More pics than usual in this post, so I apologize in advance for overloading your browser! So settle in, grab a beer, because this is a long one!
The bumper is that large horizontal metal bar that covers the cyclotron and is bolted to the sides of the pack. It's a very strangely shaped piece, and particularly difficult to shape.
I was going to bend a piece of hot wheels track and call it good, but thanks to the wonderful feedback I've gotten on this thread, I figured I had better step up my game a little bit and try for something a little more authentic. Especially since the bumper is one of the most noticeable parts on the pack. Whew, it was a seriously big task!
I don't have the skills or tools to take this into full-blown woodworking territory, so even though this build has turned out to be a bit labor-intensive, it would not call it a "highly-skilled" undertaking, and it certainly didn't require major power tools. It did, however, require lots of extra time and patience.
And sanding, lots of sanding.
First things first. I measured the outside width of my pack at the synchronous generator, and found that dimension to be exactly 13". Too big to make the bumper according to plans, and too big to use a prefab resin bumper. So I took Stefan's blueprints, and using Photoshop, I stretched the arms at the right points so that the inside horizontal dimension of the bumper would be 13".
I printed four copies on card stock and taped them together (too big to fit on one piece of paper). Then, I cut them out. Two for the side "rails" (which will be plywood), two for the inside "core" (which will be styrofoam). Where the rails and core line up, I left extra material, since the core can be easily shaped to meet the rails.
I picked up a piece of 12" x 24" x 1/8" Baltic Birch plywood from Michaels for the rails.
I cut the wood longways down the middle, and then shortened the two pieces to about 13-1/2" long. This can be done with any hand saw.
I wanted to make sure the rails match each other perfectly (matching to each other is more important than accuracy to the pattern), so I used a technique I learned online to temporarily stick the two planks together. The trick involves first covering one side of each piece with masking tape:
Then, I used superglue to mate the two planks together on the tape side. That way, I will be able to pull them apart later.
Next, I used a VERY
light coat of spray adhesive to stick the rails pattern onto each side of the stuck-together pieces, lining them up on each side as perfectly as I could. I did this with lots of marking and checking. The spray adhesive is light enough for me to remove and reposition as necessary, but tacky enough to hold when I need it.
Then, I rough cut around the pattern, using a combination of hand saw, coping saw, and dremel, until I was as close as I could reasonably get.
After that, I sanded the piece up to the solid lines. To do this, I used the drill and sanding drum as shown before, again zip-tying the trigger in a closed state and holding the wood up to the drum.
I took it slow; this took half an hour or more, just being careful. Even so, I still made some mistakes!
Again, hitting the pattern perfectly is not as crucial as consistency between the two pieces, so I wasn't too worried. This won't really be noticeable. You can see above that I also pulled the pieces apart and cleaned them up with a bit of fine-grit hand-sanding.
For the core, I got this piece of 11-7/8" x 9-7/8" x 1-3/16" styrofoam on Amazon. It got my attention because of its price and ideal thickness for this part. I won't have to to use two layers!A word about cutting the styrofoam: Cutting styrofoam is easy, obviously, but can leave jagged edges and mess everywhere. Instead, I used a hot wire cutter to do all my styro cutting. I had previously built a nice table one using the guidance in this video, but there are cheaper alternatives, even some you can make for as little as a dollar, or even less. It is worth taking the time!
So, I cut the foam piece in half across its width, and glued the two pieces together end-to-end using superglue (after testing my Gorilla CA glue on it to ensure that it doesn't melt the styro). This gave me a piece that was roughly 5-7/8" high by almost 22" long. I shortened it to 13-1/2" long, and this was my working piece:
Similar to the wood process, I stuck the pattern on both sides (reversing the back pattern) with a light coat of spray adhesive...
...and rough cut around the pattern first with my foam cutter, and then sanded it by hand.Again, where the core lines up with the wood rails (solid lines), I did not sand all the way up to the pattern. I will sand the core up to the wood later. I only sanded up to the pattern at the dotted lines.
And then I peeled off the paper patterns.
Now, about that styrofoam. It is full of holes, and will melt if I try to spray paint it. This piece needed a lot of reinforcement, and a smooth surface. Some of that coating I can do after the bumper is mostly assembled, but the parts where the core is below the rails will be pretty hard to do. So I opted to coat the dotted line areas before assembly. For this, I used Bondo body filler:
This stuff is pretty cool, in that it's fairly easy to sand and cures in 30-60 minutes. I had only used Bondo once or twice before, but it is very easy to work with, and is very forgiving. It comes as a can of paste that I put in a Dixie cup, and then I stir in a tiny bit of hardener (which comes with it in a small toothpaste tube). The more hardener I use, the faster it cures, so I can use that to give me as much working time as I need. I only ever use a tiny drop of hardener, and I stir it really well in the Dixie cup using a popsicle stick, until it's fully mixed.
On the right side of the core, I slathered a bunch of mixed Bondo right where the dotted lines of the pattern would have been, with a popsicle stick, scraping it off the sides.
It cured in about 20 minutes, and then I sanded it down carefully, until it was nice and even:
It really is quite easy to work with. Sure, there are a few air bubbles there, but I planned to fill them later. I also wasn't worried about ragged edges on this piece, as I planned to fill the inside edges of the core later.
Then, I went through the same process on the right side dotted lines, which has much more surface to apply, but doesn't have any corners to worry about.It's around this time that my core styrofoam piece snapped in half! Too much stress working on it. But no worries, I kept working on the halves separately, and it all glued together perfectly during assembly with the wood rails.
Ready to assemble! I did this with superglue. Notice the foam sticking out past the wood? This is intentional.
I was then ready to sand the extra styrofoam material right up to the wood rails (where the solid lines had been). I decided to go even farther than the rails, leaving a bit of a "trough" in all of these areas, so that it could all be covered more easily with Bondo.
For the center plate pieces, I took two pieces of leftover 1/4" MDF and white glued them together, making a half-inch thick piece. I then rough-cut it to size with a saw:
For shaping the corners and rounded blends, I once again used the improvised drum sander in the form of a drill, taking care to move very slowly!
Then, after gluing the side pieces onto the bumper with epoxy, I slathered a layer of Bondo on top, and a little around the rounded "join" areas, where the side blocks blend into the bumper arm.
I then sanded that surface smooth, using a sanding block, and also worked on the recessed "sloped" area where the one arm comes into contact with the center plate. There are still plenty of imperfections at this point, but the plan is to fill them with spot putty later.
What ensued after this were many, many rounds of Bondo application and sanding, followed by more Bondo, and more sanding. It was probably at least a dozen, if not more, of these cycles, so here are a couple more snapshots of what that was like:
There were times that I over-sanded, but reapplication of Bondo is an easy repair. This process took a long time.
Shaping the bottom of the arm was a similar process, and here's what that looked like:
After I was happy with the shaping, I then used the spot putty for filling imperfections and smoothing the surfaces. I also used it to round the inside corners, similar to a "caulking," where the styrofoam core is attached to the wood rails.
The only downside is that the spot putty is more fragile than regular Bondo, so it took quite a few applications and re-sanding to get it where I felt I was ready to move on.
Finally, I had the bumper ready for the next step: finishing!
The whole thing needed not only a protective layer, but also something to help fill in a few of the remaining pock marks and scratches. White glue was the go-to for this.
I used a total of four coats,
front and back, and then followed up with a light sanding with 400-grit sandpaper. This, I hope, helped even things out just a bit.
After this, I drilled some of the mounting holes, and applied the usual black paint formula:
It was probably a bad idea to make the holes prior to painting, since this exposed some of the styrofoam, which can be melted by spray can propellant if it's too close. I think it'll be okay, though.
Yay! This part is done! I am SOOOOO ready to move on to the next piece.
It was a great deal of labor, but for me, I still think it was the best way to go, since I don't have giant saws and routers and all that other woodworking stuff. And it was a good learning experience for using Bondo!
I also added the label for this part.
Next post, I will make the shock mount, and then I will follow with mounting both parts to the pack. It's a little more involved than you might think if you want the bumper to remain removable!
Thanks for reading,
BillRUNNING PARTS COST:
$4.49 - 12" x 24" x 1/8" Baltic Birch plywood (Michaels)
$4.38 - 1-3/16" x 9-7/8" x 11-7/8" FloraCraft Styrofoam Block (Amazon)
$5.98 - Bondo body filler (Amazon)
$1,000,000.00 - All that effin' labor!$272.42 - previous total$14.85 - this stuffTOTAL: $287.27