Using the Sun to Make Glass


Pioneer squirms on the hot driveway.

Have you ever wondered if you could use a magnifying glass to melt sand into glass?  I have a very large Fresnel lens that a coworker gave to me when I worked at SGI. Using it is kind of scary.  I keep it covered while I’m carrying it around so as not to accidentally set something on fire.  I’ve used it to burn wood, but I wasn’t quite sure if it could melt sand.  My son Pioneer had been begging me to try it out.  This morning we went to the beach, and he insisted on bringing home a bucket of sand.  It was time to give it a try.

The first step was to unearth the lens.  Pioneer was a bit confused when he first saw it because he thought it would be round with a long handle ready to be gripped by an eight-story-tall Sherlock Holmes. I had to explain how a Fresnel lens works, including how it lets you have a big lens that’s not eight inches thick at the middle.  Then we spent a while washing it off because it was quite dusty from years spent under the house lonely and unused.

burnedPieceOfWoodI put a small chunk of wood out so we could have an easy and spectacular target to use for lens-aiming practice.  I put a steel plate under it to protect the driveway.  Once we’d  mastered our  half-blind welding helmet and giant lens ballet, we were ready for the big show. Ok, I admit it was more like the Hokey Pokey than ballet.  “Put your right arm down. Put your left arm up. Put your right arm in and stop shaking all about. You do the Hokey Smokey and you burn wood on the ground.  That’s what it’s all about.”

theTwoOfUsHoldingTheLensI was a bit worried that we wouldn’t have any sort of fluxing agent to lower the melting point of the sand, but my wife had just been experimenting with different low-allergy washing combinations and she had both borax and washing soda on hand.  What luck!  Time to give it a try.  We put a few spoonfuls of sand/washing soda/borax on the end of a soda can, donned our welding helmets, and fired it up.

lightOnTheCokeCanPointing that much sun at things can be pretty spectacular.  You can burn, melt, and pop things.  It’s easy to get all Gallagher.  In contrast sand is quite good at taking the heat.  Instead of a big plume of smoke or a loud popping sound  you get a very slow and silent melting action. In the end, we managed to make some smallish green globs of glass.  I think Pioneer was disappointed, but we were really limited by how long we could stand there with our arms in the air.  If we wanted to make more, I’d have to make some sort of frame to hold the lens flat and pointed at the sun.

globOfGlassStill I think it was a success. We did manage to make some glass, even if it’s not ready to go in a chandelier.

Making Cute Puppies with the Laser

puppySketchMy 5-year-old son came to me asking me to make him a wooden doggy.  I started drawing doggies on the back of an envelope.   He kept rejecting them.  Finally he told me that he really wanted one with a “mouth like an upside down Y”.  At least he was specific.  Finally we got a sketch that met with his approval. I assumed I’d make the doggy on the bandsaw and put details on using my trusty wood-burning pencil, since I’ve done a number of projects like that.  It’s always fun to semi-free-form cut on the bandsaw and improvise the shapes.  The width of the blade forces you to use broad curves, and the actual cuts in the wood are often nicer then the pencil lines you drew.

puppyPartsOnLaserFor the past few weeks, my Tech Shop night has been spent on a super-complex laser cutter project. The kind of project that won’t be finished for months with rounds of test assemblies. I realized that a purely aesthetic micro-project in the form of a cute puppy dog might be the perfect counterpoint to such a technical project. So I abandoned my original bandsaw plan.   I could get some finished objects with only about an hour of Illustrator time and some scrap 1/4″ plywood.  I could even glue them up while my next round of complex parts were being cut out, so I wouldn’t be  stealing too much time from my other project.

puppysNotFullyCutThroughThere was a bit of a glitch in that laser power output was a bit lower than usual. Wood is not an entirely uniform medium, so if you don’t have enough extra power going in, you end up with some uncut fibers.   Some of the pieces dropped right out, but a few needed to be cut free with my trusty Swiss army knife.  The tough fibers also tend to make the edges not a perfectly uniform burnt-wood color. If you care, you can touch those up after the fact with a wood-burning pencil. You can also sometimes get the pieces to come out cleanly if you sand the back of the sheet.  That way you don’t have to touch up the sides, but it’s a lot of sanding. And isn’t the best solution for plywood since you run the risk of sanding through the top ply.

puppyTwistThe nice thing about purely aesthetic pieces is you can glue them together any way you want.  That gives each puppy their own personality and lets you discover fun combinations.  I used some plywood that had one face a bit darker than the other.  I figured that would make puppies have a nice light underbelly.  The only down side is that they look a bit strange from the back.  I guess if you really wanted to make a bunch of these things, you could  cut the back legs/belly piece from plywood that was lighter on one side, then cut the head/forepaws parts from more uniform wood.

puppyBackAndSideBlueI knew that the pups would be a bit head heavy, but I thought when I glued them up, I could adjust the exact position of the hind legs so they would slightly lean back.  The only problem with that plan was that the two main contact points are only 1/4″ apart so they are  a bit tippy.   I considered scuffing them on sandpaper to give them a firmer foot hold, but then their paws would have bright flat spots on the bottom.  So I decided not to bother.   Puppies are tippy. That’s just the way they are.

threePuppiesWithBlueWallI glued one of the pups with his head down low, so he’d be the runt of the litter.  For some reason that also makes him seem a bit fatter.  I rather like this idea of cute parts that can be glued together in different configurations.  These have happy tails, but they could just as easily have sad ones.  This micro-project had a great effort-to-fun ratio.  Simon really loved his little wooden doggy: he loves the burn wood smell and thinks it’s cool that it was cut with light. He took it to school to show his friends. I haven’t really told him his pup has some brothers and sisters.  Here’s a family photo.  I could have sanded them to give them a crisper look, but I like the smudges and burn marks.  It gives them a bit more personality and it’s less work too.