So the front of the truck has a grill which holds two turn signals. The signals are round and bullet or dome shaped. Turns out the the parking/turn signal lights are held in place with a flat decorative lens. This lens is not a normal shape but has an amoeba like look. You can see them just below the dual headlights.
Prior to getting the truck, I found out that those lenses are VERY hard to find and expensive when you do. I have been told that the price for some reproductions are in the $350 range for both. Fortunately in the back of the camper were two brand new lenses. This got me to thinking. What happens if they crack or break what do I replace them with? With some interest online from others wanting pairs, I decided to make a mold and cast a few to sale at a lower price.
The purpose of this post is to show the process. Step One
First step is to build the box for the mold. I used 1 inch pine. It is dark because it was scrap and had been used for something else. I gave about a 1.5 inch excess all around the lens so the mold had a reasonably thick wall. The long walls of the box are about 1/4 inch longer than the base. You can see in the photo with the box clamped the 1/4 inch excess on left and right sides. This gives me a bit more tolerance when I clamp the box tight. Probably not needed but it doesn't hurt either.Step Two
At
this point I needed to start building a "platform" of clay for the lens
to rest on the base wood. I started with the center and built up the lens by about an inch. The important part was to push through and make sure
that the small holes and the single large hole was filled with clay. I cleaned up the excess with putty knife and my fingers.Step Three
Now its time to start filling in around the lens and create a solid foundation. As you can see all I needed to do was to keep adding clay under the lens and extending further out toward the edge of the wood base.
At the same time that I was extending out to the edge of the base I was also making sure that the horizontal plane was as flat as possible. This was anticipation of both the walls of the box as well as the mold parting line on the edge of the lens. Eventually you can see the box with the clay platform holding the lens.
Step Four
The first thing we did was to make sure the part line was clean and had enough of a reveal to "split" the two halves. Next we used a pencil to add "buttons" to the clay. This will allow the RTV mold material to almost "unzip" when we are ready to pull apart or put together. Apparently this keeps the mold from shifting when put together.
The last step was to make sure we sealed the box edges with clay and made sure all the buttons were clean. I also needed to make sure that all edges were smoothed or rounded so that we did not have any "catches" on the mold surface.
On Christmas Eve we got to pour the actual RTV mold. The first thing we needed to do was mix the Part A and Part B. Since the formula is by weight and we didn't have a scale in the room at this location we did an estimate. We marked the bucket at 1 quart poured the RTV Part A to the line. The material pours like taffy and you need to be careful as its easy to go past your line if not careful because the material that has left but not yet arrived at the bucket can be more than you think. Also notice all the bubbles inside the liquid. Those are what we want to avoid.
Next we added another line inside the bucket to mark the 10% for Part B needed. Part B is very thin like water and dribbled down the side of the container as we poured. Because it is like water it too is easy to over pour. The Part B sits on top and must be worked in. You can see the slow progression from dark red to pink as I stirred.
Step Six
Now we needed to actually pour the mold. We placed the bucket about 3 feet above the mold and put a few holes in the bottom. As you can see the stream of RTV becomes very thin toward the end. This helps in removing any trapped air bubbles. About an hour later the bucket was empty and we had our poured mold. Now I needed to wait 24 hours.
This next step was to simply remove the clay from the hardened mold. I will need to clean it out much better but I just wanted to see the result. Over the next three weeks I will be not working on the project but will resume in late January.
Although it looks wet it is just the shiny texture of the surface.
I next flipped the mold over and revealed the clay. Then I begun to pull the clay off slowly showing the mold. I had to use a small flat head screwdriver to get it off in spots.
Step Eight
The next few steps are mostly straight forward. I needed to really clean the clay from the mold surface, so I used Q-tips. They get around the buttons fairly well. The process was easy, but repetitive. Once it was clean I used a small brush to apply Vaseline on the surface. This helps the new mold to not adhere to the old mold.
Once the surface was covered in the "release" material, I reassembled the box and refilled the clay along the seams. Then we made another batch of mold material and poured it as before.
The next step after this mold has cured will be to pour the first casting.
Step Eight and a Half
Well the last mold I poured did not cover the lens. I ran out of material. So I reordered some more and unfortunately ordered the wrong RTV. The new material was significantly harder. So to make sure that the old mold and the new mold "sealed" I cut relief lines in the old mold with a sharp blade so the new material would "lock" and seal.
I then poured the new mold
onto the surface and let it cure. The surprising thing is that the
harder material has given it some strength which may be beneficial in
the long-run. The material poured very different and eventually I simply scraped it into the box as it was getting very stiff. Since the majority of the lens was already covered I was not concerned about air bubbles. 
After it cured I pulled the mold off and found that it worked perfectly. I did have some silver paint from the lens come off but other than that it did the job. In hindsight I might have done this on both molds so as to give more strength. As you can see the "sandwich" of material looks strange but is fully bonded to each other.The largest difference was when we cut the hole for the venting. The red mold was crumbly and less forgiving, while the pink mold was smooth and pliable.
Step Nine
Today I was able to finally spray the molds with a release spray and cast the first lens. There are a few more steps that were needed to prep and prepare the molds prior to this step. One of those steps was to cut a hole in the mold to allow the casting material a place to enter as well as a second hole to allow air to escape.
The casting material was mixed and then poured very slowly into the hole until it came out the vent hole.
So now we wait for 24 hours then we can pull off the mold and extract the clean lens. After the lenses are pulled I will clean them up and prep them for painting a silver coat then a protective primer just like the original.
Mis-Step Nine and a Half
Well things did not go as planned. The cure time was much longer than I expected. Even at 48 hours the material is soft, it bends and returns mostly back to its original shape slowly. Perhaps after a day or two or a better mix is required.
The other primary issue is the lack of complete coverage. We have a few spots that did not get material and therefore lack coverage. That one should be a simple fix.
Below are a few pictures. I will say that the reproduction that did work looks real nice and that is encouraging. A few tweaks and I think we will be back on track.
So yesterday we made some changes to the mold and recast. The first change was to add a bunch of vent holes to help resolve the flow issue. Second we poured a "puddle" of material on top of the pour hole in order to provide additional material just in case. Although it looks MUCH better we are still not quite at the level we need. The first set of photos are from casting No. 1 I tried to highlight the bubbles and voids so its easier to see.
Next are the vent holes we added to the top of the mold. As you an see they are filled up with casting material as to be expected.
Finally you can see casting No. 2. The voids have been greatly reduced. If you look carefully you can also see the vent holes that are now tiny towers of casting material that will need to be trimmed off.
Silver Have I None
So this last weekend I thought I would take Casting No 1 and try a coat of chrome paint. Well I can tell you that there is a lot more work ahead. Turns out that chrome paint turns grey when sprayed on plastic. I contacted the manufacturer of the casting material, as well as an expert in making mirrors. I sprayed the back side of the lens and it looked GREAT! When I turned it over to take a look it lost all its metalic apearance and was a primer grey.
Here are the theories:
1. The various chemicals in the spray paint caused a chemical reaction with the plastic.
2. The plastic is not optically clear enough.
3. The light is captured between the layer of paint and plastic and causes it to not reflect
4. The metal in the paint rises to the top which in the case is the wrong side for this application.
Lets take the first one. Yes the plastic became very soft and rubbery after the painting, so chemicals are at work. So I tried a clear coat first then a layer of paint....same result.
The second theory seems a bit out there, but I tried polishing the plastic and had the same result.
The third theory was interesting and very brilliant, pardon the pun. So I tried a simple experiment that would challenge all three theories. I simply took a clear plastic drinking bottle and a clear plastic tray, both different plastics from our casting material and optically clear. Result was the same....grey.
The fourth theory was also rather interesting, and again will be easy to replicate....simply spray paint upside down. I will try this today.
However I have three options. The first is to do a a process of applying silver to the plastic much like how a mirror is made. Its all silver and not suspended in a carrier component. This is probably what I will end up doing.
The second is to simply spray chrome on the front of the lens and then a clear coat. This will not be as nice as the OEM but it will work. This photo shows the chrome on the front side of the parking lens . It really looks nice, and had I not known what the OEM looks like I would go with this. Although it can easy be scratched, it can also be easily repainted. I did not prep the surface very well so the paint up close does not look smooth. I was just trying to see what it might look like on the outside. 
The third option is to leave them natural. As you can see the natural look is not bad and sort of compliments the lens as well. However I am not a fan of the semi frosted look. Fingerprints, imperfections and dust will show up to easily. So this is not my preferred method but would be available at a reduced cost.
I took a shot of the actual blinker on and it looks nice.
Casting No 3 was poured today. We added more vent holes, used a syringe to "force" bubbles/voids out, and made a poor-mans vibrator table to shake out any bubbles.
As for the silver paint, I have a few more tricks up my sleeve, but before I go to far I need to nail down the castings.
More to follow.
Hot Flash
One of the issues has been the casting not feeling like it is fully cured. Every Saturday morning I make pancakes for the family. I usually turn the oven on to the lowest setting to keep the pancakes warm.
Well I started thinking that perhaps a quick curing might do the casting good. So after breakfast I placed the left side of Casting No 2 into the oven at a 170 degrees for an hour. It was like soft rubber when I pulled it out. I then decided to go for 2 hours. This really seemed to help the curing process and surprisingly did not deform the lens. I will consider this part of my standard process.
Back at It
It has been a frustrating long break and some insanity as to the project (repeating the same and expecting a different outcome.)
One of the issues has been leaking. We continue to get voids and a few other issues on each casting. Seems that once poured everything looks good, but come back in an hour and I have lost 20% of the material as it leaks out the mold halves. I decided to make a contraption that would "hold" the two halves tighter and prevent leaks.
After making the "Mold Holder" I tested with water and it held!!
 |
 |
The second issue was the rigidness of the casting after it cured. I continued to get very rubbery castings. The last one I did was just about right. So I still have voids but do no longer have floppy castings. Last night I poured casting number 5. That's right, number 5.
Casting Number 1: Lots of voids and a shape shifter. Hard when cold and bendable when warm. Held its shape overall and would be ok if there were no voids.
Casting Number 2: Significantly less voids since we added vent holes to remove the pressure. Material was similar to Casting Number 1, hard when cold and bendable when warm. Heated it in the oven for a few hours and managed to harden it up some.
Casting Number 3: Added even more vent holes in stubborn areas and seems to be getting better. Ratio of A to B was off and created a flubber casting.
Casting Number 4: Looks very similar to Casting Number 3 for voids. Added more B and got a strong casting. This is the best yet for hardness. I also noticed that when I poured the casting I introduced lots of bubbles, which remained. The leaking issue is now the worst part.
Casting Number 5: The part came out rubbery after 24 hours! Not what I expected. However after another 24 hours it hardened up! That's the good news. The bad news is that I continue to have two persistent voids. As of right now I have a three more ideas as to help eliminate them and will try those next. Also I tried polishing the plastic with some Harbor Freight polishing material. The result was less than I expected. I also tried some Meguiars polishing compound with some better results but still not what I was hoping for.
