunately I made a construction mistake and built the whole thing a half inch too narrow. Rather than rebuild it I just ran it through the table saw and glued in a carefully sized piece. Then, after much swearing and fine tuning with the Dremel, it went right in.

At the rear one of the storage pockets is visible. There are two, one on each side. They don't match exactly, but you can only see one at a time anyway, so no problem. At the front is a red LED that shines down on the center console. Just in front of the storage pocket is space for the body of the FT-8800 radio. The face of the radio (removable with remote mount) will go on the side near the front, and the handset will be stored inside behind the radio face. I'll have to make a door of some sort for access to the handset. For that I'm thinking I'll just cut a hole in the bottom plate at the front and stick some magnets in there to hold it on.

The bottom plate is screwed on and can be removed without removing the entire console, which is screwed to the ceiling panels. This is so that I can mount the console on the ceiling and then connect the various power and antenna cables that attach to the parts inside, and then put the cover plate on.