Sunday, October 19, 2014

Day 98 - Eyestalk

I got inspired to work on the Plastruct disks that I had bought, and to see what kind of further progress I could make on the eye and eyestalk.  First, I needed to make a simple jig with each of the disks measured out on it and four flat nails to dissuade the disk from wandering while being drilled.  This way I could make sure I drilled in the center each time.  I decided to use a 3/8" forstner bit for cutting the disks after practicing first on a spare bit of acrylic.  Even with the jig, there was a small amount of eye-balling I needed to do make sure that the bit didn't wander too far off-center while tapping.

After the largest of the disks was done, I hammered in another set of nails for the next size down.  After drilling those, I repeated that for the smallest of the disks.  After all six disks were drilled, I also drilled the same sized hole into the back of the eye I had made previously.

I cut a small length off of my 3/8" threaded lamp rod and secured a disk onto it using two nuts above and one below.  I made sure that these were very snug (worrying a bit that I might crack the plastic) so that nothing came loose while the drill was spinning.  I put the lamp rod into the chuck of my drill press and proceeded to use a variety of methods to trim off the excess plastic that I didn't need.

Gently pressing down on a sheet of 80-grit sandpaper worked for a bit, but soon the plastic heated up and got somewhat soft.  I turned off the drill and waited for the disk to cool.  After that, I tried a hacksaw blade, and that seemed to work much better.  While the disk was spinning, I placed the hacksaw blade under it teeth upwards, and gently scraped it along the bottom of the disk, frequently checking the diameter with my calipers to make sure I was adhering to the plans.  After several minutes, I had trimmed off all that I needed.  I repeated this for the remaining disks, getting faster with each one.

After that, each disk was scuffed using steel wool and a 320-grit sandpaper sponge to get a nice frosted effect.  A quick spacing check using the aluminum I had previously cut seemed pretty satisfactory to me.  I then set these aside for a bit.

Back when I was making the inner gunbox assemblies, I kept the two 1/2" thick MDF circle offcuts my hole saw had made.  These, along with two circles of my thinner HDF board, were the 3.6cm thickness I needed for the eyestalk pivot.  I glued and clamped these together, and they're curing as I type.  Later, I will sand it smooth and drill a hole to accommodate the lamp rod.  It's just shy of the 10cm diameter needed, but the outer ribbed detailing I'll add to it should make it just the right size.

In order to make the optical illusion that the eyestalk consists of a single piece of metal, I needed to think outside the box a bit.  I have 3/8" threaded lamp rod to run the eventual wires through, but the thickness of the actual eyestalk is one inch.  This means I need to have layers built up around the rod.  Several weeks ago, I looked and looked for anything that would let me make nice, snug layers for the eyestalk, but the only thing I could find was some 3/4" PVC pipe.  It fit fairly well inside the 1" aluminum tubing that I have, but it still rattled around a bit.  Further, the threaded rod was much smaller than the PVC's inside diameter.

One day while looking for the very nuts that I used above to secure the disks onto the threaded rod, a thought struck me.  These nuts looked about the same size at the inner diameter of the PVC pipe.  A quick experiment showed me that I could fit the PVC over the nuts quite snugly, and that the whole assembly was nice and centered.

I made sections of PVC that were slightly shorter than the aluminum that will surround them (to accommodate the curvature of the eye disks once assembled).  To make the aluminum fit more snugly, I added a layer of trimmed duct tape to the PVC.

Then, I took two of the nuts and spun them way down the threaded lamp rod.  The longest piece of PVC covered them, one at each end to keep it centered.  Then I surrounded it with its aluminum part, slid an eyestalk disk down on top of that, then another nut/PVC/aluminum bit, another eyestalk disk, etc, etc, etc.

Before too long, I had finished it all off by placing the eye onto the rod, and securing it in place with a wide washer and a nut.  I was particularly pleased with how even and centered the eye disks were, keeping the illusion of one solid piece of tubing.

Now I just need to wait for my LED to arrive so that I can start with all the inner eye pieces, and get this bad boy lit up!

Monday, October 13, 2014

Day 96 and 97 - Dome cowl

I finally decided to stop being afraid of the dome cowl and actually finally make it.  I set out and bought a few more fiberglass supplies from TAP Plastic, then began cutting up pieces of cloth for the angled sections inside the mold.

I waxed the interior of the mold several times and let that sit for a bit. Then I applied a layer of PVA and let that dry.  Finally, I dusted a few coats of silicon mold release.  I wanted to make sure I had plenty of release layers between the mold and the final part!

After a little more time, I mixed up about 3oz of gel-coat and spread that on with a brush.  As it is getting colder, I added the maximum recommended amount for the catalyst.  I let the gel-coat sit for about three hours until it was only just slightly tacky, mostly dry.

I took some fiberglass strands that I pulled off of some woven cloth and placed that in the small trench in the top of the mold.  I was really afraid of having air bubbles in this little section, so I made sure to reinforce it as much as I could.

Then I placed the rest of the cur pieces in their positions, mixed up about 4oz of resin, and started brushing it on.  These cut sections didn't really overlap each other, so I then took some thin torn-up surfacing veil and applied some overlap.  Then I applied a heavy layer of overlapping chop mat on top of all that, with another 5oz of resin sealing it into place.  I rolled the mold all around in my hands while the resin started to set.  Once I no longer saw movement of the liquid, I sat it down and waited for it to cure.

The next day, I attempted to separate the part from the mold.  I have read many stories on how difficult it is to remove a cowl, but I didn't want to resort to cutting the mold into two pieces.  I placed putty wedges in similar to how I separated the dome from its mold.  On the bottom of the mold, however, I placed too many, and the cowl started to crack and split slightly.  Panicked, I removed all the wedges and decided upon a different strategy.

All around the mold, I put in one wedge, and then a second on top of it.  I then hammered in a wooden stir-stick in between the two wedges.  The stick always went in quite a bit further, so they were clearing the beveled edge of the cowl.  I repeated this this all around the cowl.

I poured in some boiling-hot water between the cowl and the mold, and eventually the two parts separated!  I quickly washed off the cowl and took a closer look at it.

The split in the middle was the most obvious.  It's going to need to be Bondo'd up a bit to conceal that.  But that's okay, because I also noticed that I had totally forgotten to place an indent in the mold for the recessed ID tag area!  When I Bondo this part, I'll be sure to include the ID tag indentation.  There was also an air pocket in one of the four corners; again, totally repairable.

I was especially happy with how well the detailing turned out on the top of the cowl!  This was the part I thought would be the most mangled.  But it's great!

I took my Dremel tool and cut/ground the hole in the cowl where the eventual eyestalk will be, and temporarily attached the cowl to the dome for a quick photo op!

Next steps: Repair the cowl and put the ID tag indentation in place, then sand the whole thing because all the ripply roughness of the mold transferred to the cowl.