At a Troop yesterday I had a discussion with a fellow Garrison TK about the strength -- or lack thereof -- of Shoulder Bridges. It occurred to me that the method I used to beef up the Bridges from my build might be useful as a standalone How-To article.
Shoulder Bridges are perhaps the most fragile part of TK armor, so it's always a good idea to reinforce them in some way. Also, since the underside of the Bridges is basically hollow there's nothing there to glue to. Most builds I've looked at fill in all those hollow spaces with slivers of ABS glued in to add both strength and gluing surface. I decided to try something different. My plan was to cover the entire underside of the Bridges with a strip of thin ABS cut from a For Sale sign I picked up at Lowe's for $1.99.
First, though, I needed to trim the Bridges down a bit to remove excess edge. I have AM armor, which comes nicely trimmed, but there is a bit extra left on so trimming these was my first step.
The AM Shoulder Bridges are already curved (almost perfectly, for that matter), so using the score-and-snap method wasn't an option and I relied on my trusty Lexan scissors. Notice here that I'm not cutting all the way to my line. That's because I'll be gluing ABS to the entire underside and I want more surface to work with. I'll trim them to their final size after the gluing is all done. I had already cut out the ABS from my For Sale sign -- again slightly oversized -- so gluing started by attaching the ABS to the Bridges at the middle. The reason for this is that all the critical gluing of the ABS is mostly around the edges, and I wanted a solid center all the way down the middle for strength and rigidity, and to support the thin ABS.
To do this, it only takes a dollop of glue on the center of each "rib" where it'll make contact to the ABS sheet. I'll use something different gluing the edges, but I'm using E6000 here for the longer working time and adjustability. With the glue dolloped on, I pressed the ABS into place and added a series of small clamps down the center and set the Bridges aside to dry. A couple things to keep in mind if you decide to do this ---
1) First, shape the Bridges as closely as possible to the shape you want them before starting this. Yes, you can still bend them afterward but it's not quite as easy, so bend them to shape now.
2) When you clamp on the ABS, ensure that you keep the curve intact the way you want it while the glue is still wet. This is pretty easy to adjust, even with the clamps on. But once the glue is dry it will hold the curve, so you want the curve to be right where you put it.
3) I've talked a number of times in my official build thread about how you can work with things glued with E6000 after only a few hours without waiting for a full cure. That doesn't apply here. You want the glue down the center to fully cure before proceeding. Why? Well, E6000 is strictly evaporative and needs air to cure. The inside of the Bridges won't have air circulation once the edges are glued. So let that glue cure at least the full recommended 24 hours.
OK, lecture over. To glue around the edges I'll use Plastic Weld, which does exactly what it says. This glue is very thin, cures very quickly, and makes a permanent, nearly invisible joint. It's also easy to use since capillary action does most of the work for you.
Work in small sections at a time -- about three or four ribs length -- from one end to the other. I alternated sides. Dip the brush into the bottle, apply liberally to the edge (the slightly oversized ABS forms a little "shelf" that acts as a guide) and capillary action instantly sucks the glue right into the joint. Brush on a bit more in the same spot, and again it'll be drawn right in. Keep doing this till no more gets sucked in; at that point the joint is fully filled and you can apply your smallest clamps. You only need minimal pressure, and you only have to leave the clamps in place for a couple minutes. The glue works that fast.
Important note: Be extremely careful with this stuff! It will instantly start fusing any plastic it touches, including your armor, so get it and anything else out of the way. Keep a cloth or paper towel handy for drips and spills -- it will also start fusing the plastic laminate on my worktable, for example -- and wipe up any spills immediately. Note how I keep the glue bottle in what I call my Tray Of Isolation that I use for glues and other caustic chemicals, plus I have it nestled into a hole in a piece of wood that prevents the bottle from tipping.
Then I just kept working down around the edge, alternating sides, until I'd gone entirely around the Bridge. Done? Nope. When this kind of glue cures, it shrinks ever so slightly, and if you look at the glue joint you might see tiny gaps that look like bubbles. Go all the way around once more with your brush applicator, adding a second line of glue. You'll see it suck right into those little gaps. Once you see no more tiny gaps, then you're done. Set it aside for an hour or two. Yeah, the glue is dry, but you want it to fully cure. An hour or two is more than enough, but best to be sure.
Now, trim that oversized ABS right up to the edge of the Bridge plastic with a sharp knife, and sand the edges smooth.
This is a straight edge, so either use a sanding block, or better yet a full sheet of paper held flat to your work surface. I did a quick rough sanding with 150-grit just to level the edges and bring them to the final size, then followed with 220-grit, then 320-grit for a really smooth edge. And here's the magic: Because this is a welded plastic joint, there is no appreciable glue line. Seriously, take a look:
There you go. The Bridges are strengthened from one end to the other, and you have a smooth, flat gluing surface ready to go on the underside for attachment to the armor. Which, by the way, we'll do after making an adjustment to the armor.
Strengthening the Shoulder Bridges is only part of reducing their fragility. The second part is how they're mounted to the armor. Here, you can see that although the shoulder extensions at the top of the Chest and Back Plates are trimmed to length and shaped to my shoulders, the ends of those extensions weren't quite in the same plane. You can see what I mean with the armor on my mannequin.
The armor feels good on and fits just right, but no way those Bridges are going to lay correctly on that. Sure, the elastic hold-down straps will force the Bridges into the correct position when you wear the armor, but that also stresses the Bridges by twisting them unnaturally. But you can fix that.
Leaving the armor on the mannequin, I reshaped those extensions by heating them with a hair dryer. (I'm terrified of using a heat gun, but a hair dryer works great on small, thin areas like this and it's far safer.) Essentially, I just heated up the ends of those extensions, then twisted them until they lay in the same plane with one another.
Once I had the left shoulder nice and planar, I did the same thing with the right shoulder. When finished, the bridges will lay perfectly over the top. Now, it was just a matter of lining up the Bridges to center them over the shoulder extensions and making a few registration marks, then removing the armor and gluing the Bridges to the Chest Plate over on my workbench. This is another critical glue joint, by the way, so allow the full curing time for the E6000.
All right, let's take off the clamps, reattach the shoulder strapping and put this back on the mannequin and see what we got.
Nice. Now, just a little cleanup for some E6000 squeeze-out, add the thin elastic hold-down loops for the backs of the Bridges, and you're ready to enjoy the strongest Shoulder Bridges ever.