Link to Arul's email detailing the mold making process. I'll continue to edit this page as I progress.
The following to-do list is adapted from Arul's original email (linked above).
Creating a support structure
Before casting the epoxy, we need to create the support structure that will help keep the epoxy mold rigid, as well as the acrylic walls that will serve as the walls for our mold.
- The walls
- The end plate
- 5x rod holes, (beginning .1” from mold bottom, as oriented while casting)
- Arul says: you may need to scallop the lower edge [of the end plate] (as I did) to clear any runners you've made. (See runners, below).
- My CAD (Onshape again): end plate.
- 5x carbon rods
- Small diameter, 5.75" in length
- Jason says: If you hold one end of the rod with a vise, the dremel can cut these rods very quickly. However, most of the cutting blades have a pretty large kerf. Cutting to about 5.75" and then sanding to fit worked pretty well for me.
- Walls (2x each)
- End plates (2x)
- Cut one hole first to test fit your rod
- It's nicer, but not required, to machine in channels (runners, from here on) so that on the permanent mold excess silicone can be evacuated easily.
- One possible geometry is at D:\bdml\Google Drive\sasuresh\Adhesive Manufacturing\Daughter Mold though you'll have to re-do toolpaths and possibly setup the tool if it's since been removed.
Note: contains a 3-4 hour cure time. Plan accordingly.
- Stick a piece of 0.010" fiberglass to the aluminum foam in one of Arul's drawers in the file cabinet using solder mask, let it dry.
- Make sure the fiberglass is larger than the aluminum foam. (We don't want to get silicone into the aluminum foam)
- Also, more fiberglass makes the daughter-mold molding easier.
- Some notes on solder mask:
- Even though the solder mask's bottle says the cure time is one hour, it turns out to be more like 3 or 4.
- Jason says: I used a lot of solder mask in my first attempt, and it took a very long time to rinse out. The next pattern I tried (in the photo below) worked out pretty well.
- Sand and prime underside of fiberglass
- Tape over edges of runners so they fill with silicone
- Cast the mold
- Arul says: When casting, keep a lot of pressure on the back; I usually put the two (approx. 6x2x0.75") rectangular weights in the TLT fumehood on top.
- Allow cast to dry (24 hours)
- Super glue
- Modeling clay
- Mann EZ release 200
- Red tape
- Cut rods
- Laser cut walls (4x total) and end plates (2x)
- Flush the aluminum foam with water in the sink until the solder mask dissolves.
- Wash out the foam and leave it by the sink to dry before putting it back in the drawer.
- Wash off the back of the fiberglass.
- Carefully peel out the master from the mold, trying not to put too much curvature into the fiberglass.
- Double-stick tape the fiberglass master to a reference flat (smooth-faced wax block ideally, makes later cleanup easier), so that the wedges are up.
- Make sure not to get any bubbles and get it as flat as possible.
- Carefully, with a microtome and/or xacto, scrape away any thin films of silicone that are not the actual adhesive, and not the runners.
- The fiberglass will define the reference surface (lowest surface) in the daughter mold, so we want to make sure there's no silicone where it shouldn't be.
- To get square edges to the daughter mold, build side walls around the master patch of adhesive using acrylic rectangles.
- You can hold these down to the fiberglass and seal the corners using very light application of superglue; we'll just snap them off later.
- Glue together the stiffener structure with superglue to hold it together while you assemble everything else.
- If you cut runners, if the resulting silicone ridges on the master mold don't reach the acrylic sidewalls, use small pieces of modeling clay to extend them out to the walls
- Mask off the area of the adhesives by covering them (and only them) with red tape.
- Spray Mann EZ release 200 (the yellow and black one) on the mold surfaces, being sure to get the sidewalls.
- Place the assembled rods and end plates (without mold release on it!) into place.
- Mix the epoxy you're using.
- The old one is EpoxACast 690. You can also use EpoxACast 650 (pretty sure that's it; top shelf), which is higher-temperature tolerant, which would be nice.
- Vacuum-degas the epoxy by itself.
- Put the master mold in the vacuum chamber, and carefully pour in the epoxy.
- Goals while doing this:
- Don't pour directly onto the wedges, let the epoxy flow over it.
- Keep the carbon fiber frame from moving; either pour carefully, or hold it in place with a stick (can't remember exactly which I did).
- Goals while doing this:
- Let epoxy cure overnight