Day 107 and 108 - Dome work, eye, and plunger

This weekend was a pretty fruitful one, being able to get a good chunk of time dedicated to some detailed areas.

I finally attached the bottom rotation plate onto the neck section.  I evened out the distances of each of the eight struts by measuring the distance from the top of the strut to the top of the upper ring.  There were only millimeters of difference there, so I marked the length of the shortest one on each that were taller than it.  After sanding the rest down to that length, I measured the length of the diameter between each pair of struts.  If I recall correctly, it was something like 46cm and some change.  I took one of the smaller off-cut circles of 3/4" MDF from the initial ring creation (back on day 19; my goodness, time flies) and routed the edge down little by little to match that length.

I was trying to factor in eventual dome rotation mechanics while doing this.  Since my struts were already pretty tall, I decided to cut notches into the plate and attach it to the strut sides instead of directly to the top.  If the plate were attached too high, the added distance of the second plate—along with the diameter of the rotation wheels—would exceed the proper distance between the bottom of the dome and the upper ring.  To prove this to myself, I sat what will eventually be the top rotation plate (the largest of the off-cut ring circles on top, with some spacers representing the distance of the wheels/bearings.  Then I placed the dome on top.  Sure enough, I should be able to get the proper distance by just routing away the outer edge of the top plate, millimeter by millimeter, the way AdamSt did.

I'll cut the inner section of the plate out later once I figure out some other stuff.  For example, I'm not sure which method I want for electric dome rotation (there are so many options that come up when searching the forums).  This will determine which plate I mount the wheels, place the motor, etc.  I don't know what any of that looks like at this point.

Now that I had the cowl in place on the dome, I could start to measure out where to place the eye pivot slot.  I knew that I wasn't going to be exactly centered—but at least pretty close—so I needed to wait to make sure that when eventually fitted the eye pivot is clear of the hole edges, and that the eyestalk clears the sides of the cowl when being moved up and down.  After a combination of relative measurements and eyeballing, and eventually marked out where the slot should be cut.

Problem was, I initially only made it 10cm instead of 14cm, and was quite confused when it proved to be such a tight fit for the pivot.  But I managed to get a couple cool photos anyway before correcting it and cutting out the extra 4cm.

Next, I turned my attention finally attaching the bushings to the aluminum plunger tubes with epoxy.  I used a product called JB Weld, which seems to be a recommended brand.  I used their strongest bond, one that sets in like a day, rather than their quick-bond stuff.

I cleaned all the tubes with 1000 grit sandpaper and Brasso metal cleaner to get them nice and shiny.  I then took a series of photos to make sure that I assembled everything in the correct order before attaching the bushings with the epoxy, because once those are on, they are not coming off without a serious fight (and probably major damage).  The acrylic hose barely fit inside the rear outer tube bushing, so I roughed up the surface of the hose a bit with coarse sandpaper.  But I ran into another problem almost immediately: once I had pushed the coupler into the hose, it expanded the circumference of the hose a fair amount, making it impossible for the bushing to fit around it.  If I had the presence of mind, I would have simply slid the bushing on from the back end of the hose (duh!), but instead, I attached a sanding burr to my Dremel and whittled the hose wall down until the bushing could fit!  What a silly person, me.

I mixed some batches of epoxy, gobbed it onto both the bushing wall and the interior wall of the tubes, pounded everything into place with a rubber mallet, and set it all out to cure overnight.

The next day, the were all completely cured and looking very solid.  I attached the (incomplete) plunger to the front, and snapped a couple more pics of it extended and retracted via the acrylic hose.  Soon, I will add black felt to the gunbox hole chamfers and mount both the gun and the plunger arm with my gunbox mounts.

Since I was working with the aluminum tubing, I decided to take an off-cut of the 1" tube and make an axle for my eyestalk pivot.  On the pivot itself, I noticed that the two-part Gorilla glue attaching the plastic outer skin to the MDF disk is coming loose, so I may need to re-glue it.  Also, the two pieces of 1/2" MDF seem to have detached from each other.  If they fall apart completely, JB Weld might be the answer!  Anyway, I slid the tube into the pre-drilled center hole and made a 5/8" hole using the pivot hole itself as a guide.  Once done, I sanded out the new tube holes a bit so that the threaded lamp rod could easily pass through.  For now, it's temporarily mounted inside the dome just to keep it somewhere out of the way (and to make Rainier look terribly awesome at the same time.)

As the weekend was wrapping up, I finally got around to sanding all the excess ABS glue that had hardened around the seams of the eye section.  Sanding ABS plastic isn't all that different than sanding wood, but I sure hated losing that smooth shine.  Ah well, it will be all smooth again once primed and painted black.  And, now that it was sanded (and then smoothed a bit more with a finer grain), I added the twelve 2.5cm "lugs".  These were cut from Plastruct half-round styrene rods that I had previously ordered with all my other plastic parts.  I initially used Krazy glue to secure them into place, and then ran a bead of acrylic cement to really bond them into place.

Then, for my final detail, I drilled the three holes for the eye piece bolts.  There doesn't seem to be an "official" distance for those holes to be drilled from the rim of the eye, so I measured a length that didn't appear to be too fragile—1cm from the rim seemed fine.  I used a bit more JB Weld to also secure some nuts to the interior for the bolts to be threaded into.  When I got up the following morning, I made sure to take my pliers to remove the bolts form the semi-cured nuts lest they be permanently cemented together!  It seems like that solution worked really well, and I'm quite happy with the results.