Introduction: Soul Cycle Mothership, a Molded Fiberglass Speaker Cabinet for Bicycles.
After creating 5 or so fully custom Soul Cycles, painstakingly, one at a time, I needed a way to create attractive cabinets in a fraction of the time. So I invested extra time in the process of making a mold to be able to reproduce an attractive curved form in fiberglass. Now Rock the Bike can bust out a Soul Cycle Mothership in about a week, not months like the previous custom bikes.
Step 1: Sketch Shape You Wish to Mold, Keeping in Mind Undercuts in Molding Process
An example of an easy shape to mold would be a beach ball. An example of a hard shape to mold to would be a stegosaurus. What makes the stegosaurus harder? It has features like legs, that will make a left / right mold unable to pull apart. The spikes on a stegasaurus' back would create steep draft angles that would make a top/bottom mold difficult but possible to release cleanly.
For my bicycle music system, I chose a shape that was relatively easy to mold with a left / right mold.
Step 2: Create a Rough Version of the Shape, in Foam.
In order to create your foam shape, you'll either have to sculpt it freeform like Michelangelo, or carve it from a block of foam with CNC tools, or use routers and templates to help you make it. I chose to use templates and routers.
In the series of photos you see that I stacked the templates (which are made by 'tracing' a master template with a router) with threaded rod. Then I shot expanding foam into the form (inside a garbage bag.)
Then I used a hot knife to slice away the excess foam. The masonite templates stop the knife from cutting too far.
Step 3: Hot Wire, Carve, and Shave Your Foam Block Down to a Curved Form.
I first tried a Shurform tool (basically a cheese grater) to remove material, but the hot wire was much more effective.
Step 4: Smear Nooks and Crannies With Some Kind of Resin or Filler That Is Sandable.
Foam has big holes that need to be filled. Thicken epoxy resin with Microballoons and smear that stuff all over your form. I recommend using a different dye for each layer that you build up, so when you're sanding later you'll know when you're about to hit foam.
Step 5: After Building Up a Candy Coating With Resin on Your Shape, Sand It Down Till the Curves Are Perfect
This is an extremely time consuming step. Don't underestimate how long it takes to reach a level of finish you are satisfied with.
When you compare your shape to the perfection of, say a motorcycle gas tank, you'll be unsatisfied by the high and low spots you can feel as you run your hand over the shape. So know going in that this part of the process could take days.
Get a sander you like using, a dust mask, and a selection of different grits of sandpaper ranging from 50 to 400 (you'll use the higher grits later for polishing). Look for low spots (still glossy) and reduce the high spots until you can no longer see the glossy lows.
Step 6: Paint Pure Resin on Sanded Positive Form, Then Polish
Pure resin is easier to polish than resin with thickeners. I hung the shape so I could paint all the important surfaces without the resin collecting on a surface in little puddles.
Step 7: Create a Parting Between the Left and Right of the Shape
The clay is used to define the parting line of your shape. In my case the parting line is also the center line. So it was obvious and easy to find. I used a flexible ruler and drew the line on my shape with a sharpie.
The role of the clay is to create a lip upon your parting line, upon which you can build one half of mold, in my case the left. After I built up the left half of the mold, I removed the clay (it separated from the mold and the positive form easily with a careful application of mold-release where needed.)
In the photo you see that I made a special mold-making table for this step. It has a hole slightly large than the positive form that holds it in place so that I can apply the clay, and then the liquid rubber. I used another
Step 8: Apply Mold Release, Then Paint Your Shape With Flexible Moldmaking Polyurethane Rubber.
Build thin coats up until you have a 1/4" - 1/2" thick mask. You paint the sticky liquid rubber on the shape, about 1/16" at a time. Many coats are required. The liquid rubber I used mixes by volume. Part A was the consistency of light honey. Part B was the consistency of creamy peanut butter. Getting equal volume is difficult with the the Part B, because when you try to put it in a cup, the voids are huge and it's impossible to measure the volume accurately. I ended up eyeballing it, which I do not recommend, because certain layers in my mold did not fully cure. In other words, I know that the longevity of this mold has been reduced by not getting accurate 1:1 by volume mixes. Next time I'd probably find what the weight ratio is and then use a scale to get 1:1 mixes.
Step 9: Get Plastered
Once the rubber mold is complete, you need a rigid outer shell, a "mother mold" to hold the rubber mold when you do your lay up. In my case I chose plaster, because it's cheap, and fast. It's also heavy, so if I were doing a larger shape, I'd think twice about using plaster. But with a shape this size, the plaster Mother Molds are still easy to handle.
As you can see from the second image here, I used baby powder as the mold release. I do not recommend this! It cakes with the moisture from the plaster. I recommend Mold Release wax or Crisco.
Step 10: Pull the Mother Mold Off the Surface / Rubber Mold, Just to Check If the Mold Release Worked.
The degree to which your part has undercuts and steep draft angles will determine whether this step is hard or easy. In my case, due to the steep draft angles on the Mothership's form, it was quite difficult and required my rugby playing assistant Geoffrey's full upper body strength. http://www.flickr.com/photos/rockthebike/2261380501/ Mom was there for moral support.
Step 11: Do the Rubber Mold for the Opposite Side.
This is a repeat of the process for layering up a the rubber mold. One key is that the clay lip we created on the other side has been replaced by a parting line in the mold itself. Be sure to coat all surfaces with mold release, especially the parting line.
Step 12: Mold Complete. Begin Lay Up by Painting and Smearing Gel Coat Inside the Left and Right Halves of the Mold.
Notice that I am working on one half of the mold. That's the key to this whole process. You get to work on the Left, then the Right, then put them together, with as subtle a parting line as possible.
Step 13: Cut Fiberglass Into Workable Strips.
Having a sharp paper cutter like this Dahle rotary cutter is key. Sharp scissors would be OK, but much slower. Remember that you're cutting through glass, so tools dull faster than paper.
Step 14: Lay Up the Glass Strips in the Mold by Painting on Resin, Paper Mache Style.
Use a paint brush, pat down the strips of fiberglass. In the photos you can see how the fiberglass cloth becomes dark when wet. If areas of the glass are still light and silvery, they don't have enough resin. Conversely, once the fibers are dark in color, don't paint more resin on them. It's wasted. Remember that all the strength is in the fibers. The resin itself is not strong. Its only role is to bond the fibers together so that they the work as a bundle. Excess resin only adds weight. Some makers use vacuum bagging to squeeze the excess resin out of the mold at this point. I chose not to do that because the set up process was too intense.
Step 15: Put the Two Halves of the Mold Together Using Bar Clamps. Glass the Parting Line.
Note how the plaster mold has flats built in for clamping. At this point, I reach in and lay glass strips along the the strip between the two halves. The hole in the mold matches the top of the Xtracycle. A second mold (using the same positive form) would be required if I wanted to make Motherships that are compatible with the MundoMundo or regular bike racks.
Step 16: Pull the Mother Mold and the Surface Mold Off the Object. You Have an Exact Replica of the Original Form.
When I pulled the mold off the object the first time, the object was too flimsy. It was rigid enough to hold its shape but not enough to serve as a good speaker cabinet. So I added a few more layers of glass on the inside, not disturbing the outer surface.
Step 17: Position the Mothership on the Xtracycle and Trim Excess Material to Achieve Desired Fit.
Step 18: Cut Holes in the Flat Side Surfaces for Speakers.
Many car audio speakers come with a cardboard cutting template on the box. If so, then by all means use it. If not, you may have to improvise. Start small, then go a little bigger each time, until the speaker just squeezes in.
Step 19: Cut Inner Panels to Seal the Left and Right Speaker Cabinets
The panels are polycarbonate, which despite being impact resistant, is quite flexible. In one of the pictures you can see how I stiffened it with ribs on the inside and outside surfaces. The ribs on the inside surface are also the shelf that rests on the Xtracycle snap deck.
I used thickened resin fillets to bond the polycarb panels to the fiberglass shape. I roughed up the polycarb around the edges and used glass strips to strength the fillets further.
Step 20: Wiring and Controls
We used a Soul Cycle DIT Head UnitSoul Cycle DIT Head Unit as the control deck for the Mothership. The DIT Head Unit is essentially a project box for bicycle customizers, and it comes with the handy Klickfix system installed. You get a one-button release for your controls. This makes it faster and easier for you to get ready to go cruising.
Wiring is a fairly painstaking process that I've described in detail on my other instructable. In this case, I was including a 4-channel mixer, human power voltage gauge. In the cabinet itself, we connected LED backlighting, and the amplifier itself.
Step 21: Install and Test Lighting. Install Speakers. Get Ready to Ride.
Step 22: Finished Soul Cycle Mothership -- Now Get Out There in Your Community, Lead Inspiring Social Rides, Amaze Small Children, Demonstrate Human Power.
The bike rolls like a normal bike but with amazing music quality: Check the video!
As you can see from the pictures, at the time of this writing I've built two Motherships, the true red one for Clif Bar, and the ectoplasmic, glow-in-the-dark sea green one. I added the Down Low Glow to both, for nighttime magic carpet effects. The glow-pigment used on the second Mothership allows us to write messages on the shell.
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