Small shepherd's sundial

Some time ago, I made a simple wooden shepherd's sundial.  It's crude and doesn't work well, but I set it on a lanyard and occasionally use it.  When I decided to use it recently, my wife asked for a small one as a necklace.  Commissioned artwork time!

Since I wanted the sundial to be stylish as well as functional, I thought a bit about materials.  I ended up with a simple design that uses 3/8" copper tubing.  It's the same stuff that you can get at the hardware store for various plumbing jobs, but it's small enough for the task.  I traced out the hour lines using a short python script, and printed them out for use as a guide.

The gnomon is held in a steel cylinder with a slight lip to retain it inside the copper tubing, which has a matching (reverse) lip bored in the end.  You slide the cylinder in from the bottom of the sundial.  Boring the copper was a bit of a problem until I got the boring bit set properly.  I also ended up bursting through the side of the first cylinder because I didn't correctly account for the thickness of the tubing. 

I cut the tubing with a jeweler's saw and filed it to final shape for the noon curve.   The cylinder has two drillings: an axial drilling for the hanging loop and a radial drilling for the gnomon.  The hanging loop is just a piece of brass wire bent into a loop at the top.  I thought of soldering it in place, but decided not to.  I hammered the bottom end of the wire into a small rivet, so the loop is free to turn. 

Here is a trial assembly.

I spent considerable time polishing the copper, the pin, and the cylinder.  The machining was not too arduous, though it did take a few tries, but the engraving was much more tricky.

Here's the final product.

I did not use a watchmaker's square graver (too unwieldy on the round surface) nor the more usual round graver (difficult to get it to bite consistently) to do the engraving.  After a bit of trial on a scrap piece of copper tubing, I found that a very small screwdriver that I had previously sharpened to a narrow cutting blade worked much better for engraving.

To keep everything aligned, I taped the printout to the surface of the copper, and cut through the paper.  This got the copper marked in roughly the right places.  Then I removed the paper and finished the engraving under the microscope.  This took about an hour, and was a bit nerve-wracking because every slip-up is visible.  I'm not too proud of how the engraving came out -- many slips, wiggles, and other awful mishaps are visible if you look closely.  However, it doesn't look embarrassingly bad if you don't use a microscope. 

The sundial certainly looks nice enough on its own, but I am not sure how practical the shiny surface will be in use.  It's cloudy now, which might be for the best!

Astrolabe cases

Two sets of friends are getting married, and as both couples are intellectually curious, I thought an astrolabe would be a nice gift.  But astrolabes alone require some kind of protection... so I decided to make cases for them.

I started from a block of black walnut cut from a tree we had taken down earlier this year.  Since I had previously split it, the wood had been drying all summer in the back yard.

Mostly, the woodworking needed for the boxes was nothing particularly special.  The steps I did were:

1. Rough cut the block of wood into blocks, each about 2 inches larger than my intended final size.  I used a chainsaw for this, and did the work outside.
2. Power planed the blocks so that the edges were square and partially smooth.  Since my power planer makes an enormous mess, I also did this outside.  (The chips from the chainsaw and power planer go in my compost...)
3. Using a large hand crosscut saw, I sliced off the lids of the boxes.  This is a somewhat delicate operation -- even though it requires lots of force -- as you must ensure that the cut is perfectly planar and parallel to (at least one of) the faces of the block.  I don't have a large enough power saw blade, so this is also a manual step!  In all honesty, this is a ripping operation, so I should have used a rip saw... but I don't have one.  My crosscut saw works well enough.
4. I did an initial sanding of the cut surfaces and did a little bit of squaring up of the other faces.
5. I recessed the parts of the box that receive the astrolabe.  This involved tracing the outline of a (disassembled) astrolabe to where the recess needed to go on both the base and the lid of the box.  I then used a router in 1/16" depth increments to cut the recess.  For the base, the recess is stepped since the thumb ring is supported in a more shallow recess than the rest of the astrolabe.  This also gives room for the pointers.  I also recessed the lid.
6. Power belt sanding.  Lots of it!  Starting with 60 grit, I got all faces parallel and square and cleaned off all the cut marks from the saws and planes.  I also rounded the edges where I wanted them round.  Then I repeated the whole process  with 80, 100, 150, and 180 grit.
7. Since I wanted a very fine finish, I then hand sanded the entire box with 220, 320, and 400 grit sandpaper.  Walnut will polish nicely with finer sandpaper if you're planning for an oil finish, but that wasn't necessary for this project.
8. Five coats of polyurethane with plenty of time for drying, and 400 grit hand sanding between each coat.  I made sure that the recesses were left unfinished, since I wanted to adhere a velvet lining.

I wanted to line the inside of the boxes with velvet to protect the astrolabe.  Since the cast acrylic I have been using recently for astrolabes is actually fairly sturdy, a velvet-lined box is surely overkill.  (I did accidentally drop my larger astrolabe, and that shattered the thumb ring.  Since super glue is actually an acrylic, it was a simple matter to fix the crack.  Super glue leaves a mostly invisible joint on acrylic and bonds almost instantly.)

Velvet is a fairly troublesome material for lining.  To make it adhere to a flat surface inside the box, you must support it.  The usual way this is done is to glue the velvet to a sheet of cardboard first, and then glue the cardboard to the box.  Since velvet frays badly, you need to roll the velvet around the back of the cardboard (a second gluing) so that no cut edges show.  Finally, since the boxes have a circular cutout to fit the astrolabe, I had to figure out how to manage that joint.

In the end, I glued the cardboard to the velvet, rolled and glued the edges, but left the circular bottom edge alone.  After the glue dried, I hand stitched the circular bottom edges together.  The result was a stiff velvet "cup" that fits tightly inside the box.

Once the velvet was glued in place, I added hinges and a front clasp.  While hinges and clasps aren't difficult to install, they require precision.  You must be especially careful since you don't want to harm the finish.  I held the box in the vice, but lined it with soft paper towel so that the finish wasn't marred by the vice.  I sharpened (under a microscope) my 1/16" drill bit before starting.  To install the tacks for the clasp, I didn't strike the tacks with the hammer directly, but rather used a recessed punch to ensure that I didn't slip and damage the finish.  When setting the tacks, I also held them in brass tweezers. 

Wooden equatorial sundial

I had a laser cut sundial in our garden, but it was destroyed.  No matter, it didn't work well in autumn.  I made a wooden replacement sundial.  Equatorial sundials are easy to lay out, since all of the hour lines are separated by 15 degrees.  You can quickly draw the plans directly on a piece of wood, as I did, with a compass and protractor.

One small point is that the dial itself will be semicircular.  To ensure that I got everything aligned first, I drilled the center of the circular arc. Even though the center will be cut out later, this way I can sight through the gnomon to ensure that everything is in alignment first.

Then I cut out the pieces,

and traced the hour lines.
 

To ensure that the hour lines are visible, I filed them into the dial.

I also woodburned them so that they are clearly visible. I also traced a vertical line so that I can install it on its mounting pole correctly.

Here is a test fit.

Once I was happy with a tight fit, I installed the gnomon, which is a 1/16" brass wire.

Finally, I put a single nail to join the two pieces.

And installed the completed sundial in the garden!

Laser cut equatorial sundials!

Just for fun, here are two laser cut sundials!

They are made from the 20190612_equatorial.svg file in my github repo.  You can't see the shadow of the gnomon on the clear one, but you can totally see it projected (correctly) on the ground!  The etching on the white background didn't show up initially, so I set some ink onto.  It's nothing fancy; I just smeared black whiteboard marker ink over the face of the dial, and then wiped off the excess ink with my hand.  It's not waterproof...

Astrolabe upgrade

American University's Design and Build Lab got a new laser cutter.  Since the astrolabe I made before was drawn as a set of SVG files, I figured that it might be nice to make another astrolabe on the laser cutter.  Indeed, the result is beautiful!

This astrolabe is cut from 1/4" black acrylic with a 1/8" clear acrylic rete (star chart).  I etched the rete on the back of the clear acrylic, so there is no visible parallax error.  The pointer is 3d printed PLA. The brass hardware was hand turned on my lathe.  All of the hardware is friction fit with no adhesive used.  This astrolabe is for a fixed latitude (39 degrees North), so the center pin is (essentially) permanent.  The movement is smooth, but tight.  This is a nice improvement over my previous astrolabe, in which the hole in the rete has enlarged over time.

Unfortunately, we had trouble aligning the back.  The horizontal alignment is perfect, but it's vertically shifted by about 2 mm.  This means that the elevation scale runs off the top of the astrolabe. None of the back scales are very useful as a result, even though it is still attractive.  I think the cause of the vertical shift was an alignment key (which doubles as the ring attachment point) that we added to the front layer, but not the back layer.  We attempted to compensate for this difference, but evidently failed.  However, the compass scale on the front can still be used for elevation sighting, although this requires subtracting 90 degrees from the reading to obtain elevation.