Good Oldie Moldie

A New Rubber Mold for the Electroliers.

The Electrolier/Line Pole Project is back on track with a new mold after the last mold failed.

This time I went with a more durable silicone rubber:

Smooth-On Mold Star. It only cost a couple bucks more but its supposed to produce a stronger mold. So we'll see.

So to recap, four useable lamps done when we last left off, and now 8 lamps to go.

Yes Sir! 8 to go!

Dandy

Well Whatdaya Know ~ All Rubber Are Not Alike

Quality Rubber - That's The  Secret Ingredient For A Successful Mold.

      What with the Backesto Bits already to go, its time to make a mold of them all. But when I went to go fetch the left over rubber compound from the Streetlamp Project, I found it has a short shelf life and had hardened.

Anxious to move forward with this project, I stopped by the craft store to pick up some of their casting rubber~ Amazing Mold Rubber. And after some time and effort, well... I found it ain't so amazing. I'm sure its fine for most crafts, but not for precision casting. In a nutshell, it shrinks!

Recycling the box from the streetlamp project, it turned out to be just the right size for this project.

There it is! In all its pink glory. Or so I thought.

The shelf life of the resin is much better. It cast just fine and faithfully with no shrinkage. But when I compared the castings with the originals, there was about 10% shrinkage with the "Amazing" rubber.

So, I'll pay the small extra for the much better quality of the Oomoo rubber compound. Lesson learned.

Yes sir! Lesson learned!

Dandy

Bubba Don't Forget Your Rubber

Making a Two Part Rubber Mold for the Streetlamp/Line Pole Project.

Even though this is a rather crazy project, the making of this rubber mold is pretty straight forward. I watched tons of YouTube videos on how to pour rubber molds until I was confident I knew exactly what I needed do. This video in particular comes closest to what I need to do, except that I'll be sandwiching a brass conduit and a couple of LEDs in the mold along with the casting resin (I told you this is a crazy project!).

I'm a beginner when it comes to casting, so I need everything, rubber, sealer, mold release, and casting resin. The guys on the Railroad Line Forums recommended using Oomoo Silicone Rubber from Smooth-On. Smooth-on offers a starter kit that has everything I need to make a mold and castings, so I went with that.

Last week I built this two-part mold box for the two-part mold (bottom part shown). Since the streetlamp master is suspended in the box I was tempted to fill the box with rubber just like that...

...but the rubber crept up the sides of the master and completely covered it in some parts. That's unacceptable for casting. I tried trimming it back when it set, but that didn't turn out too well so...

Take Two!

This time I'm going to do it the right way like all the instructions said to.

That means filling the bottom of the half of the mold box with clay, carefully working it up around all the details of the lamp right up to the half-way line. Packing the clay tightly against the master so there aren't any voids that will be filled with rubber. Some strips of clay protruding up will create a keying effect so that the two halves of the mold will snap together with some precision. 

The top of the mold box is attached and the whole thing is sprayed with sealer. After two coats and drying time, spray on mold release (clean the sprayers afterwards, mine clogged. Now I have to brush it all on!) and let dry. Now were ready for rubber!

To determine exactly how much rubber I need, I had filled the mold box with sand...

... and then poured that sand into the mixing cup. I marked its level with a Sharpie. Remove the sand, pour the liquid silicone Part 1 half way to the mark, and then part 2 the rest of the way. Mix well.

Oomoo is easy. Mix equal parts of A and B and mix it really well. A woman in one of the YouTubes suggested warming up the bottles a little first so that the compound is even thinner.

And then fill up the mold box and let set. So far so good!

Flipped the whole thing over and dug out the clay revealing the master and the first half of the mold. Success! Attached the second half of the mold box and then added the coats of sealer and release. Now were ready for the second pour.

Success! It turned out beautifully. The rubber captured the strata layers inherent from the 3D printing process perfectly!

Next week comes the crazy part: filling the two halves of the mold with resin and then placing the brass armature with LEDs into it and then sandwiching the whole thing together! That's the plan anyway. I told you this was a crazy project. Yes sir! Crazy!

Dandy

Box of Negative Space

Constructing a Simple Mold Box for a Two Part Rubber Mold.

This box will contain the liquid rubber while its poured around the streetlamp model.

The box is simply constructed with hobby board from a home improvement store.

The hobby board is cut so that the streetlamp model will have at least a 1/2" space around all sides of it.

The lamp is going to be cast with a brass armature inside of it as a conduit for wiring for the lights and to support trolley overhead span wires. The brass tube also extends down through the layout benchwork. So I had to drill a hole in the mold box to accommodate the exposed brass rod.

 This is going to be a two-part mold. Resin will be poured in both halves of the mold,then the brass armature will be placed right into the liquid resin. Then the two halves will be sandwiched together. That's the crazy plan anyway! We'll see if it works.

The two halves of the mold box are screwed tightly together. And there we have it. We're ready for the big silicone rubber pour. Yes sir! We are ready for the big pour!

Dandy